Lecture Presentation Chapter 8 Gases Karen C Timberlake

Topics covered in this Chapter • 8. 1 Properties of Gases • 8. 2 Pressure and Volume, (Boyle’s Law) • 8. 3 Temperature and Volume • 8. 4 Temperature and Pressure (Gay-Lussac’s Law) • 8. 5 The Combined Gas Law • 8. 6 Volume and Moles, Avogadro’s Law • 8. 7 Ideal Gas Law • 8. 8 Partial Pressure (Dalton’s Law) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Chapter 8 Gases Respiratory therapists assess and treat a range of patients. They perform a variety of diagnostic tests, including measuring • breathing capacity. • concentrations of oxygen and carbon dioxide in a patient’s blood, as well as blood p. H. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Chapter 8 Readiness Key Math Skills • Solving Equations (1. 4 D) Core Chemistry Skills • Using Significant Figures in Calculations (2. 3) • Writing Conversion Factors from Conversion Equalities (2. 5) • Using Conversion Factors (2. 6) • Using Molar Mass as a Conversion Factor (7. 5) • Using Mole–Mole Factors (7. 6) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

8. 1 Properties of Gases Generally molecules with fewer than five atoms from the first two periods in the periodic table are gases at room temperature. In addition, the following are also gases: • H 2, N 2, O 2, F 2, and Cl 2 • oxides of the nonmetals on the upper-right corner of the periodic table: CO, CO 2, NO 2, SO 2, and SO 3 • noble gases Learning Goal Describe the kinetic molecular theory of gases and the units of measurement used for gases. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Kinetic Molecular Theory A gas consists of small particles that 1. move randomly with high velocities. 2. have very small attractive (or repulsive) forces between molecules. 3. occupy a much larger volume than the volume of the molecules alone. 4. are in constant motion, moving rapidly in straight lines. 5. have a Kelvin temperature proportionate to the average kinetic energy of the molecules. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Gas particles which move in straight lines within a container, exert pressure when they collide with the walls of the container. © 2016 Pearson Education, Inc.

Properties That Describe a Gases are described in terms of four properties: pressure (P), volume (V), temperature (T), and amount (n). General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Volume The volume of a gas • is the same as the volume of the container it occupies. • is usually measured in liters or milliliters. • increases with an increase in temperature at a constant pressure. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Gas particles which move in straight lines within a container, exert pressure when they collide with the walls of the container. © 2016 Pearson Education, Inc.

Temperature The temperature of a gas relates to the average kinetic energy of the molecules and is measured in the Kelvin (K) temperature scale. When the temperature of a gas is • decreased, the molecules have fewer collisions. • increased, the molecules have more collisions. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Pressure is a measure of the gas particle collisions with sides of a container and is measured in units of • millimeters of mercury, mm. Hg or torr. • atmospheres, atm. • pascals, Pa, or kilopascals, k. Pa. • pounds per square inch, psi. Gas particles in the air exert pressure on us called atmospheric pressure. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Barometers Measure Pressure A barometer • measures the pressure exerted by the gases in the atmosphere. • indicates atmospheric pressure as the height in mm of the mercury column. 760 mm. Hg = 1 atm = 760 Torr The barometer was invented by Evangelista Torricelli, at exactly 1 atm the barometer tube measures exactly 760 mm high. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Units of Pressure General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C.

Atmospheric Pressure Atmospheric pressure • is the pressure exerted by a column of air from the top of the atmosphere to the surface of Earth. • decreases as altitude increases. • about 1 atm at sea level. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Altitude and Atmospheric Pressure Atmospheric pressure changes with variations in weather and altitude. • On a hot, sunny day, the mercury column rises, indicating a higher atmospheric pressure. • On a rainy day, the atmosphere exerts less pressure, which causes the mercury column to fall. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check 1. What is 475 mm. Hg expressed in atm? A. 475 atm B. 0. 625 atm C. 3. 61 105 atm 2. The pressure in a tire is 2. 00 atm. What is this pressure in mm. Hg? A. 2. 00 mm. Hg B. 1520 mm. Hg C. 22 300 mm. Hg General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check 1. The downward pressure on the Hg in a barometer is _____ the pressure of the atmosphere. A. greater than B. less than C. the same as 2. A water barometer is 13. 6 times taller than an Hg barometer (d. Hg = 13. 6 g/m. L) because A. H 2 O is less dense than mercury. B. H 2 O is heavier than mercury. C. air is more dense than H 2 O. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

8. 2 Pressure and Volume, (Boyle’s Law) The inverse relationship between the pressure and volume of a gas is known as Boyle’s law. Changes occur in opposite directions. When volume increases, the pressure decreases, provided the temperature and moles of the gas remains constant. The anesthetic N 2 O gas, is used for pain relief. Learning Goal Use the pressure–volume relationship (Boyle’s law) to determine the final pressure or volume when the temperature and amount of gas are constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Boyle’s Law Boyle’s law states that • the pressure of a gas is inversely related to its volume when T is constant. • the product P V is constant when temperature and amount of a gas is held constant • if volume decreases, the pressure increases. P 1 V 1 = P 2 V 2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Boyle’s Law: PV = Constant Pressure × volume is a constant, provided the temperature and amount of the gas remains the same. P 1 V 1 = 8. 0 atm × 2. 0 L = 16 atm L P 2 V 2 = 4. 0 atm × 4. 0 L = 16 atm L P 3 V 3 = 2. 0 atm × 8. 0 L = 16 atm L Boyle’s law can be stated as P 1 V 1 = P 2 V 2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake (T is constant. ) © 2016 Pearson Education, Inc.

Chemistry Link to Health: Boyle’s Law and Breathing During an inhalation, • the lungs expand. • the pressure in the lungs decreases. • air flows toward the lower pressure in the lungs. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Chemistry Link to Health: Boyle’s Law and Breathing During an exhalation, • lung volume decreases. • pressure within the lungs increases. • air flows from the higher pressure in the lungs to the outside. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Guide to Using Gas Laws General, Organic, and Biological Chemistry: Structures of Life, 5/e

Calculations Using Boyle’s Law Freon-12, CCl 2 F 2, was used in refrigeration systems. What is the new volume of an 8. 0 L sample of Freon gas initially at 550 mm. Hg after its pressure is changed to 2200 mm. Hg at constant temperature and moles? STEP 1 Organize the data in a table of initial and final conditions. ANALYZE Conditions 1 Conditions 2 Know Predict THE P 1 = 550 mm. Hg P 2 = 2200 mm. Hg P increases PROBLEM V 1 = 8. 0 L V 2 = ? V decreases Temperature and moles remain constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Calculations Using Boyle’s Law STEP 2 Rearrange the gas law equation to solve for the unknown quantity. P 1 V 1 = P 2 V 2 Boyle’s law To solve for V 2 , divide both sides by P 2. × STEP 3 Substitute values into the gas law equation and calculate. × General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check A sample of oxygen gas has a volume of 12. 0 L at 600. mm. Hg. What is the new pressure when the volume changes to 36. 0 L at a constant T and n? A. 200. mm. Hg B. 400. mm. Hg C. 1200 mm. Hg General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check For a cylinder containing helium gas, indicate if cylinder A or cylinder B represents the new volume for the following changes (n and T are constant). 1. pressure decreases cylinder B 2. pressure increases Cylinder A General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check If a sample of helium gas has a volume of 120 m. L and a pressure of 850 mm. Hg, what is the new volume if the pressure is changed to 425 mm. Hg at a constant T and n? A. 60 m. L B. 120 m. L C. 240 m. L General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check A sample of helium gas in a balloon has a volume of 6. 4 L at a pressure of 0. 70 atm. At 1. 40 atm (T and n are constant), is the new volume represented by A, B, or C? General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

8. 3 Temperature and Volume (Charles’s Law) If we increase the temperature of a gas sample, kinetic molecular theory states that the motion (kinetic energy) of the gas particles will also increase. If the amount and pressure of the gas is held constant, the volume of the container will increase. Learning Goal Use the temperature–volume relationship (Charles’s law) to determine the final temperature or volume when the pressure and amount of gas are constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Charles’s Law In Charles’s law, • the Kelvin temperature (K) of a gas is directly related to its volume. • pressure and moles of gas are constant. • when the temperature of a sample of gas increases, its volume increases at constant pressure. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Charles’s Law: V and T • For two conditions, Charles’s law is written (P and n are constant) • Rearranging Charles’s law to solve for V 2: × × General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake × © 2016 Pearson Education, Inc.

Study Check Solve Charles’s law expression for T 2. Rewrite Charles law as: V 1 T 2 = V 2 T 1, now solve for T 2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Calculations Using Charles’s Law A balloon has a volume of 785 m. L at 21 °C. If the temperature drops to 0 °C, what is the new volume of the balloon at constant pressure and moles? STEP 1 Organize the data in a table of initial and final conditions. Pressure and moles remain constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Calculations Using Charles’s Law STEP 2 Rearrange to solve for unknown quantity: V 2. × × × STEP 3 Substitute the values into the gas law equation and calculate. × General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check A sample of oxygen gas has a volume of 420 m. L at a temperature of 18 °C. At what temperature (in °C) will the volume of the oxygen be 640 m. L (P and n are constant)? A. 443 °C B. 170 °C C. − 82 °C ANALYZE Conditions 1 Conditions 2 Know Predict THE V 1 = 420 m. L V 2 = 640 m. L V increases PROBLEM T 1 = 18 C = 291 K T 2 = ? T increases General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check Use the gas laws to complete each sentence with increases or decreases. increaseswhen V decreases at constant A. Pressure _______ temperature and moles. B. When T decreases, Vdecreases _______ at constant pressure and moles. C. Pressure decreases _______ when V changes from 12 L to 24 L at constant temperature and moles. D. Volumeincreases _______when T changes from 15 °C to 45 °C at constant pressure and moles. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

8. 4 Temperature and Pressure (Gay-Lussac’s Law) Gay-Lussac’s law: When the Kelvin temperature of a gas doubles at constant volume and amount of gas, the pressure also doubles. Learning Goal Use the temperature–pressure relationship (Gay-Lussac’s law) to determine the final temperature or pressure when the volume and amount of gas are constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Gay-Lussac’s Law In Gay-Lussac’s law, • the pressure exerted by a gas is directly related to the Kelvin temperature of the gas. • volume and amount of gas are constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check Solve Gay-Lussac’s law for P 2. Rewrite as P 1 T 2 = P 2 T 1 then solve for P 2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Calculations Using Gay-Lussac’s Law A gas has a pressure at 2. 0 atm at 18 °C. What is the new pressure when the temperature is 62 °C (constant volume and moles)? STEP 1 Organize the data in a table of initial and final conditions. Volume and moles remain constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Calculations Using Gay-Lussac’s Law STEP 2 Rearrange to solve for unknown quantity P 2. Solve Gay-Lussac’s law for P 2: × × × STEP 3 Substitute the values into the gas law equation and calculate. × General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check A gas has a pressure of 645 Torr at 128 °C. What is the temperature in Celsius if the pressure increases to 824 Torr (V and n remain constant)? General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Vapor Pressure and Boiling Point When liquid molecules with sufficient kinetic energy break away from the surface of a liquid, they become a vapor. • In an open container, all the liquid will eventually evaporate. • In a closed container, the vapor accumulates and creates pressure called vapor pressure. A liquid • exerts its own vapor pressure at a given temperature. • boils when its vapor pressure becomes equal to the external pressure. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Altitude and Boiling Point At high altitudes, • atmospheric pressure is lower than 1 atm, 760 Torr. • the boiling point of water is lower than 100 °C. In a closed container, such as a pressure cooker, • a pressure greater than 1 atm, 760 Torr, can be obtained. • water boils at a higher temperature than 100 °C. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Pressure and the boiling point of water. © 2016 Pearson Education, Inc.

Vapor Pressure and Boiling Point General, Organic, and Biological Chemistry: Structures of Life, 5/e

Study Check Explain why water boils at a lower temperature in the mountains than at sea level. Atmospheric pressure in the mountains is less than at sea level. The vapor pressure of the water reaches the atmospheric pressure at a lower temperature. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

8. 5 The Combined Gas Law Under water, the pressure on a diver is greater than the atmospheric pressure. The combined gas law comes from the pressure–volume–temperature relationships for gases that we have studied. Learning Goal Use the combined gas law to calculate the final pressure, volume, or temperature of a gas when changes in two of these properties are given and the amount of gas is constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

The Combined Gas Law The combined gas law uses the pressure–volume– temperature relationships from Boyle’s law, Charles’s law, and Gay-Lussac’s law where n is constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Calculations Using Combined Gas Law A gas has a volume of 675 m. L at 35 °C and 646 mm. Hg pressure. What is the volume (m. L) of the gas at − 95 °C and a pressure of 802 mm. Hg (n is constant)? STEP 1 Organize the data into a table of initial and final conditions. ANALYZE Conditions 1 Conditions 2 THE P 1 = 646 mm. Hg P 2 = 802 mm. Hg PROBLEM V 1 = 675 m. L V 2 = ? T 1 = 35 C + 273 T 2 = − 95 C + 273 = 308 K = 178 K Moles of gas remain the same. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Calculations Using Combined Gas Law STEP 2 Rearrange to solve for unknown quantity V 2. × × STEP 3 Substitute the values into the gas law equation and calculate. × General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake × © 2016 Pearson Education, Inc.

Study Check A sample of helium gas has a volume of 0. 180 L, a pressure of 0. 800 atm, and a temperature of 29 °C. At what temperature (°C) will the helium have a volume of 90. 0 m. L and a pressure of 3. 20 atm (n remains constant)? Rewrite Combined Gas Law as: P 1 V 1 T 2 = P 2 V 2 T 1 ANALYZE Conditions 1 THE P 1 = 0. 800 atm PROBLEM V 1 = 0. 180 L (180 m. L) T 1 = 29 C + 273 = 302 K General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Conditions 2 P 2 = 3. 20 atm V 2 = 90. 0 m. L T 2 = ? © 2016 Pearson Education, Inc.

Solution A sample of helium gas has a volume of 0. 180 L, a pressure of 0. 800 atm, and a temperature of 29 °C. At what temperature (°C) will the helium have a volume of 90. 0 m. L and a pressure of 3. 20 atm (n remains constant)? Substitute the values into the gas law equation and calculate. × × - General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

8. 6 Volume and Moles, Avogadro’s Law The molar volume of a gas at STP is about the same as the volume of three basketballs. The volume of 1 mole of gas is 22. 4 liters. Learning Goal Use Avogadro’s law to calculate the amount or volume of a gas when the pressure and temperature are constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Avogadro’s Law: Volume and Moles In Avogadro’s law, • the volume of a gas is directly related to the number of moles (n) of gas. • T and P are constant. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Calculations Using Avogadro’s Law If 0. 75 mole of helium gas occupies a volume of 1. 5 L, what volume (L) will 1. 2 moles of helium occupy at the same temperature and pressure? A. 0. 94 L B. 1. 8 L Rewrite as V 1 n 2 = V 2 n 1 C. 2. 4 L Solve for V 2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Standard Temperature and Pressure The volumes of gases can be compared at STP, Standard Temperature and Pressure, when they have • the same temperature. • a standard temperature (T) of 0 °C or 273 K. • the same pressure. • a standard pressure (P) of 1 atm (760 mm. Hg). General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Molar Volume, STP At standard temperature and pressure (STP), 1 mole of a gas occupies a volume of 22. 4 L, which is called its molar volume. Use this equality as a conversion factor for gas at STP: 22. 4 L = 1 mole gas General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Molar Volume Avogadro’s law indicated that 1 mole of any gas at STP has a volume of 22. 4 L. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Guide to Using Molar Volume General, Organic, and Biological Chemistry: Structures of Life, 5/e

Calculations Using Molar Volume What is the volume occupied by 2. 75 moles of N 2 gas at STP? STEP 1 State the given and needed quantities. Pressure and temperature remain constant. STEP 2 Write a plan to calculate the needed quantity. Moles N 2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Volume N 2 © 2016 Pearson Education, Inc.

Calculations Using Molar Volume STEP 3 Write conversion factors including 22. 4 L/mole at STP. At STP, 22. 4 L = 1 mole N 2. STEP 4 Set up the problem with factors to cancel units. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check 1. What is the volume at STP of 4. 00 g of CH 4? A. 5. 60 L B. 11. 2 L C. 44. 8 L mass CH 4 moles CH 4 volume CH 4 2. How many grams of He are present in 8. 00 L of gas at STP? A. 25. 6 g B. 0. 357 g C. 1. 43 g volume He moles He mass He General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

8. 7 Ideal Gas Law When camping, butane is used as a fuel for a portable gas stove. Given the pressure, volume, and temperature of the gas in the tank, we can use the ideal gas law equation to determine the amount of gas present. Learning Goal Use the ideal gas law equation to solve for P, V, T, or n of a gas when given three of the four values in the ideal gas law equation. Calculate mass or volume of a gas in a chemical reaction. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

The Ideal Gas Law The ideal gas law is the combination of the four properties used in the measurement of a gas— pressure (P), volume (V), temperature (T), and amount of a gas (n)—to give a single expression, which is written as Ideal Gas Law PV = n. RT Core Chemistry Skill Calculating Mass or Volume of a Gas in a Chemical Reaction General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

R, Ideal Gas Constant Rearranging the ideal gas law equation shows that the four gas properties equal a constant, R. • To calculate the value of R, we substitute the STP conditions (273 K, 1 atm) for molar volume into the expression: 1 mole of gas = 22. 4 L at STP. • Real gases show some deviations in behavior; however, the ideal gas law closely approximates the behavior of real gases at typical conditions. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

R, Ideal Gas Constant The value for the ideal gas constant, R, is 0. 0821 L atm per mole K. • If we use 760 mm. Hg for the pressure, we obtain another useful value for R of 62. 4 mm. Hg per mole K. • In working problems using the ideal gas law, the units of each variable must match the units in the R you select. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Guide to Using the Ideal Gas Equation General, Organic, and Biological Chemistry: Structures of

Study Check Dinitrogen oxide, N 2 O, which is used in dentistry, is an anesthetic also called laughing gas. What is the pressure, in atmospheres, of 0. 350 mole of N 2 O at 22 °C in a 5. 00 -L container? STEP 1: General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solution Dinitrogen oxide, N 2 O, which is used in dentistry, is an anesthetic also called laughing gas. What is the pressure, in atmospheres, of 0. 350 mole of N 2 O at 22 °C in a 5. 00 -L container? STEP 2 Rearrange the ideal gas law equation to solve for the needed quantity. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solution Dinitrogen oxide, N 2 O, which is used in dentistry, is an anesthetic also called laughing gas. What is the pressure, in atmospheres, of 0. 350 mole of N 2 O at 22 °C in a 5. 00 -L container? STEP 3 Substitute the gas data into the equation and the needed quantity. × General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake × © 2016 Pearson Education, Inc.

R, Unit Summary for Ideal Gas Constant General, Organic, and Biological Chemistry: Structures of

Gas Laws and Chemical Reactions Gases are involved as reactants and products in many chemical reactions. Typically, the information given for a gas in a reaction is its pressure (P), volume (V), and temperature (T). We can use the ideal gas law equation to determine • the moles of a gas in a reaction if we are given the number of moles for one of the gases in a reaction. • the moles of any other substance using a mole–mole factor. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Guide to Using the Ideal Gas Law for Reactions General, Organic, and Biological Chemistry:

Study Check Nitrogen gas reacts with hydrogen gas to produce ammonia (NH 3) gas. How many liters of NH 3 can be produced at 0. 93 atm and 24 °C from a 16. 0 -g sample of nitrogen gas and an excess of hydrogen gas? N 2(g) + 3 H 2(g) 2 NH 3(g) grams Molar mass moles Mole−mole ratio moles liters of N 2 of NH 3 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solution Set up the problem to calculate moles of needed quantity which is moles of NH 3. Substitute moles of NH 3 as the value for n in V = n. RT P General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Gases in Chemical Reactions The volume or amount of a gas at STP in a chemical reaction can be calculated from • STP conditions. • mole−mole factors from the balanced equation. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 76

Gases in Equations at STP What volume (L) of O 2 gas is needed to completely react with 15. 0 g of aluminum at STP? General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 77

Gases in Equations at STP What volume (L) of O 2 gas is needed to completely react with 15. 0 g of aluminum at STP? General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

8. 8 Partial Pressure (Dalton’s Law) Our cells continuously use oxygen and produce carbon dioxide. Both gases move in and out of the lungs through the membranes of the alveoli, the tiny air sacs at the ends of the airways in the lungs. Learning Goal Use Dalton’s law of partial pressures to calculate the total pressure of a mixture of gases. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Partial Pressure The partial pressure of a gas is the pressure that each gas in a mixture would exert if it were by itself in the container. Core Chemistry Skill Calculating Partial Pressure General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Dalton’s Law of Partial Pressures Dalton’s law of partial pressures indicates that • pressure depends on the total number of gas particles, not on the types of particles. • the total pressure exerted by gases in a mixture is the sum of the partial pressures of those gases. PT = P 1 + P 2 + P 3 +. . General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Total Pressure For example, at STP, 1 mole of a pure gas in a volume of 22. 4 L will exert the same pressure as 1 mole of a gas mixture in 22. 4 L. Gas mixtures 1. 0 mole N 2 1. 0 atm 0. 4 mole O 2 0. 6 mole He 1. 0 mole 1. 0 atm General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 0. 5 mole O 2 0. 3 mole He 0. 2 mole Ar 1. 0 mole 1. 0 atm © 2016 Pearson Education, Inc.

Total Pressure The air we breathe • is a mixture of different gases. • contains mostly N 2 and O 2, and contains small amounts of other gases. What we call the atmospheric pressure is actually the sum of the partial pressures of the gases in the air General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Guide to Solving for Partial Pressure General, Organic, and Biological Chemistry: Structures of Life,

Solving for Partial Pressure A scuba tank contains O 2 with a pressure of 0. 450 atm and He at 855 mm. Hg. What is the total pressure in mm. Hg in the tank (volume and temperature are constant)? STEP 1 Write the equation for the sum of the partial pressures. Ptotal = PO 2 + PHe STEP 2 Rearrange the equation to solve for the unknown pressure. Convert units to match. Ptotal = PO 2 + PHe General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solving for Partial Pressure A scuba tank contains O 2 with a pressure of 0. 450 atm and He at 855 mm. Hg. What is the total pressure in mm. Hg in the tank (volume and temperature are constant)? STEP 3 Substitute known pressures and calculate the unknown partial pressure. Ptotal = PO 2 + PHe Ptotal = 342 mm. Hg + 855 mm. Hg = 1. 20 x 103 mm. Hg General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check For a deep dive, a scuba diver uses a mixture of helium and oxygen with a pressure of 8. 00 atm. If the oxygen has a partial pressure of 1280 mm. Hg, what is the partial pressure of the helium (volume and temperature are constant)? Ptotal = PO 2 + Phe A. 520 mm. Hg B. 2040 mm. Hg C. 4800 mm. Hg PHe = 6080 mm. Hg – 1280 mm. Hg = 4800 mm. Hg or 4. 80 × 103 mm. Hg The answer is C, 4800 mm Hg. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Chemistry Link to Health: Blood Gases • In the lungs, O 2 enters the blood, while CO 2 from the blood is released. • In the tissues, O 2 enters the cells, which releases CO 2 into the blood. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Chemistry Link to Health: Blood Gases In the body, • O 2 flows into the tissues because the partial pressure of O 2 is higher in blood and lower in the tissues. • CO 2 flows out of the tissues because the partial pressure of CO 2 is higher in the tissues and lower in blood. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Chemistry Link to Health: Partial Pressures in Blood and Tissue General, Organic, and Biological

Gas Exchange During Breathing General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen

Study Check • If I have a balloon with a volume of 4. 5 liters, and a pressure of 567 mm. Hg, what will the pressure be when the volume is 2. 5 liters? • 15 m. L of a gas is collected at 25 C and 650 mm. Hg. What is the volume at STP? • 2. 5 L of a gas at 64 C and 700 mm. Hg is now subjected to a temperature of -33 C and a pressure of 900 mm. Hg. What is the new volume? • An unknown gas having a mass of 5. 5 g is collected in 4 L glass bulb. It is found to have a pressure of 400 mm. Hg and a temperature of 27 C. How many moles of gas do you have? What is the molar mass of the gas? General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.