Topic 32 Introduction to Gases EQ How do

Topic #32: Introduction to Gases EQ: How do we use the Kinetic Molecular Theory to explain the behavior of gases?

States of Matter b 2 main factors determine state: • The forces (inter/intramolecular) holding particles together • The kinetic energy present (the energy an object possesses due to its motion of the particles) • KE tends to ‘pull’ particles apart

Kinetic Energy , States of Matter & Temperature b Gases have a higher kinetic energy because their particles move a lot more than in a solid or a liquid b As the temperature increases, there gas particles move faster, and thus kinetic energy increases.

Characteristics of Gases b Gases expand to fill any container. • random motion, no attraction b Gases are fluids (like liquids). • no attraction b Gases have very low densities. • no volume = lots of empty space

Characteristics of Gases b Gases can be compressed. • no volume = lots of empty space b Gases undergo diffusion & effusion (across a barrier with small holes). • random motion

Kinetic Molecular Theory of ‘Ideal’ Gases b Particles in an ideal gas… • have no volume. • have elastic collisions (ie. billiard ball particles exchange energy with eachother, but total KE is conserved • are in constant, random, straight-line motion. • don’t attract or repel each other. • have an avg. KE directly related to temperature ( temp= motion= KE)

Real Gases b Particles in a REAL gas… • have their own volume • attract each other (intermolecular forces) b Gas behavior is most ideal… • at low pressures • at high temperatures Why? ? ?

Real Gases b At STP, molecules of gas are moving fast and are very far apart, making their intermolecular forces and volumes insignificant, so assumptions of an ideal gas are valid under normal temp/pressure conditions. BUT… • at high pressures: gas molecules are pushed closer together, and their interactions with each other become more significant due to volume • at low temperatures: gas molecules move slower due to KE and intermolecular forces are no longer negligible

Pressure Which shoes create the most pressure?

Atmospheric Pressure b The gas molecules in the atmosphere are pulled toward Earth due to gravity, exerting pressure b Why do your ears ‘pop’ in an airplane?

Pressure b Barometer • measures atmospheric pressure Mercury Barometer

Units of Pressure b At Standard Atmospheric Pressure (SAP) 101. 325 k. Pa (kilopascal) 1 atm (atmosphere) 760 mm Hg (millimeter Hg) 760 torr 14. 7 psi (pounds per square inch)

Standard Temperature & Pressure STP Standard Temperature & Pressure 0°C 1 atm -OR- 273 K 101. 325 k. Pa

Temperature: The Kelvin Scale b Always use absolute temperature (Kelvin) when working with gases. ºC -273 K 0 0 100 273 373 K = ºC + 273

Kelvin and Absolute Zero b Scottish physicist Lord Kelvin suggested that -273 o. C (0 K) was the temperature at which the motion particles within a gas approaches zero. . And thus, so does volume) Absolute Zero: http: //www. youtube. com/watch? v=JHXx. Pnmy. Dbk b Comparing the Celsius and Kelvin Scale: http: //www. youtube. com/watch? v=-G 9 Fd. Nq. UVBQ b

Why Use the Kelvin Scale? b Not everything freezes at 0 o. C, but for ALL substances, motion stops at 0 K. b It eliminates the use of negative values for temperature! Makes mathematic calculations possible (to calculate the temp. twice warmer than -5 o. C we can’t use 2 x(5 o. C) because we would get -10 o. C!)

Kelvin Scale vs Celsius Scale

Converting between Kelvin and Celsius K = ºC + 273 a) b) c) d) e) f) g) 0 o. C =_____K 100 o. C= _____K 25 o. C =______K -12 o. C = ______K -273 K = ______o. C 23. 5 K = ______o. C 373. 2 K= ______o. C

How Did We Do So Far? Learning Goal: I will be able to understand what kinetic energy is and how it relates to gases and temperature, describe the properties of a real and ideal gas and understand what Absolute Zero is and how to convert between the Kelvin and Celsius temperature scales.

Part B: The Gas Laws Part B: Learning Goals I will be able to describe Boyle’s, Charles’ and Gay-Lussac’s Laws relating T, P and/or V and be able to calculate unknown values using the equations derived from these laws, as well as the combined gas law.

1. Intro to Boyle’s Law b Imagine that you hold the tip of a syringe on the tip of your finger so no gas can escape. Now push down on the plunger of the syringe. What happens to the volume in the syringe? What happens to the pressure the gas is exerting in the syringe?

1. Boyle’s Law

1. Boyle’s Law b P V The pressure and volume of a gas are inversely proportional (as one increases, the other decreases, and vice versa • at constant mass & temp

1. Boyle’s Law leads to the mathematical expression: *Assuming temp is constant P 1 V 1=P 2 V 2 Where P 1 represents the initial pressure V 1 represents the initial volume, And P 2 represents the final pressure V 2 represents the final volume

Example Problem: A weather balloon with a volume of 2000 L at a pressure of 96. 3 k. Pa rises to an altitude of 1000 m, where the atmospheric pressure is measured to be 60. 8 k. Pa. Assuming there is no change in the temperature or the amount of gas, calculate the weather balloon’s final volume.

You Try: Atmospheric pressure on the peak of Kilimanjaro can be as low as 0. 20 atm. If the volume of an oxygen tank is 10. 0 L, at what pressure must the tank be filled so the gas inside would occupy a volume of 1. 2 x 103 L at this pressure?

2. Intro to Charles’ Law b Imagine that you put a balloon filled with gas in liquid nitrogen What is happening to the temperature of the gas in the balloon? What will happen to the volume of the balloon?

2. Charles’ Law

2. Charles’ Law b The volume and absolute temperature (K) of a gas are directly proportional (an increase in temp leads to an increase in volume) • at constant mass & pressure V T

2. Charles’ Law

2. Charles’ Law Ø Charles’ Law leads to the mathematical expression: *Assuming pressure remains constant

Example Problem: A birthday balloon is filled to a volume of 1. 5 L of helium gas in an air-conditioned room at 293 K. The balloon is taken outdoors on a warm day where the volume expands to 1. 55 L. Assuming the pressure and the amount of gas remain constant, what is the air temperature outside in Celsius?

You Try: A beach ball is inflated to a volume of 25 L of air at 15 o. C. During the afternoon, the volume increases by 1 L. What is the new temperature outside?

3. Intro to Gay-Lussac’s Law b Imagine you have a balloon inside a container that ensures it has a fixed volume. You heat the balloon. What is happening to the temp of the gas inside the balloon? What will happen to the pressure the gas is exerting on the balloon?

3. Gay-Lussac’s Law b The pressure and absolute temperature (K) of a gas are directly proportional (as temperature rises, so does pressure) • at constant mass & volume P T

2. Gay-Lussac’s Law Ø Gay-Lussac’s Law leads to the mathematical expression: *Assuming volume remains constant Egg in a bottle to show Gay-Lussac's Law: T & P relationship: http: //www. youtube. com/watch? v=r_Jn. UBk 1 JPQ

Example Problem: The pressure of the oxygen gas inside a canister with a fixed volume is 5. 0 atm at 15 o. C. What is the pressure of the oxygen gas inside the canister if the temperature changes to 263 K? Assume the amount of gas remains constant.

You Try: The pressure of a gas in a sealed canister is 350. 0 k. Pa at a room temperature of 15 o. C. The canister is placed in a refrigerator that drops the temperature of the gas by 20 K. What is the new pressure in the canister?

4. Combined Gas Law By combining Boyle’s, Charles’ and Gay Lussac’s Laws, the following equation is derived: P 1 V 1 T 1 = P 2 V 2 T 2

Example Problem: A gas occupies 7. 84 cm 3 at 71. 8 k. Pa & 25°C. Find its volume at STP.

Any Combination Questions a) A gas occupies 473 cm 3 at 36°C. Find its volume at 94°C b) A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr

How Did You Do? Part B: Learning Goals I will be able to describe Boyle’s, Charles’ and Gay-Lussac’s Laws relating T, P and/or V and be able to calculate unknown values using the equations derived from these laws, as well as the combined gas law.