The Behavior of Gases The Behavior of Gases

The Behavior of Gases

The Behavior of Gases • The behavior of gases rely heavily on the properties of pressure, temperature, moles and volume.

Laws • • • Boyles Law – relates P and V Charles Law – relates V and T Gay-Lussac – relates P and T Combined Gas Law – relates P. V, T Ideal Gas Law – relates P, V, T and moles

Pressure & Force • Pressure (P) is defined as the force per unit of area on a surface. • Atmospheric pressure (atm) is the pressure exerted on an object due to the weight of the column of the air above it in the atmosphere. • A barometer is a device used to measure atmospheric pressure.

Units of Pressure • Pascal (Pa) • millimeters of mercury (mm Hg) • torr (torr) • pounds per square inch (psi or lbs/in 2) • atmosphere (atm) - This is the unit of pressure that we will use in chemistry. All pressure units must be converted to atmospheres

Relationships between units of pressure • 1. 0 atm = 760 mm. Hg • 1. 0 atm = 760 torr • 1. 0 atm = 1. 0135 x 105 Pa • 1. 0 atm = 14. 700 psi PRACTICE: Convert 78. 9 psi to units of atm.

Temperature • A temperature is a numerical measure of hot and cold. • We will measure or calculate temperature in units of Kelvin, not Celsius. • K = °C + 273. 15

Example • Convert 30 degrees C to Kelvin • Pretttyyy easy!!!

Volume • A gas’ volume can change; gases can be compressed or expanded. • Units of liters (L). • Remember, there are 1000 m. L in 1 L.

Standard Temperature and Pressure • Abbreviated as STP • Standard temperature is equal to 0 °C, which is 273. 15 K. • Standard Pressure is 1 atm • When at STP, 1 mole of any gas occupies 22. 4 Liters

Direct Relationship vs. Inverse Relationship • Direct Relationship: • Inverse both variables Relationship: one increase together variable increases or both variables while the other decrease together. variable decreases or vice versa.

The Gas Laws Boyle’s Law: the pressure-volume relationship of gases • Boyle’s Law states that the volume of a fixed mass of a gas at a constant temperature varies inversely with its pressure. P 1 V 1 = P 2 V 2

Problem #1 A balloon filled with helium gas has a volume of 500 m. L at a pressure of 1 atm. The balloon is released into the air where the pressure is 0. 5 atm. If the temperature has remained the same, what volume does the gas occupy at this height?

The Gas Laws Charles’ Law: the Volume-Temperature relationship • Charles’ Law states that the volume of a fixed mass of gas held at a constant pressure varies directly with its Kelvin temperature. V 1 T 1 = V 2 T 2

Problem #2 A gas has an initial volume of 752 m. L at a temperature of 25 degrees C. The gas is heated to 100 degrees C. What is the new volume?

The Gas Laws Gay-Lussac’s Law: the pressure-temperature relationship in gases • Gay-Lussac’s Law states that the pressure of a fixed mass of a gas held at a constant volume will vary directly with its Kelvin temperature. P 1 T 1 = P 2 T 2

Problem #3 A gas has an initial temperature of 120 degrees C with a pressure of 1. 07 atm. The gas is heated to a temperature of 205 degrees Celsius.

The Gas Laws The Combined Gas Law • The combined gas law expresses the relationship between pressure, volume, and the Kelvin temperature of a fixed amount of gas. (This means that the number of moles is held constant) P 1 V 1 T 1 = P 2 V 2 T 2

Problem #4 V 1 = 27. 5 m. L V 2 = ? P 1 = 0. 974 atm P 2 = 0. 993 atm T 1 = 22˚C T 2 = 15˚C

The Ideal Gas Law • The ideal gas law is the mathematical relationship among pressure, temperature, volume, and the number of moles of a gas. • PV = n. RT . P = pressure V = volume n = # moles R = ideal gas constant (pg 384) T = Kelvin temperature

Problem #5 • Calculate the grams of CO 2 that would occupy a volume of 22. 4 liters at STP.

Diffusion & Effusion • diffusion is the gradual mixing of two gases due to their spontaneous, random motion • effusion is the process by which molecules of a gas confined in a container randomly pass through a small opening in the container