Properties  Gases take the shape and volume of their container  Weak intermolecular forces  Volume is dependent on temperature and pressure Increase temperature, volume increases Increase pressure, volume decreases

STP STP = Standard Temperature and Pressure –Standard pressure = 1 atm = 101.3kPa = 760 torr = 760 mmHg –Standard temperature = 0 o C = 273K

Unit Conversions Convert the following: atm = ______ kPa atm = ______ torr kPa = _____ atm 4.350K = ______ o C

Kinetic Molecular Theory (KMT)  For an ideal gas, all particles:  Are in random, constant, straight-line motion  Have no attractive forces between them  Collisions are perfectly elastic. When collisions between gas particles occur there is only a transfer of energy, not a loss of energy  No volume – gas particles are separated by relatively large distances  See Molecular Motion See Molecular Motion See Molecular Motion

Ideal Gases Real gases are not perfectly ideal because they do attract each other, and occupy volume Gases behave most like an ideal gas at high temperatures, low pressure, and small masses (this is when they agree most with the KMT)

Ideal Gas Examples 1. Which gas will behave most ideal at STP? a. Ar b. Ne c. N 2 d. O 2 2. Under which conditions will hydrogen behave most ideal? a. 20 o C and 1 atm a. 20 o C and 1 atm b. 20 o C and 0.5atm c. 50 o C and 1 atm d. 50 o C and 0.5atm

Kinetic Theory of Gases AAt a high temperature they have a high velocity (speed) AAt a low temperature they have a low velocity (speed)

Combined Gas Laws Temperature, Volume, Pressure are changing Temperature must be in Kelvin (K) P 1 V 1 = P 2 V 2 T 1 T 2

Examples 1. A sample of gas has a volume of 260mL, temperature is 85 o C, and pressure is 0.85atm. If the temperature changes to 25 o C and the volume changes to 240mL, what is the new pressure?

Examples 2. An ideal gas has a volume of 1200mL a temperature of 25 o C and a pressure of 85kPa. The sample is changed to STP. What is the new volume?

Boyle’s Law Relationship between pressure and volume Temperature is constant Leave temperature out of the equation (since it is constant) Volume varies inversely with pressure (an inverse relationship) P 1 V 1 = P 2 V 2 Boyle’s Law Movie Clip

Boyle’s Law Examples 1. A 500.mL sample of gas at 120kPa is compressed to 100.mL. What is the new pressure? 2.If 40.0mL of a gas is stored at standard pressure, what is the new volume if the pressure is increased to 1.25atm? 3.A gas sample occupies 10.0mL at 1.0 atm. If the volume changes to 20.0mL, what is the new pressure?

Charles’ Law Relationship between temperature and volume Pressure is constant Leave pressure out of the equation (since it is constant) Volume is directly proportional to temperature (direct relationship)

Charles’ Law Temperature must be in Kelvin (K)

Charles’ Law Examples 1.The volume of a gas at 298K is 40.0mL. The volume is decreased to 35.0mL, what is the new temperature? 2.The volume of a gas is 50.0mL at 27 o C. The temperature is raised to 127 o C, what is the new volume? 3.At 30. o C the volume of a gas is 200.mL. The temperature is raised by 15 o C, what is the new volume?

Partial Pressure The sum of the pressure exerted by each of the gases in a gas mixture is equal to the total pressure of all the gases Total Pressure = sum of the parts P T = P 1 + P 2 + P 3 +… *All of the pressures must have the same units*

Partial Pressure Examples 1.There are 4 gases present in a mixture. The total pressure is 800.mmHg. The pressure of the first 3 gases is 200.mmHg, 250.mmHg, and 250.mmHg. What is the pressure of the 4th gas? 2.A sealed flask contains a mixture of 3.0 moles of N 2 (g), 1.0 mole of O 2 (g), and 2.0 moles of CO 2 (g) at 25 o C. If the total pressure of this mixture is 12atm, find the partial pressure of each of the 3 gases.

Graham’s Law of Diffusion Gases diffuse at different rates depending on their velocity (velocity is dependant on mass) Lighter gases will have a higher velocity and therefore will diffuse faster than heavier gases

Examples 1. Which of the following gases would diffuse the fastest: H 2, O 2, N 2, Cl 2, Ne? 2. Which of the following gases would diffuse the slowest: H 2, O 2, N 2, Cl 2, Ne?

Avogadro's Hypothesis Under the same conditions of temperature and pressure, equal volumes of all gases contain the same number of particles Under the same conditions of temperature and pressure, equal volumes of all gases contain the same number of particles –1 mole = 6.02 x particles –1 mole = 22.4L at STP

Density and Molecular Mass Density = molecular mass 22.4L/mole Examples: 1.The density of a gas is 1.96g/L at STP. What is the molecular mass? 2. Calculate the density of NO 2 (g).