Gas!!! It’s Everywhere!!!!

Kinetic Molecular Theory Most of the volume occupied by a gas is empty space Collisions between gas particles are elastic collisions Energy is transferred between the particles

Kinetic Molecular Theory Gas particles are in constant motion Possess kinetic energy (energy of motion) Kinetic Energy in a gas depends on the temperature KE = ½ mv2

Kinetic Molecular Theory Expansion No definite shape or volume Fluidity Gases flow like liquids Low Density Most of the volume is empty space Compressibility Since mostly empty space, particles can be squeezed into a smaller volume

Diffusion Spontaneous mixing of gas particles caused by their random motion

Effusion A process by which gas particles pass through a small opening

Diffusion vs. Effusion

Real vs. Ideal Ideal Gas – An imaginary gas that perfectly fits all of the assumptions of the Kinetic Molecular Theory Real Gas – A gas that does not behave completely according to the assumptions of the Kinetic Molecular Theory A real gas can behave like an ideal gas under high temperature and low pressure conditions

STP STP = Standard Temperature and Pressure Standard Temperature = 0°C Standard Pressure = 1 atm

Pressure The force per unit area on a surface Barometer – a device used to measure atmospheric pressure

Units of Pressure Millimeters of mercury – mmHg Torr Atmosphere – atm Pascal – Pa Kilopascal - kPa

Important Conversion 1 atm = 760 mmHg 1 atm = 760 torr 1 atm = 101.325 kPa

Temperature Kelvin is the standard temperature scale used when dealing with gases Absolute zero = 0 K Unreachable! Temperature in Kelvin = Temperature in Celsius + 273 Temperature in Celsius = Temperature in Kelvin – 273 0°C = 273 K 25°C = 298 K (Room Temp) 0 K = -273°C (Absolute Zero)

Boyle’s Law The volume of a gas at constant temperature varies indirectly with pressure.

Example The pressure exerted on a 240 mL sample of hydrogen gas at constant temperature is increased from 0.428 atm to 0.724 atm. What will the final volume of the sample be? V1 = 240.0 mL V2= ? P1 = 0.428 atm P2 = 0.724 atm P1V1 = P2V2 (0.428 atm)(240.0 mL) = (0.724 atm)V2 V2 = 142 mL

Charles’ Law The volume of a gas at constant pressure varies directly with the temperature

Example A sample of air has a volume of 140.0 mL at 67°C. At what temperature will its volume be 50.0 mL at constant pressure? V1 = 140.0 mL V2= 50.0 mL T1 = 67°C + 273 = 340 K T2 = ? V1 V2 V2 T1 (50.0 mL)(340K) T2 = = = 121 K = 140.0 mL T1 T2 V1

Gay-Lussac’s Law The pressure of a gas at constant volume varies directly with the temperature

Combined Gas Law

Example A helium filled balloon has a volume of 50.0 L at 25°C and 1.08 atm. What volume will it have at 0.855 atm and 10°C?

Solution Step 1: List what you are given. V1 = 50.0 L V2= ???? P1 = 1.08 atm P2 = 0.855 atm T1 = 25°C + 273 = 298 K T2 = 10°C + 273 = 283 K Must Convert to Kelvin!!!!

Solution Step 2: Solve the Combined Gas Law for your unknown.

Solution Step 3: Solve! V2 = V2 = (1.08 atm)(50.0 L)(283 K) (0.855 atm)(298 K) V2 = 60.0 L He

Dalton’s Law The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases. PT = P1 + P2 + ..... + Pn

Example What is the total pressure of a gas containing a mixture of three gases whose partial pressures are 20 kPa, 10 kPa, and 30 kPa? PT = P1 + P2 + ..... + Pn PT = 20 kPa + 10 kPa + 30 kPa PT = 60 kPa

Ideal Gas Law The mathematical relationship among pressure, volume, temperature, and the number of moles of a gas.

Example Calculate the volume, in liters, occupied by 2.00 mol of H2 at 300 K and 1.25 atm. (R = 0.0821) PV = nRT nRT V = P (2.00mol)(0.0821)(300K) V = 1.25 atm V = 39.4 L

Avogadro’s Law Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Gas Stoichiometry 2CO + O2 2CO2 How many liters of oxygen are required to produce 2 L of carbon dioxide? 2CO + O2 2CO2 2L CO2 1L O2 = 1L O2 2L CO2