Chapter 11 Gases

kinetic molecular theory

model for understanding the behavior of gases; predicts the correct behavior for most gases under many conditions

1. collection of particles in constant motion—kinetic

2. no attractions or repulsions between particles; collisions like billiard ball collisions; attractions are negligible—elastic so no loss of energy

3. a lot of space between particles compared to the size of the particles themselves—why gases are compressible

4. The speed of particles increase with increasing temperature–speed in direction increase, velocity increases

What assumptions are made for easier gas law calculations

• Negligible volume of gas molecules:

  The volume occupied by individual gas particles is assumed to be insignificant compared to the total volume of the gas. 

• No intermolecular forces:

  Gas molecules are assumed to exert no attractive or repulsive forces on each other. 

• Perfectly elastic collisions:

  Collisions between gas molecules and the walls of the container are assumed to be perfectly elastic, meaning there is no loss of kinetic energy. 

• Constant random motion:

  Gas molecules are in continuous, random motion, moving independently of each other. 

pressure

result of the constant collisions between the atoms of molecules in a gas and the surfaces around them

• Allows us to use straws, inflate basketballs, and move air in and out of out lungs

• Variation in pressure in the atmosphere creates wind and changes in pressure help predict weather

  • high pressure = fair weather

  • low pressure = stormy weather

• 

• Pressure increases when the number of particles in a volume increase

  • Fewer gas particles, the lower the pressure

Conversion between different units of pressure

4 variables

• Pressure—P—atm

• Temperature—T—K

• Volume—V—L

• # of moles—n—mol

Boyle's Law

The volume of a gas ad its pressure are inversely proportional

• the pressure of the gas sample depends, in part, on its volume

• Constant variables: temperature and moles

• if the temperature and amount of gas are constant, the pressure of a gas sample increases for a decrease in volume and decreases for an increase in volume

• P₁V₁=P₂V₂

Charles' Law

the volume (V) of a gas and its Kelvin temperature (T) are directly proportional

• Constant variables: pressure and moles

• If the temperature of a gas sample is increased, the gas particles move faster, and if the pressure is to remain constant, the volume must increase

• ***temperature always expressed in kelvins

  

Gay-Lussac's (Amonton’s) Law

the pressure of a gas is directly proportional to its temperature

• if the temperature of a gas increases the pressure will also increase, and vice versa

• Constant variables: volume and moles

Avogadro’s Law

the volume of a gas and the amount of gas in moles are directly proportional

• Constant variables: temperature and pressure

Combined Gas Law

combination of three other gas laws

• Used when multiple variables change at one

Ideal Gas Law

PV = nRT

• R is the ideal gas constant

  

Relationship between simple gas laws and ideal gas law

Conditions of P and T that Gas best display properties

• Ideal gas conditions

  • High temperature

  • Low pressure

    • Particle size is insignificant compared to space between particles

    • Interactions between particles are insignificant

• Non Ideal gas conditions

  • Low temperature

  • High pressure

    • Particle size is significant compared to space between particles

    • Interactions between particles are significant

  

Dalton's Law

the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture

• P_tot = P_a + P_b + P_c + …

Partial pressure

the pressure due to any individual component in a gas mixture 

• Fractional composition time the total pressure of the mixture

Vapor pressure

when a gas from a chemical reaction is collected through water, water molecules become mixed with the gas molecules. The final pressure of water vapor in the final mixture

STP

standard temperature and pressure 

• The volume occupied by 1 mol of gas at  0 °C (273.15 K) and 1 atm is 22.4 L.

• Volume occupied by 1 mole of gas under these conditions is called the molar volume 

  • 1 mol : 22.4 L