MCAT EK Chemistry Lecture 2

What is STP?
1 atm and 0 degrees Celsius
Define ‘mean free path’
The distance traveled by a gas molecule between collisions
What are the four characteristics of an ideal gas?
1. Gas molecules have zero volume

2. Gas molecules exert no forces other than repulsive forces due to collisions

3. Gas molecules make completely elastic collisions

4. The average kinetic energy of gas molecules is directly proportional to the temperature of the gas

What is the equation for the ideal gas law?
PV = nRT

R = 0.0821 (atm L)/(mol K)


R = 8.314 J/(K mol)

What is ‘standard molar volume’?
One mole of gas at STP occupies 22.4 L
What is Dalton’s Law?
The total pressure exerted by a gaseous mixture is the sum of the partial pressures of each of its gases

Partial Pressure of One Gas = mole fraction of that gas X total pressure of the mixture

What is the equation relating Kinetic Energy and the temperature of a gas?
KE = (3/2)RT
What are the two equations associated with Graham’s Law?

(v1/v2) = (vm2)/(vm1)


(Effusion Rate1/Effusion Rate2) = (vM2)/(vM1)

Explain the difference between Effusion and Diffusion

Effusion is the spreading of a gas from high pressure to very low pressure through a pinhole (an opening smaller than the average distance between the gas molecules)


Diffusion is the spreading of one gas into another gas or into empty space

What two conditions cause gases to deviate from ideal gas behavior?
High pressure (above 10 atm) or low temperature (near the gas’ boiling point)
What two characteristics of gases are affected when they deviate from ideal gas behavior and how?

Vreal > Videal


Preal < Pideal

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