Topics 4 and 5: Kinetic Theory and Thermodynamics

What exactly is an ideal gas? State its formula.

An ideal gas is one that obeys the gas laws and is given by the equation: PV= nRT or PV= NkT

Why is the molar heat capacity of a gas at constant volume different from that of a gas at constant pressure?

At constant pressure, the molar heat capacity of a gas is greater that at constant volume. This is because a gas must expand to move a piston when heat energy is supplied but the pressure needs to remain constant. In this process, the molecules gain kinetic and potential energy. However, is the volume is fixed, the heat energy supplied is used to raise the temperature. Thus less energy is used.

State Avogadro's law and constant.

Avogadro's Law states that equal volumes of all gases at the same temperature and pressure may contain the same number of molecules. 6.02214076 × 10^23 mol-1

Define Boyle's Law and state how it can be used.

Boyle's law states that for a fixed mass of gas, the pressure is inversely proportional to its volume, given the temperature remains constant. (pV= k) p1V1 = p2V2

State Charles' Law and how it can be used.

Charles' Law states that for a fixed mass of gas, the volume is directly proportional to its absolute temperature, given its pressure remains constant. (V=kT) V1/T1 = V2/T2

How are molar heat capacity at constant pressure and constant volume related.

Cp - Cv= R R= 8.31 Jmol^-1 K^-1 (molar gas constant)

State the first law of thermodynamics and state the equation associated with it.

The first law of thermodynamics states that the change in internal energy of a system is equal to the energy supplied to the system plus the work done on the system. ΔU= ΔQ+ WΔ

What is the basic assumption of the kinetic theory of gases.

The kinetic theory of gases assumes that a gas is made up of many small particles that move around randomly at high speeds.

Define the term molar heat capacity.

The molar heat capacity of a substance is the amount of thermal energy required to increase the temperature of 1 mole of a substance by 1 degree. Eh = nCp∆θ OR Eh = nCv∆θ

What is the Pressure Law? How can it be used?

The pressure law stated that for a fixed mass of gas, its pressure is directly proportional to its absolute temperature, given the volume is kept constant. (p=kT) p1/T1 = p2/T2

How do you calculate work done on a gas?

W = pΔV

How is molecular movement responsible for the pressure exerted by a gas?

When a container is filled with a gas, the gas exerts a pressure on the walls of the container. The kinetic theory explains the pressure exerted because the molecules are moving around and colliding with the walls of the container. With these collisions, the molecules undergo a change in momentum since their direction changes. (Newton's second law)