Lecture 3

Question 1

State the ideal gas law and state the assumptions that are made for an ideal gas.

Answer 1

𝑝 𝑉 = 𝑚 𝑅 𝑇

An ideal gas is a theoretical gas composed of many randomly
moving point particles whose only interactions are perfectly
elastic collisions.

Assumptions:
The gas particles have negligible volume. The gas particles are equally sized and do not have intermolecular forces (attraction or repulsion) with other gas particles. The gas particles move randomly in agreement with Newton’s Laws of Motion.

Question 2

What does Avogadro’s law say?

Answer 2

Equal volumes of all ideal gases, at the same temperature
and pressure, have the same number of molecules

Question 3

Define specific heat capacity, explain the difference between cp and cv, as well as
specifying units.

Answer 3

The amount of heat needed to be added to raise the
temperature of one kilogram of the substance by one degree.

cp: Constant pressure [J/(kgK)]
cv: Constant volume [J/(kgK)]

Question 4

Explain why cp and cv for a gas have different values.

Answer 4

In the constant pressure heat addition process, the volume of the gas increases, thus, energy given by integration pdv is also added to the gas. In the constant volume heat addition process this term integration pdv is zero. Thus, cp and cv are different and cp is greater than cv.