Thermal Physics

Question 1

What is meant by the internal energy (U) of a system?

Answer 1

› The sum of the internal kinetic and potential energies
› In an ideal gas, there is no potential energy, and so U = (3/2)(nRT)
› Internal energy is minimum at absolute zero (0K / - 273.15 °C)

Question 2

What is meant by the heat energy (Q) of a system?

Answer 2

› The energy flow from high temperatures to low temperatures through its container wall
› It is either flowing into or out of a system

Question 3

When is work done by a system?

Answer 3

› When pressure is applied, causing expansion (a change in volume), meaning work is done

› W = pΔV

Question 4

What is the first law of thermodynamics?

Answer 4

› The change in internal energy is equal to the heat energy transferred to the system minus the work done by the system

› ΔU = Q - W

Question 5

On a pressure-volume graph, how is work done found?

Answer 5

Work done is the area underneath the graph

Question 6

What is meant by the specific heat capacity of a material?

Answer 6

The heat energy needed to raise 1kg of the material by 1°C