Chapter 6:Heat Engines and Cycles

Question 1

Area enclosed in a pV graph: does this represent work done on the gas or work done by the gas?

Answer 1

• Work done on the gas
• More work is done on the gas when compressing than by gas when expanding
• OR W=p(delta)V and compression occurs at higher pressures

Question 2

For an isothermal change in an ideal gas, explain why (delta) U = 0

Answer 2

Constant temperature

Question 3

Explain the effects on Q and W when (delta) U = 0

Answer 3

• Heat supplied to the system= work done by system

- Work done on system = heat transferred to the surroundings

Question 4

State the meaning of positive values for

• (delta) U
• Q
• W

Answer 4

• U= increase in internal energy
• Q= heat transfer to the system
• W= work done by the gas on the system