Heat and thermodynamics

Written by Dr. Hamza Farooq (Physics)

ECAT · Physics · 5 questions

Name: ____________________ Date: ____________

For a fixed mass of ideal gas in a rigid container, doubling the absolute temperature will:
- A Halve the pressure
- B Double the pressure
- C Leave the pressure unchanged
- D Quadruple the pressure
What is the efficiency of a Carnot engine working between 500 K and 300 K?
- A 80%
- B 40%
- C 60%
- D 20%
The average kinetic energy of the molecules of an ideal gas is proportional to:
- A Pressure
- B Volume
- C Mass of the gas
- D Absolute temperature
How much heat is needed to melt 0.5 kg of ice at 0 degrees C? (Latent heat of fusion = 334 kJ/kg)
- A 334 kJ
- B 668 kJ
- C 83.5 kJ
- D 167 kJ
In an isothermal process for an ideal gas, the change in internal energy is:
- A Positive
- B Equal to the work done on the gas
- C Negative
- D Zero

Answer key

1. B, 2. B, 3. D, 4. D, 5. D

At constant volume, pressure is proportional to absolute temperature (Gay-Lussac's law).
Efficiency = 1 - T_cold / T_hot = 1 - 300/500 = 0.4, which is 40%.
The mean kinetic energy per molecule equals 3/2 kT, where T is the absolute temperature.
Q = mL = 0.5 x 334 = 167 kJ.
Internal energy of an ideal gas depends only on temperature, and the temperature does not change.