Example 1      Answer

Assume that an ideal gas expands without a change in temperature (isothermally) and, in the process, 3.40 x 10³ J of work is performed.

a. What is the change in internal energy of the gas?

b. How much heat is absorbed during this expansion

a. We use the first law of thermodynamics DU = Q - W. Since work is done by the gas, the sign of W is positive (be careful with signs).  DU = 0 for this process since the temperature did not change.

b. From above Q = DU + W = 0 + 3.40x10³ J = 3.40x10³ J

Example 2    Answer

Assume that you have 2 L of an ideal gas that is at atmospheric pressure (1 atm). The gas is cooled at constant pressure to 1/2 its original volume. It is then expanded isothermally bact to 2.0 L. At that point the pressure is increased at constant volume until the original pressure is reached.

Draw the PV diagram

Example 3    Answer

A heat engine exhausts 8200 J of heat while performing 3200 J of useful work. What is the efficiency of the engine?

Example 4    Answer

Assume that a heat engine exhausts 8200 J of heat while it performs 3200 J of useful work. What is the efficiency of this engine?

Example 5   Answer

Given that the low temperature of a freezer cooling coil is -10 degrees C and the discharge temperature is 30 degrees C. What is the maximul theoretical coefficient of performance?