Exam 15: Thermodynamics

A refrigerator keeps food in the freezer portion at −15°C and dumps excess heat into the kitchen, whose temperature is 20°C. If the refrigerator has half the coefficient of performance of an ideal reversible refrigerator, what is the refrigerator's coefficient of performance under these conditions?

A heat pump uses 100 J of work to output heat at some temperature. If the heat pump withdraws 60 J of heat from the lower temperature reservoir, then what is the coefficient of performance for the heat pump?

An ideal reversible heat pump is used to heat a house in Minnesota in the winter. If the outside air temperature is −15°C and the indoor temperature desired is 20°C, what is the expected coefficient of performance for the heat pump under these conditions?

A heat pump uses 200 J of work to output 300 J of heat into a heat reservoir at 200 K. What is the coefficient of performance for the heat pump?

1.00 mol of oxygen gas (O₂) is heated at constant pressure of 1.00 atm from 10.0°C to 25.0°C. What is the change of volume of the gas in this process?

A refrigerator extracts 65 J of heat from a heat reservoir at 0.00°C. If the coefficient of performance of the refrigerator is 2.5, then how much work is needed to run the refrigerator?

It can be shown that the change in entropy in heating or cooling a sample is given by the relation ΔS = mc ln (T_F/T_i), where m is the mass of the sample, c is the specific heat of the sample, and T_F and T_i are the final and initial temperatures, respectively. What is the change in entropy when 20.0 grams of aluminum with a specific heat of 0.900 J/g K is heated from 10.0°C to 60.0°C?

A heat pump uses 100 J of work to output 150 J of heat at some temperature. What is the heat that is withdrawn from some lower temperature?

A refrigerator keeps food in the freezer portion at −15°C and dumps excess heat into the kitchen, whose temperature is 22°C. If the refrigerator has half the coefficient of performance of an ideal reversible refrigerator, and if its motor consumes 250 W of power, what is the rate of heat flow out of the freezer portion of the refrigerator?

In an isochoric process, the internal energy of a system decreases by 50 J. What is the heat flow to the system?

2.00 moles of an ideal gas freely expands from 1.50 liters to 4.00 liters. The change in entropy in the expansion is

According to the second law of thermodynamics, for any process that may occur within an isolated system, which answer applies?

For a system undergoing an adiabatic process,

Using 0.0200 mol of an ideal monatomic gas, an isochoric process from state A (230 kPa, 1.0 L) to B (98 kPa, 1.0 L) results in what change in internal energy?

The internal energy of a system increases by 500 J while 610 J of work are performed on it. What was the heat flow into the system?

In the first law of thermodynamics (ΔU = Q + W), the variables Q and W stand for

On a PV diagram where pressure is in atmospheres and V is in liters the area is measured in liter-atmospheres. What is the number of Joules in 1.00 liter-atmosphere?

If 50 kJ of heat flows into a system and 35 kJ of work is done by the system, then what is the change in internal energy?

A toy steam engine has a mass of 1.00 kg. The toy starts from rest and reaches a velocity of 4.00 m/s in a time of 3.00 seconds while covering a distance of 4.50 meters. During that time the toy takes in 30 J of heat. What is the change in the internal energy of the toy?

What is the maximum theoretical efficiency for an engine operating between 100°C and 400°C?