Exam 15: Thermodynamics

100 coins are tossed randomly onto a table. The macrostate is defined as the number of heads that appear after the toss. A microstate is a specification of the outcome of each individual coin. What is the value for the number of heads that has the greatest number of possible microstates?

A engine goes through a cyclic process. During the cyclic process the engine does 600 J of work and has a heat output of 2,400 J. What is the efficiency of the engine?

An engine delivers 40.0 J of work while it takes in energy from a 400 K thermal source. If the engine discharges energy into a thermal reservoir at 200 K, then what is the least amount of heat needed to run the engine?

A refrigerator uses 40.0 J of work to extract 90.0 J from a heat reservoir at 0.00°C. What is the coefficient of performance for the refrigerator?

If 30 kJ of heat flows into a system and the internal energy increases by 15 kJ, then what is the work done by the system?

In an isochoric process, the internal energy of a system decreases by 50 J. What is the work done on the system?

A heat engine has an efficiency of 25.0% and a power output of 600 W. What is the rate of heat input?

During an isothermal process, 5.0 J of heat are removed from an ideal gas. What is the change in internal energy?

An engine takes in 150 J of energy from a 400 K thermal source. If the engine discharges energy into a thermal reservoir at 150 K, then what is the maximum amount of work one can get out of the engine?

120 J of heat flows by thermal conduction from 100°C to 0.00°C. What is the net change in entropy for this process?

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

When the first law of thermodynamics is applied to an ideal gas that is taken through an isothermal process

A heat pump takes in 60.0 J of energy from a 250 K thermal reservoir outside a house and discharges heat energy into a 350 K thermal reservoir inside a house. What is the minimum amount of work needed to make the pump work?

A system in a certain macrostate has 2 × 10²³ microstates. Through some process, the system changes the number of microstates to 3 × 10²³. What is the change in entropy for the process?

A heat pump takes in energy from a 250 K thermal reservoir outside a house and discharges 140 J of energy into a 350 K thermal reservoir inside a house. What is the minimum amount of work needed to make the pump work?

A friend tells you that he knows of a situation in which bowl of ice sitting by itself on a table in a room whose air temperature is 20°C gives up heat to the surrounding air. What's wrong with this concept?

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 into the kitchen?

One mole of an ideal gas freely expands from 1.00 liter to 2.00 liters. The change in entropy of the gas in the expansion is

A heat pump uses 100 J of work to output 150 J of heat at some temperature. What is the coefficient of performance for the heat pump?

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 cooled from 60.0°C to 10.0°C?