The Zeroth law of thermodynamics states: if object A is in thermal equilibrium with object C, and object B is in thermal equilibrium with object C, then A and B are in thermal equilibrium with each other. What engineering application does this underpin?

Heat engine design — ensures the hot reservoir always contains more energy than the cold sink Temperature measurement — a thermometer (C) can determine that two objects are at the same temperature without directly comparing them Insulation design — confirms that insulated objects never reach equilibrium Refrigeration — proves that cold objects always absorb heat from warm surroundings

The First law of thermodynamics states Q = ΔU + W. In this equation, what does W represent?

Work done ON the system by external forces Work done BY the system on its surroundings The total thermal energy stored in the system The rate of heat transfer in Watts

A gas expands in a cylinder, doing 500 J of work on a piston while receiving 800 J of heat from a burner. What is the change in the gas's internal energy?

1,300 J increase 500 J decrease 300 J increase 800 J increase

The Second law of thermodynamics says heat flows spontaneously only from hot to cold. Which everyday observation best illustrates this?

Stirring cream into coffee mixes it uniformly without separating A hot cup of coffee always cools toward room temperature; it never spontaneously heats up Ice melts faster in a warm room than in a cold room Water boils at 100 °C at sea level but at lower temperatures at altitude

What is entropy?

The total heat content of a system The temperature difference between a hot and cold reservoir A measure of the number of possible microscopic arrangements (disorder) of a system The rate at which a system loses energy to its surroundings

A heat engine operates between a hot reservoir at 600 K and a cold reservoir at 300 K. What is its Carnot (maximum theoretical) efficiency?

25% 50% 75% 100%

Increasing the hot reservoir temperature of a heat engine (while keeping the cold sink temperature fixed) has what effect on Carnot efficiency?

Carnot efficiency decreases because the engine must work harder Carnot efficiency is unchanged because it only depends on the cold reservoir Carnot efficiency increases because the temperature ratio Tc/Th decreases Carnot efficiency increases because more fuel is burned per cycle

Why is it impossible to build a perpetual motion machine of the first kind (one that produces more energy than it consumes)?

It would violate the Second law — entropy would decrease It would violate the First law of thermodynamics — energy cannot be created It would violate the Zeroth law — temperature equilibrium cannot be avoided No engineer has been clever enough to design one yet

Why does a refrigerator require electrical energy to operate, even though it is simply moving heat from cold to warm?

Because electricity is needed to power the interior light Because the First law requires the refrigerant to be heated before it can cool food Because the Second law forbids spontaneous heat flow from cold to warm — external work must be done to force this transfer Because friction in the motor generates heat that must be removed

A coal power station converts heat into electricity with 38% efficiency. If the station produces 800 MW of electrical power, how much heat does it reject to the environment per second?

~304 MW ~800 MW ~1,305 MW ~2,105 MW

A perfectly insulated (adiabatic) system undergoes an irreversible process. What happens to its entropy?

Entropy decreases because no heat is exchanged with the surroundings Entropy stays constant in all adiabatic processes Entropy increases Entropy can increase or decrease depending on the direction of the process

A heat pump heats a building in winter by extracting heat from cold outside air and delivering it indoors. How does it achieve a coefficient of performance (COP) greater than 1 — seemingly getting more heat out than electrical energy in?

Heat pumps violate the First law by converting cold air into extra electrical energy It does not create energy; it uses work to move heat from outside, so the heat delivered equals electrical work plus heat extracted from outside The compressor generates extra heat through friction that supplements the electrical input At COP > 1 the system violates the Second law and must eventually fail