Science: Laws of Thermodynamics Worksheet

Question 1

State the zeroth law of thermodynamics in your own words and explain what it means for measuring temperature.

Accepted Answer

The zeroth law of thermodynamics states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This means temperature can be measured consistently because a thermometer can be used as the third system to compare temperatures.

Question 2

A gas in a cylinder absorbs 250 J of heat and does 90 J of work on its surroundings. Use the first law of thermodynamics to find the change in internal energy of the gas.

Accepted Answer

The change in internal energy is 160 J. Using the first law, ΔU = Q - W, so ΔU = 250 J - 90 J = 160 J.

Question 3

A metal spoon is placed in a cup of hot soup. Identify the direction of thermal energy transfer and explain which law of thermodynamics helps define when transfer stops.

Accepted Answer

Thermal energy transfers from the hot soup to the cooler spoon. The transfer stops when the soup and spoon reach thermal equilibrium, which is described by the zeroth law of thermodynamics.

Question 4

Describe the first law of thermodynamics and explain how it is related to conservation of energy.

Accepted Answer

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed. In a thermodynamic system, the change in internal energy equals the heat added to the system minus the work done by the system, so it is a statement of conservation of energy.

Question 5

A refrigerator removes heat from its cold interior and releases it into a warmer kitchen. Explain why this process does not violate the second law of thermodynamics.

Accepted Answer

This process does not violate the second law because the refrigerator requires external work from an electric motor. The second law says heat does not flow spontaneously from a colder object to a hotter one, but it can be forced in that direction when work is added.

Question 6

What does the second law of thermodynamics say about entropy in an isolated system?

Accepted Answer

The second law of thermodynamics says that the entropy of an isolated system tends to increase over time or remain constant in ideal reversible processes. This means natural processes usually move toward greater disorder or greater energy spreading.

Question 7

A heat engine takes in 600 J of heat from a hot reservoir and releases 420 J to a cold reservoir. How much work does the engine do?

Accepted Answer

The engine does 180 J of work. For a heat engine, the work output equals the heat absorbed minus the heat released, so W = 600 J - 420 J = 180 J.

Question 8

Explain why no heat engine can be 100 percent efficient according to the second law of thermodynamics.

Accepted Answer

No heat engine can be 100 percent efficient because some thermal energy must always be transferred to a colder reservoir. The second law prevents all absorbed heat from being converted completely into work in a cyclic process.

Question 9

State the third law of thermodynamics and explain what it says about reaching absolute zero.

Accepted Answer

The third law of thermodynamics states that as a system approaches absolute zero, its entropy approaches a minimum value. It also implies that absolute zero cannot be reached by any finite number of physical processes.

Question 10

A student says that if a process decreases the entropy of one object, then the second law is broken. Explain why this statement is incorrect.

Accepted Answer

This statement is incorrect because the second law applies to the total entropy change of the system and its surroundings, not just one object. One part of a system can decrease in entropy as long as the entropy increase elsewhere is large enough that the total entropy does not decrease.

Question 11

Compare a reversible process and an irreversible process in terms of entropy and energy transfer.

Accepted Answer

A reversible process is an ideal process that happens infinitely slowly and can be reversed without increasing the total entropy of the universe. An irreversible process happens naturally with effects such as friction, turbulence, or unrestrained expansion, and it increases the total entropy of the universe.

Question 12

Give one real-world example for each of the following: the zeroth law, the first law, and the second law of thermodynamics.

Accepted Answer

A real-world example of the zeroth law is using a thermometer to compare temperatures of different liquids. A real-world example of the first law is a car engine converting chemical energy in fuel into work and heat while conserving total energy. A real-world example of the second law is an ice cube melting in a warm room as thermal energy spreads from warmer surroundings to the colder ice.

Science: Laws of Thermodynamics

Science: Laws of Thermodynamics

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