Free First Law of Thermodynamics MCQs with Answers

• A. the work done by the system alone
• B. the increase in internal energy plus the work done by the system
• C. the fall in internal energy
• D. the temperature rise multiplied by the mass

Explanation: The law is conservation of energy applied to heat: energy entering as heat either raises the internal energy or leaves again as work done…

• A. the internal energy falls
• B. no heat is exchanged
• C. the temperature and therefore the internal energy stay constant, so the heat supplied equals the work done
• D. the work done is zero

Explanation: Constant temperature means constant internal energy for an ideal gas, so by the first law every joule of heat entering leaves again as…

• A. the temperature of the gas rises because work is done on it with no heat escaping
• B. the temperature falls
• C. the temperature stays constant
• D. heat flows into the gas from outside

Explanation: With no heat exchange, the work done on the gas must all go into internal energy, so the temperature rises, which is why a bicycle pump…

• A. energy can be created in a heat engine
• B. no heat engine can convert all the heat it takes in into work
• C. heat always flows from cold to hot on its own
• D. entropy always decreases

Explanation: Some heat must always be rejected to a cold reservoir, so efficiency is necessarily less than 100 per cent however well the engine is…

• A. 20 per cent
• B. 50 per cent
• C. 75 per cent
• D. 100 per cent

Explanation: Carnot efficiency is 1 minus the ratio of the cold to the hot absolute temperature, which is 1 minus 300 over 600, giving 0.5 or 50 per…

• A. creating cold and pumping it into the cabinet
• B. using work to move heat from a cold interior to the warmer room
• C. destroying heat inside the cabinet
• D. lowering the entropy of the universe

Explanation: Heat does not flow from cold to hot on its own, so a compressor does work to drive it that way, which is why the pipes at the back of the…

• A. increases by the work done
• B. decreases by the heat rejected
• C. returns to its original value, so the net heat supplied equals the net work done
• D. becomes zero

Explanation: Internal energy is a function of state, so returning to the same pressure, volume and temperature restores it exactly, and the first law…

• A. Isothermal
• B. Isobaric
• C. Isochoric
• D. Adiabatic

Explanation: Adiabatic means thermally isolated, so the system exchanges energy only as work.

• A. maximum
• B. zero
• C. equal to the heat supplied
• D. negative

Explanation: Work in this context is pressure multiplied by change in volume, and with no volume change there is no displacement of the surroundings…

• A. the total heat in a system
• B. the disorder of a system
• C. the temperature of a system
• D. the pressure of a system

Explanation: A system with many possible microscopic arrangements has high entropy, so melting ice or letting a gas expand into a vacuum both increase…

• A. Increase
• B. Decrease
• C. Remain constant
• D. Become zero

Explanation: The first law states that the change in internal energy equals the heat added plus the work done on the system, so with no work term every…

• A. Internal energy
• B. work and heat
• C. Enthalpy
• D. Entropy

Explanation: Heat and work depend on the path followed during a process, so they are path functions, whereas internal energy, enthalpy and entropy are…

• A. open system
• B. Closed system
• C. Isolated system
• D. Inert system

Explanation: An open system can exchange both matter and energy with its surroundings, such as steam flowing through a turbine.

• A. Isochoric
• B. Isobaric
• C. adiabatic
• D. Isothermal

Explanation: An adiabatic process has no heat transfer, so Q = 0 J, although the system's temperature may still change because work can be done.

• A. in adiabatic expansion
• B. in adiabatic compression
• C. in isothermal expansion
• D. in isothermal compression

Explanation: In an adiabatic process, heat transfer is zero, so the work done on the gas changes its internal energy.

• A. isothermal
• B. isochoric
• C. isobaric
• D. isentropic

Explanation: For an ideal gas in an isothermal process, temperature and therefore internal energy remain constant, so the first law gives Q = W.

• A. cyclic process
• B. operated at certain temperature difference
• C. both A and B
• D. none of these

Explanation: A heat engine must operate cyclically so that its working substance returns to its initial state, and it needs a temperature difference…

• A. constant
• B. variable
• C. zero
• D. depends on situation

Explanation: In an isochoric process, volume remains constant, so the work W = integral of P dV is zero because dV = 0.

• A. It is sum of all forms of energies associated with molecules of a system
• B. It is a state function of a system
• C. It is proportional to transnational K.E of the molecules
• D. All are correct

Explanation: Internal energy is the total microscopic energy of a system, including molecular kinetic and potential energies, and it is a state…

• A. rapid escape of air from a burst tyre
• B. rapid expansion of air
• C. conversion of water into ice in refrigerator
• D. cloud formation in the atmosphere

Explanation: An adiabatic process involves no appreciable heat exchange, which is possible during rapid expansion, rapid air escape, and some…