Thermodynamics Quiz

Grade 11 · Science · Quiz

Challenge your understanding of thermodynamic laws, processes, entropy, and heat engine efficiency.

Questions

  1. A gas expands isothermally and does 500 J of work on its surroundings. How much heat is absorbed by the gas?

    1. 0 J
    2. 250 J
    3. 500 J
    4. 1000 J
    Show answer

    Answer: 500 J

    For an isothermal process of an ideal gas, ΔU = 0. Therefore from ΔU = Q - W: Q = W = 500 J.

  2. Which thermodynamic process is represented by a vertical line on a PV diagram?

    1. Isothermal
    2. Isobaric
    3. Isochoric
    4. Adiabatic
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    Answer: Isochoric

    A vertical line on a PV diagram means volume is constant — that is an isochoric process.

  3. A heat engine absorbs 1000 J from a hot reservoir and rejects 400 J to a cold reservoir. What is its efficiency?

    1. 40%
    2. 60%
    3. 67%
    4. 250%
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    Answer: 60%

    Efficiency = W_out/Q_in = (Q_hot - Q_cold)/Q_hot = (1000 - 400)/1000 = 600/1000 = 60%.

  4. What is the SI unit of entropy?

    1. Joules (J)
    2. Watts (W)
    3. Joules per Kelvin (J/K)
    4. Kelvin (K)
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    Answer: Joules per Kelvin (J/K)

    Entropy S has units of J/K (joules per kelvin), since ΔS = Q_rev/T.

  5. Ice melting at 0°C is an example of which type of process?

    1. Adiabatic
    2. Isobaric phase change
    3. Isochoric
    4. Carnot cycle
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    Answer: Isobaric phase change

    Melting ice at constant atmospheric pressure is an isobaric phase change; heat is absorbed (latent heat) at constant temperature and pressure.

  6. In a Carnot cycle, what is true about the two adiabatic processes?

    1. They involve heat exchange with reservoirs
    2. They occur at constant temperature
    3. No heat is exchanged during them
    4. They define the efficiency alone
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    Answer: No heat is exchanged during them

    The two adiabatic steps in a Carnot cycle involve no heat exchange (Q = 0); they connect the isothermal expansion and compression steps.

  7. All reversible heat engines operating between the same two temperatures have the same efficiency.

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    Answer: True

    This is a consequence of the Second Law (Carnot's theorem): all reversible engines between the same temperatures achieve the Carnot efficiency; no engine can do better.

  8. The equation Q = mcΔT is used to calculate the _____ heat absorbed or released by a substance.

    Show answer

    Answer: sensible

    Q = mcΔT calculates sensible heat — heat that causes a temperature change. Latent heat (Q = mL) applies during phase changes at constant temperature.

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