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Energy, Heat and Work: Flashcards

Revise forms and units of energy, heat versus temperature, gas expansion work and the first law of thermodynamics.

10 cardsBeginner

10 cards

  1. Question
    What is energy?
    Answer

    The capacity to do work or to transfer heat. SI unit: the joule, J (1 J = 1 kg m² s⁻²).

  2. Question
    Give the formulas for kinetic energy and gravitational potential energy.
    Answer

    Ek=12mv2E_\text{k} = \tfrac{1}{2}mv^2 and Ep=mghE_\text{p} = mgh

  3. Question
    How many joules are in 1 cal, 1 kcal and 1 kWh?
    Answer

    1 cal = 4.184 J; 1 kcal = 4184 J; 1 kWh = 3.6 × 10⁶ J

  4. Question
    What is the difference between heat and temperature?
    Answer

    Temperature reflects the average kinetic energy of the particles; heat is energy transferred because of a temperature difference.

  5. Question
    Open, closed or isolated: which systems exchange energy but not matter?
    Answer

    Closed systems.

  6. Question
    State the first law of thermodynamics as an equation.
    Answer

    ΔU=q+w\Delta U = q + w: energy is conserved.

  7. Question
    What is the sign of w when a gas expands? And of q when heat leaves the system?
    Answer

    Both negative: the system loses energy.

  8. Question
    Give the formula for the work done when a gas expands against a constant external pressure.
    Answer

    w=−Pext ΔVw = -P_\text{ext}\,\Delta V

  9. Question
    How many joules are in 1 L·atm?
    Answer

    101.325 J

  10. Question
    A gas absorbs 1200 J of heat and does 456 J of work. What is ΔU?
    Answer

    ΔU = (+1200 J) + (−456 J) = +744 J