Specific heat capacity and specific latent heat in calculations · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Warming, melting and heater maths

Science · Energy · ages 15-17
Name ______________________   Date ____________

  1. A heater supplies 12000 J. Of this, 3000 J warms the container and surroundings. With no other energy transfers, how much reaches the sample, in J?

    Answer: ______________

  2. A 50 W heater runs for 120 s. How much energy does it supply in joules?

    Answer: ______________

  3. Pure ice melting at normal atmospheric pressure stays at about 0°C while ice and liquid water remain together at the melting temperature.

    Circle one:   True   False

  4. A heating curve for pure water has a horizontal section while positive net energy enters at constant pressure. Which process does this section show?

    • Melting or boiling
    • Solid warming steadily
    • Liquid warming steadily

  5. 0.5 kg of ice warms from -20°C to 0°C without melting. Use c_ice = 2100 J/(kg°C). How much energy does this warming stage take?

    • 2100 J
    • 21000 J
    • 42000 J

  6. A positive mass of pure ice melts at constant pressure. Since its temperature change is zero, the energy needed for melting must be zero.

    Circle one:   True   False

  7. At normal atmospheric pressure, 250 g of ice at -8°C becomes water at 12°C. Use c_ice = 2100 J/(kg°C), L = 334000 J/kg and c_water = 4200 J/(kg°C). Ignore losses. Find the total absorbed energy in J.

    Answer: ______________

  8. 0.5 kg of liquid water warms by 10°C without boiling. Use c = 4200 J/(kg°C). How much energy does the water absorb in joules?

    Answer: ______________

  9. If some heater output warms the container and surroundings, the sample still receives all of P x t.

    Circle one:   True   False

  10. At normal atmospheric pressure, 200 g of ice at -10°C becomes water at 40°C. Which order of stages is needed?

    • Melt the ice, warm the ice, then warm the water
    • Warm the ice, warm the water, then melt the ice
    • Warm the ice, melt it, then warm the water
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Answer key

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Warming, melting and heater maths W1-mt_GKNPAJgroW-s1

  1. 9000 · Energy reaching the sample is 12000 - 3000 = 9000 J.
  2. 6000 · E = Pt = 50 x 120 = 6000 J. This is heater output, before accounting for transfers elsewhere.
  3. True · During melting under these conditions, energy changes the state while temperature stays at the melting point.
  4. Melting or boiling · Under the stated conditions, the horizontal section shows a state change at constant temperature.
  5. 21000 J · The rise is 20°C. Q = 0.5 x 2100 x 20 = 21000 J.
  6. False · The zero temperature change does not remove the melting energy. Melting uses Q = mL, which is positive for a positive melted mass.
  7. 100300 · Warm ice: 4200 J. Melt: 83500 J. Warm water: 12600 J. Total = 100300 J.
  8. 21000 · Q = mcΔT = 0.5 x 4200 x 10 = 21000 J.
  9. False · P x t is total heater output. Energy transferred elsewhere must be subtracted to find the sample's share.
  10. Warm the ice, melt it, then warm the water · First warm the solid to 0°C, then melt it at 0°C, then warm the liquid water to 40°C.
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