Why temperature stays constant during a change of state, Q = ml for melting and boiling, determining latent heats, and the difference between evaporation and boiling.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
Ice at 0 °C cools a drink more than water at 0 °C does, because melting absorbs a large amount of energy without any temperature change.
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Copy these into your notebook in your own words — that is how they stick.
Temperature constant; energy breaks bonds (increases potential energy).
Energy to change the state of 1 kg without a temperature change; J/kg.
Q = ml.
l_f = 3.34 × 10⁵ J/kg; l_v = 2.26 × 10⁶ J/kg.
l = Pt ÷ m.
Any temperature; surface; slow; causes cooling.
Fixed temperature; throughout; fast; bubbles.
Perspiration, refrigerator, air conditioner, earthenware pots.
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8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
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Question 1 [15 marks]
A student heats 0.50 kg of ice at 0 °C with an electric heater. Take l_f = 3.34 × 10⁵ J/kg, c(water) = 4 200 J/kg °C and l_v = 2.26 × 10⁶ J/kg.
(a) (a) Define specific latent heat of fusion. [2]
(b) (b) Calculate the energy needed to melt all the ice. [3]
(c) (c) Calculate the energy needed to raise the water from 0 °C to 100 °C. [3]
(d) (d) Calculate the energy needed to boil away 0.10 kg of the water at 100 °C. [2]
(e) (e) State, using the kinetic theory, why the temperature does not rise while the ice melts. [2]
(f) (f) Distinguish between boiling and evaporation (two differences). [2]
(g) (g) Explain why perspiration cools the body. [1]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.