Discussion
How much heat is needed to raise 10 kilograms of a liquid of heat capacity 2.5 kilojoules per kilogram kelvin from 20 to 60 degrees Celsius?
Answer: B
Correct answer: 1000 kilojoules
\[ Q = mc_p\Delta T = 10 \times 2.5 \times (60-20) = 10 \times 2.5 \times 40 = 1000\ \mathrm{kJ}. \] The temperature difference may be taken in Celsius because a kelvin and a Celsius degree are the same size - only a *difference* permits that, and an absolute temperature must be used wherever the value itself enters.
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