The quantity of heat energy (Q) gained or lost by a substance is equal to the mass of the substance (m) multiplied by its specific heat capacity (C) multiplied by the change in temperature (final temperature - initial temperature)
Q = m x C x (Tf - Ti)
Memorize this formula well.
- Specific Heat Capacity (C) of a substance is the amount of heat required to raise the temperature of 1 gram of the substance by 1o C (or by 1 K).
- Heat capacity (H) is defined as the mass multiplied by the specific heat capacity. H = m x C
- The quantity of heat can therefore be defined as heat capacity multiplied by the change in temperature. Q = H x C
Example:
Calculate the quantity of heat needed to raise the temperature of 250 grams of water from 20o C to 56o C. (Heat capacity of water is Cg = 4.18 J oC-1 g-1)
Solution: Q = m x C x (Tf - Ti)
m = 250 g; Tf = 56oC; Ti = 20oC
q = 250 x 4.18 x (56 - 20)
q = 250 x 4.18 x 36
q = 37620 J = 38 kJ
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