Hi Nayi, For any pure substance, we can convert from the specific heat per gram to the specific heat per mole simply by multiplying by the formula weight of the substance. For instance, the molar specific heat of water would be
4.184 J X 18.0153 g = 75.38 J
g°C mole mole°C
For mixtures like soil, we have an approximate specific heat per gram, 0.84 J/g°C, depending on the composition of the soil, but since this is not a pure substance we can't convert this to molar specific heat because we don't have a formula weight. The same would apply to materials like wood, stone, tile, roof shingles, brick, and other materials that are not pure substances.
For your second question, calculating the heat capacity of a substance, remember that the units of heat capacity are J/°C or J/K, or kJ may be used instead of joules. These are the same units as specific heat capacity except that the amount of substance (one gram or one mole) is not specified. It does not matter whether you use Celsius or Kelvin temperature units. As long as you are using a temperature difference, DT, the value will be the same.
In this problem DT = 1K; it would be correct to say 1°C also. The amount of heat energy needed to cause this increase was 100.0 J. Therefore,
Heat Capacity = Heat = 100.0 J = 100 J/K.
DT 1K
When the problem says the temperature "increase" was such and such, or the temperature "decrease" was such and such, you know this is DT.
Steve
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