Question

Suppose an amount of heat ΔQ supplied to a substance changes its temperature from T to T + ΔT. Heat capacity of a substance to be S = ΔQ/ΔT. We expect ΔQ and, therefore, heat capacity S to be proportional to the mass of the substance. Further, it could also depend on the temperature, i.e., a different amount of heat may be needed for a unit rise in temperature at different temperatures. To define a constant characteristic of the substance and independent of its amount, we divide S by the mass of the substance m in kg: s = S/m = (1/m) ΔQ/ΔT, s is known as the specific heat capacity of the substance. It depends on the nature of the substance and its temperature. The unit of specific heat capacity is J kg-1 K-1

ASSERTION: Specific heat capacity of a body is always lesser than its heat capacity. REASON: Heat capacity is heat required to raise temperature of unit mass of substance by unity.

ASSERTION: If placed in same refrigerator, iron will always lose heat at higher rate than water at same temperature if their mass is same. REASON: rate of fall of temperature is directly proportional to temperature difference of system and surrounding only.

Specific heat capacity is defined in terms of heat required to raise the temperature of unit mass of a substance by unity. While molar specific heat is heat required to raise temperature of one mole of substance by unity. Generally in case of a gas we usually discuss about molar specific heat only but it does not imply that we cannot calculate specific heat of a gas. Generally we take two types of specific heats in gases at constant volume and at constant pressure.