Calorimetry

Card # 36‐Calorimetry It is the science of heat and its measurement. Calorimeter is used to measure heat. Joule is the unit of heat in S.I. unit system. Calorie is the unit of heat in C.G.S. system. The heat required to raise the temperature of 1 gm of pure water 1o C from 14.5o C to 15.5o C be called one calorie. It is observed that the heat required to raise the temperature of 1gm of pure water at different temperature is different that is why a specific range 14.5o C to 15.5o C is chosen as reference also 1 calorie = 4.18 Joule or 1 Kilo calorie = 1000 calorie = 4.18 x 103 Joule Specific Heat If Q is the heat required to raise the temperature by T of a body of mass m then ΔQ α m and ΔQ α ΔT ΔQ α m ΔT ΔQ = S m ΔT Here S is specific heat a constant for a given body which depends on the nature of the body if m =1 and ΔT = 1˚C then ΔQ = S. Thus specific heat of a substance is the amount of heat required to raise the temperature of the unit mass of the substance by 1 ο C . Molar specific heat: The amount of heat required to raise the temperature of 1 mole of the substance by 1 ο C or 1 ο K is called its molar specific heat. ΔQ = m CΔT m = 1mole ΔT = 1˚C or 1˚K ΔQ = C = molar specific heat Its units are J/mole K (S.I. Units) or Calorie/Mole ο C (C.G.S. Units) The substance having two specific heats will get heated up or cooled down easily and the substance having high specific heat will be heated up or cooled down after a long duration. Heat capacity The amount of heat required to raise the temperature of a substance by 1 called heat capacity ΔQ = m SΔT If ΔT = 1˚C

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ΔQ = m S Heat capacity = mass x specific heat Water equivalent The amount of water that requires same quantity of heat to raise its temperature by 1 ο C as the body needs for 1 ο C rise in temperature is called water equivalent of that body. It is denoted by W. Water equivalent = mass x specific heat Water equivalent = Heat capacity Water has high specific heat capacity compared to other substances. For this reason water is used as a coolant in automobiles as well as a heater in hot water bags.