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Example The measurement of heat change at constant pressure with a neat diagram. |
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Answer» Solution :Heat change at constant PRESSURE ( at atmospheric pressure) can be measured using a coffee cup calorimeter. A SCHEMATIC REPRESENTATION of acoffee cup calorimeter is given in Figure. Instead of bomb, a Styrofoam cup is used in this calorimeter. It Acts as good adiabatic walland doesn't allow transfer of heat produced during the reaction to its surroundings. This entire heat ENERGY is ABSORBED by the water inside the cup. This method can be used for the reactions where there is no appreciable change in volume . The change in the temperature of water is measured and used to calculate the amount of heat that has been absorbed or evolved in the reaction using the following expression. `q=m_(w)C_(W)DeltaT` Where `m_(W)`is the molar mass of water and `C_(W)` is the molar heat capacity of water `(75.29 kJ K^(-1) mol^(-1))` 
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