In the laboratory a \"coffee cup\" calorimeter, or constant pressure calorimeter

Question

In the laboratory a "coffee cup" calorimeter, or constant pressure calorimeter, is frequently used to determine the specific heat of a solid, or to measure the energy of a solution phase reaction. A chunk of tin weighing 19.85 grams and originally at 98.20 °C is dropped into an insulated cup containing 79.13 grams of water at 20.94 °C. The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.79 J/°C. Using the accepted value for the specific heat of tin (See the References tool), calculate the final temperature of the water. Assume that no heat is lost to the surroundings.

Explanation / Answer

We apply heat transfer principle:

Qgained = -Qlost

(mCpdeltaT)water + CpcaldeltaT= -(mCpdeltaT)tin

[0.07913kg * 4.182 kJ / kg K * (Tf - 20.94)ºC] + [0.00179*(Tf - 20.94)]  = - 0.01985kg * .21 kJ/kg K * (Tf - 98.20)ºC

0.3309Tf - 6.93 + 0.00179Tf - 0.03748 = - 0.004169Tf + 0.4093

0.336859Tf = 7.37678

Tf = 21.9 ºC

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