|In the laboratory a
"coffee cup" calorimeter, or constant
pressure calorimeter, is frequently used to determine the specific
heat capacity of a solid, or to measure the enthalpy of a solution
Since the cup itself can absorb energy, a separate experiment is needed to determine the heat capacity of the calorimeter. This is known as calibrating the calorimeter and the value determined is called the calorimeter constant.
One way to do this is to use a common metal of known heat capacity. In the laboratory a student heats 90.89 g zinc to 98.35 °C and carefully lowers it into a cup containing 80.47 g water at 24.20 °C. She measures the final temperature to be 31.20 °C.
Using the accepted value for the specific heat capacity of zinc (0.388), calculate the calorimeter constant.
Heat lost by hot zinc = heat gained by water + heat gained by calorimeter
now we do each in steps
Heat lost by hot zinc = specific heat of zinc x mass of zinc x temperature change
= 0.388 J/gC x 90.89 g x ( 98.35 - 31.2) C
= 2368 J
Heat gained by water = specfici heat of water x mass of water x temp change
= 4.184 J/gC x 80.47g x ( 31.2 - 24.2) C
= 2357 J
Now using equation we find heat gained by calorimter
2368 = 2357 + heta gained by calorimeter
heat gained by calorimeter = 11 J
Now heat gained by calorimeter = calorimetr constant x temp change
11 J = Constant x ( 31.2 - 24.2) C
Constant = ( 11 J) / ( 31.2 -24.2) C = 1.57 J/C
Thus calorimeter constant is 1.57 J / C
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