A coffee-cup calorimeter is constructed from two nested polystyrene cups, a snugly fitting lid, and a thermometer. To test the calorimeter before using it in a thermochemistry investigation, a student pours 100.0g of liquid water at 24.50∘C into the cup and then quickly adds 100.0g of water at 78.35∘C. The highest temperature recorded after stirring is 50.68∘C. Assume the density of water is 1.00gmL−1 and that the specific heat capacity of liquid water is essentially constant over the temperature range investigated.
Parts:
(a) Describe qualitatively what occurs, at the molecular level, when the hot and cold portions of water are mixed in the calorimeter.
(b) Explain why the final equilibrium temperature is lower than the arithmetic mean of the two initial temperatures.
(c) Identify two reasons why the measured highest temperature might be slightly lower than the true equilibrium temperature in an ideal, perfectly insulated calorimeter, and describe how each reason affects the accuracy of the measured heat change.
(d) The student wants to determine the heat capacity of the calorimeter so it can be used in future experiments. Outline the experimental steps the student should take, using only the information already collected, to calculate this value without performing any additional trials.