Determining the Heat of Fusion of Water Calorimetry

Calorimetry n Measuring the heat of a chemical reaction or process in a calorimeter

Heat n Exothermic (reaction mixture produces heat) n n n Letter designation: q Units:

Determine ∆Hfus for Water n Heat water (60– 100˚C) n Mass empty calorimeter n

General Notes n n The exact temperature of the hot water, as long as

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Determining the Heat of Fusion of Water

Calorimetry n Measuring the heat of a chemical reaction or process in a calorimeter n Components: q Insulated container n q q n (e. g. ) coffee cup Reaction mixture (water and ice) Thermometer Changes in temperature indicate direction of heat flow

Heat n Exothermic (reaction mixture produces heat) n n n Letter designation: q Units: Joules (J) or kilojoules (k. J) Definition: Energy that spontaneously transfers from high to low temperatures In chemistry, heat is exchanged between the reaction and the surroundings. q Direction indicated by sign n Endothermic (reaction mixture absorbs heat from surroundings) n Exothermic reaction – Heat released by reaction or process (q) Endothermic reaction – Heat absorbed by reaction or process (+q)

Enthalpy n

Determine ∆Hfus for Water n Heat water (60– 100˚C) n Mass empty calorimeter n Add ~50 m. L of hot water to the calorimeter. q Record total mass q No need to measure volume. q Record temperature just before adding ice n Add 6– 8 “dried” ice cubes. q Temperature should drop below 10˚C. If not, add more ice. q If temperature drops to ~2– 3˚C, remove any solid ice. q Record lowest temperature. q Record total mass. n Repeat for a second trial.

Calculations n

General Notes n n The exact temperature of the hot water, as long as it is known, is not critical. However, the error decreases as ∆T increases. Starting with hot water results in a larger temperature drop (larger ∆T) and, thus, a smaller error. The temperature of the hot water does not need to completely stabilize before adding the ice. However, the temperature should not be rapidly changing. Typically waiting a minute or two is sufficient. It may be difficult to see solid ice in the water. Listen for it to clink against thermometer as you gently swirl. Ideally, the final temperature should be very cool (~2˚C). The calculation does not account for the warming of the melted ice to the final temperature. This error will become more significant as Tf increases.