Calorimetry is a method used to measure enthalpy, or heat, changes that occur du

Question

Calorimetry is a method used to measure enthalpy, or heat, changes that occur during chemical processes. Two common calorimeters are constant-pressure calorimeters and constant-volume (or "bomb") calorimeters. Bomb calorimeters are used to measure combustion and other gas-producing reactions, where the reaction is observed in a strong, sealed vessel. A simple constant-pressure calorimeter can be made from a foam coffee cup and a thermometer; energy changes in a reaction are observed via a temperature change of the solution in the cup. The idea behind calorimeters is that if they are sufficiently insulated from the outside environment, any energy gained or lost in the chemical reaction will be directly observable as a temperature and/or pressure change in the calorimeter. A total of 2.00mol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 191g of solution. The reaction caused the temperature of the solution to rise from 21.0 to 24.7 Degree C. What is the enthalpy of this reaction? Assume that no heat is lost to the surroundings or to the coffee cup itself and that the specific heat of the solution is the same as that of pure water.

Explanation / Answer

basically you treat the coffee cup like a bomb calorimeter here (an ideal system). use the formula Q=mCpdT, where: Q = heat energy absorbed by water m = mass water Cp = heat capacity of water (take it as 4.184kJ/kgK - this is a value you should get to know) dT = change in temperature (in kelvin of celsius - doesn't matter so Q = (111/1000)kg x (4.184kJ/kgK) x (24.7-21)K = 1.7183688 kJ ~ 1.72kJ (this is standard metric units, you might need to convert to calories if your in America: 239.01calories = 1kJ) This means the enthalpy of the reaction is 1.72kJ. The "2 moles" is irrelevant as long s you don't have a chemical equation to work with.

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