A total of 2.00 mol of a compound is allowed to react with water in a foam coffe

Question

A total of 2.00 mol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 159g of solution. The reaction caused the temperature of the solution to rise from 21.00 to 24.70 ?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. Enter your answer in kilojoules per mole of compound to three significant figures. ?H = __________________kJ/mol

Explanation / Answer

A total of 2.00 mol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 159g of solution. The reaction caused the temperature of the solution to rise from 21.00 to 24.70 ?C. What is the enthalpy of this reaction?

H = enthalpy = mc?T, where m = mass of water, c = specific heat of water = 4.184 J/g.C, and ?T = T(final) - T(initial)
Calculate the heat gained by the water.
H(water) = 159 g(4.184 J/g.C)(24.7 C - 21.0 C) = 2461 J
The law of conservation of energy states that the heat gained by one object must be lost by another.
H(water) + Hrxn = 0, so
Hrxn = -H(water) = -2461 J(1 kJ)/(1000 J) = - 2.461 kJ

Hrxn per mole = -2.461 kJ/2.00 mol = -1.21 kJ/mol

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