Coffee Cup Calorimetry

Question

2 moles of a compound are allowed to react in a foam coffee cup that contains 195 grams of water. The reaction caused the temperature of the water to rise from 21 to 24.7 degrees Celsius. What is the enthalpy of this reaction? Assume that no heat is lost to the surrounding or to the coffee cup itself.

Answer 1

The heat of reaction, the enthalpy change, is converted to a sensible heat change of the water (and products and reactants).  Ignoring the latter, deltaH = m*Cp*deltaT .

Cp of water is 1 calorie/gm/degC

(195gm)*(1 cal/gm/degC)(24.7-21) = 721 calories

Answer 2

H=-(195 * 4.18 *(24.7-21.0))

H=-3.0kJ

-3.0kJ/2mol = -1.5kJ/mol = molar enthalpy