When 3.00 g of butane, C4H10, are combusted in a calorimeter containing 800. g of water, the temperature of the water changes by 44.4 °C. What is the heat of combustion of butane in kilojoules per mole? The molar mass of butane is 58.123 g/mol. The specific heat of water is 4.18 J/g·°C. Please indicate whether the reaction was endothermic or exothermic with the sign of your answer.

Answer 1

q = mass H2O x specific heatH2O x delta T.
Solve for q. Since the temperature rose you know the heat was generated by the combustion of the butane so it was an exothermic reaction. That q is in J/3.00 g. Change to kJ/3.00 g, then
kJ/3.00 g x (molar mass butane) = kJ/mol.