Question

A bomb calorimeter was used to measure the heat of combustion of naphthalene (C10H8 ). The temperature of the water rose from 25.00°C to 30.70°C. If 1.44 g of naphthalene was used, what is the heat of combustion of one mole of naphthalene? The heat capacity of the calorimeter and its surroundings is 10.17 kJ/°C.

Answer 1

Answer:

• 5,160. kJ/mol

Explanation:

Since a bomb calorimeter is assumed to be insulated, by the law of conservation of energy, the heat of combusion of the reaction is equal to the heat absorbed by the calorimeter.

1. Calculate the heat absorbed by the calorimeter, Q

• Q = Heat capacity of the calorimeter × Increase in temperature

• Q = 10.17kJ/°C × (30.70°C - 25.00°C)

• Q = 57.969kJ

2. Calculate the heat of combustion of one mole of naphtalene

• molar mass of naphtalene = 128.174g/mol

• number of moles = mass in grams / molar mass

• number of moles = 1.44g / 128.174g/mol = 0.01123473mol

• heat of combustion = 57.969kJ/0.01123473mol = 5,159.8 kJ/mol

Round to four significant figures: 5,160. kJ/mol (the point indicates that the last 0 is significant).