Question

It has been suggested that hydrogen gas obtained by the decomposition of water might be a substitute for natural gas (principally methane). To compare the energies of combustion of these fuels, the following experiment was carried out using a bomb calorimeter with a heat capacity of 11.3 kJ/oC. When a 1.50 g sample of methane gas was burned with excess oxygen in the calorimeter, the temperature increased by 7.3oC. When a 1.15 g sample of hydrogen gas was burned with excess oxygen, the temperature increase was 14.3oC. Compare the energies of combustion (per gram) for hydrogen and methane.

Answer 1

Answer:

Hydrogen: -141 kJ/g

Methane: -55kJ/g

The energy released per gram of hydrogen in its combustion is higher than the energy released per gram of methane in its combustion.

Explanation:

According to the law of conservation of the energy, the sum of the heat released by the combustion and the heat absorbed by the bomb calorimeter is zero.

Qc + Qb = 0

Qc = -Qb  [1]

We can calculate the heat absorbed by the bomb calorimeter using the following expression.

Q = C . ΔT

where,

C is the heat capacity

ΔT is the change in the temperature

Hydrogen

Qc = -Qb = -C . ΔT = -(11.3 kJ/°C) . (14.3°C) = -162 kJ

The heat released per gram of hydrogen is:

$\frac{-162kJ}{1.15g} =-141 kJ/g$

Methane

Qc = -Qb = -C . ΔT = -(11.3 kJ/°C) . (7.3°C) = -82 kJ

The heat released per gram of methane is:

$\frac{-82kJ}{1.50g} =-55kJ/g$