Question

How much energy is released when the following amounts of propane are burnt?

Answer 1

Answer: i) -444.0 KJ/mol.

ii) -8880 KJ/mol.

iii) -1660.56 KJ/mol.

Explanation:

• To solve this problem, we should mention the reported value of burning one mole of propane (ΔH°combustion = -2220 KJ/mol).

C₃H₈ + O₂ → 3CO₂ + 4H₂O

i) The energy released from burning 0.2 mol:

Using cross multiplication:

1.0 mol → -2220 KJ/mol

0.2 mol → ??? KJ/mol

The energy released = (-2220 KJ/mol x 0.2 mol) / (1.0 mol) = -444.0 KJ/mol.

ii) The energy released from burning 4.0 mol:

Using cross multiplication:

1.0 mol → -2220 KJ/mol

4.0 mol → ??? KJ/mol

The energy released = (-2220 KJ/mol x 4.0 mol) / (1.0 mol) = -8880 KJ/mol.

iii) The energy released from burning 33.0 g of propane:

Firstly, we should convert the number of grams to moles.

n = mass/molar mass = (33.0) / (44.1 mol/g) = 0.748 mol.

Using cross multiplication:

1.0 mol → -2220 KJ/mol

0.748 mol → ??? KJ/mol

The energy released = (-2220 KJ/mol x 0.748 mol) / (1.0 mol) = -1660.56 KJ/mol.