The industrial synthesis of ammonia from nitrogen and hydrogen is represented by the chemical equation below using displayed formulae:
Some standard bond energies are provided in the table below:
| Bond | Bond energy in kJ/mol\text{kJ/mol}kJ/mol |
|---|---|
| N≡N\text{N}\equiv\text{N}N≡N | 945 |
| H−H\text{H}-\text{H}H−H | 436 |
| N−H\text{N}-\text{H}N−H | 391 |
Which expression shows how to calculate the overall energy change for this reaction?
945+436−391 kJ/mol945 + 436 - 391 \text{ kJ/mol}945+436−391 kJ/mol
945+(3×436)−(2×391) kJ/mol945 + (3 \times 436) - (2 \times 391) \text{ kJ/mol}945+(3×436)−(2×391) kJ/mol
945+(3×436)−(6×391) kJ/mol945 + (3 \times 436) - (6 \times 391) \text{ kJ/mol}945+(3×436)−(6×391) kJ/mol
(6×391)−945−(3×436) kJ/mol(6 \times 391) - 945 - (3 \times 436) \text{ kJ/mol}(6×391)−945−(3×436) kJ/mol