Question

The enthalpy of formation of CH_4(g), HP_(cl) and CO_2(g) are respectively – 74.8 kJ mol^–1, – 285.5 kJ mol^–1 and – 393.5 kJ mol^–1. Then, the standard enthalpy of combustion of CH_4(g) is:

Options

• + 890.3 kJ mol^–1

• – 604.5 kJ mol^–1

• + 604.5 kJ mol^–1

• – 809.3 kJ mol^–1

Answer 1

– 809.3 kJ mol^–1 

Explanation:

2O₂ + CH_4(g) `→` CO_2(g) + 2H₂O_(l)

ΔH = `Δ°H_(fco_2) + 2 xx Δ°H_(f_(H_2o) - Δ°H_(f_CH_4)`

= – 393.5 + 2 × – 285.8 – (– 74.8)

= – 889.7 kJ/mol ≈ – 890.3 kJ mol^–1