Enthalpy

Question

The enthalpy of combustion of methane at 298 K is −890 kJ mol⁻¹. What is the amount of heat released when 5.0 g of methane is completely burnt at this temperature?

RankGuru · Accepted Answer

1. **Find Moles of Methane**: 
- Molecular formula: $CH_4$
- Molar mass $= 12 (C) + 4 	imes 1 (H) = 16 	ext{ g/mol}$
- Moles of $CH_4 = \frac{	ext{Mass}}{	ext{Molar mass}} = \frac{5.0}{16} = 0.3125 	ext{ moles}$
2. **Calculate Heat Released**: 
- $\Delta H_c = -890 	ext{ kJ/mol}$ (Heat released for 1 mole)
- Heat released $= n 	imes \Delta H_c = 0.3125 	ext{ mol} 	imes (-890 	ext{ kJ/mol}) = -278.125 	ext{ kJ} \approx -278 	ext{ kJ}$

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