Question

The combustion of methane, CH4, releases 890.4

kJ/mol. That is, when one mole of methane is burned,
890.4 kJ are given off to the surroundings. This means
that the products have 890.4 kJ less than the reactants.
Thus, AH for the reaction = - 890.4 kJ. A negative symbol
forAH indicates an exothermic reaction.
CH (g) + 20 (g)> CO2 (g) + 2 H0 (1); AH = - 890.4 kg
a) How much energy is given off when 2.00 mol of CH,
are burned?
b) How much energy is released when 22.4g of CH. are
burned?​

Answer 1

`\boxed{\text{a) 1.78 MJ; b) 1.25 MJ}}`

Step-by-step explanation:

`\rm CH$_4$ + 2O$_2 \longrightarrow \,$ CO$_2$ + 2H$_2$O; \Delta H = - 890.4 \text{ kJ}$\cdot$\text{mol}$^(-1)$`

a) Energy from 1 mol

`\Delta_{\text{c}}H^(\circ) = \text{2.00 mol} * \frac{\text{-890.4 kJ}}{\text{1 mol}}=\text{-1780 kJ} = \textbf{-1.78 MJ}\\\\\text{The reaction gives off } \boxed{\textbf{1.78 MJ}}`

b) Energy from 22.4 g

(i) Convert grams to moles

`n = \text{22.4 g } * \frac{\text{1 mol }}{\text{16.04 g}} = \text{1.399 mol}`

(ii) Convert moles to energy

`\Delta_{\text{c}}H^(\circ) = \text{1.399 mol} * \frac{\text{-890.4 kJ}}{\text{1 mol}}=\text{-1250 kJ} = \textbf{-1.25 MJ}\\\\\text{The reaction releases } \boxed{\textbf{1.25 MJ}}`