Question

In the presence of excess oxygen, methane gas burns in a constant-pressure system to yield carbon dioxide and water: CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) ΔH = -890.0 kJ Calculate the value of q (kJ) in this exothermic reaction when 1.60 g of methane is combusted at constant pressure.

Answer 1

Answer : The heat value of 'q' in exothermic reaction is -8900 kJ

Explanation :

First we have to calculate the number of moles of methane.

`\text{Moles of methane}=\frac{\text{Mass of methane}}{\text{Molar mass of methane}}`

Molar mass of methane = 16 g/mole

`\text{Moles of methane}=(1.60g)/(16g/mole)=0.1mole`

Now we have to calculate the heat released in the reaction.

`\Delta H=(q)/(n)`

or,

`q=\Delta H* n`

where,

`\Delta H` = enthalpy change = 890.0 kJ/mol

q = heat released = ?

n = number of moles of methane = 0.1 mol

Now put all the given values in the above formula, we get:

`q=(-890.0kJ/mol)* (0.1mol)=-8900kJ`

Therefore, the heat value of 'q' in exothermic reaction is -8900 kJ