Consider the reaction: CH4(g) + O2(g) → CO2(g) + 2 H2O(g) H0rxn= −802.3 kJ

What mass of CH4 must be burned to emit 267 kJ of heat?

 

The enthalpy change is quoted per mole of reaction as written. That is combustion of 1 mol of methane to produce carbon dioxide and water vapour generates −802.3kJ

precisely. The reaction can be written in this way, and treat the energy as a product.

CH4(g) + 2O2(g) → CO2(g) + 2 H2O(g) +802.3kJ

If 267 kJ are produced then the moles used is given as. 267/802.3 ×1=0.3328 moles

Moles= mass/molar mass

Rearranging the formular to get mass then,

Mass=moles×molar mass

=0.3328*16=5.32g