The Calculation of Energy

Energy Calculation

--the return of mole

CH₄+2O₂àCO₂+2H₂O

△H for this exothermic reaction is expressed using the coefficients of the balanced equation:

-812KJ/1mol CH₄ or -812KJ/2mol O₂ = -406KJ/1mol O₂

So the value of △H depends on which chemical you are referring to

1.    The value of △H changes with different reactions; -812KJ is only specific to this reaction. Thus like molar mass is different for each compound, △H depends on the chemical reaction

2.    △H is not a constant like Avogadro’s number

Ex. How many moles of CH₄ are needed to produce 2100KJ of energy?

CH₄+2O₂àCO₂+2H₂O+812KJ

-2100KJ×-1mol CH₄/812KJ =2.6mol