Let's take first an exothermic combustion reaction.....
CH_4(g) + 2O_2(g) rarr CO_2(g)+2H_2O(l)
DeltaH_"reaction"^@=-891*kJ*mol^-1
And what does we mean by mol^-1? This means "PER MOLE of reaction as written". That is the combustion of 16*g methane, with 64*g dioxygen gives 44.0*g carbon dioxide, and 36.0*g of water PLUS 891*kJ of energy, which we can use for our hot water service, or to cook our meals, or even drive a car.....
Another way I could look at the reaction is to designate the energy as a product of the reaction.....which indeed it is.
CH_4(g) + 2O_2(g) rarr CO_2(g)+2H_2O(l)+891*kJ
And we could also calculate the energy output in terms of J*g^-1 of methane, i.e. here we gets 55.7*kJ*g^-1 of methane upon complete combustion. And thus when we use quoted values, we must be mindful of the reaction we perform. And these combustion data are routinely quoted in these terms.
And so in your given example.....
A+BCrarrB+AC;DeltaH^@=100*kJ*mol^-1
...metathesis of "MOLAR QUANTITIES" of A with BC to give stoichiometric B and AC REQUIRES AN ENERGY INPUT of 100*kJ; and so again it is a case of moles of reaction AS WRITTEN.
Are you happy with this spray?
