In: Chemistry
The enthalpy change for a chemical reaction is the sum of the energy consumed in breaking bonds and the energy released during bond formation. One way to determine the overall energy change for a chemical reaction is to apply Hess’s law to add together a group of reactions which can be arranged such that the chemical equations, when combined, give the overall equation we are trying to characterize.
The average propane cylinder for a residential grill holds
approximately 18 kg of propane. How much energy (in kJ) is released
by the combustion of 15.50 kilograms of propane in sufficient
oxygen?
balanced equation: C3H8(g)+5O2(g) --->
3CO2(g)+4H2O(l)
dH°reaction = (3*dH°f(CO2)+4*dH°f(H2O))-(1*dH°f(C3H8)+5*dH°f(O2))
= (3*-393.5+4*-285.83)-(1*-103.85+5*0)
= -2220 kj
1 mol Propane = 44 g propane = 2220 kj
no of mol of propane burned = 15.5/44 = 0.3523 kmol
amount of energy released(q) = n*DHrxn
= 0.3523*10^3*2220
= 7.82*10^5 kj