Question

the enthalpy of combustion of propane, C3H8, is -2202kj/mol. what amount of heat is liberated when a sufficient amount of propane is combusted to form 1.25kg of carbon dioxide?

Answer 1

we have the Balanced chemical equation as:

C3H8 + 5 O2 ---> 3 CO2 + 4 H2O

Molar mass of CO2 = 1*MM(C) + 2*MM(O)

= 1*12.01 + 2*16.0

= 44.01 g/mol

mass of CO2 = 1.25 Kg = 1250 g

mol of CO2 = (mass)/(molar mass)

= 1250/44.01

= 28.4026 mol

From balanced chemical reaction, we see that

when 3 mol of CO2 produced, 1 mol of C3H8 is reacting

mol of C3H8 recats = (1/3)* moles of CO2

= (1/3)*28.4026

= 9.4675 mol

heat change = number of mol * delta h

= 9.4675 mol * (-2202 KJ/mol)

= - 2.08*10^4 KJ

negative sign shows that heat has been liberated

Answer: 2.08*10^4 KJ