Question

what is the mass in kg of CO2 formed by combusting enough fuel to release 1.0 kJ of energy for this equation?

C3H8 + 5O2 -> 3CO2 + 4H2O

Answer 1

Given:

Hof(C3H8(g)) = -103.8 KJ/mol

Hof(O2(g)) = 0.0 KJ/mol

Hof(CO2(g)) = -393.509 KJ/mol

Hof(H2O(g)) = -241.818 KJ/mol

Balanced chemical equation is:

C3H8(g) + 5 O2(g) ---> 3 CO2(g) + 4 H2O(g)

ΔHo rxn = 3*Hof(CO2(g)) + 4*Hof(H2O(g)) - 1*Hof( C3H8(g)) - 5*Hof(O2(g))

ΔHo rxn = 3*(-393.509) + 4*(-241.818) - 1*(-103.8) - 5*(0.0)

ΔHo rxn = -2044 KJ

when -2044.0 KJ of heat is involved, 3 mol of CO2 is produced

So,

for -1 KJ, mol of CO2 = -1*3/-2044.0 KJ

= 1.468*10^-3 mol

Molar mass of CO2,

MM = 1*MM(C) + 2*MM(O)

= 1*12.01 + 2*16.0

= 44.01 g/mol

use:

mass of CO2,

m = number of mol * molar mass

= 1.468*10^-3 mol * 44.01 g/mol

= 6.459*10^-2 g

= 6.459*10^-5 Kg

Answer: 6.46*10^-5 Kg