Question

Thermochemistry Consider the combustion of propane: CzHe (g) + 5 02 (g) - 3 CO2 (g) + 4 H20 (g) Use the heats of formation in the table to calculate AH reaction. substance C.H. (g) CO2 (g) 02 (9) H2O(g) AH" (kl/mol) -105 -394 0 -242 Is this reaction exothermic or endothermic? Explain your choice. The surroundings would become (circle one) warmer cooler Energy is (circle one) released from absorbed by the reaction.

Answer 1

1)

Given:

Hof(C3H8(g)) = -105 KJ/mol

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

Hof(CO2(g)) = -394 KJ/mol

Hof(HH2O(g)) = -242 KJ/mol

Balanced chemical equation is:

C3H8(g) + 5 O2(g) ---> 3 CO2(g) + 4 HH2O(g)

ΔHo rxn = 3*Hof(CO2(g)) + 4*Hof(HH2O(g)) - 1*Hof( C3H8(g)) - 5*Hof(O2(g))

ΔHo rxn = 3*(-394) + 4*(-242) - 1*(-105) - 5*(0.0)

ΔHo rxn = -2045 KJ

Answer: -2045 KJ

2)

ΔHo rxn is negative.

So, this is exothermic

Answer: exothermic

3)

The reaction releases heat and surrounding absorbs it.

So, surround’s ending becomes warmer

Answer: warmer

4)

ΔHo rxn is negative.

So, energy is released from the reaction

Answer: released from