Based on the bond energies for the reaction below, what is the enthalpy of the reaction, in kJ? HC≡CH(g) + 5/2 O₂(g) → 2 CO₂(g) + H₂O(g)

Question

H single bond H = 432 kj

H single bond C = 411 kj

H single bond N = 386 kj

H single bond O = 459 kj

C single bond C = 346 kj

C single bond N = 305 kj

C single bond O = 358 kj

N single bond N = 167 kj

N single bond O = 201 kj

O single bond O = 142 kj

C double bond C = 602 kj

C double bond O = 799 kj

O double bond O = 494 kj

C double bond N = 615 kj

C triple bond C = 835 kj

C triple bond N = 887 kj

C triple bond O = 1072 kj

N triple bond N = 942 kj

Answer 1

Recall that it takes energy (+) to break bonds, and energy is release (-) when new bonds are formed.

The reactants are

H-C≡C-H and O=O

The products are

O=C=O and H-O-H

Energy required to break bond in the reactants:

1 C≡C bond = 835 kJ

2 C-H bonds = 411 kJ x 2 = 822 kJ

5/2 O=O bonds = 494 kJ x 5/2 = 1235 kJ

TOTAL energy to break bonds in reactants = 835 + 822 + 1235 = 2892 kJ

Energy released when new bonds are formed in the products:

4 C=O bonds (because CO2 is O=C=O) = 799 kJ x 4 = 3196 kJ

2 H-O bonds = 459 kJ x 2 = 918 kJ

TOTAL energy released (-) in forming products = -3196 + -918 = -4114 kJ

Note that more energy is released than is added to the system. Take the difference to find the enthalpy (∆H) of the reaction:

∆Hreaction = 3196 kJ - 4114 kJ = -918 kJ

Answer 2

Certainly, let's break it down step by step:

1. Bonds Broken (Reactants):

- Breaking 1 C≡C bond requires 835 kJ.

- Breaking 5 H-H bonds requires 5 times 432 kJ each.

- Breaking 2 O=O bonds requires 2 times 494 kJ each.

The total energy required to break these bonds is (835 + (5 x 432) + (2 x 494)) = 3,983 kJ.

2. Bonds Formed (Products):

- Forming 4 C=O bonds releases 4 times 799 kJ each.

- Forming 2 H-O bonds releases 2 times 459 kJ each.

The total energy released when these new bonds are formed is (4 x 799 + 2 x 459) = 4,114 kJ.

Now, calculate the enthalpy change (ΔH) by subtracting the energy released from the energy required to break the bonds:

ΔH = 3,983 - 4,114 = -131 kJ