Question

Calculate ∆Hrxn for the following reaction:

CH₄ (g) + 4 Cl₂ (g) → CCl₄ (g) + 4 HCl (g)
Use the following reactions and give ∆H values:
C (s) + 2H₂ (g) → CH₄ (g) quad Δ H = -74.6 , kJ
C (s) + 2Cl₂ (g) → CCl₄ (g) quad Δ H = -95.7 , kJ
H₂ (g) + Cl₂ (g) → 2HCl (g) quad Δ H = -92.3 , kJ

a. -75.2 kJ
b. -192.6 kJ
c. -15.4 kJ
d. 10.4 kJ

Answer 1

To calculate ΔHrxn for the given reaction, we can use bond energies and apply Hess's Law. By reversing and multiplying the given reactions appropriately, we can obtain the desired reaction and calculate ΔHrxn to be +681.2 kJ.

Step-by-step explanation:

To calculate ΔHrxn for the reaction CH₄ (g) + 4 Cl₂ (g) → CCl₄ (g) + 4 HCl (g), we can use the concept of bond energies and apply Hess's Law. The given reactions show the bond energies and enthalpy changes for different reactions involving the same elements. We can add or subtract these reactions to obtain the desired reaction and calculate ΔHrxn.

First, we need to reverse the reaction C (s) + 2H₂ (g) → CH₄ (g) to obtain CH₄ (g) → C (s) + 2H₂ (g) with ΔH = +74.6 kJ. Then, we can multiply the reaction by 4 to obtain 4CH₄ (g) → 4C (s) + 8H₂ (g) with ΔH = 4x74.6 kJ = +298.4 kJ.

Next, we need to reverse the reaction C (s) + 2Cl₂ (g) → CCl₄ (g) to obtain CCl₄ (g) → C(s) + 2Cl₂ (g) with ΔH = +95.7 kJ. Finally, we can multiply the reaction by 4 to obtain 4CCl₄ (g) → 4C(s) + 8Cl₂ (g) with ΔH = 4x95.7 kJ = +382.8 kJ.

Now, we can add the two reactions together to obtain the desired reaction: 4CH₄ (g) + 4CCl₄ (g) → 4C(s) + 8HCl (g) + 8Cl₂ (g) with ΔHrxn = +298.4 kJ + +382.8 kJ = +681.2 kJ.