Problem: Calculate ΔHrxn for the following reaction:CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g)Use the following reactions and given ΔH′s.C(s) + 2H2(g) → CH4(g)     ΔH = −74.6kJC(s) + 2Cl2(g) → CCl4(g)    ΔH = −95.7kJH2(g) + Cl2(g) → 2HCl(g)   ΔH = −184.6kJ

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  • For Hess's Law, we need to get the corresponding equation below using the sequence of reactions given

  • By manipulating the reaction, either reversing them or multiplying/dividing them to a certain factor, we can get to the target equation as well as the total enthalpy

CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g)


C(s) + 2H2(g) → CH4(g)     ΔH = −74.6kJ (needs to reverse)

C(s) + 2Cl2(g) → CCl4(g)    ΔH = −95.7kJ (retain)

H2(g) + Cl2(g) → 2HCl(g)   ΔH = −184.6kJ (multiply by 2 to get 4Cl2 and cancel out 4 HCl and 4 H2)


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Problem Details

Calculate ΔHrxn for the following reaction:
CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g)

Use the following reactions and given ΔH′s.
C(s) + 2H2(g) → CH4(g)     ΔH = −74.6kJ
C(s) + 2Cl2(g) → CCl4(g)    ΔH = −95.7kJ
H2(g) + Cl2(g) → 2HCl(g)   ΔH = −184.6kJ

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