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

FREE Expert Solution

Hess’s Law →  sum of ΔH° of individual steps is equal to ΔH° of overall reaction (ΔH°rxn)


Reaction 1: C(s)+2H2(g)→CH4(g)     ΔH1 =−74.6kJ

Reaction 2: C(s)+2Cl2 (g)→CCl4(g)    ΔH2=−95.7kJ

Reaction 3: H2 (g)+Cl2 (g)→2HCl(g)   ΔH3=−184.6kJ


Overall reaction: CH4(g)+4Cl2(g)→CCl4(g)+4HCl(g)       ΔH°rxn = ??


Recall that:

  • Reversing a reaction → ΔH changes sign
  • Changing coefficients by multiplication → multiply  ΔH with same factor


To get overall eqn: 

  • Get reverse of rxn (1)

CH4(g)     C(s)+2H2(g)            ΔH1,rev =+74.6kJ

  • Multiply rxn (3) by 2:

[H2 (g)+Cl2 (g)→ 2HCl(g)] x 2   2(ΔH3)

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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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