Hess's Law and Thermochemical Equations

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[SOLVED] Hess's Law and Thermochemical Equations

Homework Statement


Question: 5.63:
The standard heat of formation of gaseous hydrogen bromine was first evaluated by means of the standard enthalpy values measured for the following reactions. The last three are standard heats of solution.

Cl2(g) + 2KBr(aq) --> Br2(aq) + KCl(aq) Delta H = -96.2kJ
H2(g) + Cl2(g) --> 2KCl (g) Delta H = -184kJ
HCl(aq) + KOH(aq) --> KCl(aq) + H2O Delta H = -57.3kJ
HBr(aq) + KOH(aq) --> KBr(aq) + H2O Delta H = -57.3kJ
HCl(g) --> HCl(aq) Delta H = -77.0kJ
Br2(g) --> Br2(aq) Delta H = -4.2kJ
HBr(g) --> HBr(aq) Delta H = -79.9kJ

Write the thermochemical equation for the formation of 1 mol of HBr(g) from its elements, including its value for Delta H final.

Homework Equations


(Included in question)

The Attempt at a Solution


I assumed you would have to isolate 1/2H2 and 1/2Br2 to make the final equation of 1/2H2 + 1/2Br2 --> HBr(g). No matter which way I work the equations I end up without H2 or Br2 depending on my method. However, I am wondering if I was on the right track. Is that what I am looking for?

EDIT: Realized my mistake. Disregarded the states of compounds. SOLVED
 
Last edited:

Answers and Replies

  • #2
TeethWhitener
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Looks good, slight typo in the HCl formation equation (not KCl).
 

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