A simple Hess's law problem I can't seem to get right!?

  • Thread starter Thread starter Curious Guy 89
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Curious Guy 89

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Given the following thermochemical equations:

CaO(s) + Cl2(g) --> CaOCl2(s) ΔH= -110.9 kJ
2NaCl(s) + Ca(OH)2(s) + Br2(l) --> H2O(l) + CaOCl2(s) + 2NaBr(s) ΔH= +60.2 kJ
Ca(OH)2(s) --> CaO(s) + H2O(l) ΔH= +65.1kJ

determine the value of ΔH (in kJ) for the reaction:
1/2 Cl2(g) + NaBr(s) --> NaCl(s) + 1/2 Br2 (l)

a) 14.4 kJ
b) -53.0 kJ
c) -20.5 kJ
d) -108 kJ
e) -14.4 kJ

According to the teacher's key the answer SHOULD be choice B, but I keep getting C and can't figure out how he is getting B. Could someone tell me what I'm doing wrong? The teacher is not available for office hours and isn't responding to my email and my final is tomorrow!
 
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