Predict the sign for ΔSrxn for the following reaction at 298 K (no appendix required)?
Predict the sign for ΔSrxn for the following reaction at 298 K (no appendix required):
H2(g)+Cl2(g)→ 2HCl(g)
a) Negative
b) Positive
c) Zero
d) Not enough information given to answer the question
answer is b, can someone explain why?
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the number of gas molecules hasnt changed but what has changed are the actual molecules themselves.
S is entropy (i assume) and is a measure of disorder. H2 and Cl2 are more ordered than HCl
ie two pure substances have become mixed. therefore less ordered. since S is a measure of disorder, less ordered is a positive S value.
you need to calculate the entropy change for the reaction. You can calculate this by looking it up in standard tables. H2 has standard molar entropy 130.7, Cl2 is 223.0, and HCl is 186.9 (all units are in J/molºK). Now subtract reactants from products, and you get a net entropy change of:
dS = 2*186.9 - 223.0 - 130.7 = 20.1 J/molºK
which is +ve so ans is b