Given the options, and entropy data, which gives the correct #DeltaS^@_"rxn"# for the reaction.... #2NH_3(g)rarrN_2(g)+3H_2(g)# #"A. -299"*J*K^-1*mol^-1# #"B. -199"*J*K^-1*mol^-1# #"C. +199"*J*K^-1*mol^-1# #"D. +99"*J*K^-1*mol^-1#?

1 Answer
anor277
Aug 8, 2017

This is simple summation.....I gets #C#

Explanation:

Look at your reaction:

#2NH_3(g) rarr N_2(g) + 3H_2(g)#

You produce 4 moles of gas from 2 moles of gas; the entropy, the statistical probability for disorder is likely to INCREASE......and so that leaves only #B# and #C# as viable answers.....

To decide, we have to an entropy summation......

#DeltaS_"rxn"^@=Sigma{S_"products"^@-S_"reactants"^@}#

But we have been given the individual entropies....and so.....

#DeltaS_"rxn"^@={3xx131+192-2xx193}*J*K^-1*mol^-1#

#=199*J*K^-1*mol^-1#, where #mol^-1# means per mole of REACTION as written.........

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