Question

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`?

Answer 1

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.........