# 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?

Aug 8, 2017

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

#### Explanation:

Look at your reaction:

$2 N {H}_{3} \left(g\right) \rightarrow {N}_{2} \left(g\right) + 3 {H}_{2} \left(g\right)$

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.....

$\Delta {S}_{\text{rxn}}^{\circ} = \left\{3 \times 131 + 192 - 2 \times 193\right\} \cdot J \cdot {K}^{-} 1 \cdot m o {l}^{-} 1$

$= 199 \cdot J \cdot {K}^{-} 1 \cdot m o {l}^{-} 1$, where $m o {l}^{-} 1$ means per mole of REACTION as written.........