Question 17.3: Calculate the standard entropy of reaction at 25 °C for the ......

Chemistry [1089329]

Calculate the standard entropy of reaction at 25 °C for the Haber synthesis of ammonia:

N_{2}(g) + 3  H_{2}(g)\longrightarrow 2  NH_{3}(g)

STRATEGY

To calculate ΔS° for the reaction, subtract the standard molar entropies of all the reactants from the standard molar entropies of all the products. Remember to multiply the S° value for each substance by its coefficient in the balanced chemical equation.

IDENTIFY
Known	Unknown
S° values for reactants and products (Appendix B)	Standard entropy of reaction (ΔS°)

Step-by-Step

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ΔS°=2  S°(NH_{3})  –  [S°(N_{2}) + 3  S°(H_{2})]

=(2  mol)(192.3\frac{J}{K  \cdot  mol})-[(1  mol)(191.5\frac{J}{K  \cdot  mol})+(3  mol)(130.6\frac{J}{K  \cdot  mol})]

= – 198.7 J/K

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