Question

If ammonia is manufactured at 356 K, is the reaction spontaneous, given that the enthalpy and entropy change for the reaction are -93 kJ/mol and -198 J/mol K, respectively?

A. Yes, the ∆G is -22.5 kJ/mol.
B. No, the ∆G is 22.5 kJ/mol.
C. No, the ∆G is 92kJ/mol.
D. Yes, the ∆G is -92kJ/mol.

Answer 1

A. Yes, the ∆G is -22.5 kJ/mol.

Further explanation

Gibbs free energy is the maximum possible work given by chemical reactions at constant pressure and temperature. Gibbs free energy can be used to determine the spontaneity of a reaction

If the Gibbs free energy value is <0 (negative) then the chemical reaction occurs spontaneously. If the change in free energy is zero, then the chemical reaction is at equilibrium, if it is> 0, the process is not spontaneous

Free energy of reaction (G) is the sum of its enthalpy (H) plus the product of the temperature and the entropy (S) of the system

Can be formulated: (at any temperature)

`\large {\boxed {\bold {\Delta G = \Delta H-T. \Delta S}}}`

or at (25 Celsius / 298 K, 1 atm = standard)

`\tt \Delta G=-93-(356* -0.198)\\\\\Delta G=-22.512~kJ/mol`

ΔG<0 ⇒ reaction spontaneous