Using the information below, answer the following questions. MgO (s) + CO_2 (g)

Question

Using the information below, answer the following questions. MgO (s) + CO_2 (g) rightarrow MgCO_3 (s) Delta H degree rxn = - 178 kJ Delta S degree rxn = -161 J/K a. Will the above reaction be spontaneous at 900 degree C? Show your work for full credit. b. When the above reaction occurs spontaneously, it does so because i. it is entropy favored at high temperatures. ii. it is entropy favored at low temperatures. iii. it is enthalpy favored at high temperatures. iv. it is enthalpy favored at low temperatures. v. it is always spontaneous under any temperature conditions.

Explanation / Answer

a)

H = -178 KJ

S = -161 J/k

= -0.161 KJ/mol.K

T = 900 oC =(900+ 273) K

= 1173 K

use:

G = H - T*S

G = -178 - 1173 * -0.161

G = 10.9 KJ/mol

Since G is positive, the reaction is non spontaneous

b)

G = H - T*S

so, negative H will favour reaction

and positive S will favour reaction

Here H is negative, so it is enthalpy favoured reaction and will be spontaneous at low temperature

Answer: iv

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