Answer to Question #161823 in Physical Chemistry for BECCA

Question

On the basis of your experience, predict which of the following reactions are spontaneous. Explain each of your answer 

(a) CO2(s) : CO2(g) at 25°C                        

(b) NaCl(s) →: NaCl(,) at 25°C 

(c) 2 NaCl(s) → 2 Na(s) + Cl2(g) 

(d) CO2(g) →: C(s) + O2(g)

Answer 1

a. Spontaneous: Solid carbon (IV) oxide, dry ice sublimes to gaseous carbon (IV) oxide at -78.5°C

b. Spontaneous: Solid NaCl dissolves in water to form the salt solution at ordinary room temperature.

C. Non spontaneous: This chemical decomposition requires an input of energy especially by using an electrolytic cell. It is a form of electrolysis.

D. Non spontaneous: With experience, it is not realistic for gaseous carbon dioxide to mysteriously change to Carbon and oxygen at room temperature. From literature review, the free energy change of the reaction is highly positive, which means it is not spontaneous. Normally, Carbon dioxide decomposes to Carbon monoxide and oxygen at a very high temperature of about 3600K.