Question

For each of the following reactions, calculate ΔH∘rxnΔHrxn∘, ΔS∘rxnΔSrxn∘, and ΔG∘rxnΔGrxn∘ at 25 ∘C∘C. State whether or not the reaction is spontaneous. If the reaction is not spontaneous, would a change in temperature make it spontaneous? If so, should the temperature be raised or lowered from 25 ∘C∘C?

Part A

2CH4(g)→C2H6(g)+H2(g)2CH4(g)→C2H6(g)+H2(g)

Express your answer to one decimal place.

Part B

Calculate ΔS∘rxnΔSrxn∘ at 25 ∘C∘C.

Express your answer to one decimal place.

Part D

2NH3(g)→N2H4(g)+H2(g)2NH3(g)→N2H4(g)+H2(g)

Express your answer to one decimal place.

Part E

Calculate ΔS∘rxnΔSrxn∘ at 25 ∘C∘C.

Express your answer to one decimal place.

Part G

N2(g)+O2(g)→2NO(g)N2(g)+O2(g)→2NO(g)

Express your answer using three significant figures.

Part H

Calculate ΔS∘rxnΔSrxn∘ at 25 ∘C∘C.

Express your answer to one decimal place.

Part J

2KClO3(s)→2KCl(s)+3O2(g)2KClO3(s)→2KCl(s)+3O2(g)

Express your answer to one decimal place.

Part K

Calculate ΔS∘rxnΔSrxn∘ at 25 ∘C∘C.

Express your answer to one decimal place.

Answer 1

Sol.

Part A :

Reaction : 2CH4(g) <----> C2H6(g) + H2(g)

Standard change in enthalpy of reaction = deltaH°rxn

= deltaHf°(C2H6 , g ) + deltaHf°(H2 , g ) - 2 × deltaHf°(CH4 , g )

= - 84.68 + 0 - 2 × ( - 74.6 )

= 64.5 KJ

Part B :

Reaction : 2CH4(g) <----> C2H6(g) + H2(g)

Standard change in entropy  of reaction = deltaS°rxn

= deltaSf°(C2H6 , g ) + deltaSf°(H2 , g ) - 2 × deltaSf°(CH4 , g )

= 229.2 + 130.7 - 2 × 186.3

= - 12.7 J / K

Part D :

Reaction : 2NH3(g) ----> N2H4(g) + H2(g)  

Standard change in enthalpy of reaction = deltaH°rxn

= deltaHf°(N2H4 , g ) + deltaHf°(H2, g) - 2 × deltaHf°(NH3 , g)

= 95.4 + 0 - 2 × ( - 45.9 )

= 187.2  KJ

Part E :

Reaction : 2NH3(g) ----> N2H4(g) + H2(g)  

Standard change in entropy of reaction = deltaS°rxn

= deltaSf°(N2H4 , g ) + deltaSf°(H2, g) - 2 × deltaSf°(NH3 , g)

= 238.5 + 130.7 - 2 × 192.8

= - 16.4  J / K