Question

Given the values of ΔH∘rxn, ΔS∘rxn, and T below, determine ΔSuniv.

Predict whether or not each reaction will be spontaneous.

1.
ΔH∘rxn=− 118 kJ , ΔS∘rxn= 261 J/K , T= 294 K
ΔSuniv = ??? (J/K)

2.
ΔH∘rxn= 118 kJ , ΔS∘rxn=− 261 J/K , T= 294 K .
ΔSuniv = ??? (J/K)

3.
ΔH∘rxn=− 118 kJ , ΔS∘rxn=− 261 J/K , T= 294 K .
ΔSuniv = ??? (J/K)

4.
ΔH∘rxn=− 118 kJ , ΔS∘rxn=− 261 J/K , T= 565 K .
ΔSuniv = ??? (J/K)

Answer 1

Given the values of ΔH∘rxn, ΔS∘rxn, and T below, determine ΔSuniv.

Predict whether or not each reaction will be spontaneous.

1.
ΔH∘rxn=− 118 kJ , ΔS∘rxn= 261 J/K , T= 294 K
ΔSuniv = ??? (J/K)

Solution-

Given-

ΔH∘rxn=− 118 kJ = -118000 J/K

ΔS∘rxn= 261 J/K = S system

T= 294 K

We know the equation

ΔSsurroundings = -ΔH∘rxn / T = 118000 J/K/294K = 401.36J/K

Lets calculate the ΔSuniv

ΔSuniv = S system + S surroundings = 261 J/K + 4401.36J/K

ΔSuniv = 662.36 J/K

The entropy of the universe always increases in spontaneous reaction. At equilibrium, the entropy of the universe remains constant. A non-spontaneous reaction will never occur delta S of universe is negative never arise.

Therefore ΔSuniv is negative it means that the reaction is nonspontaneous and for positive ΔSuniv reaction is spontaneous.

Answer: ΔSuniv = 662.36 J/K ΔSuniv is positive therefore reaction is spontaneous.

2.
ΔH∘rxn= 118 kJ , ΔS∘rxn=− 261 J/K , T= 294 K .
ΔSuniv = ??? (J/K)

Solution-

Given-

ΔH∘rxn=118 kJ = 118000 J/K

ΔS∘rxn= -261 J/K = S system

T= 294 K

We know the equation

ΔSsurroundings = -ΔH∘rxn / T = -118000 J/K/294K = -401.36J/K

Lets calculate the ΔSuniv

ΔSuniv = S system + S surroundings = -261 J/K – 401.36J/K

ΔSuniv = -662.36 J/K

Answer: ΔSuniv = -662.36 J/K. ΔSuniv is negative therefore reaction is nonspontaneous.

3.
ΔH∘rxn=− 118 kJ , ΔS∘rxn=− 261 J/K , T= 294 K .
ΔSuniv = ??? (J/K)

Solution-

Given-

ΔH∘rxn= -118 kJ = -118000 J/K

ΔS∘rxn= -261 J/K = S system

T= 294 K

We know the equation

ΔSsurroundings = -ΔH∘rxn / T = 118000 J/K/294K = 401.36J/K

Lets calculate the ΔSuniv

ΔSuniv = S system + S surroundings = -261 J/K + 401.36J/K

ΔSuniv = 140.36 J/K

Answer: ΔSuniv = 140.36 J/K. ΔSuniv is positive therefore reaction is spontaneous.

4.
ΔH∘rxn=− 118 kJ , ΔS∘rxn=− 261 J/K , T= 565 K .
ΔSuniv = ??? (J/K)

Solution-

Given-

ΔH∘rxn= -118 kJ = -118000 J/K

ΔS∘rxn= -261 J/K = S system

T= 565 K

We know the equation

ΔSsurroundings = -ΔH∘rxn / T = 118000 J/K/565K = 208.84J/K

Lets calculate the ΔSuniv

ΔSuniv = S system + S surroundings = -261 J/K + 208.84J/K

ΔSuniv = -52.15 J/K

Answer: ΔSuniv = -52.15 J/K. ΔSuniv is negative therefore reaction is nonspontaneous.