Entropy notes

Question 1

Definition of entropy

Answer 1

The measure of dispersal of energy in a system. The greater the entropy, the greater the dispersal of energy, the greater the disorder. Units: JK^-1mol^-1.

Question 2

What are the units of entropy?

Answer 2

JK^-1mol^-1.

Question 3

Why is entropy always a positive number?

Answer 3

All substances possess a degree of disorder, as particles are always moving.

Question 4

Give two examples of chemical changes that involve an increase in entropy.

Answer 4

1. Reactants are solids or liquids and the products include a gas.
2. There is no change in state but there are more particles of products than reactants.

Question 5

What is the equation for calculating entropy change.

Answer 5

*Refer to entropy notes.

Question 6

Describe how a system being more disordered affects the entropy change.

Answer 6

If a change makes a system more disordered, the entropy change is positive.

Question 7

Describe how a system being more ordered affects the entropy change.

Answer 7

If a change makes a system more ordered, the entropy change is negative.

Question 8

What is the equation for Gibbs free energy?

Answer 8

*Refer to entropy notes.

Question 9

What are the units for enthalpy change in the Gibbs free enrgy change equ?

Answer 9

kJmol^-1

Question 10

What are the units for entropy change in the Gibbs free energy change equ?

Answer 10

JK^-1mol^-1

Question 11

What are the units for temperature in the Gibbs free enrgy change equ?

Answer 11

Kelvin, K.

Question 12

When is a reaction feasible based on Gibbs free energy change value?

Answer 12

When the Gibbs free energy value is negative, the reaction is feasible.

Question 13

Is the reaction feasible when the standard enthalpy change is negative, the standard entropy change is positive and Gibbs free energy is always negative?

Answer 13

Reaction is always feasible.

Question 14

Is the reaction feasible when the standard enthalpy change is positive, the standard entropy change is negative and Gibbs free energy is always positive?

Answer 14

Reaction is never feasible.

Question 15

Is the reaction feasible when the standard enthalpyc hange is negtaive, the standard entropy change is negtive and Gibbs free energy is negtaive at low temperatures?

Answer 15

Feasible at low temperatures.

Question 16

Is the reaction feasible when the standard enthalpy change is positive, the standard entropy change is positive and Gibbs free energy is negative at high temperatures?

Answer 16

Feasible at high temperatures.

Question 17

What are the two conditions for an endothermic reaction to occur?

Answer 17

1. Entropy change must be positive.
2. The temperature must be high enough for (temperature x entropy change) > enthalpy change.

Question 18

What is the limitation of using Gibbs free energy values to predict feasibility?

Answer 18

The sign of the change of Gibbs free energy indicates the thermodynamic feasibility. It does not take into account the kinetics or rate of reaction.

Question 19

If a graph is plotted, what is the m and y?

Answer 19

m is (negtive entropy change).
y is the enthalpy change.