Entropy 178-179

Question 1

Define entropy.

Answer 1

Entropy, S, is the quantitative measure of the degree of disorder in a system.

Question 2

Why is the value of entropy always positive?

Answer 2

All substances posses some degree of disorder because particles are always in constant motion. Thus, S is always a positive number.

Question 3

Explain how entropy changes naturally for in most systems?

Answer 3

Nature tends to move from order to disorder in isolated systems. For example, gas molecules spread out over time to fill a space, increasing their entropy over time.

Question 4

Give some examples of when entropy increases.

Answer 4

• The entropy of a pure substance increases with increasing temperature.
• Entropy increases during the changes in state that give more randomness: solid →liquid→gas.
• Entropy increases when a solid lattice dissolves.
• Entropy increases in a reaction in which there is an increases in the number of gaseous molecules.

Question 5

What are the units of standard entropies?

Answer 5

J K^-1 mol^-1

Question 6

How can the entropy change of a reaction be calculated?

Answer 6

Change is S = ΣS_(products) - ΣS_(reactants)

Question 7

Define standard entropy change of reaction.

Answer 7

The entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.