[22.4] entropy

Question 1

define entropy

Answer 1

measure of dispersal of energy in a system

Question 2

what is the symbol and units for entropy?

Answer 2

• symbol = S
• units = J K⁻¹mol⁻¹

Question 3

describe the energy dispersal in a system with a large entropy value

Answer 3

• more energy dispersal
• greater disorder in a system

Question 4

describe the relative entropies for solids, liquids, and gases

Answer 4

• solid = smallest entropy
• liquid = greater entropy
• gas = greatest entropy

Question 5

what happens when a system changes to become more or less random?

Answer 5

• if a system changes to become more random, energy can be spread out more so there will be an entropy change ΔS which is positive
• if a system changes to become less random, energy becomes concentrated so entropy change ΔS will be negative

Question 6

when is a spontaneous reaction most likely?

Answer 6

• solid ➞ liquid ➞ gas
• few molecules ➞ more molecules
• solute + solvent ➞ solution

Question 7

what happens to the entropy of a system if you increase the temperature

Answer 7

• if you add more energy, the randomness of particles increases
• energy is spread out more and ΔS is psoitive
• when any substance changes state from solid to liquid to gas

Question 8

what happens to the entropy of a system if you increase the number of gaseous molecules?

Answer 8

• more molecules increases the disorder of particles
• energy is spread out mroe and ΔS is positive

Question 9

what is the standard entropy S of a substance?

Answer 9

• entropy of one mole of a substnace under standard conditions (100 kPa and 298K)
• it is always positive

Question 10

how can you calculate entropy changes?

Answer 10

ΔS = ∑S (products) - ∑S (reactants)

Question 11

explanations for decreased entropy (exam q) [5]

reverse for increased entropy

Answer 11

• X has less disorder
• more order
• fewer ways of arranging energy
• less freedom
• less random molecules