Thermodynamics Part 2

Question 1

What is entropy a measure of

Answer 1

Disorder in a system

Question 2

Symbol for entropy

Answer 2

S

Question 3

Why are the values for entropy always positive

Answer 3

Particles always have energy

Question 4

Units of entropy

Answer 4

JK-1mol-1

Question 5

What needs to be done when combining entropy with enthalpy

Answer 5

/1000

Question 6

Factors which determine the entropy of a substance

Answer 6

• state of matter
• dissolving
• mixtures
• number of particles

Question 7

What is the entropy trend in state of matter and why

Answer 7

Entropy increases solid>liquid>gas as they’re more disordered

Question 8

Trend in dissolving solid + solvent> solution

Answer 8

Entropy increases

Question 9

Trend in entropy in formation of mixtures

Answer 9

Entropy increases

Question 10

Trend in entropy as number of particles increases

Answer 10

Entropy increases

Question 11

How to calculate delta S

Answer 11

Sum of S(prods) - Sum of S(reacts)

Question 12

Effect of temperature on entropy: entropy is zero at 0K as

Answer 12

The particles have no kinetic energy therefore no movement

Question 13

Effect of temperature on entropy: why does entropy increase as temperature increases

Answer 13

Particles move more and become more disordered

Question 14

Effect of temperature on entropy: why is the second increase in entropy much bigger than the first

Answer 14

Gas particles have far more disorder than liquid therefore the entropy change from liquid to gas if much greater than solid to liquid

Question 15

What can the values for entropy change be despite S values always being positive

Answer 15

Either positive or negative

Question 16

When is Delta S positive

Answer 16

When there is an increase in disorder

Question 17

Examples of positive delta S

Answer 17

• dissolving
• increase in number of moles of gas
• melting
• boiling

Question 18

Why is delta S positive when dissolving occurs

Answer 18

The solution is more disordered than the solvent and solute

Question 19

Why is delta S positive when there is an increase in the number of miles of gas

Answer 19

More moles of gas are more disordered

Question 20

When is delta S positive when melting occurs

Answer 20

Liquids are more disordered than solids

Question 21

Why is delta S positive when boiling occurs

Answer 21

Gases are much more disordered than liquids

Question 22

What is a positive delta S favourable in terms of

Answer 22

Entropy

Question 23

When is delta S negative

Answer 23

When there is a decrease in disorder

Question 24

Examples of negative delta S

Answer 24

• precipitation
• decrease in number of moles of gas
• freezing
• condensing

Question 25

Why is delta S negative in precipitation reactions

Answer 25

The solid is less disordered than the aqueous ions

Question 26

Why is delta s negative when there’s a decrease in the number of moles of gas

Answer 26

Less moles of gas are less disordered

Question 27

Why is delta s negative when freezing occurs

Answer 27

Solids are led disordered than liquids

Question 28

Why is delta s negative when condensing occurs

Answer 28

Liquids are much less disordered than gases

Question 29

What is a negative delta unfavourable in terms of

Answer 29

Entropy

Question 30

Units of enthalpy change

Answer 30

kJmol-1

Question 31

What is delta H in an exothermic reaction

Answer 31

Negative

Question 32

When is a negative delta H favourable in terms of

Answer 32

Enthalpy change

Question 33

What is delta h in an endothermic reaction

Answer 33

Positive

Question 34

What is a positive delta h unfavourable in terms of

Answer 34

Enthalpy change

Question 35

How to calculate delta H for a reaction

Answer 35

Sum of delta H products - sum of delta H reactants

Question 36

What three factors contribute to whether a reaction will be feasible at a given temperature

Answer 36

Temperature Entropy change Enthalpy change

Question 37

What do the 3 factors that contribute to whether a reaction is feasible at given temperature combine to give

Answer 37

A new quantity called the Gibbs free energy change

Question 38

Gibbs free energy change

Answer 38

Delta G = delta H- T delta S

Question 39

What must delta G be for a reaction to be feasible

Answer 39

Zero or negative

Question 40

Why must delta s be converted to kJK-1mol-1

Answer 40

The units of Delta g and delta H are kJmol-1

Question 41

Does the sign of delta G tell us anything about the rate of a reaction

Answer 41

No, it only tells us whether a reaction is thermodynamically feasible

Question 42

When may a reaction not happen even if it is thermodynamically feasible

Answer 42

If the activation energy is too high

Question 43

Why am endothermic reaction can take place spontaneously at room temp: when does a spontaneous process oroceed

Answer 43

When delta g is less than or equal to 0

Question 44

Why am endothermic reaction can take place spontaneously at room temp: what does TdeltaS have to be greater than for a reaction to be spontaneous at room temp

Answer 44

Delta H

Question 45

Why can a relation with a negative (unfavourable) entropy change be feasible at room temperature

Answer 45

Even though delta S is negative, delta H is also negative

Question 46

Formula relating the calculation of temperature at which a reaction becomes feasible

Answer 46

T= deltaH/deltaS

Question 47

What do free energy graphs show

Answer 47

The relationship between free energy and temperature

Question 48

What can free energy graphs be used to find

Answer 48

The temperature at which a reaction becomes feasible

Question 49

What equation can we use for free energy graphs and why

Answer 49

The plot is always a straight line Y=mx+c