15.2 Entropy and spontaneity (HL)

Question 1

Entropy

Answer 1

Measure of the distribution of energy among particles in a system

Question 2

What does greater entropy imply?

Answer 2

That there are more ways for the energy to be dispersed

Question 3

Spontaneous process

Answer 3

Occurs without the addition of energy, other than that required to overcome the initial activation energy barrier

Question 4

Which state of matter has the highest entropy?

Answer 4

Gases have highest entropy as energy can be distributed in more ways

Question 5

What happens when energy is dispersed?

Answer 5

It becomes less able to “do work” otherwise known as low-quality energy

Question 6

Does entropy increase or decrease when going from solids to gases? Is entropy change positive or negative?

Answer 6

Entropy increases and so change is positive

Question 7

Does increase in amt. of moles of gas lead to increase or decrease in entropy?

Answer 7

Increase in entropy so change is positive

Question 8

Unit for entropy

Answer 8

Jk/mol

Question 9

Standard entropy

Answer 9

Consequential entropy change from heating the substance from absolute 0K to thermodynamic standard temp. of 298K

Question 10

How can you calculate change in entropy?

Answer 10

Total entropy of products - Total entropy of reactants

Question 11

How do you calculate total entropy?

Answer 11

Entropy of system + entropy of surroundings

Question 12

Does a spontaneous reaction have a positive or negative entropy change?

Answer 12

Positive

Question 13

What is happening when there is an increase in entropy of surroundings?

Answer 13

Heat is being released from the system

Question 14

What is the equation for entropy of surroundings? How does this relate to entropy of the universe?

Answer 14

• Entropy of surroundings= - (Enthalpy change of process)/Abs. temperature (K)
• Entropy change of universe = Entropy change of system - (enthalpy change of process)/Abs. temp.

Question 15

Using equation for entropy of universe, calculate Gibbs free energy

Answer 15

> -TEntropy change of universe= Change in enthalpy - TEntropy change of system
Gibbs free energy change= Change in enthalpy - T*Entropy change of system

Question 16

Gibbs free energy

Answer 16

Energy associated with chemical reaction that can be used to do work. Total entropy change of universe

Question 17

Expansion work

Answer 17

Due to change in volume of system by expansion or contraction

Question 18

Position of equilibrium and why

Answer 18

When there is max value of entropy and min value of Gibbs free energy because there is maximum disorder and less “useful work”

Question 19

What happens during position of equilibrium?

Answer 19

The reaction will not proceed

Question 20

Factors which increase disorder

Answer 20

• Increased number of gaseous particles
• Mixing of particles
• Change of state to greater distance (Solid–>gas)
• Increased particle movement (eg. Increase temp.)

Question 21

Gibbs free energy change of formation

Answer 21

Free energy change when 1 mole of a compound is formed from its elements under standard conditions

Question 22

Equation for Gibbs free energy change of reaction

Answer 22

Gibbs free energy change (Products)- Gibbs free energy change (Reactants)

Question 23

Which reaction occurs despite not being spontaneous or energetically favorable?

Answer 23

Decomposition of calcium carbonate

Question 24

Are products or reactants more energetically stable?

Answer 24

Reactants are more energetically stable than products

Question 25

How can one decide spontaneity of a reaction?

Answer 25

By looking at the temperature at which they react

Question 26

What are the factors of spontaneity?

Answer 26

• Sign of entropy change
• Sign of enthalpy change
• Temp. at which reaction takes place

Question 27

What is sign of change in Gibbs free energy if reaction is spontaneous?

Answer 27

Change in G will be negative

Question 28

What are the signs of DeltaS and DeltaH when DeltaG is definitely negative?

Answer 28

DeltaH will be Negative and Delta S will be positive as -TDeltaS will be negative

Question 29

What happens to Delta G if Delta S and Delta H are both positive?

Answer 29

DeltaG will become more negative as temperature increases so more spontaneous as temp. increases

Question 30

What happens to Delta G if DeltaH is positive and DeltaS is negative?

Answer 30

DeltaG will be positive so reaction will never be spontaenous

Question 31

Are elements more or less stable when compounds have negative free energy change?

Answer 31

They are less thermodynamically stable than the compounds

Question 32

What is favored when a reaction has positive DeltaG?

Answer 32

The reverse reaction

Question 33

What can the sign of DeltaG tell and not tell us?

Answer 33

Sign can tell us spontaneity but not rate at which it will occur i.e. it can be spontaneous but happen really slowly

Question 34

If DeltaG is positive, does equilibrium lie closer to reactants or products?

Answer 34

Equilibrium lies closer to reactants

Question 35

What does equilibrium get closer to as DeltaG gets more negative?

Answer 35

It gets closer to pure products