Thermodynamics and kinetics (inorganic)

Question 1

Standard enthalpy of formation definition

Answer 1

The enthalpy change when one mole of a substance is formed from its elements at standard states.

Question 2

Standard states/conditions

Answer 2

1 atmosphere pressure
1 mol l-1 concentration
298K temperature

Question 3

What does a nought mean in enthalpy formulas

Answer 3

It means at standard conditions.

Question 4

298K at degrees Celsius

Answer 4

25 degrees Celcius

Question 5

Enthalpy of combustion definition

Answer 5

The enthalpy change of a when one mole of a substance completely burns in oxygen.

Question 6

Standard enthalpy of formation symbol

Answer 6

ΔHf°

Question 7

Standard enthalpy calculation formula

Answer 7

ΔH° = ΣΔHf°(products)- ΣΔHf°(reactants)
(Take into account mole ratio)

Question 8

Enthalpy of formation of elements

Answer 8

Equals 0

Question 8

Where do you find enthalpies of formation

Answer 8

In the data booklet with the enthalpies of combustion.

Question 9

Entropy symbol

Answer 9

S

Question 10

Entropy

Answer 10

The measure of disorder in a system

Question 11

When does entropy increase

Answer 11

When temperatures rise
Where a substance melts, boils or dissolves (change of state)

Question 12

Solids entropy

Answer 12

Low due to atoms being closely packed together.

Question 13

Gas entropy

Answer 13

High due to atoms being able to move freely.

Question 14

Liquid entropy

Answer 14

Medium due to irregular arrangement of atoms.

Question 15

When does entropy increase in state changes

Answer 15

Right after the melting or boiling point there is a rapid increase in the entropy, then entropy flattens off again.

Question 16

First law of thermodynamics

Answer 16

Energy can’t be destroyed or created, only changed from one form to another.

Question 17

Second law of thermodynamics

Answer 17

The entropy of a reaction system and its surroundings increases for a spontaneous process.

Question 18

Third law of thermodynamics

Answer 18

The entropy of a perfect crystal at 0K is zero.

Question 19

Kelvin to degrees

Answer 19

0 degrees is 273 kelvin

Question 20

Change in standard entropy

Answer 20

ΔS°= ΣS°(products) - ΣS°(reactants)

Question 21

When is a reaction feasible

Answer 21

When free energy (ΔG) is <0

Question 22

Free energy formula

Answer 22

ΔG = ΔH - TΔS
Where t is in kelvin and s is in J K-1 mol -1

Question 23

Temperature where a reaction becomes feasible

Answer 23

T= ΔH -ΔG/ΔS

Question 24

Standard free energy of formation formula

Answer 24

ΔG° = ΣΔG°f(products) - ΣΔG°f(reactants)

Question 25

ΔG at equilibrium

Answer 25

ΔG= 0

Question 26

ΔG when forwards reaction is favoured

Answer 26

ΔG° <0

Question 27

ΔG when reverse reaction is favoured

Answer 27

ΔG°>0

Question 28

why are standard states no longer required at eqiulibrium.

Answer 28

When the reaction starts there is no longer 1 mol l-1 concentration due to products being formed, therefore standard conditions aren’t used.

Question 29

Where does equilibrium occur in free energy

Answer 29

When the G value of the mixture is lowest

Question 30

How does free energy indicate equilibrium position

Answer 30

A reaction is feasible if the free energy is less than 0, if the free energy of a forwards reaction is negative the forwards reaction will be favoured since the reverse reaction will have positive free energy.
The reverse is also true so if the reverse reaction free energy is less and 0 the forwards reaction free energy will be positive and the reverse reaction will be favoured.

Question 31

Order of reaction if the rate doubles when concentration of reactant doubles

Answer 31

1st order

Question 32

Order of reaction if rate quadruples when concentration doubles

Answer 32

2nd order

Question 33

Order of reaction if rate remains constant when concentration of reactant doubles

Answer 33

Zero order

Question 34

Reaction rate formula

Answer 34

Rate =k[A]^m[B]^n

Question 35

Overall order of a reaction

Answer 35

Add the rate orders

Question 36

Calculating rate constant k

Answer 36

Produce rate equation
Rearrange for k
Substitute in values
Find the units

Question 37

Zero order on graph

Answer 37

Straight line downwards

Question 38

1st order in graph

Answer 38

Flat exponential line downwards

Question 39

2nd order graph

Answer 39

Steep exponential line downwards

Question 40

Rate determining step rule

Answer 40

A reaction cannot go faster than the slowest step of the reaction.

Question 41

Rate determining step

Answer 41

The slowest step in the reaction.

Question 42

Finding an order of a multi step reaction

Answer 42

Look at the slowest step and the reactants in that stage, the look at the number of moles and that is your reaction order.

Question 43

Free energy in equilibrium explanation

Answer 43

If ΔG <0 for forwards reaction then this reaction is feasible but the reverse reaction is not feasible. And vice versa.
This means the forwards reaction will occur which will change reactants into products and standard conditions will be lost since there is no longer 1mol l-1 of either reactants or products.
As reactants are converted into products entropy (disorder) increases which will decrease the ΔG value since ΔG =ΔH - TΔS. (Since we are subtracting a bigger and bigger entropy value)
ΔG will decrease until a minimum value which is where equilibrium is achieved.