Entropy

Question 1

What is electron affinity?

Answer 1

The enthalpy change when 1 mole of electrons is added to 1 mole of atoms in the gaseous phase to form 1 mole of 1- ions

Question 2

What is enthalpy of atomisation?

Answer 2

The enthalpy change that takes place when 1 mole of gaseous atoms form from the element in its standard state

Question 3

What is lattice enthalpy?

Answer 3

The enthalpy change when 1 mole of an ionic substance is formed from its gaseous ions under STD conditions

Question 4

What is the strength of an ionic bond related to?

Answer 4

Lattice enthalpy

Question 5

If a compound has greater ionic bonding, will it be more EXO or ENDO?

Answer 5

More exo

Question 6

Why can’t lattice enthalpy be measured directly?

Answer 6

As cannot form 1 mole of ionic lattice from gaseous ions

Question 7

What factors affect lattice enthalpy?

Answer 7

Charge

Size

Question 8

Why does charge affect lattice enthalpy?

Answer 8

Bigger ion = stronger attraction = more exo

Question 9

Why does size affect lattice enthalpy?

Answer 9

Smaller = ions more tightly packed together = greater attraction = more exo

Question 10

What happens to decomposition temperatures down a group?

Answer 10

Increase

Question 11

Why do decomposition temperatures increase down a group?

Answer 11

Mg2+ = smaller than Ba2+
So charge occupies smaller vol
= Mg2+ has higher “charge density”
This distorts electron cloud within negative ion
Weakening ionic bonding = reduces decomp temp

Question 12

What can Born-Haber cycles be used to calculate?

Answer 12

Ionic bond strength based on experimental data

Question 13

What equation do you use to calculate a missing enthalpy change on a Born-Haber cycle?

Answer 13

Lattice enthalpy = formation - sum of rest

Question 14

What is the cycle of a Born-Haber cycle?

Answer 14

Formation
Atomisation of metal
Atomisation of non-metal
1st IE of metal
1st electron affinity of non-metal 
Lattice enthalpy of compound

Question 15

What should you do to the enthalpy change when there is two moles of an element?

Answer 15

Multiply it by 2

Question 16

Which ions have a more negative lattice enthalpy?

Answer 16

Smaller sized ions as they can get closer together = stronger attraction

Question 17

What is enthalpy of solution?

Answer 17

The enthalpy change when 1 mole of ionic compound is completely dissolved in water under STD conditions

Question 18

What happens when you dissolve an ionic compound?

Answer 18

Break up ionic lattice into gaseous ions

Question 19

What is enthalpy of solution the reverse of?

Answer 19

Lattice enthalpy

Question 20

What is enthalpy of hydration?

Answer 20

The enthalpy change when 1 mole of gaseous ions are dissolved in water forming 1 mole of aqueous ions under STD conditions

Question 21

What should all hydration values be?

Answer 21

Exo

Question 22

Why is enthalpy of hydration exo?

Answer 22

Because it is bond making

Question 23

What equation must you use to calculate enthalpy of solution from a cycle?

Answer 23

L.E + enthalpy of solution = sum of enthalpies of hydration

Question 24

What factors affect enthalpy of hydration?

Answer 24

Charge

Size

Question 25

Why does charge affect enthalpy of hydration?

Answer 25

Higher charge on ion = greater attraction for H2O molecule = more exo

Question 26

Why does size affect enthalpy of hydration?

Answer 26

Smaller sized ions have greater charge density compared to large ions = greater attraction for H2O = more exo

Question 27

Why do exothermic chemical reactions happen?

Answer 27

A chemical reaction will proceed if products are energetically more stable than reactants

Question 28

What is entropy?

Answer 28

The measure of the dispersal of energy in a system

Question 29

What is more likely exist disordered or ordered states?

Answer 29

Disordered

Question 30

How is entropy related to spontaneous direction of change?

Answer 30

Spontaneous direction of change is from a less probable to more probable Meaning entropy always INCEASES

Question 31

What is the symbol for entropy?

Answer 31

S | ΔS

Question 32

What number will entropy produce?

Answer 32

Always a positive number

Question 33

What are the units for entropy?

Answer 33

J K-1 mol-1 | K = kelvin

Question 34

Out of a solid, liquid and gas which has the lowest entropy?

Answer 34

Solid = more order but still some entropy as particles vibrate in fixed position

Question 35

Out of a solid, liquid and gas which has the highest entropy?

Answer 35

Gas = least order

Question 36

What happens to entropy as temperature increases?

Answer 36

Entropy increases

Question 37

What happens to ΔS if a change makes the system more random?

Answer 37

+ΔS

Question 38

What happens to ΔS if a change makes the system less random (more order)?

Answer 38

-ΔS

Question 39

For chemical reactions we can predict entropy change to be +/-, by using what?

Answer 39

State symbols

Question 40

CaCO3 (s) ----> CaO (s) + CO2 (g)

Answer 40

+ΔS

Question 41

N2O4 (g) ----> 2NO2 (g)

Answer 41

+ΔS | As more moles on right side = more chance for disorder

Question 42

2CH3OH (l) + 3O2 (g) ----> 2CO2 (g) + 4H2O (l)

Answer 42

-ΔS | As less moles of gas on right side

Question 43

What is the definition for calculating entropy?

Answer 43

The entropy change that accompanies a reaction in molar quantities expressed in the equation, under STD conditions

Question 44

What is the equation for calculating entropy?

Answer 44

ΔS = sum of S products - sum of S reactants

Question 45

What are the steps for calculating entropy?

Answer 45

Decide whether +/-ΔS from symbol equation | Put values given in question in equation

Question 46

What type of reaction must it be for it to be spontaneous?

Answer 46

Exo

Question 47

Why must a reaction be exo to be spontaneous?

Answer 47

As the heat given out by the recations it increases the disorder (entropy) of the surroundings so in the universe disorder increases

Question 48

What is the equation of entropy of surroundings?

Answer 48

ΔS surroundings = - ΔH / Temp

Question 49

In the entropy of surroundings equation what must the ΔS be?

Answer 49

Positive

Question 50

Why must the ΔS be positive in the equation for entropy of surroundings?

Answer 50

For spontaneous change

Question 51

What is the Gibbs Free Energy equation?

Answer 51

ΔG = ΔH -TΔS <0

Question 52

What is the Gibbs Free Energy equation dictated by?

Answer 52

Temperature

Question 53

What mus you always do if you get an equation on the Gibbs Free Energy?

Answer 53

Write out the equation

Question 54

What must ΔG be for a reaction to proceed?

Answer 54

Negative

Question 55

If ΔG is positive what will happen?

Answer 55

Th reaction won't be feasible

Question 56

What does ΔG= at the point of feasibility?

Answer 56

0

Question 57

What is the assumption made for the point of feasibility?

Answer 57

ΔH and ΔS do not vary with temperature

Question 58

What does temperature adjust in the GIbbs Free Energy equation?

Answer 58

The significance of ΔS system

Question 59

At low temperature what happens in Gibbs Free Energy equation?

Answer 59

ΔG= ΔH (-TΔS = negible) | So only reations with -ΔH can proceed so ΔG<0

Question 60

At high temperatures what happens in Gibbs Free Energy equation?

Answer 60

ΔG = -TΔS (ΔH = negible) | So any reactions with +ΔH can proceed as -TΔS<0

Question 61

What are the limitations of ΔG?

Answer 61

Even if ΔG is negative the reaction may not be feasible Because AE might be too high Or rate of reaction is very slow

Question 62

How do you calculate ΔG (feasibility)?

Answer 62

Calculate ΔS Calculate ΔH Divide ΔS by 1000 (for kJ) Then put into ΔG= ΔH -TΔS

Question 63

What units must the temperature be in for Gibbs Free Energy equation?

Answer 63

Kelvin

Question 64

If you calculate the value of ΔG, and it is positive what does this mean?

Answer 64

The reaction is not feasible as it must be <0

Question 65

How would you then use the Gibbs Free Energy equation to calculate the temperature?

Answer 65

Assume feasibility = ΔG = 0 So ΔH -TΔS = 0 Rearrange to give ΔH/ ΔS = T The convert answer to degrees C

Question 66

How do you calculate ΔS?

Answer 66

Products - reactants

Question 67

How do you calculate Δf?

Answer 67

Products - reactants