Energetics

Question 1

Define enthalpy of formation

Answer 1

Enthalpy change when one mole of substance is formed from its constituent elements with substances in standard states

Question 2

Define enthalpy of combustion

Answer 2

Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with substances in standard states

Question 3

Define enthalpy of neutralisation energy

Answer 3

Enthalpy change when 1 mole of water is formed in a reaction between acid and alkali under standard conditions

Question 4

Define first ionisation enthalpy

Answer 4

Enthalpy change when each atom in a mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions

Question 5

Define first electron affinity

Answer 5

Enthalpy change when one each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions

Question 6

Define enthalpy of atomisation

Answer 6

Enthalpy change when one mole of gaseous atoms is produced from an element in its standard state

Question 7

Define hydration enthalpy

Answer 7

Enthalpy change when one mole of gaseous ions becomes hydrated (dissolved in water)

Question 8

Define enthalpy of solution

Answer 8

Enthalpy change when one mole of ionic solid dissolved in an amount in water large enough that the dissolved ions are seperated

Question 9

Define bond dissociation enthalpy

Answer 9

Enthalpy change when one mole of covalent bonds are broken in the gaseous state

Question 10

Define lattice enthalpy of formation

Answer 10

Enthalpy change when one mole of solid ionic compound is formed from its gaseous constituent ions

Question 11

Define lattice enthalpy of dissociation

Answer 11

Enthalpy change when one mole of a solid ionic compound is broken up into its gaseous constituent ions

Question 12

Define enthalpy of vapourisation

Answer 12

Enthalpy change when one mole of a liquid is turned into a gas

Question 13

Define enthalpy of fusion

Answer 13

Enthalpy change when one mole of a solid is turned into a liquid

Question 14

What is a born-Haber cycle

Answer 14

Represents the energy change through a reaction

Question 15

Enthalpy change equation

Answer 15

Enthalpy change is bonds broken - bond broken

Question 16

Factors affecting lattice enthalpy

Answer 16

Ionic charge- the higher the charge on the ion, the stronger the electrostatic attraction and hence more energy released when bond formed

Ions radii- the smaller the ionic radii, the closer the electrons sit together, the stronger the attraction and the more exothermic the lattice enthalpy

Question 17

Factors affecting enthalpy of hydration

Answer 17

Ionic charge- the higher the charge, the stronger the attraction to the polar water molecules, the stronger the electrostatic attraction and hence the more energy released

Ionic radii- smaller ions have a higher charge density, meaning they attract water molecules more and have more exothermic enthalpy

Question 18

What is the entropy

Answer 18

The measurement of disorder

Question 19

How does entropy change across states

Answer 19

Solid has lowest enthalpy, water has middling and gas the highest

Question 20

When is there zero entropy

Answer 20

At absolute zero

Question 21

What is Specific heat capacity and it’s equation

Answer 21

The energy required (in joules) to raise the temp of 1g of substance by 1K

E= mc delta T

Question 22

What is the quanta

Answer 22

The package of energy

Question 23

Name the three types of molecular movement

Answer 23

Translation- molecules moving one place to another
Rotation- molecules spinning
Vibration- bonds stretching and compressing

Question 24

The order of quanta size

Answer 24

Vibration > rotation > translation

Question 25

How does heating affect entropy

Answer 25

Heating increases the total number of quanta, increasing the possible orders, increasing entropy

Question 26

When will entropy increase

Answer 26

Heating
Reduced pressure
More molecules
Physical state

Question 27

What is a spontaneous reaction

Answer 27

A physical or chemical change that occurs with no outside intervention

NOTE: energy may be initially supplied

Question 28

When is a reaction feasible

Answer 28

Total entropy change is +ve

Question 29

Second law of thermodynamics

Answer 29

For a spontaneous process, the total entropy change in a system and it’s surroundings will increase

Question 30

Equation for Change in entropy of surroundings

Answer 30

Delta S surroundings = negative delta H/ T

Delta S surroundings measured in JKmol-1
Delta H measures d in kJmol-1
T measured in K

Question 31

What does Gibbs free energy change tell us and what is it’s symbol

Answer 31

Delta G
Tells us if a reaction is feasible

Question 32

Equation for Gibbs free energy

Answer 32

Delta G = delta H minus T delta system

Question 33

If the enthalpy change is exothermic and entropy change is increased, is the reaction feasible

Answer 33

Yes Gibbs free energy is always negative

Question 34

If the enthalpy change is exothermic and entropy change is decreased, is the reaction feasible

Answer 34

Only feasible at low temperatures

Question 35

If the enthalpy change is endothermic and entropy change is increased, is the reaction feasible

Answer 35

Only feasible at high temperatures

Question 36

If the enthalpy change is endothermic and entropy change is decreased, is the reaction feasible

Answer 36

Never feasible, delta G always positive

Question 37

Key rule for Gibbs feee energy

Answer 37

Is delta G < 0, the reaction is feasible

Question 38

Equation for delta H in terms of Q

Answer 38

Delta H = (Q/1000) / moles reacted