Chapter 2 Energy

Question 1

Definition of lattice enthalpy?

Answer 1

The enthalpy change for the formation of 1 mole of an ionic lattice from gaseous ions.

Question 2

Definition of enthalpy of hydration?

Answer 2

Enthalpy change when one mole of gaseous ions are dissolved in water.

Question 3

Definition of enthalpy of solution?

Answer 3

Enthalpy change when one mole of a solute dissolves in water.

Question 4

Is enthalpy change of hydration endothermic or exothermic?

Answer 4

Exothermic as bonds are being made with water.

Question 5

What are the trends of enthalpy of hydration down a group?

Answer 5

Enthalpy of hydration becomes less exothermic down a group because as the size of the ions increases, the attraction to the water molecules weakens. Less energy is released when the bonds form.

Question 6

What is the trend of enthalpy of hydration of metal ions across a period?

Answer 6

Enthalpy of hydration becomes more exothermic due to charge increasing and metal ions getting smaller. This means attraction to water molecules increases so more energy is released when bonds form.

Question 7

Definition of enthalpy change of atomisation?

Answer 7

Enthalpy change when one mole of gaseous atoms is formed from its elements in its standard state.

Question 8

Definition of first electron affinity?

Answer 8

The enthalpy change when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous ions, each with a charge of -1 under standard conditions.

Question 9

Definition of first ionisation energy?

Answer 9

Energy required to remove one mole of electrons from one mole of gaseous atoms.

Question 10

What dictates the size of lattice enthalpy?

Answer 10

• size of ions involved
• charges on the ions
• ionic bond strength

Question 11

What are standard conditions?

Answer 11

• 1 mol dm^3
• 100kPa
• 298k/ 25°C

Question 12

Definition of entropy?

Answer 12

Measure of the dispersal of energy in a system. The more disorder in a system the higher the entropy.

Question 13

What is the entropy at 0 kelvin?

Answer 13

0 J k^-2 mol^-1 (perfect crystals)

Question 14

What is the effect of temperature increasing on entropy?

Answer 14

As temperature increases the particles gain kinetic energy so arrangement of particles is more random and they become less ordered.

Question 15

Definition of ‘standard’ entropy?

Answer 15

The entropy content of one mole of a substance under standard conditions.

Question 16

How does the number of gas molecules affect entropy?

Answer 16

An increase in the number of gas molecules causes an increase in entropy, vice versa.

Question 17

How do you calculate enthalpy/ entropy change?

Answer 17

(sum of enthalpy/ entropy of products) - (sum of enthalpy/ entropy of reactants)

Question 18

How do you calculate free energy change to see if a reaction is feasible?

Answer 18

Gibbs equation: ΔG = ΔH – TΔS
ΔG = change in free energy
ΔH = change in enthalpy
T = temperature (K)
ΔS = change in entropy

Question 19

What value must ΔG be for the reaction to be feasible?

Answer 19

ΔG<0

Question 20

Which direction do electrons flow in electrochemical cells?

Answer 20

From the most reactive metal to least

Question 21

What is the purpose of a salt bridge in electrochemical cells?

Answer 21

Allows ions to flow through to balance out the charges and forces electrons to flow in the wire.

Question 22

What conditions are required to measure voltage using an electrochemical cell?

Answer 22

Standard conditions

Question 23

What is a standard electrode potential?

Answer 23

The voltage of the half-cell reaction relative to a standard hydrogen electrode under standard conditions.

Question 24

What are all electrode potentials relative to?

Answer 24

Hydrogen (H2/H+) half cell

Question 25

What are salt bridges made of?

Answer 25

Filter paper soaked in potassium nitrate (inert electrolyte)

Question 26

What is the purpose of the inert platinum electrode?

Answer 26

Allow electrons to pass into or out of the half cell via a connecting wire.

Question 27

What does a standard hydrogen half cell consist of?

Answer 27

• HCl of concentration 1 mol dm^-3 (source of H+ ions)
• Hydrogen gas at 100kPa pressure
• An inert platinum electrode

Question 28

What is an electrochemical series?

Answer 28

list of standard electrode potentials

Question 29

How do you calculate the standard electrode potential (Eꝋ)?

Answer 29

Eꝋ = E reduction ꝋ - E oxidation ꝋ
Eꝋ = right - left

Question 30

Which side is the more negative electrode potential on when drawing a cell?

Answer 30

left (oxidation)

Question 31

What are limitations of using standard electrode potentials?

Answer 31

• Conditions are not always standard, which will alter the value of an electrode potential.
• Increasing concentration means electrode potential may change due to le Chatelier’s principle, making predictions on the basis of the standard value invalid.

Question 32

How can an increase in concentration of ions affect standard electrode potentials?

Answer 32

• equilibrium opposes the change by moving to the left/ right
• electrons are removed from equilibrium
• electrode potential becomes more/less negative

Question 33

What Eꝋ value must each half cell differ by for the reaction to proceed normally if there are not standard conditions?

Answer 33

More than 0.4V

Question 34

What are the 3 main types of cell?

Answer 34

• Non-rechargeable - chemicals react to provide electrical energy until voltage falls.
• Rechargeable - Chemicals in the cell, providing electrical energy (chemicals can be regenerated)
• Fuel cells - Cell reaction uses external supplies of a fuel and an oxidant, which are continuously supplied, continually providing electrical energy.

Question 35

What is a use of chromium?

Answer 35

Stainless steel as it has resistance to corrosion.

Question 36

Definition of Average bond enthalpy?

Answer 36

Enthalpy required to break one mole of bonds in gaseous molecules.

Question 37

How do you calculate bond enthalpy?

Answer 37

reactants - products

Question 38

How do you calculate activation energy using a graph?

Answer 38

-Ea/R = gradient
Ea = -gradient x R

Question 39

Which out of cis and trans isomers have optical isomerism?

Answer 39

Cis isomers