Term 1

Question 1

Define (first) electron affinity.

Answer 1

The first electron affinity of an atom is the energy released when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions. This is always exothermic.

Question 2

Why does fluorine have an EA less than Chlorine?

Answer 2

Fluorine is a small atom, so when you are putting a new electron into a region of space already crowded with electrons there is a significant amount of repulsion.

Question 3

Why are second and subsequent EAs endothermic?

Answer 3

You are forcing an electron into an already negative ion so there will be repulsion.

Question 4

Define lattice enthalpy.

Answer 4

The energy change when one mole of an ionic lattice is formed at 298K and 1atm from its isolated gaseous ions.

Question 5

What two factors influence lattice enthalpy?

Answer 5

Size of ion and charge of ion. These contribute to the ion’s charge density. The smaller the ion and the higher charged the ion the greater the charge density and vice versa. The greater the charge density the more exothermic the lattice enthalpy.

Question 6

Define enthalpy change of solution.

Answer 6

The enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.

Question 7

Define enthalpy change of hydration.

Answer 7

The energy change when 1 mole of gaseous ions are dissolved in sufficient water to give an infinitely dilute solution.

Question 8

Give the equation for Hess’s cycle.

Answer 8

♤H(soln) = €♤H(hyd) - ♤H(lat)

Question 9

Describe what a born-haber cycle looks like.

Answer 9

Three points:
Top left = ions in gaseous state
Top right = ionic compound (s)
Bottom middle = elements in their standard states

♤H(latt) running left to right at the top
♤Hf from elements to compound
♤H1 from elements to gaseous ions (multiple steps)

Question 10

Define entropy.

Answer 10

A measure of the ‘disorder’ of a system, and a system becomes more stable when energy is spread around in a more ‘disordered’ state.

Question 11

Give the Gibbs free energy change equation.

Answer 11

♤G = ♤H - T♤S

Question 12

In the Gibbs free energy equation, what indicates whether a spontaneous reaction is possible?

Answer 12

♤G is -ve

Question 13

Give the definitions of Lewis acids and bases.

Answer 13

Lewis acid - electron pair acceptor

Lewis base - electron pair donor

Question 14

Give the definitions of Brønsted-Lowry acids and bases.

Answer 14

Brønsted-Lowry acid - proton donor

Brønsted-Lowry base - proton acceptor

Question 15

Define amphoteric

Answer 15

A substance which can act as a base or an acid.

Question 16

Define amphiprotic.

Answer 16

A substance that can donate or accept an H+ ion.

Question 17

Give the value of the ionic product of water (Kw)

Answer 17

1×10‐¹⁴ mol² dm‐⁶ at 25°C

Question 18

Give the equations involving only pH and [H+]

Answer 18

pH = -log[H+]

[H+] = 10^-pH

Question 19

Give the equation for Ka and how to find pKa.

Answer 19

Ka = [H+]×[A-] / [HA]

pKa = -log(Ka)

Question 20

How to calculate the pH of a weak acid:

Answer 20

[H+] = root (Ka[HA])

Since: pH = -log[H+]

pH = -log(root(Ka[HA]))

Question 21

Give the Henderson-Hassalbach equation.

Answer 21

pH = pKa + log ( [base] / [acid] )

Question 22

Give an eauation for calculating [H+] in terms of Ka, Kw, and [A-].

Answer 22

[H+] = root ( Ka×Kw / [A-] )

Question 23

Using the ionic product and Ksp, how can we tell if precipitation occurs?

Answer 23

If I.P is greater than Ksp.

Question 24

What is the order of reaction?

Answer 24

The power to which a concentration is raised in the rate equation.

Question 25

How can we determine the difference between 1st and 2nd order reaction?

Answer 25

Length of half life is constant for 1st order.

Length of half life increases with decreasing concentration.

Question 26

Give the Arrhenius equation.

Answer 26

k = Ae^-Ea/RT

Question 27

Give the trend for thermal stability of carbonates in group 2.

Answer 27

Carbonates become more stable to heat as you go down the group.

Question 28

Give the trend of thermal stability of the nitrates of group 2.

Answer 28

Nitrates become more stable to heat as you go down the group.

Question 29

Give the trend for the solubility of group 2 sulphates.

Answer 29

Solubility decreases down the group.

Question 30

Give the trend of solubility of group 2 hydroxides.

Answer 30

Solubility increases down the group.