The table shows the enthalpy changes needed to calculate the lattice energy of potassium oxide, K 2 O . Type of enthalpy change Value of enthalpy change/ kJ mol - 1 first ionisation energy of potassium + 418 first electron affinity of oxygen - 141 second electron affinity of oxygen + 798 enthalpy change of formation of K 2 O - 361 enthalpy change of atomisation of potassium + 89 enthalpy change of atomisation of oxygen + 249 Explain why the second electron affinity of oxygen has a positive value.

The addition of first electron to the neutral oxygen atom makes it negatively charged. As the electron is negatively charged, there will be repulsion between the ion and the electron making second electron affinity endothermic, hence the positive value.

The table shows the values for all but one of the enthalpy changes relevant to this cycle. Enthalpy change Value/ kJ mol - 1 lattice energy - 2327 enthalpy change of hydration of Mg 2 + ion - 1920 enthalpy change of hydration of I - ion - 314 Define enthalpy change of hydration.

The enthalpy change of hydration is the enthalpy change when one mole of aqueous ions are formed from one mole of ions in the gaseous state. The enthalpy change of hydration is always exothermic.

MEDIUM

AS and A Level

IMPORTANT

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Describe how, and explain why, the lattice energy of sodium oxide differs from that of potassium sulfide, $K_{2} S$ .

Important Questions on Lattice Energy

MEDIUM

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>EXAM-STYLE QUESTIONS>Q 1

The table shows the enthalpy changes needed to calculate the lattice energy of potassium oxide, $K_{2} O$ .

Type of enthalpy change	Value of enthalpy change/ $kJ {mol}^{- 1}$
first ionisation energy of potassium	$+ 418$
first electron affinity of oxygen	$- 141$
second electron affinity of oxygen	$+ 798$
enthalpy change of formation of $K_{2} O$	$- 361$
enthalpy change of atomisation of potassium	$+ 89$
enthalpy change of atomisation of oxygen	$+ 249$

Explain why the second electron affinity of oxygen has a positive value.

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>EXAM-STYLE QUESTIONS>Q 2

Define the term first ionisation energy.

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>EXAM-STYLE QUESTIONS>Q 2

Define the term enthalpy change of atomisation.

MEDIUM

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>EXAM-STYLE QUESTIONS>Q 2

Draw and label a Born-Haber cycle to calculate the lattice energy of sodium chloride.

MEDIUM

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>EXAM-STYLE QUESTIONS>Q 2

Explain why the lattice energy of sodium chloride has a value that is lower than the lattice energy of lithium chloride.

MEDIUM

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>EXAM-STYLE QUESTIONS>Q 3

Draw an energy cycle to show the dissolving of magnesium iodide in water.

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>EXAM-STYLE QUESTIONS>Q 3

The table shows the values for all but one of the enthalpy changes relevant to this cycle.

Enthalpy change	Value/ $kJ {mol}^{- 1}$
lattice energy	$- 2327$
enthalpy change of hydration of ${Mg}^{2 +}$ ion	$- 1920$
enthalpy change of hydration of $I^{-}$ ion	$- 314$

Define enthalpy change of hydration.

MEDIUM

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>EXAM-STYLE QUESTIONS>Q 3

The table shows the values for all but one of the enthalpy changes relevant to this cycle.

Enthalpy change	Value/ $kJ {mol}^{- 1}$
lattice energy	$- 2327$
enthalpy change of hydration of ${Mg}^{2 +}$ ion	$- 1920$
enthalpy change of hydration of $I^{-}$ ion	$- 314$

Use the values in the table to calculate the value for the enthalpy change of solution of magnesium iodide. (Only give the value without units)

Describe how, and explain why, the lattice energy of sodium oxide differs from that of potassium sulfide, K2S.

Important Questions on Lattice Energy

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Describe how, and explain why, the lattice energy of sodium oxide differs from that of potassium sulfide, $K_{2} S$ .