The diagram shows the enthalpy changes when sodium chloride is dissolved in water. Define the term enthalpy change of solution.

The enthalpy change of solution, ∆ H f is the energy absorbed or released when one mole of an ionic solid dissolves in sufficient water to form a very dilute solution.

The diagram shows the enthalpy changes when sodium chloride is dissolved in water. Write symbol equation that describe the enthalpy change of solution of sodium chloride.

The enthalpy change of solution for zinc chloride is described by the thermochemical equation given below: NaCl ( s ) + aq → NaCl ( aq ) ∆ H = + 3 . 9 kJ mol - 1 Or, NaCl ( s ) + aq → Na + ( aq ) + Cl - ( aq ) ∆ H = + 3 . 9 kJ mol - 1 Note:- The symbol 'aq' represents the very large amount of water used. A compound is likely to be soluble in water only if ∆ H is negative or has a small positive value. The substances with large positive values of ∆ H are relatively insoluble.

The diagram shows the enthalpy changes when sodium chloride is dissolved in water. Name the enthalpy changes labelled A, B and C.

In step A, gaseous ions are combining to form an ionic solid crystal. Therefore, the equation represents the lattice enthalpy, ∆ H latt for NaCl . Na + ( g ) + Cl - ( g ) → NaCl ( s ) In step B, gaseous ions Na + and Cl - dissolves in sufficient water to form a very dilute solution. Therefore, the equation represents the enthalpy change of hydration, ∆ H hyd . Na + ( g ) + Cl - ( g ) + aq → Na + ( aq ) + Cl - ( aq ) In step C, 1 mole of ionic solid, NaCl dissolves in sufficient water to form a very dilute solution. Therefore, the equation represents the standard enthalpy change of solution, ∆ H sol for NaCl . NaCl ( s ) → Na + ( aq ) + Cl - ( aq )

MEDIUM

AS and A Level

IMPORTANT

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The lattice energy of magnesium bromide, ${MgBr}_{2}$ can be calculated using the enthalpy changes shown in the table.

Type of enthalpy change Value / $kJ {mol}^{- 1}$

first ionisation energy of magnesium $+ 736$

second ionisation energy of magnesium $+ 1450$

first electron affinity of bromine $- 325$

enthalpy change of formation of ${MgBr}_{2}$ $- 524$

enthalpy change of atomisation of magnesium $+ 150$

enthalpy change of atomisation of bromine $+ 112$

Draw and label a Born-Haber cycle to calculate the lattice energy of magnesium bromide and calculate the lattice energy of magnesium bromide.

Important Questions on Lattice Energy

EASY

AS and A Level

IMPORTANT

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

Draw a fully labelled reaction pathway diagram (energy profile diagram) for an endothermic reaction. Explain, how this diagram shows that the reaction is endothermic?

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 5

In some crystal lattices, some of the ions are polarised. State the meaning of the term ion polarisation.

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 5

Use ideas about ion polarisation to explain why barium carbonate is more stable to thermal decomposition than magnesium carbonate.

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 6

The diagram shows the enthalpy changes when sodium chloride is dissolved in water.

Question Image

Define the term enthalpy change of solution.

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 6

The diagram shows the enthalpy changes when sodium chloride is dissolved in water.

Question Image

Write symbol equation that describe the enthalpy change of solution of sodium chloride.

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 6

The diagram shows the enthalpy changes when sodium chloride is dissolved in water.

Question Image

Name the enthalpy changes labelled A, B and C.

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 6

Explain, in terms of differences of lattice energies and enthalpy changes of hydration, why magnesium sulfate is more soluble in water than calcium sulfate.

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 19 - Lattice Energy>BEFORE YOU START>Q 4

Write the equation which represents the enthalpy change of neutralisation of sulphuric acid by sodium hydroxide.

Type of enthalpy change	Value / $kJ {mol}^{- 1}$
first ionisation energy of magnesium	$+ 736$
second ionisation energy of magnesium	$+ 1450$
first electron affinity of bromine	$- 325$
enthalpy change of formation of ${MgBr}_{2}$	$- 524$
enthalpy change of atomisation of magnesium	$+ 150$
enthalpy change of atomisation of bromine	$+ 112$

Important Questions on Lattice Energy

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