Ammonium nitrate, NH4NO3, is soluble in water (approximately 2.5 mol/100 g at 25°C). The molar enthalpy of solution of a solid is defined as the enthalpy change when one mole of the solid is dissolved in water. NH4NO3(s) ⇌ NH4+(aq) + NO3−(aq) ΔHsol = +26.5 kJ mol−1 (a) (i) Predict how the temperature of water, initially at 25°C, would change as ammonium nitrate is dissolved. Explain this prediction in terms of lattice energy and the enthalpy of hydration of ions. Prediction of the temperature change Explanation (ii) In the space below, sketch a graph to show your prediction of temperature change with concentration. Use two labelled axes and include an origin. (b) If you were to carry out an experiment to investigate how the temperature change of the solution varies as the concentration changes name, (i) the independent variable, (ii) the dependent variable.

A-Level CIE Chemistry 1.6 Energetics: Ammonium nitrate, NH4NO3, is sol

Ammonium nitrate, NH4NO3, is soluble in water (approximately 2.5 mol/100 g at 25°C) - CIE - A-Level Chemistry - Question 1 - 2013 - Paper 1

Question 1

Ammonium nitrate, NH4NO3, is soluble in water (approximately 2.5 mol/100 g at 25°C). The molar enthalpy of solution of a solid is defined as the enthalpy change when... show full transcript

Worked Solution & Example Answer:Ammonium nitrate, NH4NO3, is soluble in water (approximately 2.5 mol/100 g at 25°C) - CIE - A-Level Chemistry - Question 1 - 2013 - Paper 1

Step 1

Predict how the temperature of water would change as ammonium nitrate is dissolved.

96%

114 rated

Answer

The temperature of the water would decrease.

Step 2

Explain this prediction in terms of lattice energy and the enthalpy of hydration of ions.

99%

104 rated

Answer

The dissolution of ammonium nitrate is an endothermic process, meaning it absorbs heat from the surroundings. The lattice energy of ammonium nitrate is considerable and must be overcome to separate the ions. The enthalpy of hydration, which refers to the energy released when the ions are surrounded by water molecules, is less negative than the lattice energy. As a result, the overall reaction absorbs heat, causing a decrease in the temperature of the water.

Step 3

Sketch a graph to show your prediction of temperature change with concentration.

96%

101 rated

Answer

One possible representation is a downward sloping line that starts at 25°C and descends as the concentration of ammonium nitrate increases, indicating that as more solute is added, the temperature decreases.

Step 4

Identify the independent variable.

98%

120 rated

Answer

The independent variable is the concentration of the ammonium nitrate solution.

Step 5

Identify the dependent variable.

97%

117 rated

Answer

The dependent variable is the temperature change of the solution.

Ammonium nitrate, NH4NO3, is soluble in water (approximately 2.5 mol/100 g at 25°C) - CIE - A-Level Chemistry - Question 1 - 2013 - Paper 1

Worked Solution & Example Answer:Ammonium nitrate, NH4NO3, is soluble in water (approximately 2.5 mol/100 g at 25°C) - CIE - A-Level Chemistry - Question 1 - 2013 - Paper 1

Predict how the temperature of water would change as ammonium nitrate is dissolved.

Explain this prediction in terms of lattice energy and the enthalpy of hydration of ions.

Sketch a graph to show your prediction of temperature change with concentration.

Identify the independent variable.

Identify the dependent variable.

Join the A-Level students using SimpleStudy...

Other A-Level Chemistry topics to explore