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Question 27

A student carries out an experiment to measure the temperature change when ammonium nitrate dissolves in water.

The student uses 100 g100\text{ g}100 g of water. The thermometer readings before and after adding the ammonium nitrate are:

  • Temperature before adding ammonium nitrate: 21.8∘C21.8^\circ\text{C}21.8∘C
  • Temperature after adding ammonium nitrate: 18.3∘C18.3^\circ\text{C}18.3∘C
a.

Calculate the temperature change in ∘C^\circ\text{C}∘C.

[1]
b.

Calculate the heat energy change, in joules, using the expression:

heat energy change (J)=mass of water (g)×4.2×temperature change (∘C) \text{heat energy change (J)} = \text{mass of water (g)} \times 4.2 \times \text{temperature change (}^\circ\text{C)} heat energy change (J)=mass of water (g)×4.2×temperature change (∘C)
[1]
c.

The student used 4.0 g4.0\text{ g}4.0 g of ammonium nitrate. Calculate the amount, in moles, of ammonium nitrate dissolved (Mr of NH4NO3=80M_r\text{ of NH}_4\text{NO}_3 = 80Mr​ of NH4​NO3​=80).

[1]
d.

Calculate the molar enthalpy change, in kJ/mol\text{kJ/mol}kJ/mol, for dissolving ammonium nitrate. Since the temperature decreased, include the appropriate sign (+++ or −-−) with your value.

[2]
Markscheme

Energetics Questions

  1. IGCSE
  2. /Chemistry
  3. /Energetics

35 exam-style questions on Edexcel IGCSE Chemistry Energetics. Each one has a worked solution and a mark scheme showing where the marks go.

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