1. 1
   A student heats blue hydrated copper sulfate crystals in a dry test tube. The crystals turn white and water droplets collect on the cooler upper part of the tube. The student then allows the white solid to cool and adds a few drops of water to it.

   (a)

   A student heats blue hydrated copper sulfate crystals in a test tube, and the crystals turn white while water droplets form on the cool part of the tube. What has happened to the copper sulfate?

   [1 mark]

   • AIt has lost water of crystallisation to form anhydrous copper sulfate
   • BIt has gained water to form hydrated copper sulfate
   • CIt has decomposed into copper metal and oxygen
   • DIt has reacted with the glass of the test tube

   (b)

   When the student adds a few drops of water to the cooled white solid, it turns blue again. What type of reaction is this overall process an example of?

   [1 mark]

   • AAn irreversible reaction
   • BA reversible reaction
   • CA neutralisation reaction
   • DA displacement reaction

   (c)

   State whether the forward reaction (heating hydrated copper sulfate) and the reverse reaction (adding water to anhydrous copper sulfate) are each exothermic or endothermic, giving a reason for each answer.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist sets up a reversible reaction inside a sealed glass vessel, from which no substances can escape or enter, and monitors the concentrations of the reactants and products over time until they stop changing.

   (a)

   A reversible reaction is set up in a sealed container so that nothing can enter or leave. What is this type of container called?

   [1 mark]

   • AA distillation apparatus
   • BAn open system
   • CA catalytic converter
   • DA closed system

   (b)

   After some time, the concentrations of reactants and products in the sealed vessel stop changing, even though the reaction has not stopped. What is this state called?

   [1 mark]

   • ANeutralisation
   • BCombustion
   • CEquilibrium
   • DElectrolysis

   (c)

   Explain, in terms of the forward and reverse reactions, what is happening at equilibrium, even though the concentrations of reactants and products appear constant.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A laboratory technician demonstrates the reversible reaction between hydrated and anhydrous copper sulfate to a group of students, then sets up a separate, sealed reaction vessel containing a different reversible reaction to demonstrate the idea of equilibrium in a closed system.

   (a)

   Define what is meant by a reversible reaction, and give the example of hydrated and anhydrous copper sulfate to illustrate your answer.

   [3 marks]

   (b)

   Explain why equilibrium can only be reached for the reversible reaction in the sealed vessel, and explain why using copper sulfate in an open test tube (as in the earlier demonstration) would not allow equilibrium to be reached in the same way.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A university lecturer sets a question comparing a reversible reaction carried out in an open container with the same reaction carried out in a sealed, closed system, to test students' understanding of equilibrium.

   (a)

   Describe fully what is meant by a reversible reaction and by equilibrium, using the example of hydrated and anhydrous copper sulfate, and explain the conditions that must be met for a reversible reaction to reach equilibrium.

   [6 marks]

   (b)

   Explain why equilibrium cannot be established for a reversible reaction carried out in an open container, even if the same reactants and conditions are used as in a closed system, and discuss the practical implications of this for industrial processes that rely on reversible reactions.

   [6 marks]

   Total for question 4: 12 marks

End of questions