Chapter 3 Practice Paper: Chemical Energetics — question paper

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

1. 1

   Which observation shows that a reaction is exothermic?

   1. Athe mixture warms above its starting temperature
   2. Bthe mixture cools below its starting temperature
   3. Ca gas is released
   4. Dthe mixture changes colour
   ( )
2. 2

   Ammonium nitrate dissolving in water is endothermic. When crystals dissolve, the solution

   1. Awarms because heat is released
   2. Bcools because heat is taken in from the water
   3. Cboils
   4. Dstays at exactly the same temperature
   ( )
3. 3

   Which change needs a continuous supply of heat to keep going?

   1. Aneutralisation of NaOH and HCl
   2. Bmagnesium burning in air
   3. Ccalcium carbonate decomposing
   4. Dquicklime slaking in water
   ( )
4. 4

   Solutions at 22.0 °C and 24.0 °C are mixed; the peak temperature is 28.5 °C. The temperature rise is

   1. A4.5 °C
   2. B6.5 °C
   3. C5.5 °C
   4. D23.0 °C
   ( )
5. 5

   A hand warmer and a cold pack differ because the hand warmer must use

   1. Aan endothermic process
   2. Ban exothermic process
   3. Cno energy change
   4. Da neutralisation only
   ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided. Show all necessary working. Give numerical answers to 3 significant figures where appropriate, with units.

1. 1

   A student mixes 25.0 cm³ of dilute hydrochloric acid with 25.0 cm³ of sodium hydroxide solution in a polystyrene cup. The acid starts at 21.5 °C and the alkali at 22.5 °C. The maximum temperature after mixing is 30.0 °C.

   1. (a)

      Calculate the temperature rise of the mixture.

      [2]
   2. (b)

      State the type of energy change, with a reason.

      [2]
   3. (c)

      Name the type of chemical reaction and the salt formed.

      [2]
2. 2

   A sports cold pack works by dissolving a salt inside the pack when it is squeezed.

   1. (a)

      Name the salt used and state the type of energy change when it dissolves.

      [2]
   2. (b)

      Explain, in terms of energy flow, why the pack cools an injured ankle.

      [2]
   3. (c)

      Suggest one safety instruction that should appear on the pack.

      [1]
3. 3

   A student heats powdered calcium carbonate strongly in a roasting tube and bubbles the escaping gas through limewater, which turns milky.

   1. (a)

      Identify the gas and the type of change (exothermic or endothermic) taking place in the tube.

      [2]
   2. (b)

      Write the balanced equation for the decomposition.

      [1]
   3. (c)

      The student claims the reaction is exothermic because the tube is hot. Explain the error.

      [2]
4. 4

   Four mixtures are made in identical insulated cups, all starting at 20.0 °C: (1) magnesium + dilute acid; (2) ammonium nitrate + water; (3) sodium hydroxide + dilute acid; (4) copper + dilute hydrochloric acid. Final extremes: (1) 30.0 °C; (2) 15.5 °C; (3) 27.0 °C; (4) 20.0 °C.

   1. (a)

      Classify each mixture as exothermic, endothermic or no energy change.

      [2]
   2. (b)

      Explain the result in mixture 4.

      [2]