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CIE iGCSE Co-Ordinated Science C5.1 Exothermic and endothermic reactions Exam Style Questions Paper 1

CIE iGCSE Co-Ordinated Science Paper 1 - All Chapters

Question

The initial and final temperatures of four different experiments are measured.

Which experiment is the most endothermic?

▶️ Answer/Explanation

An endothermic reaction takes in thermal energy from the surroundings, which causes the temperature of the surroundings to decrease. Therefore, the most endothermic reaction will be the one where the temperature decreases the most (i.e., the largest drop in temperature).

Calculating the temperature change for each experiment:

  • A: Final − Initial = \(19 – 20 = -1^\circ\text{C}\) (decrease of 1°C)
  • B: \(27 – 20 = +7^\circ\text{C}\) (increase of 7°C — exothermic)
  • C: \(26 – 21 = +5^\circ\text{C}\) (increase of 5°C — exothermic)
  • D: \(20 – 22 = -2^\circ\text{C}\) (decrease of 2°C)

Experiment D shows the largest temperature decrease (2°C), so it is the most endothermic reaction. Experiment A also shows a decrease but only by 1°C, so it is less endothermic than D.

✅ Answer: (D)

Question

Which statements about endothermic reactions are correct?

  1. Thermal energy is taken in from the surroundings.
  2. Thermal energy is released to the surroundings.
  3. The temperature of the reaction mixture decreases.
  4. The temperature of the reaction mixture increases.

A. 1 and 3
B. 1 and 4
C. 2 and 3
D. 2 and 4

▶️ Answer/Explanation
During endothermic reactions, thermal energy is absorbed from the surroundings, causing the temperature of the reaction mixture to decrease. Statement 1 and statement 3 correctly describe this process. Statement 2 and statement 4 describe exothermic reactions, where energy is released and temperature increases. Therefore, the correct combination is 1 and 3.
✅ Answer: (A)

Question

Equal masses of four substances are added separately to different samples of 10 cm³ of dilute hydrochloric acid at 22°C.

The final temperature of each reaction mixture is measured.

Which reaction is most endothermic?

▶️ Answer/Explanation
An endothermic reaction takes in thermal energy from the surroundings, causing a decrease in temperature.
The reaction with the lowest final temperature (17°C) shows the greatest decrease from the initial 22°C, indicating it is the most endothermic.
✅ Answer: (D)

Question

Which row describes an endothermic reaction?

▶️ Answer/Explanation
An endothermic reaction absorbs thermal energy from the surroundings, so thermal energy is not transferred to the surroundings (✗). Since energy is taken in from the surroundings, the temperature of the reaction mixture decreases (✓). This matches row C, which correctly describes an endothermic reaction.
✅ Answer: (C)

Question

Magnesium ribbon is added to dilute hydrochloric acid. Which observation shows that this process is exothermic?

A. The pH of the solution decreases.
B. The pH of the solution increases.
C. The temperature of the solution decreases.
D. The temperature of the solution increases.

▶️ Answer/Explanation
An exothermic reaction releases thermal energy to the surroundings, so the temperature of the solution increases. The pH would change because acid is being used up (the pH would increase), but that is not the observation that directly shows heat release. A temperature rise is the defining observation for an exothermic process.
✅ Answer: (D)
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