CIE iGCSE Co-Ordinated Science C5.1 Exothermic and endothermic reactions Exam Style Questions Paper 1
Question
Hydrogen reacts with iodine to form hydrogen iodide. The equation for this reaction is shown.
\(H_{2}\) + \(I_{2}\) → 2HI
During this reaction, the temperature increases.
Which statement explains why the temperature increases?
A. One molecule of hydrogen is forming two molecules of hydrogen iodide.
B. The reaction is exothermic.
C. The reaction is very fast.
D. The reaction takes in energy.
▶️Answer/Explanation
Answer: B
Explanation: The temperature increases because the reaction is exothermic, meaning it releases energy in the form of heat.
Question
The apparatus used to investigate the combustion of ethanol is shown.
The products of combustion are passed over anhydrous cobalt(II) chloride.
How does the colour of the cobalt(II) chloride change during the investigation?
A. blue to pink
B. blue to white
C. pink to blue
D. white to blue
▶️Answer/Explanation
Answer: A
Explanation: Anhydrous cobalt(II) chloride is blue, but it turns pink when it absorbs water. During the combustion of ethanol, water is produced, causing the cobalt(II) chloride to change from blue to pink.
Question
The same masses of four substances are added separately to four 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?
| Substance | Final Temperature (°C) |
|---|---|
| A | 29 |
| B | 27 |
| C | 20 |
| D | 17 |
▶️Answer/Explanation
Answer: D. 17
Explanation: An endothermic reaction absorbs heat from the surroundings, causing the temperature to decrease. The reaction with the lowest final temperature (17°C) is the most endothermic.
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
Answer: D) The temperature of the solution increases.
Explanation: An exothermic reaction releases heat, causing the temperature of the solution to increase.