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.
Question
The initial and final temperatures of four different experiments are measured.
Which experiment is the most endothermic?
A 22°C → 17°C
B 21°C → 25°C
C 20°C → 27°C
D 20°C → 18°C
▶Answer/Explanation
Answer: A
Explanation: An endothermic reaction absorbs heat, causing the temperature to decrease. Experiment A shows the largest temperature drop, indicating it is the most endothermic.
Question
Ammonium nitrate is dissolved in a beaker of water.
The temperature of the water decreases by 5 C.
Which type of reaction occurs?
A endothermic
B exothermic
C oxidation
D reduction
▶️Answer/Explanation
Ans :A
Question
Which word describes reactions that give out heat energy?
A endothermic
B exothermic
C oxidation
D reduction
▶️Answer/Explanation
Ans :A
Question
Hydrogen reacts with iodine to form hydrogen iodide.
The equation for this reaction is shown.
H2 + I2 → 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
Ans : B
Question
The temperature change as the result of a chemical reaction may go up or down.
Which rows about reactions are correct?
(A) 1 and 3
(B) 1 and 4
(C) 2 and 3
(D) 2 and 4
▶️Answer/Explanation
Ans: A
Question
Equal amounts of substances W, X, Y and Z are reacted separately with equal amounts of dilute acid.
The following temperature changes are recorded.
Which substances produce the most exothermic and the least endothermic reactions?
▶️Answer/Explanation
Ans : D
Question
The initial and final temperatures in two experiments, X and Y, are shown.
Which row shows the types of change that take place in these two experiments?
▶️Answer/Explanation
Ans : C
Question
Potassium chloride is added to water.
The temperature of the solution decreases as the potassium chloride dissolves.
Which type of reaction occurs?
A endothermic
B exothermic
C oxidation
D reduction
▶️Answer/Explanation
Ans : A
Question
Which statement about exothermic and endothermic reactions is correct?
(A) An endothermic reaction involves heat energy being taken in by the reactants.
(B) An exothermic reaction involves heat energy being taken in by the products.
(C) In an endothermic reaction, the temperature of the reaction mixture increases.
(D) In an exothermic reaction, the temperature of the reaction mixture decreases.
▶️Answer/Explanation
Ans : A
Question
In a test-tube, magnesium reacts with dilute hydrochloric acid to form a salt and hydrogen.
The reaction makes the test-tube warm.
Which statement about the reaction explains this observation?
(A) It is a combustion reaction.
(B) It is a neutralisation reaction.
(C) It is endothermic.
(D) It is exothermic.
▶Answer/Explanation
Ans : D
Question
When aqueous sodium hydroxide reacts with dilute hydrochloric acid, the temperature of the reaction mixture increases.
Ice cubes take in energy when they melt.
Which row is correct?
▶️Answer/Explanation
Ans: B
Question
The diagram shows the energy change for the reactions between hydrogen and the halogens.
The reaction is \(H_{₂}\) + \(X_{₂}\) → 2HX.
The size of the energy change is different for each halogen.
The diagram shows that the reactions are ……1……. The most reactive halogen is ……2…… and therefore the energy change for this element is ……3…….
Which words complete gaps 1, 2 and 3?
A. endothermic, fluorine, least
B. endothermic, iodine, least
C. exothermic, fluorine, greatest
D. exothermic, iodine, greatest
▶️Answer/Explanation
Answer: C. exothermic, fluorine, greatest
Explanation: The reactions between hydrogen and halogens are exothermic, meaning they release energy. Fluorine is the most reactive halogen, and the energy change for its reaction with hydrogen is the greatest because it releases the most energy.
Question
Which statement about the Haber process is correct?
A All of the raw materials are obtained from the air.
B It requires a catalyst.
C It uses a low pressure and a high temperature.
D Sulfuric acid is produced in the process.
▶️Answer/Explanation
Answer: B It requires a catalyst.
Explanation: The Haber process synthesizes ammonia from nitrogen and hydrogen using an iron catalyst. It operates at high pressure and moderate temperature, and sulfuric acid is not produced in this process.
Question
Which statement describes the meaning of exothermic?
A. Heat energy is given out.
B. Heat energy is taken in.
C. Oxygen is given out.
D. Oxygen is taken in.
▶️Answer/Explanation
Answer: A. Heat energy is given out.
Explanation: An exothermic reaction releases heat energy to the surroundings, causing an increase in temperature.
Question
Two processes are listed:
- the conversion of liquid water into steam
- the combustion of magnesium ribbon
Which row describes the two processes?
▶️Answer/Explanation
Answer: B) process 1: endothermic, process 2: exothermic
Explanation: The conversion of liquid water into steam requires heat (endothermic), while the combustion of magnesium releases heat (exothermic).
Question
The initial and final temperatures of four different experiments are measured.
Which experiment is the most endothermic?
| Initial temperature/°C | Final temperature/°C | |
|---|---|---|
| A | 20 | 19 |
| B | 20 | 27 |
| C | 21 | 26 |
| D | 22 | 20 |
▶️Answer/Explanation
Answer: D. Experiment D
Explanation: An endothermic reaction absorbs heat from the surroundings, causing a decrease in temperature. Experiment D shows the largest temperature drop (from 22°C to 20°C), indicating it is the most endothermic.
Question
A student investigates temperature changes in four chemical reactions, as shown. Which reactions are endothermic?
| reaction | initial temperature /°C | final temperature /°C |
|---|---|---|
| 1 | 22 | 16 |
| 2 | 22 | 27 |
| 3 | 20 | 28 |
| 4 | 20 | 18 |
A. 1 and 3
B. 1 and 4
C. 2 and 3
D. 2 and 4
▶️Answer/Explanation
Answer: B. 1 and 4
Explanation: Endothermic reactions absorb heat, causing the temperature to decrease. Reactions 1 and 4 show a decrease in temperature, indicating they are endothermic.
Question
Equal amounts of four different substances are added to equal volumes of the same acid of the same concentration in reactions W, X, Y and Z. The initial temperature of the acid before each reaction is 21°C. The final temperatures of the mixtures are measured. The results are shown.
| reaction | W | X | Y | Z |
|---|---|---|---|---|
| final temperature/°C | 28 | 19 | 26 | 17 |
Which row is correct?
| most endothermic reaction | most exothermic reaction | |
|---|---|---|
| A | W | Z |
| B | Z | W |
| C | X | Y |
| D | Y | X |
▶️Answer/Explanation
Answer: B
Explanation: An endothermic reaction absorbs heat, causing the temperature to decrease. Reaction Z has the lowest final temperature (17°C), indicating it is the most endothermic. An exothermic reaction releases heat, causing the temperature to increase. Reaction W has the highest final temperature (28°C), indicating it is the most exothermic.
Question
The table shows the temperature of some water before and after a solid is dissolved in it. Which change is the most exothermic?
▶️Answer/Explanation
Answer: B
Explanation: An exothermic reaction releases heat, causing the temperature to rise. The greatest temperature increase is from 20°C to 40°C.
Question
An acid is added to an alkali until the final solution is just neutral. The reaction is exothermic. Which graph shows how the temperature changes as the acid is being added to the alkali?
▶️Answer/Explanation
Answer: C
Explanation: In an exothermic reaction, the temperature increases as the reaction proceeds. Graph C shows a gradual increase in temperature as the acid is added, reaching a maximum at the point of neutralization.