Chemistry 9th Chap 8 : Topic 2 - Maryam Publications

Chemistry Chapter 8 : Topic 2

Exothermic and Endothermic Reactions

1 / 20

A student observes that when quicklime (calcium oxide) is added to water, the beaker becomes hot and steam is released. This happens due to energy changes in the reaction. Which conclusion is most accurate?

A) The reaction depends only on pressure, not energy change

B) The reaction absorbs heat from surroundings, so it is endothermic

C) The reaction neither absorbs nor releases heat, so it is neutral

D) The reaction releases heat to surroundings, so it is exothermic

2 / 20

During photosynthesis, plants absorb sunlight and convert carbon dioxide and water into glucose and oxygen. Which statement best describes this process in terms of energy?

A) It releases energy in the form of heat, so it is exothermic

B) It absorbs energy from sunlight, so it is endothermic

C) It produces energy by breaking glucose

D) It occurs without any energy change

3 / 20

When ammonium nitrate is dissolved in water during instant cold packs, the temperature of the pack decreases significantly. What type of reaction is occurring?

A) Endothermic, because heat is absorbed from surroundings

B) Neutral, because no energy change occurs

C) Combustion reaction

D) Exothermic, because heat is released to surroundings

4 / 20

Which of the following correctly distinguishes exothermic reactions from endothermic reactions?

A) Exothermic reactions release heat, while endothermic absorb heat

B) Both release energy in the same way

C) Both absorb heat but at different rates

D) Exothermic reactions absorb heat, while endothermic release heat

5 / 20

Burning of methane in a gas stove produces heat and light energy. Which statement best explains this observation?

A) No energy change occurs during combustion.

B) Energy is released when bonds form in products.

C) Methane stores cold energy that is released.

D) Energy is absorbed to break methane molecules.

6 / 20

When ice melts into water at room temperature, it absorbs heat from surroundings. This process is:

A) A chemical reaction producing gas.

B) Neither endothermic nor exothermic.

C) Exothermic because heat is released.

D) Endothermic because heat is absorbed.

7 / 20

A reaction has ΔH=- 75 kJ mol⁻¹. What does this indicate about the reaction?

A) It has no energy change.

B) It is always slow.

C) It releases 75 kJ of energy per mole.

D) It absorbs 75 kJ of energy per mole.

8 / 20

Which of the following processes is an example of an endothermic reaction?

A) Combustion of coal

B) Respiration in humans

C) Thermal decomposition of calcium carbonate

D) Neutralization of acid and base

9 / 20

In an exothermic reaction, the energy of products compared to reactants is:

A) Lower than reactants

B) Equal to reactants

C) Higher than reactants

D) Independent of reactants

10 / 20

During respiration, glucose is broken down in cells releasing energy used by the body. This process is classified as:

A) Physical change

B) Exothermic reaction

C) Endothermic reaction

D) Neutral reaction

11 / 20

Which statement about endothermic reactions is correct?

A) They occur only in solids

B) They always feel hot to touch

C) They absorb energy from surroundings

D) They release energy to surroundings

12 / 20

When calcium chloride dissolves in water and the solution becomes hot, this indicates:

A) No energy change

B) Physical freezing process

C) Endothermic dissolution

D) Exothermic dissolution

13 / 20

Which of the following best explains why breaking chemical bonds requires energy?

A) Energy is needed to overcome attractive forces

B) No energy is involved in bond breaking

C) Bonds become stronger when broken

D) Bonds release energy when broken

14 / 20

Which everyday phenomenon is an example of an exothermic reaction?

A) Evaporation of alcohol

B) Burning of wood

C) Boiling of water

D) Melting of ice

15 / 20

A reaction absorbs 120 kJ of energy from surroundings. Which statement is correct?

A) It is exothermic and releases energy

B) It is endothermic and absorbs energy

C) It is a physical change only

D) It is neutral

16 / 20

Which of the following correctly describes bond formation in chemical reactions?

A) It always absorbs energy

B) It stops reactions from occurring

C) It has no energy change

D) It releases energy

17 / 20

Why does an exothermic reaction increase the temperature of its surroundings?

A) Because it stops molecular motion.

B) Because it removes all energy from system.

C) Because it absorbs heat from surroundings.

D) Because it releases heat to surroundings.

18 / 20

Which of the following is a correct pair of reactions?

A) Both are endothermic

B) Photosynthesis - Exothermic, Combustion - Endothermic

C) Both are exothermic

D) Photosynthesis - Endothermic, Combustion - Exothermic

19 / 20

A reaction mixture feels cold after completion. This indicates that:

A) Products are unstable

B) Energy is released to surroundings

C) No reaction occurred

D) Energy is absorbed from surroundings

20 / 20

Which statement best describes energy change in chemical reactions?

A) Energy depends only on mass of reactants.

B) Energy is neither created nor destroyed but transformed.

C) Energy is always destroyed in reactions.

D) Energy is always created in reactions.

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