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 neither absorbs nor releases heat, so it is neutral

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

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

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 occurs without any energy change

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

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

D) It produces energy by breaking glucose

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) Combustion reaction

B) Exothermic, because heat is released to surroundings

C) Neutral, because no energy change occurs

D) Endothermic, because heat is absorbed from surroundings

4 / 20

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

A) Exothermic reactions release heat, while endothermic absorb heat

B) Exothermic reactions absorb heat, while endothermic release heat

C) Both release energy in the same way

D) Both absorb heat but at different rates

5 / 20

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

A) Energy is released when bonds form in products.

B) No energy change occurs during combustion.

C) Energy is absorbed to break methane molecules.

D) Methane stores cold energy that is released.

6 / 20

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

A) Neither endothermic nor exothermic.

B) Exothermic because heat is released.

C) A chemical reaction producing gas.

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 absorbs 75 kJ of energy per mole.

B) It releases 75 kJ of energy per mole.

C) It has no energy change.

D) It is always slow.

8 / 20

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

A) Thermal decomposition of calcium carbonate

B) Respiration in humans

C) Neutralization of acid and base

D) Combustion of coal

9 / 20

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

A) Equal to reactants

B) Lower than 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 release energy to surroundings

B) They occur only in solids

C) They absorb energy from surroundings

D) They always feel hot to touch

12 / 20

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

A) Endothermic dissolution

B) Physical freezing process

C) Exothermic dissolution

D) No energy change

13 / 20

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

A) Energy is needed to overcome attractive forces

B) Bonds become stronger when broken

C) Bonds release energy when broken

D) No energy is involved in bond breaking

14 / 20

Which everyday phenomenon is an example of an exothermic reaction?

A) Burning of wood

B) Boiling of water

C) Evaporation of alcohol

D) Melting of ice

15 / 20

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

A) It is neutral

B) It is a physical change only

C) It is exothermic and releases energy

D) It is endothermic and absorbs energy

16 / 20

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

A) It always absorbs energy

B) It has no energy change

C) It stops reactions from occurring

D) It releases energy

17 / 20

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

A) Because it releases heat to surroundings.

B) Because it absorbs heat from surroundings.

C) Because it removes all energy from system.

D) Because it stops molecular motion.

18 / 20

Which of the following is a correct pair of reactions?

A) Both are endothermic

B) Both are exothermic

C) Photosynthesis - Endothermic, Combustion - Exothermic

D) Photosynthesis - Exothermic, Combustion - Endothermic

19 / 20

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

A) No reaction occurred

B) Products are unstable

C) Energy is absorbed from surroundings

D) Energy is released to surroundings

20 / 20

Which statement best describes energy change in chemical reactions?

A) Energy is always created in reactions.

B) Energy depends only on mass of reactants.

C) Energy is always destroyed in reactions.

D) Energy is neither created nor destroyed but transformed.

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