Chemistry 9th Chap 8 : Topic 8 - Maryam Publications

Chemistry Chapter 8 : Topic 8

Bond Energy and Enthalpy

1 / 20

In a chemical reaction, bonds in reactants must first be broken before products are formed. Which statement correctly explains the energy changes involved during this process?

A) Energy is only released when bonds in reactants break

B) No energy change occurs during bond breaking and forming

C) Energy is only required to form bonds, not to break them

D) Energy is absorbed when bonds break and released when bonds form

2 / 20

The enthalpy change of a chemical reaction is best described as:

A) The net result of energy absorbed in breaking bonds and energy released in forming bonds

B) The energy stored only in chemical bonds of reactants

C) The difference between reactant masses and product masses

D) The total energy released only during bond breaking

3 / 20

During a reaction, if the energy required to break bonds is greater than the energy released when new bonds form, the reaction will be:

A) Endothermic

B) Exothermic

C) Spontaneous only at high pressure

D) Neutral

4 / 20

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

A) It always releases energy into surroundings

B) It only happens in exothermic reactions

C) It occurs without any energy change

D) It requires absorption of energy from surroundings

5 / 20

When new chemical bonds are formed in products, the process is best described as:

A) Energy releasing

B) Energy absorbing

C) Mass increasing

D) Temperature independent

6 / 20

In a reaction where 500 kJ is required to break bonds and 700 kJ is released during bond formation, the reaction is:

A) Endothermic, - 200 kJ

B) Exothermic, + 200 kJ

C) Endothermic, + 200 kJ

D) Exothermic, - 200 kJ

7 / 20

The correct formula for calculating enthalpy change using bond energies is:

A) Energy of bonds broken - Energy of bonds formed

B) Energy of bonds formed - Energy of bonds broken

C) Energy of reactants × products

D) Sum of masses of reactants - products

8 / 20

Which statement correctly explains why bond breaking is always endothermic?

A) Energy is needed to overcome attractive forces between atoms

B) New bonds are immediately formed

C) Atoms lose mass during breaking bonds

D) Electrons disappear during the process

9 / 20

A reaction is most likely exothermic when:

A) Energy absorbed equals energy released

B) More energy is used to break bonds than released in forming bonds

C) More energy is released during bond formation than absorbed in bond breaking

D) No bonds are involved

10 / 20

Which of the following best represents energy changes during a chemical reaction at molecular level?

A) Only bond breaking involves energy change

B) Both bond breaking and bond formation involve energy changes

C) Neither bond breaking nor formation involves energy change

D) Only bond formation involves energy change

11 / 20

If a reaction has equal energy absorbed in bond breaking and energy released in bond formation, the enthalpy change will be:

A) Infinite

B) Positive

C) Zero

D) Negative

12 / 20

Which statement best explains why chemical reactions involve energy changes?

A) Molecules disappear during reactions

B) Bonds between atoms are broken and new bonds are formed

C) Elements lose electrons permanently

D) Atoms change their mass during reactions

13 / 20

During an endothermic reaction, the correct energy relationship is:

A) Energy absorbed > Energy released

B) No energy exchange occurs

C) Energy absorbed = Energy released

D) Energy released > Energy absorbed

14 / 20

Which step in a chemical reaction always requires energy input?

A) Condensation of gases

B) Cooling of system

C) Formation of products

D) Breaking of reactant bonds

15 / 20

If a reaction releases 300 kJ during bond formation and absorbs 250 kJ during bond breaking, the reaction is:

A) Endothermic, + 550 kJ

B) Exothermic, - 50 kJ

C) Endothermic, - 50 kJ

D) Exothermic, + 50 kJ

16 / 20

Which statement correctly links enthalpy change to molecular bonding?

A) It is determined only by atomic masses.

B) It depends only on physical state changes.

C) It is independent of chemical bonds.

D) It depends on the energy difference between bonds broken and formed.

17 / 20

Why is energy released during bond formation?

A) System reaches a more stable, lower energy state.

B) Mass is converted into energy.

C) Atoms become less stable.

D) Atoms move further apart.

18 / 20

Which of the following correctly summarizes a chemical reaction at energy level?

A) Energy is only stored in products.

B) Energy is destroyed during reactions.

C) Energy is created during reactions.

D) Energy is neither created nor destroyed but transferred.

19 / 20

In bond energy calculations, the energy required to break all bonds in reactants is called:

A) Total bond dissociation energy

B) Heat of formation

C) Activation energy only

D) Released energy

20 / 20

Which of the following best describes enthalpy change in terms of microscopic interactions?

A) Change in number of atoms

B) Difference in kinetic energy of atoms

C) Net energy change due to breaking and forming chemical bonds

D) Change in physical size of molecules

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