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

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

D) No energy change occurs during bond breaking and forming

2 / 20

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

A) The total energy released only during bond breaking

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

C) The energy stored only in chemical bonds of reactants

D) The difference between reactant masses and product masses

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) Spontaneous only at high pressure

B) Exothermic

C) Endothermic

D) Neutral

4 / 20

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

A) It always releases energy into surroundings

B) It occurs without any energy change

C) It requires absorption of energy from surroundings

D) It only happens in exothermic reactions

5 / 20

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

A) Energy absorbing

B) Energy releasing

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) Exothermic, + 200 kJ

B) Exothermic, - 200 kJ

C) Endothermic, - 200 kJ

D) Endothermic, + 200 kJ

7 / 20

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

A) Energy of reactants × products

B) Energy of bonds broken - Energy of bonds formed

C) Energy of bonds formed - Energy of bonds broken

D) Sum of masses of reactants - products

8 / 20

Which statement correctly explains why bond breaking is always endothermic?

A) New bonds are immediately formed

B) Electrons disappear during the process

C) Energy is needed to overcome attractive forces between atoms

D) Atoms lose mass during breaking bonds

9 / 20

A reaction is most likely exothermic when:

A) No bonds are involved

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

C) Energy absorbed equals energy released

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

10 / 20

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

A) Only bond formation 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 breaking 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) Negative

B) Infinite

C) Zero

D) Positive

12 / 20

Which statement best explains why chemical reactions involve energy changes?

A) Elements lose electrons permanently

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

C) Atoms change their mass during reactions

D) Molecules disappear during reactions

13 / 20

During an endothermic reaction, the correct energy relationship is:

A) Energy released > Energy absorbed

B) Energy absorbed = Energy released

C) No energy exchange occurs

D) Energy absorbed > Energy released

14 / 20

Which step in a chemical reaction always requires energy input?

A) Condensation of gases

B) Breaking of reactant bonds

C) Formation of products

D) Cooling of system

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) Endothermic, - 50 kJ

C) Exothermic, - 50 kJ

D) Exothermic, + 50 kJ

16 / 20

Which statement correctly links enthalpy change to molecular bonding?

A) It is independent of chemical bonds.

B) It depends only on physical state changes.

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

D) It is determined only by atomic masses.

17 / 20

Why is energy released during bond formation?

A) Mass is converted into energy.

B) Atoms become less stable.

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

D) Atoms move further apart.

18 / 20

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

A) Energy is destroyed during reactions.

B) Energy is only stored in products.

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) Heat of formation

B) Released energy

C) Activation energy only

D) Total bond dissociation energy

20 / 20

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

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

B) Difference in kinetic energy of atoms

C) Change in physical size of molecules

D) Change in number of atoms

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