MCQs — Energetics

Practice questions for Chemistry.

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Question 61

Continuing this calculation, the sum of bond energies of the products (2 moles of HF) is:

A. 567 kJ/mol

B. 1134 kJ/mol

C. 591 kJ/mol

D. 283.5 kJ/mol

Question 62

Using these values, the standard enthalpy change for H2(g) + F2(g) -> 2HF(g) is calculated to be approximately:

A. +543 kJ/mol

B. -543 kJ/mol

C. +1134 kJ/mol

D. -591 kJ/mol

Question 63

Comparing the two calculated reactions (H2+I2 -> 2HI at -11 kJ/mol, and H2+F2 -> 2HF at -543 kJ/mol), which reaction releases substantially more energy?

A. The reaction between hydrogen and iodine (H2+I2 -> 2HI)

B. The reaction between hydrogen and fluorine (H2+F2 -> 2HF)

C. Both release exactly the same amount of energy

D. Neither reaction releases any energy

Question 64

What does the very large negative enthalpy change for the hydrogen-fluorine reaction suggest about the strength of the H-F bond formed, compared to the H-I bond?

A. The H-F bond is considerably weaker than the H-I bond

B. The H-F bond is considerably stronger (has a higher bond energy) than the H-I bond, releasing much more energy when formed

C. The two bonds must have identical strength

D. Bond strength cannot be inferred from enthalpy data

Question 65

Collision theory was proposed mainly to explain:

A. The color changes seen in chemical reactions

B. The observed kinetics (rates) of chemical reactions

C. The physical states of matter

D. The structure of the periodic table

Question 66

For a chemical reaction to occur, the bonding atoms or molecules must first:

A. Be heated to their boiling point

B. Collide with each other

C. Be dissolved in water

D. Be exposed to light

Question 67

Whether a collision between reacting particles is effective or ineffective depends mainly on:

A. The color of the particles

B. The energy and direction (orientation) of the colliding particles

C. The temperature of the room only

D. The number of electrons in the nucleus

Question 68

An effective collision can only occur if the energy of the colliding particles is high enough to:

A. Overcome the repulsion between the electrons surrounding the reacting particles

B. Exceed the boiling point of the reaction mixture

C. Match the mass of the heaviest reactant

D. Prevent any bonds from forming

Question 69

Besides having sufficient energy, an effective collision also requires that the colliding particles have the:

A. Same temperature as the surroundings

B. Correct orientation, so that the atoms needed to form new bonds actually collide with each other

C. Identical mass

D. Same physical state

Question 70

The minimum amount of energy that, in addition to the average kinetic energy, particles must have for an effective collision is called the:

A. Bond energy

B. Activation energy

C. Enthalpy of reaction

D. Ionization energy

Question 71

If the energy of the reacting particles is lower than the activation energy, what will happen?

A. The reaction will proceed, but slowly

B. No reaction will occur

C. The reaction will proceed instantly

D. The particles will fuse together permanently

Question 72

The speed (rate) of a chemical reaction is generally related to its activation energy such that:

A. A higher activation energy corresponds to a higher reaction rate

B. A higher activation energy corresponds to a lower reaction rate

C. Activation energy has no relationship to reaction rate

D. A lower activation energy always stops the reaction completely

Question 73

In a reaction pathway diagram, the highest energy point along the pathway, representing an unstable intermediate arrangement of atoms, is called the:

A. Ground state

B. Transition state

C. Rest state

D. Final state

Question 74

In a reaction pathway diagram, the vertical distance from the reactants' energy level up to the transition state represents the:

A. Enthalpy change of the reaction

B. Activation energy

C. Bond dissociation energy of the products

D. Reaction time

Question 75

In a reaction pathway diagram for an exothermic reaction, the products are shown at a lower energy level than the reactants, and the difference between these two levels represents the:

A. Activation energy

B. Enthalpy change of the reaction

C. Transition state energy

D. Bond energy of the reactants only

Question 76

In the collision between molecules A2 and B2, if the two molecules collide with correct orientation and sufficient energy to form an unstable activated complex that then breaks apart into product molecules, this is an example of a(n):

A. Ineffective collision

B. Effective collision

C. Non-reactive collision

D. Elastic collision with no bond changes

Question 77

If two colliding molecules bounce apart completely unchanged after collision, despite colliding, this best illustrates a(n):

A. Effective collision

B. Ineffective collision

C. Catalyzed collision

D. Endothermic collision

Question 78

Why might two reacting molecules collide with enough energy, yet still fail to react?

A. Because energy is the only factor that matters in any collision

B. Because even with sufficient energy, the molecules may not be oriented correctly relative to each other, so the necessary atoms do not actually come into contact to form new bonds

C. Because molecules with enough energy always react successfully, with no exceptions

D. Because reaction outcomes are entirely random and unrelated to collisions

Question 79

On a reaction pathway diagram, why is the transition state drawn at a higher energy level than both the reactants and the products?

A. Because the transition state represents a temporary, unstable, high-energy arrangement of atoms that must be passed through before the reaction can proceed to products

B. Because the diagram is simply drawn incorrectly by convention

C. Because the transition state contains extra atoms not present in the reactants or products

D. Because the transition state is actually the most stable point in the reaction

Question 80

On a reaction pathway diagram for an endothermic reaction, would you expect the products to be positioned at a higher or lower energy level than the reactants?

A. A lower energy level, since the reaction releases energy overall

B. A higher energy level, since the reaction absorbs energy overall

C. The same energy level as the reactants

D. Products are never shown on such diagrams

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