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QUESTION 8 [14 marks]

Consider the following potential energy diagram (shown in Figure 2 below)
which shows the change in potential energy for a reversible reaction.
Figure 2: Potential energy diagram for A + B ⇌ C + D
Question 8.1 [2 marks]
Define activation energy.
QUESTION 8.2
Which of the letters (from E1
, E2 and E3
) on the graph represent the following:
Question 8.2.1 [1 mark]
The energy state of the activated complex.
Question 8.2.2 [1 mark]
The energy of the reactants.
Question 8.2.3 [1 mark]
The energy of the products.
Question 8.2.4 [2 marks]
Use the symbols (from E1
, E2 and E3
) to write an equation to describe how you
would calculate the activation energy of the reverse reaction.
Question 8.2.5 [2 marks]
Use the symbols (from E1
, E2 and E3
) to write an equation to describe how you
would calculate the enthalpy of the forward reaction.
Question 8.3 [2 marks]
Is the forward reaction an endothermic or exothermic reaction? Explain your
answer.
QUESTION 8.4 [3 marks]
Draw a sketch graph of the reverse reaction. Include all the labels:

1 answer

Let's address each part of the question step by step.

QUESTION 8.1 [2 marks]

Define activation energy.
Answer: Activation energy is the minimum amount of energy required for a chemical reaction to occur. It is the energy needed to break the bonds in the reactants so that new bonds can form in the products. It represents the energy barrier that must be overcome for a reaction to proceed.

QUESTION 8.2

Which of the letters (from E1, E2, and E3) on the graph represent the following:

Question 8.2.1 [1 mark]

The energy state of the activated complex.
Answer: E2 represents the energy state of the activated complex.

Question 8.2.2 [1 mark]

The energy of the reactants.
Answer: E1 represents the energy of the reactants.

Question 8.2.3 [1 mark]

The energy of the products.
Answer: E3 represents the energy of the products.

Question 8.2.4 [2 marks]

Use the symbols (from E1, E2, and E3) to write an equation to describe how you would calculate the activation energy of the reverse reaction.
Answer: The activation energy for the reverse reaction can be calculated as follows:
Activation Energy (reverse) = E2 - E3

Question 8.2.5 [2 marks]

Use the symbols (from E1, E2, and E3) to write an equation to describe how you would calculate the enthalpy of the forward reaction.
Answer: The enthalpy change for the forward reaction can be calculated as follows:
ΔH (forward) = E3 - E1

QUESTION 8.3 [2 marks]

Is the forward reaction an endothermic or exothermic reaction? Explain your answer.
Answer: The forward reaction is an endothermic reaction. This is because the energy of the products (E3) is higher than the energy of the reactants (E1), which indicates that energy is absorbed during the reaction. In an endothermic reaction, the system absorbs heat from the surroundings.

QUESTION 8.4 [3 marks]

Draw a sketch graph of the reverse reaction. Include all the labels.
While I cannot literally draw here, I can describe the sketch:

  1. Y-axis (Potential Energy) – Label this axis with "Potential Energy."
  2. X-axis (Reaction Progress) – Label this axis with "Reaction Progress."
  3. Plot the graph:
    • Start at a point representing the energy of the products (E3) on the left side of the graph.
    • Draw a rising curve to the peak, which represents the activated complex (E2).
    • Then, draw the curve downward to the energy of the reactants (E1) on the right side of the graph.
  4. Label the points:
    • Label the starting point (left side) as E3 (energy of the products).
    • Label the peak as E2 (energy of the activated complex).
    • Label the endpoint (right side) as E1 (energy of the reactants).

You would create a diagram that resembles an inverted version of the potential energy diagram for the forward reaction, illustrating that the reverse reaction starts at a higher energy level.