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CHEMISTRY, M4 EQ-Bank 12

The energy profile diagram below shows the energy changes that occur during a specific chemical reaction in the absence of a catalyst.
 

 

  1. Draw the energy profile for this reaction with a catalyst on the diagram above.   (1 mark)

  2. Describe the impact of a catalyst on this reaction, using the diagram as a reference.   (2 marks)
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a.    
     

b.   Catalyst impact:

  • A catalyst offers an alternative pathway for the reaction to occur that requires less activation energy.
  • On the energy profile diagram, this would appear as a lower peak, indicating the reduction in the energy needed for the reaction to proceed.
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a.   
     
 

b.   Catalyst impact:

  • A catalyst offers an alternative pathway for the reaction to occur that requires less activation energy.
  • On the energy profile diagram, this would appear as a lower peak, indicating the reduction in the energy needed for the reaction to proceed.

CHEMISTRY, M4 2015 VCE 16 MC

Consider the following energy profile for a particular chemical reaction, where \(\text{I, II}\) and \(\text{III}\) represent enthalpy changes during the reaction.
 

Which one of the following statements is correct?

  1. The activation energy for the reverse reaction is \(\text{(III–II)}\).
  2. The net energy released for the forward reaction is represented by \(\text{II}\).
  3. The energy required to break the reactant bonds is represented by \(\text{II}\).
  4. The energy released by the formation of new bonds is represented by \(\text{I}\).
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\(B\)

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  • \(\text{I:}\) energy needed to break reactant bonds (activation energy)
  • \(\text{II:}\) energy released by forward reaction
  • \(\text{III:}\) energy released when product bonds form (activation energy of reverse reaction)

\(\Rightarrow B\)

CHEMISTRY, M4 2021 VCE 24 MC

Which one of the following statements describes the effect that adding a catalyst will have on the energy profile diagram for an exothermic reaction?

  1. The energy of the products will remain the same.
  2. The shape of the energy profile diagram will remain the same.
  3. The peak of the energy profile will move to the left as the reaction rate increases.
  4. The activation energy will be lowered by the same proportion in the forward and reverse reactions.
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\(A\)

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  • The energy content of both the products and reactants is the same in both reactions (\(\Delta H\) unchanged).
  • Although the activation energy of the forward and reverse reaction decreases by the same amount in the uncatalysed vs catalysed reactions, the proportions are different (i.e. the decrease is a higher proportion of the forward reaction’s activation energy).

\(\Rightarrow A\)

CHEMISTRY, M4 2019 VCE 21 MC

The diagram below represents the Maxwell-Boltzmann distribution of an uncatalysed reaction.
 

The effect of adding a catalyst could be:

    1. the curve flattens to reflect the lower activation energy barrier
    2. the curve shifts to the right
    3. the \(E_\text{a}\) shifts to the left.

Which of the statements above are correct?

  1. 1 only
  2. 1 and 2
  3. 2 and 3
  4. 3 only
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\(D\)

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  • The shape of the curve is not changed with the introduction of a catalyst.
  • A catalyst will decrease the activation energy of the reaction (shifting it left from \(E_{\text{a}}\) to \(E_{\text{c}}\)).
  • The shaded area under the curve represents the proportion of successful collisions.

\(\Rightarrow D\)

CHEMISTRY, M4 2019 VCE 9 MC

A reaction has the energy profile diagram shown below.
 

Which of the following represents the energy profile of the reverse reaction.
 

  \(\text{Final product energy}\)
\(\text{(kJ mol}^{−1})\)		 \(\Delta H\)
\(\text{(kJ mol}^{−1})\)
A.   \(40\) \(+10\)
B. \(50\) \(+10\)
C. \(50\) \(-10\)
D. \(40\) \(-10\)
 
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\(B\)

Show Worked Solution
  • Reverse reaction  \(\Rightarrow\)  Endothermic
   \(\Delta H \) \(=\ \text{E(products) – E(reactants)}\)  
  \(= 50-40\)  
  \(=10\ \text{kJ mol}^{-1}\)  

 
\(\Rightarrow B\)

CHEMISTRY, M4 2018 VCE 13 MC

The energy profile diagram below represents a particular reaction. One graph represents the uncatalysed reaction and
the other graph represents the catalysed reaction.
 

Which of the following best matches the energy profile diagram?
 

  \(E_\text{a}\)
\(\text{uncatalysed reaction}\)
\(\text{(kJ mol}^{-1})\)		 \(\Delta H\)
\(\text{catalysed reaction}\)
\(\text{(kJ mol}^{-1}) \)
A.   \(40\) \(-140\)
B. \(90\) \(-140\)
C. \(40\) \(-50\)
D. \(90\) \(-50\)
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\(D \)

Show Worked Solution
  • The \(\text{E}_{a}\) of the uncatalysed reaction is higher (90) than the catalysed reaction (40).
  • The \(\Delta H\) energy changes are based off the zero reading (pre-reaction) to the final energy. 

\(\Rightarrow D \)

CHEMISTRY, M4 2017 VCE 29 MC

The following energy profile shows the results obtained during an enzyme-catalysed reaction. Each stage of the reaction is labelled: M represents the initial reactants, N represents a stable intermediate and P represents the final products.
 

Which one of the following statements is correct?

  1. The energy change from M to N is exothermic and the energy change from N to P is exothermic.
  2. The energy change from M to P is exothermic and the energy change from N to P is endothermic.
  3. The energy change from M to N is endothermic and the energy change from N to P is endothermic.
  4. The energy change from M to N is endothermic and the energy change from M to P is endothermic.
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\(D\)

Show Worked Solution

\(\text{M → P}\) is endothermic since energy of products > energy of reactants.

\(\text{M → N}\) is endothermic

\(\text{N → P}\) is exothermic

\(\Rightarrow D\)