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CHEMISTRY, M3 EQ-Bank 17

How does the presence of a catalyst influence the rate of a chemical reaction?   (2 marks)

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  • Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process.
  • They work by providing an alternative reaction pathway with a lower activation energy, which is the energy required for the reaction to occur. Because of this, more reactant particles can successfully collide with enough energy to undergo the reaction at a given temperature.
  • As a result, the reaction occurs faster when a catalyst is present.
Show Worked Solution
  • Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process.
  • They work by providing an alternative reaction pathway with a lower activation energy, which is the energy required for the reaction to occur. Because of this, more reactant particles can successfully collide with enough energy to undergo the reaction at a given temperature.
  • As a result, the reaction occurs faster when a catalyst is present.

CHEMISTRY, M3 EQ-Bank 11

Brian measured the reaction rate of 0.5 g of sodium metal in 2.0 mol/L nitric acid. The volume of hydrogen gas produced per minute was recorded both without a catalyst and with copper as a catalyst.

\begin{array} {|c|c|c|}
\hline \text{Time (minutes)} & \text{Volume of hydrogen gas (mL)} & \text{Volume of hydrogen gas (mL)} \\ & \text{no catalyst} & \text{catalyst}  \\
\hline \text{0}  & 0 & 0  \\
\hline \text{1} & 16 & 7 \\
\hline \text{2} & 30 &  13\\
\hline \text{3} & 43 & 19 \\
\hline \text{4}  & 44 & 26 \\
\hline \text{5} & 44 &  32 \\
\hline \text{6} & 44 & 38 \\
\hline \text{7} & 44 &  44 \\
\hline \end{array}

  1. On the grid below, plot a line graph for the data in the table.   (3 marks)
     
  2. Write a conclusion for the experiment.   (2 marks)

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a.    
       

b.   Experiment conclusion:

  • The rate of reaction was significantly faster when copper was used as a catalyst compared to when no catalyst was present.
  • This is because the copper catalyst provided an alternative reaction pathway with a lower activation energy, allowing the reactant particles to collide more frequently and effectively.

Show Worked Solution

a.   
     

b.   Experiment conclusion:

  • The rate of reaction was significantly faster when copper was used as a catalyst compared to when no catalyst was present.
  • This is because the copper catalyst provided an alternative reaction pathway with a lower activation energy, allowing the reactant particles to collide more frequently and effectively.

CHEMISTRY, M3 EQ-Bank 2 MC

Select the correct characteristic of a catalyst from the options below:

  1. A catalyst slows down the rate of reaction
  2. A catalyst doubles during a chemical reaction
  3. A catalyst is used up in a chemical reaction
  4. A catalyst speeds up the rate of reaction
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\(D\)

Show Worked Solution
  • A catalyst speeds up the rate of a reaction by providing an alternative pathway with lower activation energy.
  • It remains chemically unchanged at the end of the reaction and is not consumed during the process.

\(\Rightarrow D\)

CHEMISTRY, M3 EQ-Bank 9

Consider the statement:

The effectiveness of a metal catalyst is not dependent upon its surface area.

Explain if this statement correct, giving reasons for your answer.   (2 marks)

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  • The statement is incorrect.
  • Metal catalysts are solid and reactions occur on the catalyst surface.
  • It follows that the larger the surface, the more effective the catalyst (i.e. its “effectiveness” is dependent on the surface area).
Show Worked Solution
  • The statement is incorrect.
  • Metal catalysts are solid and reactions occur on the catalyst surface.
  • It follows that the larger the surface, the more effective the catalyst (i.e. its “effectiveness” is dependent on the surface area).

CHEMISTRY, M3 2013 VCE 11*

The following is a student’s summary of catalysts. It contains some correct and incorrect statements.

    1. A catalyst increases the rate of a reaction.
    2. All catalysts are solids.
    3. The mass of a catalyst is the same before and after the reaction.
    4. All catalysts align the reactant particles in an orientation that is favourable for a reaction to occur.
    5. A catalyst lowers the enthalpy change of a reaction, enabling more particles to have sufficient energy to successfully react.
  1. Identify two correct statements.   (1 mark)

  2. Evaluate the student’s summary by identifying two incorrect statements. In each case, explain why it is incorrect.   (4 marks)

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a.    Statements 1 and 3 are correct.

b.    Answers could include two of the following:

Incorrect statement: All catalysts are solids

  • Catalysts can be solids, liquids, gases or within aqueous solutions.

Incorrect statement: All catalysts align the reactant particles in an orientation that is favourable for a reaction to occur.

  • Although solid catalysts orient reactant particles to favor reactions, liquid and gaseous catalysts do not arrange reactants in this manner.

Incorrect statement: A catalyst lowers the enthalpy change of a reaction, enabling more particles to have sufficient energy to successfully react.

  • A catalyst does not change the relative energy contents of reactants and products.
  • It does, however, lower the activation energy/increases the proportion of successful collisions/provides an alternative reaction pathway with the same overall \(\Delta H.\)
Show Worked Solution

a.    Statements 1 and 3 are correct.

b.    Answers could include two of the following:

Incorrect statement: All catalysts are solids

  • Catalysts can be solids, liquids, gases or within aqueous solutions.

Incorrect statement: All catalysts align the reactant particles in an orientation that is favourable for a reaction to occur.

  • Although solid catalysts orient reactant particles to favor reactions, liquid and gaseous catalysts do not arrange reactants in this manner.

Incorrect statement: A catalyst lowers the enthalpy change of a reaction, enabling more particles to have sufficient energy to successfully react.

  • A catalyst does not change the relative energy contents of reactants and products.
  • It does, however, lower the activation energy/increases the proportion of successful collisions/provides an alternative reaction pathway with the same overall \(\Delta H.\)
♦ Mean mark (b) 51%.

CHEMISTRY, M3 EQ-Bank 7

Explain the role of a catalyst in altering the rate of a reaction.   (2 marks)

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  • A catalyst increases the rate of a reaction by providing an alternate reaction pathway with a lower activation energy \((\text{E}_{a})\), and does not undergo any permanent chemical change in this process.
  • This means the threshold kinetic energy \((\text{E}_{a})\) for a successful collision between particles is lowered.
  • This leads to more successful collisions and an increase in reaction rate.
Show Worked Solution
  • A catalyst increases the rate of a reaction by providing an alternate reaction pathway with a lower activation energy \((\text{E}_{a})\), and does not undergo any permanent chemical change in this process.
  • This means the threshold kinetic energy \((\text{E}_{a})\) for a successful collision between particles is lowered.
  • This leads to more successful collisions and an increase in reaction rate.

CHEMISTRY, M3 EQ-Bank 5

The following reaction is exothermic

\(\ce{N2(g) + 3H2(g) \rightarrow \ 2NH3(g)} \)

Lead \(\ce{(Pb)}\) can be used as a catalyst for this exothermic reaction. Describe what is meant by catalyst and how it influences this chemical reaction.   (3 marks)

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  • A catalyst increases the rate of a chemical reaction without undergoing any permanent chemical reaction itself.
  • The addition of \(\ce{Pb}\) in this reaction lowers the activation energy of a successful reaction.
  • More particles will exceed activation energy \(\ce{(E_{a})}\) when they collide with each other which increases the reaction rate.
Show Worked Solution
  • A catalyst increases the rate of a chemical reaction without undergoing any permanent chemical reaction itself.
  • The addition of \(\ce{Pb}\) in this reaction lowers the activation energy of a successful reaction.
  • More particles will exceed activation energy \(\ce{(E_{a})}\) when they collide with each other which increases the reaction rate.

CHEMISTRY, M3 2012 HSC 3 MC

What effect does a catalyst have on a reaction?

  1. It increases the rate.
  2. It increases the yield.
  3. It increases the heat of reaction.
  4. It increases the activation energy.
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\(A\)

Show Worked Solution
  • A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.

\(\Rightarrow A\)

CHEMISTRY, M3 2017 VCE 1 MC

A catalyst

  1. slows the rate of reaction.
  2. ensures that a reaction is exothermic.
  3. moves the chemical equilibrium of a reaction in the forward direction.
  4. provides an alternative pathway for the reaction with a lower activation energy.
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\(D\)

Show Worked Solution
  • A catalyst increases the rate of a chemical reaction by reducing the activation energy of the reaction. Thus, by collision theory, particles require less energy than normal to react to form products.

\(\Rightarrow D\)