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CHEMISTRY, M3 EQ-Bank 16

Describe how activation energy, collision frequency, and molecular orientation work together to determine the rate of a chemical reaction. In your answer, define what each term refers to and relate these factors to collision theory.   (5 marks)

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→ Activation Energy: For a reaction to occur, the colliding molecules must have enough energy to overcome the activation energy barrier, which is the minimum energy required to break the bonds in the reactants and initiate the reaction. 

→ Collision Frequency: The rate of a reaction is also influenced by how frequently reactant molecules collide.

→ Molecular Orientation: In addition to having enough energy, molecules must collide with the correct orientation for a reaction to take place. Reactant molecules need to align in a way that allows bonds to break and new bonds to form. 

→ Increasing collision frequency increases the number of opportunities for molecules to collide, but only those collisions with enough energy and the correct orientation will lead to successful bond rearrangements.

→ For the maximum rate of reaction there needs to be a lower activation energy which makes it easier for collisions to result in a reaction, the proper orientation that ensures when collisions occur, they lead to the formation of products and a high collision frequency.

Show Worked Solution

→ Activation Energy: For a reaction to occur, the colliding molecules must have enough energy to overcome the activation energy barrier, which is the minimum energy required to break the bonds in the reactants and initiate the reaction. 

→ Collision Frequency: The rate of a reaction is also influenced by how frequently reactant molecules collide.

→ Molecular Orientation: In addition to having enough energy, molecules must collide with the correct orientation for a reaction to take place. Reactant molecules need to align in a way that allows bonds to break and new bonds to form. 

→ Increasing collision frequency increases the number of opportunities for molecules to collide, but only those collisions with enough energy and the correct orientation will lead to successful bond rearrangements.

→ For the maximum rate of reaction there needs to be a lower activation energy which makes it easier for collisions to result in a reaction, the proper orientation that ensures when collisions occur, they lead to the formation of products and a high collision frequency.

CHEMISTRY, M3 EQ-Bank 8 MC

Which statement best explains how molecular orientation affects the rate of a chemical reaction according to collision theory?

  1. Reactant molecules must collide with enough energy, but the orientation of the molecules is irrelevant.
  2. Correct orientation only affects reactions that involve more than two reactant molecules.
  3. Incorrect molecular orientation increases the activation energy required for the reaction to proceed.
  4. Even with sufficient energy, reactants must collide in the correct orientation to allow bonds to break and form.
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\(D\)

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→ For a reaction to occur, not only must reactants collide with sufficient energy, but they must also collide in the correct orientation to break existing bonds and form new ones.

→ Even if the reactants have enough energy, incorrect orientation can prevent a successful reaction.

\(\Rightarrow D\)

CHEMISTRY, M3 EQ-Bank 7 MC

Which of the following best describes the role of activation energy in a chemical reaction?

  1. It is the total energy released when bonds are broken in a reaction.
  2. It is the minimum energy required for reactants to collide and form products.
  3. It is the energy needed to cool the reactants and stop the reaction.
  4. It increases the number of collisions between molecules.
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\(B\)

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→ Activation energy is the minimum energy that reactants must have during a collision for a reaction to occur and form products.

→ If the reactants do not have sufficient energy, they will collide but fail to react.

\(\Rightarrow B\)

CHEMISTRY, M3 EQ-Bank 14

A student conducted an experiment to investigate how the concentration of hydrochloric acid affects the rate of its reaction with magnesium ribbon. They measured the volume of hydrogen gas produced at regular intervals in reactions using 1.0 M, 2.0 M, and 3.0 M hydrochloric acid, keeping other variables constant.

  1. Explain how the concentration of hydrochloric acid influences the rate of reaction with magnesium, using collision theory.   (2 marks)
  1. Describe how the student could modify the experiment to investigate the effect of temperature on the reaction rate.   (2 marks)
  1. Identify and explain one advantage of a student using digital technologies such as a gas pressure sensor to collect or analyse data from the experiment.   (2 marks)
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a.   \(\ce{[HCl]} influence on the rate of reaction:

→ As the concentration increases, the number of acid particles in a given volume also increases.

→ This leads to more frequent collisions between hydrochloric acid molecules and the magnesium surface.

→ As a result, a higher concentration of hydrochloric acid increases the chance of successful collisions, which increases the reaction rate and causes hydrogen gas to be produced more quickly.
 

b.   Experiment modifications:

→ To investigate the effect of temperature on the reaction rate, the student could modify the experiment by conducting the reaction at different temperatures while keeping the concentration of hydrochloric acid constant.

→ They could use a water bath or hot plate to control the temperature for each trial. For example, the student could perform the reaction at 20°C, 30°C, and 40°C, then measure and compare the volume of hydrogen gas produced over time at each temperature.
 

c.   Advantage of digital technologies:

→ Using a gas pressure sensor in the experiment allows for continuous and precise data collection without human intervention.

→ This reduces the chances of human error when measuring the volume of gas produced manually at intervals, leading to more accurate and reliable results.

→ Additionally, the sensor can automatically record data over time, providing detailed information about the reaction rate that can be easily analysed using digital tools such as graphing software.

Show Worked Solution

a.   \(\ce{[HCl]} influence on the rate of reaction:

→ As the concentration increases, the number of acid particles in a given volume also increases.

→ This leads to more frequent collisions between hydrochloric acid molecules and the magnesium surface.

→ As a result, a higher concentration of hydrochloric acid increases the chance of successful collisions, which increases the reaction rate and causes hydrogen gas to be produced more quickly.
 

b.   Experiment modifications:

→ To investigate the effect of temperature on the reaction rate, the student could modify the experiment by conducting the reaction at different temperatures while keeping the concentration of hydrochloric acid constant.

→ They could use a water bath or hot plate to control the temperature for each trial. For example, the student could perform the reaction at 20°C, 30°C, and 40°C, then measure and compare the volume of hydrogen gas produced over time at each temperature.
 

c.   Advantage of digital technologies:

→ Using a gas pressure sensor in the experiment allows for continuous and precise data collection without human intervention.

→ This reduces the chances of human error when measuring the volume of gas produced manually at intervals, leading to more accurate and reliable results.

→ Additionally, the sensor can automatically record data over time, providing detailed information about the reaction rate that can be easily analysed using digital tools such as graphing software.

CHEMISTRY, M3 EQ-Bank 6 MC

How does increasing the surface area of a reactant, such as using a powdered solid instead of a solid block, affect the rate of a reaction?

  1. It allows more particles to be exposed to the reactant, increasing collision frequency.
  2. It decreases the energy required for successful collisions between particles.
  3. It decreases the temperature of the system, making the reaction faster.
  4. It increases the number of particles that remain unreacted at the end.
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\(A\)

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→ Increasing the surface area of a reactant (e.g., using powdered solids) exposes more of the particles to the other reactants, resulting in a greater number of collisions per unit of time.

→ Since collision frequency is a key factor in the rate of reaction, having more available particles in contact increases the likelihood of successful collisions, which speeds up the reaction.

\(\Rightarrow A\)

CHEMISTRY, M3 EQ-Bank 13

A certain chemical reaction begins with a high reaction rate but over time this rate of reaction slows until the reaction is complete.

Explain this statement using collision theory.   (3 marks)

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→ At the start of the reaction, there is a high concentration of reactant molecules, which increases the frequency of collisions between them. According to collision theory, more frequent and effective collisions lead to a higher reaction rate.

→ As the reaction progresses, the concentration of reactants decreases, leading to fewer collisions. With fewer successful collisions occurring over time, the reaction rate slows down.

→ Eventually, when most or all of the reactants are used up, the reaction reaches completion, and the rate drops to zero.

Show Worked Solution

→ At the start of the reaction, there is a high concentration of reactant molecules, which increases the frequency of collisions between them. According to collision theory, more frequent and effective collisions lead to a higher reaction rate.

→ As the reaction progresses, the concentration of reactants decreases, leading to fewer collisions. With fewer successful collisions occurring over time, the reaction rate slows down.

→ Eventually, when most or all of the reactants are used up, the reaction reaches completion, and the rate drops to zero.

CHEMISTRY, M3 EQ-Bank 3 MC

When molecules react, the final rate of a chemical reaction is determined by which of the following factors?

  1. The proportion of collisions where the number of molecules are keep the same.
  2. The proportion of collisions where molecules have the correct orientation
  3. The proportion of collisions where atoms are destroyed
  4. The proportion of collisions where molecules form larger structures
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\(B\)

Show Worked Solution

→ For a reaction to occur, it is not enough for molecules to simply collide.

→ They must collide with the correct orientation for bonds to break and new ones to form. Even if the energy is sufficient, an incorrect orientation will not result in a successful reaction.

→ Therefore, the rate of a chemical reaction is largely determined by the proportion collisions that occur with the proper orientation between reacting molecules.

\(\Rightarrow B\)

CHEMISTRY, M3 EQ-Bank 1 MC

According to Collision Theory, to increase the rate of a reaction, which of the following must occur? 

  1. A decrease in temperature
  2. An increase in the concentration of a reactant
  3. An increase in the surface area of a reactant
  4. An increase in the frequency of successful collisions
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\(D\)

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→ Options A and C will increase the rate of a reaction but neither “must” occur for the rate of a reaction to increase.

→ The frequency of successful collisions defines the rate of reaction.

\(\Rightarrow D\)

CHEMISTRY, M3 2013 VCE 14-15 MC

\(\ce{Cu(s) + 4HNO3(aq)\rightarrow Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)}\)
 

\(\text{Question 14}\)

Which one of the following will not increase the rate of the above reaction?

  1. decreasing the size of the solid copper particles
  2. increasing the temperature of \(\ce{HNO3}\) by 20 °C
  3. increasing the concentration of \(\ce{HNO3}\)
  4. allowing \(\ce{NO2}\) gas to escape

 
\(\text{Question 15}\)

In the above reaction, the number of successful collisions per second is a small fraction of the total number of collisions.

The major reason for this is that

  1. the nitric acid is ionised in solution.
  2. some reactant particles have too much kinetic energy.
  3. the kinetic energy of the particles is reduced when they collide with the container’s walls.
  4. not all reactant particles have the minimum kinetic energy required to initiate the reaction.
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\(\text{Question 14:}\ D\)

\(\text{Question 15:}\ D\)

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\(\text{Question 14}\)

→ Options \(A, B\) and \(C\) will all increase the rate of the given chemical reaction.

\(\Rightarrow D\)
 

\(\text{Question 15}\)

→ Successful collisions occur only if the particles involved have at least the minimum kinetic energy required and the correct orientation.

\(\Rightarrow D\)