Worksheet: Reaction Profiles

In this worksheet, we will practice reading reaction profile energy diagrams and identifying and describing the energy transfers involved.

Q1:

Shown in the reaction profile are the changes in chemical energy during a reaction.

Energy cannot be created nor destroyed, only changed from one form to another. Which of the following processes is least likely to occur due to the change in chemical energy shown in the figure?

  • AThe container for the reaction mixture vibrates less rapidly.
  • BAir molecules above the reaction mixture increase in temperature.
  • CLight is emitted by reacting molecules.
  • DReactant and product molecules gain kinetic energy.
  • ESolvent evaporates from the reaction mixture.

Q2:

Labelled in the diagram are the chemical energies of three compounds, a–c.

Which of the labelled compounds is highest in energy?

  • Ac
  • Bb
  • Ca

Which of the labelled compounds is lowest in energy?

  • Ab
  • Ba
  • Cc

Which of the labelled compounds is most stable?

  • Ac
  • Ba
  • Cb

Which of the labelled compounds is least stable?

  • Ab
  • Ba
  • Cc

Q3:

Illustrated in the reaction profiles are the changes in chemical energy during a range of processes.

Which of the diagrams best describes the changes in chemical energy for a stick of dynamite during an explosion?

  • A(b)
  • B(a)
  • C(c)

Which of the diagrams best describes the changes in chemical energy for a packet of pasta stored in a kitchen cupboard?

  • A(b)
  • B(a)
  • C(c)

Which of the diagrams best describes the changes in chemical energy for a piece of aluminum being heated by a blowtorch?

  • A(a)
  • B(b)
  • C(c)

Which of the diagrams best describes the changes in chemical energy for a tank of burning petrol?

  • A(a)
  • B(b)
  • C(c)

Q4:

A reaction profile shows the relative energies of chemicals in a chemical reaction.

Shown in the reaction profile are the relative energies of chemicals in a simple chemical reaction.

Which components of a chemical reaction are indicated by A?

  • AIntermediates
  • BCatalysts
  • CProducts
  • DTransition states
  • EReactants

Which components of a chemical reaction are indicated by B?

  • ATransition states
  • BReactants
  • CProducts
  • DCatalysts
  • EIntermediates

Which components have more energy, those at A or those at B?

  • AThose at A have more energy.
  • BThose at B have more energy.

Which components are more stable, those at A or those at B?

  • AThose at B are more stable.
  • BThose at A are more stable.

Would this reaction happen spontaneously?

  • AMore information is needed.
  • BNo
  • CYes

Q5:

Illustrated in the reaction profile are the changes in chemical energy during a reaction as the reactant molecules are converted to products.

Based on the reaction profile, is energy absorbed or released during the reaction?

  • AReleased
  • BMore information is needed.
  • CAbsorbed

Q6:

Illustrated in the reaction profile are the changes in chemical energy as reacting molecules are converted to products.

Which of the following is the best description of this chemical reaction?

  • AEnergy is absorbed by the reaction and the products are more stable than the reactants.
  • BEnergy is absorbed by the reaction and the products are less stable than the reactants.
  • CEnergy is released by the reaction and the products are less stable than the reactants.
  • DEnergy is released by the reaction and the products are more stable than the reactants.

Q7:

The reaction profile for a chemical reaction is shown in the diagram below. Which label corresponds to the activation energy?

  • ANone of the labels
  • BC
  • CB
  • DA

Q8:

The reaction profile diagram for a two-step chemical reaction is shown below. In step 1, compound a reacts to form compound b, and in step 2, compound b reacts to form compound c.

Which step has the highest activation energy?

  • AStep 1 and step 2 have equal activation energies.
  • BStep 2
  • CStep 1

Which step is an exothermic reaction?

  • ANeither step 1 nor step 2
  • BStep 2
  • CStep 1

Q9:

The reaction profile for a chemical reaction is shown in the diagram below. Which label corresponds to the change in enthalpy, Δ𝐻, of the reaction?

  • AA
  • BNone of the labels
  • CB
  • DC

Q10:

The reaction profile diagram below shows that graphite is more stable than diamond. However, the conversion from diamond to graphite is very difficult. Which of the following statements explains why?

  • ADiamond does not conduct electricity.
  • BThe energy required to break the covalent bonds between carbon atoms is low.
  • CThe reaction is exothermic, not endothermic.
  • DThe energy difference between diamond and graphite is very small.
  • EThe activation energy for the conversion of diamond into graphite is very high.

Q11:

Three compounds, a–c, are labeled in the reaction profile below. Which compound corresponds to the activated complex, otherwise known as the transition state?

  • Ab
  • Bc
  • Ca
  • DNone of the labels

Q12:

Some substances are able to reduce the activation energy. How would this affect the energy changes during a chemical reaction?

  • AMore energy would be required for the reaction to proceed.
  • BThe reaction would release energy to the surroundings, instead of absorbing energy.
  • CThere would be a decrease in the total enthalpy change of the reaction.
  • DThere would be an increase in the total enthalpy change of the reaction.
  • ELess energy would be required for the reaction to proceed.

Q13:

A reaction profile diagram for a reaction is shown.

What is the activation energy for this reaction?

What is the molar enthalpy change for this reaction?

Q14:

A chemical reaction is found to have a molar reaction enthalpy (Δ𝐻) of 80 kJ/mol and an activation energy of 25 kJ/mol. Which of the following reaction profiles represents this reaction?

  • A
  • B
  • C
  • D

Q15:

A reaction profile for a chemical reaction is shown below. Which of the following statements best describes this reaction profile?

  • AThe reaction is endothermic, with a molar reaction enthalpy (Δ𝐻) of 240 kJ/mol and an activation energy of 70 kJ/mol.
  • BThe reaction is exothermic, with a molar reaction enthalpy (Δ𝐻) of 70 kJ/mol and an activation energy of 170 kJ/mol.
  • CThe reaction is endothermic, with a molar reaction enthalpy (Δ𝐻) of 140 kJ/mol and an activation energy of 70 kJ/mol.
  • DThe reaction is exothermic, with a molar reaction enthalpy (Δ𝐻) of 170 kJ/mol and an activation energy of 240 kJ/mol.
  • EThe reaction is endothermic, with a molar reaction enthalpy (Δ𝐻) of 70 kJ/mol and an activation energy of 170 kJ/mol.

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