Q1:
The reaction profile for a chemical reaction is shown in the diagram below. Which label corresponds to the activation energy?
- A None of the labels
- B C
- C B
- D A
Q2:
The reaction profile for a chemical reaction is shown in the diagram below. Which label corresponds to the change in enthalpy, , of the reaction?
- A A
- B None of the labels
- C B
- D C
Q3:
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?
- A Diamond does not conduct electricity.
- B The energy required to break the covalent bonds between carbon atoms is low.
- C The reaction is exothermic, not endothermic.
- D The energy difference between diamond and graphite is very small.
- E The activation energy for the conversion of diamond into graphite is very high.
Q4:
A reaction profile for a chemical reaction is shown below. Which of the following statements best describes this reaction profile?
- A The reaction is endothermic, with a molar reaction enthalpy () of 240 kJ/mol and an activation energy of 70 kJ/mol.
- B The reaction is exothermic, with a molar reaction enthalpy () of kJ/mol and an activation energy of 170 kJ/mol.
- C The reaction is endothermic, with a molar reaction enthalpy () of kJ/mol and an activation energy of 70 kJ/mol.
- D The reaction is exothermic, with a molar reaction enthalpy () of 170 kJ/mol and an activation energy of 240 kJ/mol.
- E The reaction is endothermic, with a molar reaction enthalpy () of 70 kJ/mol and an activation energy of 170 kJ/mol.
Q5:
This chemical equation describes the reaction of carbon monoxide and nitrogen dioxide gas molecules:
The reaction occurs as carbon monoxide and nitrogen dioxide molecules combine and form a transition-state complex. This information is described in the following graph.
Which label represents the potential energy of the transition-state complex?
- A D
- B C
- C E
- D A
- E B
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?
- A Energy is absorbed by the reaction and the products are more stable than the reactants.
- B Energy is absorbed by the reaction and the products are less stable than the reactants.
- C Energy is released by the reaction and the products are less stable than the reactants.
- D Energy is released by the reaction and the products are more stable than the reactants.
Q7:
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?
- A Released
- B More information is needed.
- C Absorbed
Q8:
Three compounds, a–c, are labelled in the reaction profile below. Which compound corresponds to the activated complex, otherwise known as the transition state?
- A b
- B c
- C a
- D None of the labels
Q9:
A chemical reaction is found to have a molar reaction enthalpy () of kJ/mol and an activation energy of 25 kJ/mol. Which of the following reaction profiles represents this reaction?
-
A
-
B
-
C
-
D
Q10:
Some substances are able to reduce the activation energy. How would this affect the energy changes during a chemical reaction?
- A More energy would be required for the reaction to proceed.
- B The reaction would release energy to the surroundings, instead of absorbing energy.
- C There would be a decrease in the total enthalpy change of the reaction.
- D There would be an increase in the total enthalpy change of the reaction.
- E Less energy would be required for the reaction to proceed.
Q11:
The graph describes different reaction pathways for one type of chemical reaction. The reaction is between the ozone molecule and an oxygen radical.
Which pathway has the largest activation energy barrier?
- A D
- B A
- C C
- D B
- E E
Q12:
The figure shows the reaction profile for a chemical reaction. The reactants produce three different transition-state complexes before they make any product molecules.
Which letter represents the energy of the least stable transition-state complex?
- A C
- B A
- C B
- D D
- E E
Q13:
Which of the following statements about the following diagram is correct?
- A Less energy is released when making bonds of the products than is taken in when breaking bonds of the reactants, so it is an exothermic reaction.
- B Less energy is released when making bonds of the products than is taken in when breaking bonds of the reactants, so it is an endothermic reaction.
- C More energy is released when making bonds of the products than is taken in when breaking bonds of the reactants, so it is an endothermic reaction.
- D More energy is released when making bonds of the products than is taken in when breaking bonds of the reactants, so it is an exothermic reaction.
Q14:
The figure shows a reaction pathway that includes more than one transition-state complex. Which difference of energy equation, , shows that the reaction pathway is exothermic?
- A
- B
- C
- D
- E
Q15:
Which of the following diagrams represents the highest heat released by the reactants?
-
A
-
B
-
C
-
D
Q16:
Based on the reaction diagram, how many intermediates are formed in the reaction ? Which step is the slowest?
- A 1,
- B 2,
- C 1,
- D 3,
- E 2,
Q17:
Using the diagram, determine which letter indicates the heat change of the reaction ().
- A Letter B
- B Letter A
- C Letter C
- D Letter D
Q18:
Which of the following best describes the heat change of this reaction according to the diagram shown?
- A The heat content of the reactants is greater than the heat content of the products and the sign of is positive.
- B The heat content of the products is less than the heat content of the reactants and the sign of is negative.
- C The heat content of the reactants is less than the heat content of the products and the sign of is negative.
- D The heat content of the products is greater than the heat content of the reactants and the sign of is positive.
Q19:
Which diagram represents the reaction whose is kJ?
-
A
-
B
-
C
-
D
Q20:
The equation describes an endothermic reaction that happens during a thunderstorm:
It describes the production of nitrogen monoxide from molecular nitrogen and oxygen.
What is the reaction profile for this endothermic chemical reaction process?
-
A
-
B
-
C
-
D
-
E
Q21:
If the chemical potential energy of the product molecules is lower than the potential energy of the reactant molecules, what kind of chemical reaction has taken place?
- A Endothermic
- B Exothermic
Q22:
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?
- A The container for the reaction mixture vibrates less rapidly.
- B Air molecules above the reaction mixture increase in temperature.
- C Light is emitted by reacting molecules.
- D Reactant and product molecules gain kinetic energy.
- E Solvent evaporates from the reaction mixture.
Q23:
The following diagram shows two different reaction pathways for the same reaction at the same temperature. Which pathway is faster? Why?
- A (A), because it requires more energy to initiate the reaction
- B (B), because it requires more energy to initiate the reaction
- C (A), because it requires less energy to initiate the reaction
- D (B), because it requires less energy to initiate the reaction
Q24:
Using the given diagram, calculate the value of the energy change during the following reaction.
- A kJ/mol
- B +60 kJ/mol
- C kJ/mol
- D +20 kJ/mol
Q25:
In which of the following energy diagrams is the absorbed energy the lowest?
- A Diagram A
- B Diagram C
- C Diagram B
- D Diagram D
