Chemistry worksheet focusing on energy changes in reactions, including kinetic energy, activation energy, and reaction mechanisms.
A worksheet with chemistry questions about kinetic energy, bond strength, reaction rates, activation energy, and activated complexes.
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Show Answer Key & Explanations
Step-by-step solution for: Potential Energy Diagrams: Key Concepts for Understanding ...
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Show Answer Key & Explanations
Step-by-step solution for: Potential Energy Diagrams: Key Concepts for Understanding ...
Here are the answers to the questions on your worksheet, based on general chemistry principles regarding kinetics and energy.
9. Which species or set of species has the highest kinetic energy?
The reactants (assuming the reaction is exothermic, which is implied by question 13 asking if the forward reaction is faster). In an exothermic reaction, the reactants start at a higher energy level than the products. Since they have more potential energy to begin with, and assuming standard conditions, they represent the starting high-energy state before activation energy is added. *Note: If this refers to a specific graph not shown here, the answer is whichever side of the graph is physically higher up on the y-axis.*
10. Which species or set of species has the weakest bonds?
The Activated Complex (or Transition State). At this point, old bonds are breaking and new bonds are forming, but neither is complete. This makes the structure very unstable and the "bonds" effectively the weakest compared to stable reactants or products.
11. Which species or set of species has the strongest bonds?
The species with the lowest Potential Energy. Usually, this is the Products in an exothermic reaction (where energy is released because strong bonds formed) or the Reactants in an endothermic reaction. Without seeing the graph, the general rule is: Lower Potential Energy = Stronger Bonds.
12. What is $\Delta H$ for the reaction: $X_2Y_2 \rightarrow X_2 + Y_2$?
$\Delta H$ (Change in Enthalpy) is calculated as:
$$\Delta H = \text{Potential Energy of Products} - \text{Potential Energy of Reactants}$$
*(You need to look at your graph to get the specific numbers. Subtract the PE of $X_2Y_2$ from the combined PE of $X_2 + Y_2$.)*
13. Which do you think would be faster, the forward reaction or the reverse reaction? Explain.
The Forward Reaction is likely faster.
Explain: Reactions with lower Activation Energy ($E_a$) happen faster. In most textbook diagrams for this type of decomposition, the "hill" to go over from reactants to products is smaller than the hill to go back from products to reactants. Therefore, it is easier for molecules to move forward.
14. Which species or set of species has the lowest kinetic energy?
The Products (in an exothermic reaction). As the reaction proceeds and releases heat, the resulting product molecules often have less stored potential energy. *Note: Kinetic energy is related to temperature. If the system loses heat to the surroundings, the remaining particles may have lower average KE.*
15. Show the $H$, the Activation Energy for the forward reaction and the Activation Energy for the reverse reaction on the graph above.
*(Since I cannot draw on your paper, here is how you label it):*
* $\Delta H$: Draw a vertical arrow from the flat line of the Reactants to the flat line of the Products.
* Activation Energy (Forward): Draw a vertical arrow from the Reactants' flat line up to the very top peak of the curve.
* Activation Energy (Reverse): Draw a vertical arrow from the Products' flat line up to the very top peak of the curve.
16. As reactant particles approach each other before a collision, the Potential Energy goes \_\_\_\_\_\_\_\_\_\_, while the Kinetic Energy goes \_\_\_\_\_\_\_\_\_\_.
Potential Energy goes up (increases), while the Kinetic Energy goes down (decreases).
*(Reasoning: They slow down as they push against each other's electron clouds, converting motion energy into stored potential energy.)*
17. As particles of newly formed products move away from one another, the Potential Energy goes \_\_\_\_\_\_\_\_\_\_, while the Kinetic Energy goes \_\_\_\_\_\_\_\_\_\_.
Potential Energy goes down (decreases), while the Kinetic Energy goes up (increases).
*(Reasoning: As they settle into stable bonds, they release stored energy and speed up.)*
18. As reactant molecules approach each other, they exert \_\_\_\_\_\_\_\_\_\_ forces on each other. Thus, as they move together, their speed \_\_\_\_\_\_\_\_\_\_ and their Potential Energy \_\_\_\_\_\_\_\_\_\_.
They exert repulsive forces on each other. Thus, as they move together, their speed decreases and their Potential Energy increases.
19. State the meaning of Activated Complex.
The Activated Complex is a temporary, unstable arrangement of atoms that exists for a split second at the very top of the energy curve. It is the transition point where old bonds are breaking and new bonds are beginning to form. It has the highest potential energy of the entire reaction.
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Final Answer:
9. Reactants (typically)
10. Activated Complex
11. Species with lowest Potential Energy (usually Products in exothermic reactions)
12. $\Delta H = PE_{products} - PE_{reactants}$
13. Forward reaction (because it usually has lower Activation Energy)
14. Products (typically)
15. [See explanation for drawing instructions]
16. Up; Down
17. Down; Up
18. Repulsive; Decreases; Increases
19. A temporary, high-energy, unstable state where bonds are breaking and forming.
9. Which species or set of species has the highest kinetic energy?
The reactants (assuming the reaction is exothermic, which is implied by question 13 asking if the forward reaction is faster). In an exothermic reaction, the reactants start at a higher energy level than the products. Since they have more potential energy to begin with, and assuming standard conditions, they represent the starting high-energy state before activation energy is added. *Note: If this refers to a specific graph not shown here, the answer is whichever side of the graph is physically higher up on the y-axis.*
10. Which species or set of species has the weakest bonds?
The Activated Complex (or Transition State). At this point, old bonds are breaking and new bonds are forming, but neither is complete. This makes the structure very unstable and the "bonds" effectively the weakest compared to stable reactants or products.
11. Which species or set of species has the strongest bonds?
The species with the lowest Potential Energy. Usually, this is the Products in an exothermic reaction (where energy is released because strong bonds formed) or the Reactants in an endothermic reaction. Without seeing the graph, the general rule is: Lower Potential Energy = Stronger Bonds.
12. What is $\Delta H$ for the reaction: $X_2Y_2 \rightarrow X_2 + Y_2$?
$\Delta H$ (Change in Enthalpy) is calculated as:
$$\Delta H = \text{Potential Energy of Products} - \text{Potential Energy of Reactants}$$
*(You need to look at your graph to get the specific numbers. Subtract the PE of $X_2Y_2$ from the combined PE of $X_2 + Y_2$.)*
13. Which do you think would be faster, the forward reaction or the reverse reaction? Explain.
The Forward Reaction is likely faster.
Explain: Reactions with lower Activation Energy ($E_a$) happen faster. In most textbook diagrams for this type of decomposition, the "hill" to go over from reactants to products is smaller than the hill to go back from products to reactants. Therefore, it is easier for molecules to move forward.
14. Which species or set of species has the lowest kinetic energy?
The Products (in an exothermic reaction). As the reaction proceeds and releases heat, the resulting product molecules often have less stored potential energy. *Note: Kinetic energy is related to temperature. If the system loses heat to the surroundings, the remaining particles may have lower average KE.*
15. Show the $H$, the Activation Energy for the forward reaction and the Activation Energy for the reverse reaction on the graph above.
*(Since I cannot draw on your paper, here is how you label it):*
* $\Delta H$: Draw a vertical arrow from the flat line of the Reactants to the flat line of the Products.
* Activation Energy (Forward): Draw a vertical arrow from the Reactants' flat line up to the very top peak of the curve.
* Activation Energy (Reverse): Draw a vertical arrow from the Products' flat line up to the very top peak of the curve.
16. As reactant particles approach each other before a collision, the Potential Energy goes \_\_\_\_\_\_\_\_\_\_, while the Kinetic Energy goes \_\_\_\_\_\_\_\_\_\_.
Potential Energy goes up (increases), while the Kinetic Energy goes down (decreases).
*(Reasoning: They slow down as they push against each other's electron clouds, converting motion energy into stored potential energy.)*
17. As particles of newly formed products move away from one another, the Potential Energy goes \_\_\_\_\_\_\_\_\_\_, while the Kinetic Energy goes \_\_\_\_\_\_\_\_\_\_.
Potential Energy goes down (decreases), while the Kinetic Energy goes up (increases).
*(Reasoning: As they settle into stable bonds, they release stored energy and speed up.)*
18. As reactant molecules approach each other, they exert \_\_\_\_\_\_\_\_\_\_ forces on each other. Thus, as they move together, their speed \_\_\_\_\_\_\_\_\_\_ and their Potential Energy \_\_\_\_\_\_\_\_\_\_.
They exert repulsive forces on each other. Thus, as they move together, their speed decreases and their Potential Energy increases.
19. State the meaning of Activated Complex.
The Activated Complex is a temporary, unstable arrangement of atoms that exists for a split second at the very top of the energy curve. It is the transition point where old bonds are breaking and new bonds are beginning to form. It has the highest potential energy of the entire reaction.
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Final Answer:
9. Reactants (typically)
10. Activated Complex
11. Species with lowest Potential Energy (usually Products in exothermic reactions)
12. $\Delta H = PE_{products} - PE_{reactants}$
13. Forward reaction (because it usually has lower Activation Energy)
14. Products (typically)
15. [See explanation for drawing instructions]
16. Up; Down
17. Down; Up
18. Repulsive; Decreases; Increases
19. A temporary, high-energy, unstable state where bonds are breaking and forming.
Parent Tip: Review the logic above to help your child master the concept of potential energy diagrams worksheet answer key chapter 12.
