CH 14: Activation energy
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Questions and Answers

What is the main difference between the potential energy diagrams of uncatalysed and catalysed endothermic reactions?

  • The uncatalysed reaction has a higher activation energy peak. (correct)
  • The uncatalysed reaction has a lower activation energy peak.
  • The catalysed reaction has a higher activation energy peak.
  • There is no difference in the activation energy peaks.

    • Which of the following statements about exothermic reactions is correct?

  • The energy level of the products is always higher than the energy level of the reactants in exothermic reactions.
  • Exothermic reactions release energy, so the energy level of the products is lower than the energy level of the reactants. (correct)
  • Catalysts do not affect the activation energy of exothermic reactions.
  • Exothermic reactions always have a higher activation energy peak than endothermic reactions.

    • What information can be determined from the difference in height between the reactants and products on the potential energy diagram?

  • The rate of the reaction.
  • The activation energy of the reaction.
  • The change in enthalpy (ΔH) of the reaction. (correct)
  • The presence of a catalyst.

    • What is the purpose of the peak point on the potential energy diagram?

    <p>It represents the energy level of the activated complex.</p> Signup and view all the answers

    How does the presence of a catalyst affect the potential energy diagram of a reaction?

    <p>The catalyst decreases the activation energy of the reaction.</p> Signup and view all the answers

    What does the area under the curve from reactants to the peak point on the potential energy diagram represent?

    <p>The activation energy of the reaction.</p> Signup and view all the answers

    Which of the following statements about the potential energy diagrams of uncatalysed and catalysed reactions is correct?

    <p>The uncatalysed and catalysed reactions have the same pathway on the diagram.</p> Signup and view all the answers

    What does the X-axis of the potential energy diagram represent?

    <p>The progress of the reaction.</p> Signup and view all the answers

    Which of the following statements about the potential energy diagram of an endothermic reaction is incorrect?

    <p>The area under the curve from reactants to the peak represents the change in enthalpy (ΔH).</p> Signup and view all the answers

    How does the presence of a catalyst affect the potential energy diagram of an exothermic reaction?

    <p>The catalyst reduces the activation energy of the reaction.</p> Signup and view all the answers

    What type of reaction absorbs energy, with products having higher energy than reactants?

    <p>Endothermic</p> Signup and view all the answers

    Which term defines the minimum energy required for reactants to form products during a chemical reaction?

    <p>Activation energy</p> Signup and view all the answers

    What represents the unstable arrangement of atoms at the peak of the activation energy barrier?

    <p>Activated complex</p> Signup and view all the answers

    In which reaction is energy released, with reactants having higher energy levels than the products?

    <p>Exothermic</p> Signup and view all the answers

    What is the role of catalysts in chemical reactions?

    <p>To decrease activation energy</p> Signup and view all the answers

    Which represents a specific momentary mixture of reactants and products during a reaction?

    <p>Activated complex</p> Signup and view all the answers

    What is the significance of activation energy in determining the rate of a reaction?

    <p>Lower activation energy leads to a faster reaction</p> Signup and view all the answers

    Which term describes the energy barrier that must be overcome for a chemical reaction to proceed?

    <p>Activation energy</p> Signup and view all the answers

    In which type of reaction are reactants requiring external energy to convert into products?

    <p>Endothermic</p> Signup and view all the answers

    What does the activated complex represent during a chemical reaction?

    <p>An intermediate state at the peak of activation energy barrier</p> Signup and view all the answers

    What is the primary function of activation energy in a chemical reaction?

    <p>To determine the rate of the reaction</p> Signup and view all the answers

    How does a higher activation energy affect the reaction rate under the same conditions?

    <p>It decreases the reaction rate</p> Signup and view all the answers

    What does the activated complex represent in a chemical reaction?

    <p>A midpoint where bonds are breaking and forming</p> Signup and view all the answers

    Which of the following statements about the activated complex is true?

    <p>It has higher energy than the products</p> Signup and view all the answers

    What is the primary function of a positive catalyst in a chemical reaction?

    <p>To lower the activation energy</p> Signup and view all the answers

    How do positive catalysts increase the rate of a chemical reaction?

    <p>By allowing more reactant particles to reach the transition state</p> Signup and view all the answers

    What is the primary function of a negative catalyst (inhibitor) in a chemical reaction?

    <p>To increase the activation energy</p> Signup and view all the answers

    Which of the following diagrams is used to represent activation energy in a chemical reaction?

    <p>Potential energy diagrams</p> Signup and view all the answers

    What is the relationship between activation energy and the energy of the activated complex?

    <p>The activation energy is higher than the energy of the activated complex</p> Signup and view all the answers

    Which of the following statements about catalysts is false?

    <p>Catalysts are consumed during the reaction</p> Signup and view all the answers

    What does the area under the curve from reactants to the peak point on the potential energy diagram represent?

    <p>The activation energy required for the reaction</p> Signup and view all the answers

    What is the primary function of activation energy in a chemical reaction?

    <p>To determine the rate of the reaction</p> Signup and view all the answers

    How does the presence of a catalyst affect the potential energy diagram of an exothermic reaction?

    <p>It decreases the activation energy and lowers the energy of the products</p> Signup and view all the answers

    What term defines the minimum energy required for reactants to form products during a chemical reaction?

    <p>Activation energy</p> Signup and view all the answers

    Which of the following statements about the potential energy diagram of an endothermic reaction is incorrect?

    <p>The potential energy of the products is lower than the potential energy of the reactants</p> Signup and view all the answers

    What represents the unstable arrangement of atoms at the peak of the activation energy barrier?

    <p>The activated complex</p> Signup and view all the answers

    How does a higher activation energy affect the reaction rate under the same conditions?

    <p>It decreases the reaction rate</p> Signup and view all the answers

    What is the primary function of a negative catalyst (inhibitor) in a chemical reaction?

    <p>To increase the activation energy and slow down the reaction</p> Signup and view all the answers

    Which type of reaction absorbs energy, with products having higher energy than reactants?

    <p>Endothermic reaction</p> Signup and view all the answers

    What is the main difference between the potential energy diagrams of uncatalyzed and catalyzed endothermic reactions?

    <p>The activation energy is lower in the catalyzed reaction</p> Signup and view all the answers

    What role do positive catalysts (catalysts) play in a chemical reaction?

    <p>Provide an alternative reaction pathway with lower activation energy</p> Signup and view all the answers

    Which term best describes the activated complex in a chemical reaction?

    <p>Midpoint between reactants and products</p> Signup and view all the answers

    How does a higher activation energy affect the rate of a reaction under the same conditions?

    <p>Slows down the reaction</p> Signup and view all the answers

    What is the primary function of negative catalysts (inhibitors) in a chemical reaction?

    <p>Increase the activation energy</p> Signup and view all the answers

    What information can be inferred from the difference in height between reactants and products on a potential energy diagram?

    <p>Activation energy value</p> Signup and view all the answers

    What characteristic differentiates activated complexes from reactants and products in a chemical reaction?

    <p>Higher energy level</p> Signup and view all the answers

    In a chemical reaction, what is the primary effect of a negative catalyst (inhibitor) on the rate of reaction?

    <p>Slows down the reaction</p> Signup and view all the answers

    What do potential energy diagrams show in terms of chemical reactions?

    <p>$\Delta E$ values</p> Signup and view all the answers

    'Isolating the activated complex is challenging due to its:' ...?

    <p>$\text{High energy level and instability}$</p> Signup and view all the answers

    What is represented by the area under the curve from reactants to the peak point on a potential energy diagram?

    <p>The activation energy barrier for the reaction</p> Signup and view all the answers

    In a potential energy diagram, what does the difference in height between the reactants and products represent?

    <p>The enthalpy change ($\Delta H$) of the reaction</p> Signup and view all the answers

    What does the area under the curve from reactants to the peak point on the potential energy diagram represent?

    <p>The activation energy of the reaction</p> Signup and view all the answers

    How does the presence of a catalyst affect the potential energy diagram of a reaction?

    <p>It lowers the activation energy peak, but the start and end points remain the same</p> Signup and view all the answers

    What does the peak point on the potential energy diagram represent?

    <p>The activated complex</p> Signup and view all the answers

    What is the primary function of activation energy in a chemical reaction?

    <p>To provide the energy required for the reaction to occur</p> Signup and view all the answers

    How do positive catalysts increase the rate of a chemical reaction?

    <p>By lowering the activation energy barrier</p> Signup and view all the answers

    What represents the unstable arrangement of atoms at the peak of the activation energy barrier?

    <p>The activated complex</p> Signup and view all the answers

    Which term defines the minimum energy required for reactants to form products during a chemical reaction?

    <p>Activation energy</p> Signup and view all the answers

    What is the role of catalysts in chemical reactions?

    <p>To lower the activation energy barrier</p> Signup and view all the answers

    Which of the following statements about the potential energy diagrams of uncatalysed and catalysed reactions is correct?

    <p>The catalysed reaction has a lower activation energy peak than the uncatalysed reaction</p> Signup and view all the answers

    What information can be determined from the difference in height between the reactants and products on the potential energy diagram?

    <p>The change in enthalpy (ΔH) of the reaction</p> Signup and view all the answers

    Which of the following statements about the potential energy diagrams of uncatalysed and catalysed reactions is correct?

    <p>The catalysed reaction has a lower activation energy peak than the uncatalysed reaction.</p> Signup and view all the answers

    What does the peak point on the potential energy diagram represent?

    <p>The activated complex</p> Signup and view all the answers

    What is the primary function of a positive catalyst in a chemical reaction?

    <p>To decrease the activation energy of the reaction</p> Signup and view all the answers

    What does the area under the curve from reactants to the peak point on the potential energy diagram represent?

    <p>The activation energy of the reaction</p> Signup and view all the answers

    Which of the following statements about catalysts is false?

    <p>Catalysts are consumed during the reaction and must be replenished.</p> Signup and view all the answers

    What is the main difference between the potential energy diagrams of uncatalysed and catalysed endothermic reactions?

    <p>The catalysed reaction has a lower activation energy peak.</p> Signup and view all the answers

    What is the primary function of activation energy in a chemical reaction?

    <p>To determine the rate of the reaction</p> Signup and view all the answers

    Which term best describes the activated complex in a chemical reaction?

    <p>The transition state</p> Signup and view all the answers

    What does the X-axis of the potential energy diagram represent?

    <p>The course of the reaction, from reactants to products</p> Signup and view all the answers

    What effect does a higher activation energy have on the rate of a reaction under the same conditions?

    <p>Decreases the rate of reaction</p> Signup and view all the answers

    Which of the following characteristics best differentiates activated complexes from reactants and products?

    <p>Exists momentarily</p> Signup and view all the answers

    What is the primary function of a positive catalyst in a chemical reaction?

    <p>Lowers the activation energy</p> Signup and view all the answers

    Which term best describes the activated complex in a chemical reaction?

    <p>Midpoint between reactants and products</p> Signup and view all the answers

    How do negative catalysts (inhibitors) affect a chemical reaction?

    <p>Increase the activation energy</p> Signup and view all the answers

    What defines a positive catalyst (catalyst) in a chemical reaction?

    <p>Lowers the activation energy</p> Signup and view all the answers

    In terms of chemical reactions, what does a negative catalyst (inhibitor) primarily do?

    <p>Stops or slows down the reaction</p> Signup and view all the answers

    What is represented by a higher activation energy in a chemical reaction?

    <p>Slows down the reaction</p> Signup and view all the answers

    What happens to the rate of a reaction when a negative catalyst is introduced?

    <p>Decreases</p> Signup and view all the answers

    What role does a positive catalyst play in relation to activation energy?

    <p>Lowers activation energy</p> Signup and view all the answers

    What is the primary characteristic that distinguishes the activated complex from the reactants and products during a chemical reaction?

    <p>It is a fleeting arrangement that quickly dissociates into products or reverts to reactants.</p> Signup and view all the answers

    In the context of potential energy diagrams, what does the area under the curve from reactants to the peak point represent?

    <p>The activation energy required for the reaction to proceed.</p> Signup and view all the answers

    How do positive catalysts increase the rate of a chemical reaction?

    <p>By lowering the activation energy of the reaction.</p> Signup and view all the answers

    Which statement about the role of negative catalysts (inhibitors) in a chemical reaction is correct?

    <p>They increase the activation energy, thereby slowing down the reaction rate.</p> Signup and view all the answers

    Which statement best describes the potential energy diagrams of uncatalyzed and catalyzed reactions?

    <p>The catalyzed reaction has a lower activation energy but the same enthalpy change.</p> Signup and view all the answers

    According to the law of conservation of energy in chemical reactions, what is the relationship between energy changes and enthalpy changes?

    <p>Energy cannot be created or destroyed, and enthalpy changes account for energy transferred as heat or work.</p> Signup and view all the answers

    Which statement accurately describes the characteristic of the activated complex during a chemical reaction?

    <p>It is a momentary arrangement that quickly dissociates into products or reverts to reactants.</p> Signup and view all the answers

    In the context of potential energy diagrams, what does the difference in height between the reactants and products represent?

    <p>The enthalpy change $\Delta$H for the overall reaction.</p> Signup and view all the answers

    Which statement accurately describes the significance of activation energy in determining the rate of a chemical reaction?

    <p>Lower activation energy results in a faster reaction rate under the same conditions.</p> Signup and view all the answers

    Which statement accurately describes the role of positive catalysts in chemical reactions?

    <p>They lower the activation energy, thereby increasing the reaction rate.</p> Signup and view all the answers

    What feature on a potential energy diagram represents the highest point on the curve, symbolizing the activated complex?

    <p>Peak point</p> Signup and view all the answers

    In a catalysed exothermic reaction, what is the primary effect on the activation energy peak?

    <p>It decreases compared to the uncatalysed reaction</p> Signup and view all the answers

    What does the X-axis represent on a potential energy diagram?

    <p>Course of the reaction</p> Signup and view all the answers

    How are activated complexes different from reactants and products in a chemical reaction?

    <p>They have higher potential energy than reactants but lower than products</p> Signup and view all the answers

    What aspect of a potential energy diagram highlights the difference made by the presence of a catalyst in a reaction?

    <p>Peak point</p> Signup and view all the answers

    In an exothermic reaction, what does it signify if the curve ends below the initial energy level of the reactants?

    <p>The reaction is exothermic</p> Signup and view all the answers

    What does the difference in height between reactants and products represent on a potential energy diagram?

    <p>Change in enthalpy of the reaction</p> Signup and view all the answers

    Which term best describes the activated complex in terms of its stability during a chemical reaction?

    <p><strong>Metastable</strong></p> Signup and view all the answers

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