Chemical Reactions: Exothermic vs Endothermic
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Questions and Answers

What is the minimum amount of energy needed for the colliding particles to react called?

  • Heat of Reaction
  • Activation Energy (correct)
  • Enthalpy
  • Thermal Energy

    • Which of the following is NOT a factor that influences the rate of a reaction?

  • The concentration of the reactants
  • The surface area of the reactants
  • The temperature of the reactants
  • The volume of the reactants (correct)

    • Which of the following statements is TRUE about endothermic reactions?

  • They always feel hot to the touch.
  • The products have a lower energy level than the reactants.
  • They require energy input from the surroundings. (correct)
  • They release energy into the surroundings.

    • Why is breaking chemical bonds an endothermic process?

    <p>Because energy is required to break the bonds. (D)</p> Signup and view all the answers

    Which of the following is true regarding the energy profile of an endothermic reaction?

    <p>The energy level of the products is higher than the reactants. (C)</p> Signup and view all the answers

    What is the term used to describe the transfer of thermal energy in a chemical reaction?

    <p>Enthalpy Change (C)</p> Signup and view all the answers

    What does a positive enthalpy change (∆H) indicate about a chemical reaction?

    <p>The reaction is endothermic and absorbs energy from the surroundings. (C)</p> Signup and view all the answers

    In a chemical reaction, what does a positive change in enthalpy (∆H) indicate?

    <p>The reaction absorbs heat from the surroundings. (D)</p> Signup and view all the answers

    Which of the following is NOT a factor that affects the rate of a chemical reaction?

    <p>Color of the reactants (C)</p> Signup and view all the answers

    A chemical reaction is considered to be fast if:

    <p>The products are formed quickly. (B)</p> Signup and view all the answers

    What is the name of the minimum amount of energy required for a chemical reaction to occur?

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

    How does increasing the surface area of a solid reactant affect the rate of reaction?

    <p>Increases the rate by increasing the number of collisions. (C)</p> Signup and view all the answers

    What is the significance of the gradient of a graph plotting the concentration of a product against time in a chemical reaction?

    <p>It represents the rate of reaction. (B)</p> Signup and view all the answers

    Which of the following is a true statement about catalysts?

    <p>Catalysts increase the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. (B)</p> Signup and view all the answers

    In a chemical reaction, what does the term "effective collision" refer to?

    <p>A collision that has sufficient energy to overcome the activation energy. (A)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of a physical change?

    <p>Involves a change in chemical composition. (B)</p> Signup and view all the answers

    Which of the following examples is NOT a chemical change?

    <p>Melting ice (D)</p> Signup and view all the answers

    Which of the following is an example of an endothermic reaction?

    <p>Photosynthesis in plants (D)</p> Signup and view all the answers

    Flashcards

    Exothermic Reaction

    A reaction that transfers thermal energy to the surroundings, increasing their temperature.

    Endothermic Reaction

    A reaction that takes in thermal energy from the surroundings, decreasing their temperature.

    Activation Energy

    The minimum energy required for colliding particles to react.

    Rate of Reaction

    The speed at which reactants are converted to products, dependent on collision frequency and energy.

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    Energy Profile

    A visual representation showing energy changes of reactants and products during a reaction.

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    Enthalpy Change (∆H)

    The transfer of thermal energy in a reaction, indicating energy absorbed or released.

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    Product Energy in Exothermic

    The energy of products is lower than that of reactants, causing negative energy change.

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    Product Energy in Endothermic

    The energy of products is higher than that of reactants, resulting in positive energy change.

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    Physical Change

    A change where no new substance is formed; only physical state changes.

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    Chemical Change

    A change involving chemical reactions, resulting in new substances.

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    Collision Theory

    For a reaction to occur, reactant particles must collide effectively.

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    Catalyst

    A substance that increases the rate of reaction without being consumed.

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    Concentration Effect

    Increasing concentration raises the reaction rate due to more collisions.

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    Law of Conservation of Mass

    Mass is neither created nor destroyed in a chemical reaction.

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    Study Notes

    Exothermic and Endothermic Reactions

    • Exothermic reaction: Releases thermal energy to the surroundings, increasing their temperature. Heat is given out.
    • Endothermic reaction: Absorbs thermal energy from the surroundings, decreasing their temperature. Heat is taken in.
    • Distinguishing feature: Exothermic reactions "exit" energy from the system, endothermic reactions "enter" energy into the system.
    • Chemical Reaction: Rearrangement of atoms in reactants to form products.
    • Breaking bonds: Requires energy (endothermic), as energy is taken in to break chemical bonds.
    • Forming bonds: Releases energy (exothermic). Energy is released to the surroundings as bonds form.
    • Collision Theory: Reactions occur when particles collide with enough energy.
    • System: The reacting chemicals.
    • Surroundings: Everything outside the reacting chemicals.
    • Activation Energy: Minimum energy needed for particles to react upon collision.

    Rate of Reaction

    • Factors affecting rate:
      • Collision frequency: Increased collisions lead to faster reactions.
      • Collision energy: Higher energy collisions are more likely to cause reactions.
    • Temperature: Higher temperature → faster reaction (increased kinetic energy).
      • Higher temperature increases collision frequency and energy → greater chance of effective collisions.
    • Concentration: Higher concentration → faster reaction (more particles, more collisions).
    • Pressure (gases): Higher pressure → faster reaction (more particles in same volume, more collisions).
    • Surface area: Larger surface area → faster reaction (more surface exposed, more collisions).
    • Catalysts: Increase reaction rate by lowering activation energy.

    Energy Profiles

    • Exothermic: Products have lower energy than reactants, energy is released. Downward arrow in energy profile. ΔH is negative.
    • Endothermic: Products have higher energy than reactants, energy is absorbed. Upward arrow in energy profile. ΔH is positive.
    • Enthalpy change (ΔH): Transfer of thermal energy during the reaction; ΔH is negative for exothermic reactions, and positive for endothermic reactions.

    Chemical vs Physical Changes

    • Physical change: No new substance is created. Same elements, different forms (e.g., melting). Mixtures can be separated.
    • Chemical change: Requires a chemical reaction. New substances with different compositions are formed. Mass is conserved (total product mass = total reactant mass).

    Rates of Reactions - Practical Methods

    • Ways to track the rate of a reactions includes monitoring changes like mass of reactants used/time, product formed/time, gas volume produced/time, or other appropriate quantities.

    Collision Theory

    • Key points:
      • Collisions are required for reactions.
      • Collisions need sufficient energy and correct orientation for product formation (effective collisions).

    Chemical Equations

    • Reactants → Products: Symbols representing substances involved in a reaction.
    • Law of Conservation of Mass: Mass of reactants equals mass of products.

    Calculating Rates from Graphs

    • Slope/Gradient: Reaction rate can be determined graphically from the slope of a graph plotting concentration versus time.

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    Quiz Team

    Description

    This quiz covers the fundamental concepts of exothermic and endothermic reactions, including definitions, distinguishing features, and energy dynamics. Explore key concepts like activation energy and the role of collision theory in chemical reactions.

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