Chemical Kinetics
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Questions and Answers

What is the condition for considering an intermediate compound as a stationary state?

  • When k1 >> k2
  • When k2 = 0
  • When k2 >> k1 (correct)
  • When k1 = k2

    • Which type of reaction involves the absorption of light energy to initiate the reaction?

  • Photophysical process
  • Parallel reaction
  • Photochemical reaction (correct)
  • Thermodynamically favored reaction

    • What is the characteristic of a parallel reaction?

  • Multiple reactions occur simultaneously (correct)
  • The reaction is thermodynamically favored
  • The reaction occurs in the dark
  • Only one reactant is involved

    • What is the energy associated with each photon in a photochemical reaction?

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

    What is the term for the process in which a molecule absorbs light energy and transitions to a higher energy level?

    <p>Photophysical process</p> Signup and view all the answers

    What is the primary reason for the dependence of photochemical reaction rates on the intensity of radiation?

    <p>The rate of absorption of photons</p> Signup and view all the answers

    In the photochemical combination of H and Cl, what is the role of the excited chlorine molecule (Cl2*)?

    <p>It decomposes to form chlorine free radicals (Cl)</p> Signup and view all the answers

    Why do different photochemical reactions have different rates?

    <p>Because they have different activation energies</p> Signup and view all the answers

    What is the effect of temperature on the rate of light-initiated reactions?

    <p>It has no effect on the rate</p> Signup and view all the answers

    What is the role of hv in the photochemical combination of H and Cl?

    <p>It is the light absorption step that forms the excited chlorine molecule (Cl2*)</p> Signup and view all the answers

    What is the significance of the negative free energy change in a thermochemical reaction?

    <p>It implies that the reaction is spontaneous and can occur without any external energy input.</p> Signup and view all the answers

    Which step is highly endothermic and limits the feasibility of the subsequent step in the reaction mechanism?

    <p>Step (III) in the reaction mechanism</p> Signup and view all the answers

    What is the reason for the lower values of HBr formation per photon of light absorbed in the given reaction mechanism?

    <p>The high recombination rate of bromine free radicals</p> Signup and view all the answers

    What is the significance of the quantum yield in a photochemical reaction?

    <p>It measures the efficiency of the reaction</p> Signup and view all the answers

    Which of the following applications is not a direct result of photochemical reactions?

    <p>Electroplating in industries</p> Signup and view all the answers

    What is the condition for equation (3) to be valid?

    <p>k1 &lt;&lt; k2</p> Signup and view all the answers

    In parallel reactions, what is the characteristic of the reactants?

    <p>They have different orders of reaction</p> Signup and view all the answers

    What is the energy required for a reactant molecule to cross the energy barrier in a photochemical reaction?

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

    What is the term for the process in which a molecule absorbs light energy and transitions to a higher energy level, and then loses its energy through a chemical reaction?

    <p>Photophysical process</p> Signup and view all the answers

    What is the characteristic of photochemical reactions that distinguishes them from thermal reactions?

    <p>They do not occur in dark</p> Signup and view all the answers

    What is the primary reason for the decrease in HBr formation per photon of light absorbed in the given reaction mechanism?

    <p>Most of the bromine free radicals recombine to give Br2 molecule</p> Signup and view all the answers

    Which step is responsible for the regeneration of free radicals in the given reaction mechanism?

    <p>Chain termination step</p> Signup and view all the answers

    What is the significance of the delta G value in photochemical reactions?

    <p>It may be positive or negative</p> Signup and view all the answers

    What is the role of light energy in photochemical reactions?

    <p>It is converted into free energy of the products</p> Signup and view all the answers

    What is the application of photochemistry in the electronic industry?

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

    What is the reason for the dependence of photochemical reaction rates on the intensity of radiation?

    <p>The amount of energy absorbed by the reactant molecules</p> Signup and view all the answers

    What is the characteristic of the excited molecule (Cl2*) in the photochemical combination of H and Cl?

    <p>It is a highly reactive species</p> Signup and view all the answers

    Why do some photochemical reactions have a higher yield of products than others?

    <p>Because of the chain reaction mechanism</p> Signup and view all the answers

    What is the significance of the wavelength of photon in a photochemical reaction?

    <p>It determines the amount of energy absorbed</p> Signup and view all the answers

    What is the role of light in a photochemical reaction?

    <p>To initiate the reaction</p> Signup and view all the answers

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