Chemical Kinetics Overview
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Questions and Answers

What are the units for the rate of a reaction when concentration is measured in mol L–1 and time in seconds?

  • mol L–1
  • atm s–1
  • mol L–1s–1 (correct)
  • L s–1

    • The average rate of a reaction does not depend on the change in concentration of the reactants or products.

    False

    What is the average rate of reaction in terms of concentration and time?

    change in concentration divided by time

    The units of rate are expressed as concentration ______ time–1.

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

    Match the following types of reactions with their rate expression:

    <p>Gaseous reactions = atm s–1 Liquid reactions = mol L–1s–1 Solid reactions = Depends on surface area Overall reaction rate = Change in concentration/time</p> Signup and view all the answers

    What is the rate determining step in a reaction?

    <p>The slowest step in the reaction</p> Signup and view all the answers

    Molecularity can be a fractional value.

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

    What is the order of the reaction given the rate law r = k [A]^(1/2) [B]^2?

    <p>2.5</p> Signup and view all the answers

    The species IO- is known as an __________ in the reaction.

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

    Match the following terms with their definitions:

    <p>Order = Experimental quantity determining reaction rate Molecularity = Count of reactant molecules in an elementary reaction Intermediate = Species formed in a reaction but not in overall equation Bimolecular = Involves two reactant molecules in a reaction step</p> Signup and view all the answers

    How many steps are involved in the decomposition of hydrogen peroxide described?

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

    For complex reactions, the molecularity is applicable.

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

    If the concentration of molecule X is increased to three times, how will it affect the rate of formation of product Y in a second order reaction?

    <p>The rate will increase by nine times.</p> Signup and view all the answers

    What is the rate law in a chemical reaction?

    <p>The expression relating the reaction rate to the concentration of reactants.</p> Signup and view all the answers

    Doubling the concentration of O2 while keeping NO constant will double the rate of formation of NO2.

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

    In the given reaction 2NO(g) + O2(g) → 2NO2(g), what happens to the rate of reaction when the concentration of NO is doubled?

    <p>The rate increases by a factor of four.</p> Signup and view all the answers

    The expression which relates the initial rate of a reaction to the concentration of reactants is called the rate _____ or rate expression.

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

    Match the following experiments with their initial rates of formation of NO2:

    <p>Experiment 1 = 0.096 mol L-1s-1 Experiment 2 = 0.384 mol L-1s-1 Experiment 3 = 0.192 mol L-1s-1 Experiment 4 = 0.768 mol L-1s-1</p> Signup and view all the answers

    From the given experimental data, how does the reaction rate relate to the concentrations of NO and O2 in this reaction?

    <p>The rate depends on the concentration of NO to the second power and O2 to the first power.</p> Signup and view all the answers

    The rate of a reaction can be influenced by changing the concentration of all reactants simultaneously.

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

    What are the initial concentrations of NO and O2 in Experiment 3?

    <p>0.30 mol L-1 for NO and 0.60 mol L-1 for O2.</p> Signup and view all the answers

    What is the half-life period of a first order reaction with a rate constant of 60 s–1?

    <p>0.693 s</p> Signup and view all the answers

    After 10 years, the amount of 90Sr in the body will still be the same as the initial amount.

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

    What is the time required for 99% completion of a first order reaction in relation to the time for 90% completion?

    <p>twice as long</p> Signup and view all the answers

    For the decomposition of 90Sr, after 60 years, the remaining amount of the initial 1 mg will be ______ mg.

    <p>0.125</p> Signup and view all the answers

    Match the following decomposition rates with their periods:

    <p>N2O5 = Half-life related to concentration change 90Sr = Half-life of 28.1 years Azoisopropane = First order reaction SO2Cl2 = Thermal decomposition data</p> Signup and view all the answers

    What does the slope represent when plotting ln [R] against time (t)?

    <p>-k</p> Signup and view all the answers

    The first order rate equation can be expressed as k = (2.303 * [R]0) / (t * [R]).

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

    What is the effect of taking the antilog of both sides of the equation ln [R] = -kt?

    <p>[R] = [R]0 e^(-kt)</p> Signup and view all the answers

    The equation for calculating rate constant k in a first order reaction is k = __________.

    <p>[R]1 ln [R]0 / ([R]2 (t2 - t1))</p> Signup and view all the answers

    Match the following components with their descriptions:

    <p>ln [R]0 = Intercept of the ln [R] vs t plot e^(-kt) = Antilog form of the first order reaction C2H4 + H2 = Reactants in a hydrogenation reaction k = Rate constant in first order kinetics</p> Signup and view all the answers

    Which of the following reactions is an example of first order kinetics?

    <p>C2H4(g) + H2(g) → C2H6(g)</p> Signup and view all the answers

    Natural and artificial radioactive decay follows zero order kinetics.

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

    What is the mathematical representation of a reaction that follows first order kinetics?

    <p>[R] = [R]0 e^(-kt)</p> Signup and view all the answers

    What effect does lowering the activation energy (Ea) have on the rate of reaction?

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

    The presence of a catalyst raises the activation energy required for a reaction.

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

    Define the term 'steric factor' in the context of collision theory.

    <p>Steric factor refers to the orientation of molecules during collisions that contributes to effective collisions.</p> Signup and view all the answers

    The equation for the rate of reaction can be expressed as k = P Z A e^{-E_a / RT}. Here, P is the ______ factor.

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

    Match the following reactions with their corresponding rate expression:

    <p>3NO(g) ---&gt; N2O(g) = Rate = k[NO]^2 H2O2(aq) + 3I–(aq) + 2H+ = Rate = k[H2O2][I–] C2H5Cl(g) ---&gt; C2H4(g) + HCl(g) = Rate = k[C2H5Cl] CH3CHO(g) ---&gt; CH4(g) + CO(g) = Rate = k[CH3CHO]^{3/2}</p> Signup and view all the answers

    What would be the order of the reaction for 2A + B ---> A2B if the rate is given as k[A][B]^2?

    <p>Third order</p> Signup and view all the answers

    For the decomposition of NH3 on a platinum surface, if the reaction is zero order, what is the relationship between the rate of reaction and the concentration of NH3?

    <p>The rate of reaction is constant and does not depend on the concentration of NH3.</p> Signup and view all the answers

    In a reaction where k = 2.0 × 10–6 mol–2 L2 s–1, the initial rate when [A] = 0.1 mol L–1 and [B] = 0.2 mol L–1 is ______.

    <p>4.0 × 10^-8 mol L^-1 s^-1</p> Signup and view all the answers

    Study Notes

    Reaction Rate Units

    • The units for the rate of a reaction when the concentration is measured in mol L–1 and time in seconds are mol L–1 s–1.
    • The average rate of a reaction is the change in concentration of a reactant or product over a specific time interval.
    • The average rate of reaction can be calculated using the formula: average rate = (change in concentration) / (change in time).

    Rate Law and Order of Reaction

    • The rate law is an equation that describes the relationship between the rate of a reaction and the concentrations of the reactants.
    • The order of a reaction with respect to a reactant is the exponent of the reactant's concentration term in the rate law.
    • For a reaction with the rate law r = k [A]^(1/2) [B]^2, the overall order of the reaction is 2.5. This is calculated by adding the exponents of the reactant concentrations (1/2 + 2 = 2.5).

    Rate Determining Step

    • The rate determining step is the slowest step in a multi-step reaction and determines the overall rate of the reaction.
    • The molecularity of a reaction refers to the number of molecules that collide and react in the rate determining step.
    • The molecularity of a reaction can be determined from the rate law for an elementary step.

    Catalyst and Intermediates

    • A catalyst is a substance that increases the rate of a reaction without being consumed in the process.
    • An intermediate is a species that is formed and consumed during a reaction but does not appear in the overall balanced equation.
    • In the reaction involving IO-, the species IO- is known as an intermediate.

    Complex Reactions

    • Complex reactions involve multiple steps and can have different molecularities for each step.
    • The molecularity of a complex reaction can be determined by examining the individual steps in the reaction mechanism.

    Effect of Concentration on Reaction Rate

    • In a second order reaction, the rate of the reaction is proportional to the square of the concentration of the reactant. Therefore, tripling the concentration of a reactant will increase the rate of formation of the product by a factor of 9.
    • In the reaction 2NO(g) + O2(g) → 2NO2(g), doubling the concentration of NO will quadruple the rate of the reaction. This is because the rate of the reaction is second order with respect to NO.

    Half-Life of a Reaction

    • The half-life of a reaction is the time it takes for the concentration of a reactant to decrease to half its initial value.
    • The half-life for a first-order reaction is independent of the initial concentration and can be calculated using the formula: t1/2 = 0.693/k, where k is the rate constant.

    Collision Theory

    • Collision theory states that for a reaction to occur, reactant molecules must collide with sufficient energy and correct orientation.
    • The activation energy (Ea) is the minimum energy required for a reaction to occur.
    • The steric factor (P) in collision theory accounts for the orientation of molecules during a collision.
    • The equation k = P Z A e^(-E_a / RT) relates the rate constant (k) to the steric factor (P), the collision frequency (Z), the frequency factor (A), the activation energy (Ea), the gas constant (R), and the temperature (T).

    Zero and First Order Reactions

    • A zero-order reaction has a rate that is independent of the concentration of the reactants.
    • A first-order reaction has a rate that is directly proportional to the concentration of one reactant.
    • The equation for calculating the rate constant k in a first-order reaction is k = (ln [R]0 - ln [R]) / t, where [R]0 is the initial concentration, [R] is the concentration at time t, and t is the time.

    Activation Energy and Catalysis

    • Lowering the activation energy (Ea) increases the rate of a reaction, as it reduces the energy barrier that molecules must overcome to react.
    • Catalysts speed up reactions by providing an alternative reaction pathway with a lower activation energy.

    Summary of Key Concepts

    • The rate of a reaction is determined by the rate law, which expresses the relationship between the rate of a reaction and the concentrations of reactants.
    • The order of a reaction is determined by the exponents in the rate law and describes how the rate of a reaction changes with the concentrations of reactants.
    • The rate of a reaction can be affected by factors such as temperature, concentration, and the presence of a catalyst.
    • Collision theory explains the rate of a reaction in terms of collisions between reactant molecules.
    • The steric factor accounts for the orientation of molecules during collisions.
    • The activation energy is the minimum energy required for a reaction to occur.
    • Catalysts increase the rate of a reaction by providing an alternative reaction pathway with a lower activation energy.

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    Chemical Kinetics PDF

    Description

    This quiz covers the fundamental concepts of chemical kinetics, including reaction rates, molecularity, and order. Explore how factors like concentration, temperature, and catalysts impact reactions, and learn to derive integrated rate equations. Test your understanding of collision theory and the feasibility of reactions.

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