Chemical Kinetics Introduction
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Questions and Answers

What is the area of chemistry concerned with reaction rates called?

  • Thermodynamics
  • Physical chemistry
  • Chemical kinetics (correct)
  • Analytical chemistry

    • The rate of a chemical reaction is determined solely by the increase in concentration of the products.

    False

    What formula expresses the rate of a chemical reaction?

    Rate = ∆c/∆t

    In the reaction A → B, the concentration of A decreases during the time interval, therefore ∆[A] is a ______ quantity.

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

    Match the following examples with their respective rates of reaction:

    <p>Rusting of iron = Slow Combustion of gasoline = Fast Ripening of fruits = Moderate Weathering of stone = Very slow</p> Signup and view all the answers

    Which reaction would likely have the fastest rate?

    <p>Combustion of gasoline</p> Signup and view all the answers

    Chemical kinetics only studies reactions that occur within a few seconds.

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

    What does ∆c represent in the rate of reaction formula?

    <p>Change in concentration of a substance</p> Signup and view all the answers

    What is the average rate of formation of NO2 during the time period 300 – 400 s?

    <p>3.7 × 10-5 mol L−1 s−1</p> Signup and view all the answers

    The concentration of NO2 increases with time as the reaction proceeds.

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

    What is the molarity of O2 produced when [N2O5] = 1.20 × 10–2 mol L−1 at 300 s?

    <p>0.4 × 10–2 mol L−1</p> Signup and view all the answers

    The molarity of NO2 produced per liter is calculated using the factor of _______ moles of NO2 per mole of N2O5.

    <p>2</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Molarity = Concentration of a solute per liter of solution Stoichiometry = Relationship between reactants and products in a chemical reaction Reaction rate = Change in concentration of a reactant or product over time Chemical equation = Represents the substances involved in a reaction</p> Signup and view all the answers

    Which statement best explains why the rate of reaction decreases over time?

    <p>The concentration of reactants decreases.</p> Signup and view all the answers

    How is the average rate of O2 formation determined during a specific time period?

    <p>By calculating the slope of the hypotenuse of the triangle using ∆[O2] and ∆t.</p> Signup and view all the answers

    At time t = 350 s, the rate of formation of NO2 can be calculated using the initial concentration of N2O5.

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

    What is the rate expression for the reaction 3O2(g) → 2O3(g)?

    <p>Rate = −1/3 ∆ [O2]/ ∆ t</p> Signup and view all the answers

    The rate of a reaction is always expressed as a positive quantity without needing adjustments for reactant disappearance.

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

    If the rate of disappearance of I− is 2.0 × 10–5 mol L–1 s–1, what would be the rate of appearance of OI− in the reaction I−(aq) + OCl−(aq) → Cl−(aq) + OI−(aq)?

    <p>2.0 × 10–5 mol L–1 s–1</p> Signup and view all the answers

    The rate of formation of N2 from the reaction 2NO(g) + 2H2(g) → N2(g) + 2H2O(g) can be expressed as ___.

    <p>2.5 × 10–5 mol L–1 s–1</p> Signup and view all the answers

    Match the following reactions with their correct rate expressions:

    <p>I−(aq) + OCl−(aq) → Cl−(aq) + OI−(aq) = Rate = −∆[I−]/∆t 3O2(g) → 2O3(g) = Rate = −1/3 ∆[O2]/∆t 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) = Rate = −1/4 ∆[NH3]/∆t 2NO(g) + 2H2(g) → N2(g) + 2H2O(g) = Rate = −1/2 ∆[NO]/∆t</p> Signup and view all the answers

    For the reaction aA + bB → cC + dD, which expression correctly represents the rate?

    <p>All of the above</p> Signup and view all the answers

    An observable property that can indicate the rate of reaction must be something that can be directly calculated as a concentration.

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

    What common observable properties can be used to determine the change in concentration over time?

    <p>Color change, temperature change, pressure change, mass change, appearance of a new substance.</p> Signup and view all the answers

    What is the term for the minimum amount of energy needed for a reaction to occur?

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

    Ineffective collisions can result in the formation of desired products.

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

    What factor increases the reaction rate by causing particles to collide more frequently?

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

    The reaction between an acid and a base, such as HCl and NaOH, occurs rapidly compared to the decomposition of ________.

    <p>hydrogen peroxide</p> Signup and view all the answers

    Match the following reactions with their characteristics:

    <p>HCl + NaOH = Rapid acid-base reaction H2O2 = Slow decomposition reaction Sodium with water = Explosive reaction Calcium with water = Moderate reaction rate</p> Signup and view all the answers

    Which factor does NOT affect the rate of a chemical reaction?

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

    Homogeneous reactions occur in different phases.

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

    What type of collisions lead to reactions forming new products?

    <p>Effective collisions</p> Signup and view all the answers

    What type of reaction occurs only at the interface between two phases?

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

    An increase in concentration of reactants generally decreases the rate of reaction.

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

    What is the effect of temperature on the rate of reaction?

    <p>Increasing the temperature generally increases the rate of reaction.</p> Signup and view all the answers

    A __________ is a substance that increases the rate of a reaction by providing a different reaction mechanism with lower activation energy.

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

    Match the following factors with their effects on reaction rates:

    <p>Concentration = Increases contacts between reacting particles Temperature = Increases kinetic energy of molecules Surface area = Increases the rate of solid reactions Catalyst = Lowers activation energy</p> Signup and view all the answers

    Which of the following statements is true regarding the effect of pressure on reaction rate?

    <p>Pressure only affects gaseous reactants</p> Signup and view all the answers

    Finely divided solids react more slowly than larger bodies of the same substance.

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

    What is activation energy in the context of chemical reactions?

    <p>The minimum energy required to start a chemical reaction.</p> Signup and view all the answers

    What is the initial rate of reaction calculated from?

    <p>The slope of a tangent at the initial point</p> Signup and view all the answers

    According to collision theory, all collisions between molecules result in a reaction.

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

    What must happen for a chemical reaction to take place according to collision theory?

    <p>Molecules must collide with proper orientation and sufficient energy.</p> Signup and view all the answers

    The rate of reaction is directly proportional to the number of ______ per second.

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

    At what time is the instantaneous rate of reaction calculated in the given example?

    <p>2 seconds</p> Signup and view all the answers

    The slope of the tangent drawn to the curve represents the instantaneous rate of reaction.

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

    In the provided gas-phase reaction, what compounds are being produced?

    <p>I2 and HCl.</p> Signup and view all the answers

    Study Notes

    Chemical Kinetics Introduction

    • Chemical reactions occur at varying speeds
    • Some reactions take days, others seconds
    • Chemical kinetics studies reaction rates
    • "Kinetic" implies movement or change
    • Chemical kinetics measures how fast reactant/product concentrations change

    Reaction Rate

    • Measures the change in reactant or product concentration per unit time
    • Determined by monitoring reactant decrease or product increase
    • Expressed as ∆c/∆t
    • ∆c = Change in concentration, ∆t = Change in time
    • Rate is positive, ∆[A]/∆t or -∆ [A]/∆t

    Rate Expressions for Complex Reactions

    • For more complex reactions, rate expressions consider stoichiometric coefficients
    • Rate = -1/a∆[A]/∆t = 1/b ∆[B]/∆t = 1/c ∆[C]/∆t= 1/d ∆[D]/∆t

    Determining Reaction Rate

    • Observable property changes over time (e.g., color, pressure, mass)
    • Measurements track concentration changes over time
    • Example: Thermal decomposition of N₂O₅ to NO₂ + O₂
    • Concentration changes can be monitored using pressure, color, or other measurable properties
    • Rate is calculated using concentration data, and time
    • Average rate is calculated using two concentration values in time interval ∆t

    Instantaneous Rate of Reaction

    • Rate at a specific time, t
    • Calculated from the slope of a tangent line to a concentration vs. time graph at point t.
    • Initial rate is the slope of a tangent at t = 0

    Factors Affecting Reaction Rates

    • Nature of Reactants: Some reactions are faster than others due to chemical nature
    • Surface Area: Larger surface area increases reaction rate for heterogeneous reactions
    • Concentration: Higher concentration of reactants leads to more frequent collisions, hence faster reaction
    • Temperature: Higher temperatures increase kinetic energy, leading to more frequent and energetic collisions, and thus a faster reaction
    • Presence of a Catalyst: Catalysts reduce activation energy; speeding up the reaction but are not consumed in the process.

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    UNIT 4 CHEMICAL KINETICS PDF

    Description

    Explore the fundamentals of chemical kinetics, where we study the rates at which chemical reactions occur. Learn how to measure reaction rates and understand complex rate expressions. This quiz covers key concepts such as concentration changes and the implications of reaction speeds.

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