Chemical Kinetics and Rate Laws
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Chemical Kinetics and Rate Laws

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Questions and Answers

What happens to the reaction rate if the specific rate constant (k) is large?

  • The reaction is slower.
  • The reaction remains the same speed.
  • The reaction does not occur.
  • The reaction is faster. (correct)

    • The exponents in the rate equation for a chemical reaction generally relate to the coefficients in the chemical equation.

    False

    What is the unit of the specific rate constant (k) for a second order reaction?

    L/mol.time

    For a first order reaction, the rate law is: Rate = k[X]____.

    <p>1</p> Signup and view all the answers

    Match the order of reaction with its corresponding unit of specific rate constant (k):

    <p>Zero order reaction = mol/L.time First order reaction = time‒1 Second order reaction = L/mol.time Third order reaction = L²/mol².time</p> Signup and view all the answers

    If the concentration of reactant X is halved in a first order reaction, what happens to the reaction rate?

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

    In a single-step reaction with a single activated complex, the exponents in the rate law are equal to the coefficients.

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

    What defines how the rate is affected by the concentration of a reactant in a reaction?

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

    What does the law of conservation of energy state?

    <p>Energy can be converted from one form to another but is neither created nor destroyed.</p> Signup and view all the answers

    Chemical potential energy is the energy stored in a substance due to its physical state.

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

    What happens to heat in an exothermic reaction?

    <p>Heat is released.</p> Signup and view all the answers

    Heat is energy that is flowing from a ______ object to a ______ object.

    <p>warmer, cooler</p> Signup and view all the answers

    Match the following units with their corresponding measurement:

    <p>Kelvin (K) = Temperature Joule (J) = Heat Celsius (℃) = Temperature Calorie (cal) = Heat</p> Signup and view all the answers

    What is the main purpose of calorimetry?

    <p>To measure heat flow in a system</p> Signup and view all the answers

    A coffee cup calorimeter can be used for high temperature reactions.

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

    What type of calorimeter is typically used to measure the caloric content of food?

    <p>Bomb calorimeter</p> Signup and view all the answers

    A calorimeter is an insulated device used for measuring the amount of heat absorbed or released during a __________.

    <p>chemical or physical process</p> Signup and view all the answers

    Match the calorimeter type with its description:

    <p>Coffee-cup calorimeter = Measures heat flow at constant pressure. Bomb calorimeter = Measures heat flow at constant volume. Constant-Pressure Calorimeter = Includes a stirrer to ensure uniform temperature. Constant-Volume Calorimeter = Used for combustion reactions in a high-pressure environment.</p> Signup and view all the answers

    What component is essential for the functioning of a bomb calorimeter during reaction initiation?

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

    Water absorbs heat in both types of calorimeters during a reaction.

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

    Why can't a coffee cup calorimeter be used for reactions that involve gases?

    <p>Gases would escape from the cup.</p> Signup and view all the answers

    Which of the following is a product in the given reaction mechanism?

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

    The intermediate in the first reaction mechanism is identified as WR.

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

    Identify the catalyst in the given reaction mechanism.

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

    The overall reaction can be summarized as ______ + W → S.

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

    Match the following terms with their corresponding definitions:

    <p>Reactant = A substance consumed in a reaction Product = A substance formed in a reaction Catalyst = A substance that increases reaction speed Intermediate = A substance produced in one step and consumed in another</p> Signup and view all the answers

    Which step is considered the rate-determining step in the first mechanism?

    <p>Step 1</p> Signup and view all the answers

    WR is an intermediate in the second reaction mechanism.

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

    List all the reactants in the first reaction mechanism.

    <p>X, W</p> Signup and view all the answers

    Which substance has a higher specific heat capacity when substance X's temperature changes twice as much as substance Y's?

    <p>Substance Y</p> Signup and view all the answers

    The formula for calculating heat absorbed is given by q = m × c × ∆T.

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

    What is the specific heat capacity (c) of water?

    <p>4.184 J/g.℃</p> Signup and view all the answers

    The change in temperature (∆T) is calculated by the formula ΔT = T ______ - T ______.

    <p>final; initial</p> Signup and view all the answers

    How much heat is absorbed by 34.0 g of water when heated from 30.0℃ to 60.0℃?

    <p>4.27 x 10^3 J</p> Signup and view all the answers

    A substance with a higher mass will always have a higher temperature change.

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

    If a 50.0 g sample of water is cooled from 74.0℃ to 40.0℃, how much heat is released?

    <p>7.11 x 10^3 J</p> Signup and view all the answers

    Match the following calculations with their correct outcomes:

    <p>Heat absorbed by 34.0 g of water from 30.0℃ to 60.0℃ = 4.27 x 10^3 J Heat released by 50.0 g of water from 74.0℃ to 40.0℃ = 7.11 x 10^3 J Specific heat capacity of a 1.55 g stainless steel sample = 0.511 J/g.℃ Specific heat capacity of a 3.4 g olive oil sample = 2.0 J/g.℃</p> Signup and view all the answers

    Study Notes

    Reaction Rate and Specific Rate Constant

    • Larger the value of the specific rate constant (k), the faster the reaction
    • The value of k is large if the products form quickly
    • The value of k is small if the products form slowly

    Rate Equation and Chemical Equation

    • In general, the exponents in the rate equation do not relate to the coefficients in the chemical equation
    • For single-step reactions with a single activated complex, the exponents are equal to the coefficients

    Units of the Rate Constant (k)

    • Zero order reaction: mol/L.time
    • First order reaction: time‒1
    • Second order reaction: M‒1.time‒1
    • Third order reaction: M‒2.time‒1

    First Order Reaction

    • Rate law of a first order reaction: Rate = k[X]
    • The rate changes in the same proportion as the concentration of the reactant ([X])
    • The rate constant (k) is equal to the slope of the line in a graph of concentration against time

    Law of Conservation of Energy

    • Energy can be converted from one form to another, but it is neither created nor destroyed

    Chemical Potential Energy

    • Energy stored in a substance due to its composition

    Exothermic and Endothermic Reactions

    • In exothermic reactions, chemical potential energy is converted to heat and released
    • In endothermic reactions, heat is absorbed and converted to chemical potential energy

    Temperature and Heat

    • Temperature: Average kinetic energy of particles in a sample of matter
    • Heat (q): Energy flowing from a warmer object to a cooler object

    Units of Temperature and Heat

    • Temperature: Kelvin (K) and Celsius (℃)
    • Heat: Joule (J), calorie (c), and Calorie (Cal)

    Specific Heat Capacity

    • The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius
    • The substance with a greater specific heat capacity undergoes a smaller temperature change

    Calculating Heat Absorbed or Released

    • Formula: q = m × c × ∆T
    • q = Heat absorbed or released (Joules)
    • m = Mass of the substance (grams)
    • c = Specific heat capacity of the substance (J/g.℃)
    • ∆T = Change in temperature (℃)

    Calorimetry

    • Measurement of heat flow into or out of a system during chemical and physical processes

    Calorimeter

    • Insulated device used to measure the amount of heat absorbed or released during a chemical or physical process

    Coffee-cup and Bomb Calorimeters

    • Coffee-cup calorimeter: Used to measure heat flow in chemical solutions.
      • Limitations: Cannot be used for reactions involving gases or high temperatures.
    • Bomb calorimeter: Used to measure heat flow for solids with low to high temperature reactions (like combustion reactions).
      • Used to determine caloric content of food.

    Reaction Mechanisms

    • Series of steps involved in a chemical reaction
    • Each step represents an elementary reaction
    • Slowest step is the rate-determining step

    Identifying Components of a Reaction Mechanism

    • Reactants: Species consumed in the overall reaction
    • Products: Species formed in the overall reaction
    • Catalyst: Substance that speeds up the reaction without being consumed
    • Intermediates: Species formed and then consumed in the reaction mechanism
    • Rate-determining step: The slowest step in the reaction mechanism

    Energy Diagram and Reaction Mechanism

    • Energy diagram: Illustrates the energy changes that occur during a reaction, showing the transition states and the activation energy of each step
    • Transition state: The highest energy point on the reaction pathway
    • Activation energy: The minimum energy required for reactants to reach the transition state and form products
    • Rate-determining step: The step with the highest activation energy
    • Products
    • Reactants and products can be identified by their energy levels
    • Intermediate: Species that are formed and then consumed in the reaction (valley on the energy diagram)
    • Activated complex: The unstable arrangement of atoms at the transition state (peak on the energy diagram)

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    Description

    Test your knowledge on chemical kinetics, including the specific rate constant and rate equations. Explore the significance of reaction order and the units of rate constants for various reactions. This quiz covers key concepts that are essential for understanding reaction rates and their implications in chemistry.

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