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Transcript of Collision Theory Reversible Chemical Reactions .Reversible Chemical Reactions BIOB111 ... creating

  • Collision Theory

    Reversible Chemical Reactions

    BIOB111

    CHEMISTRY & BIOCHEMISTRY

    Session 4

  • Key concepts: session 4From this session you are expected to develop an understanding of the following concepts:

    Concept 1: Processes that occur during a chemical reaction

    Concept 2: Collisions to begin chemical reactions

    Concept 3: Changing the rate of a chemical reaction

    Concept 4: Energy transfer in chemical reactions

    Concept 5: Activation energy

    Concept 6: Endothermic reactions

    Concept 7: Exothermic reactions

    Concept 8: Equilibrium reactions

    Concept 9: Stresses on equilibrium reactions

    These concepts are covered in the Conceptual multiple choice questions of tutorial 4

  • Session OverviewPart 1: Molecular collisions

    Chemical equations represent chemical reactions

    Collisions between molecules drive chemical reactions

    Part 2: Interpreting chemical reactions

    Chemical reaction rate

    Energy transfer in chemical reactions

    Exothermic vs endothermic reactions

    Part 3: Chemical equilibrium

    Chemical equilibrium

    Re-establishing chemical equilibrium

  • Part 1: Molecular collisions

    Chemical equations represent chemical reactions

    Collisions between molecules drive chemical reactions

  • Progression through a chemical reaction:

    Start- step 1: The chemical bonds holding the reactant molecules together are broken Chemical bond breakage requires an energy input

    Example below: Chemical bonds broken within methane and oxygen

    Middle- step 2: Once the chemical bonds have been broken, the atoms rearrange to adopt new positions

    Example below: Carbon, hydrogen and oxygen atoms rearrange

    End- step 3: After atom rearrangement, new chemical bonds form between the atoms creating the products Chemical bond formation releases energy

    Example below: New chemical bonds are formed to produce carbon dioxide and water

    Chemical equations represent chemical reactions

    Chemical reaction:

    Reactant 1 Reactant 2 Product 1Product 2

  • + +H

    H

    HH

    H H

    H H

    C C

    OO

    O OO O

    O

    O

    Reactant 1:Methane Reactant 2:

    Oxygen Product 1:Carbon dioxide

    Product 2: water

    Chemical equations represent chemical reactions

  • Start- step 1:

    Chemical bond breakage in reactants

    +H

    H

    HH C

    OO

    O O

    Reactant 1:Methane Reactant 2:

    Oxygen

    Covalent bond broken Bond

    breakage requires energy

    Chemical equations represent chemical reactions

  • Middle- step 2:

    Atom rearrangement

    +H

    H

    HH C

    OO

    O O

    Chemical equations represent chemical reactions

  • End- step 3:

    Chemical bond formation in products

    C

    O O

    H H

    O

    Product 1:Carbon dioxide

    Product 2: Water

    H

    O

    H

    Newly formed covalent bond Bond formation

    releases energy Product 2: Water

    Chemical equations represent chemical reactions

  • 1(CH4) 2(O2)+ 1(CO2) 2(H2O)+CH4 2O2+ 2H2OCO2 + Simplified representation

    Chemical equations represent chemical reactions

  • Collisions between molecules drive chemical reactions

    Collisions between different molecules drive chemical reactions Different reactant molecules must

    collide to form products

    http://phet.colorado.edu/en/simulation/legacy/reactions-and-rates

    Most collisions do not result in a

    chemical reaction, as the molecules just

    bounce off each other

    Only effective collisions allow the

    chemical reaction to begin

    http://phet.colorado.edu/en/simulation/legacy/reactions-and-rates

  • Only effective collisions result in a chemical reaction

    An effective collision requires:

    NO2 + CO NO + CO2

    Collisions between molecules drive chemical reactions

    1) Convenient orientation of molecules at the time of collision

    2) The energy of the Collision must meet the activation energy

    The collision between molecules must have sufficient energy to break specific chemical

    bonds within the reactants

    The energy of a collision depends on the speed of reactant molecules and on the angle of their

    approach

    Activation Energy: The minimum amount of energy from the collision between two

    reactant molecules that will allow the chemical reaction to begin

  • N

    O O C ON

    O OC O

    Effective collision

    High energy collision, which meets the activation energy Collision has a convenient orientation with the carbon

    (from CO) and the oxygen (from NO2) colliding

    NO2 + CO NO + CO2

    Collisions between molecules drive chemical reactions

  • NO

    O

    C ON

    O

    OC O

    NO2 + CO NO + CO2

    Unsuccessfulcollision

    Collision has an inconvenient orientation with the carbon (from CO) and the nitrogen (from NO2) colliding

    Collisions between molecules drive chemical reactions

  • N

    O O C ON

    O OC O

    Collision has a convenient orientation with thecarbon (from CO) and the oxygen (from NO2) colliding

    Low energy collision, which does not meet the activation energy

    NO2 + CO NO + CO2

    Unsuccessfulcollision

    Collisions between molecules drive chemical reactions

  • When reactant molecules (above) collide, what factors

    determine whether a chemical reaction will occur?

    G

    NO + O3 NO2 + O2

  • When reactant molecules (above) collide, what factorsdetermine whether a chemical reaction will occur? For the chemical reaction to take place, the energy of the

    collision (between the reactant molecules) must be equal to or greater than the activation energy Collision energy activation energy:

    Collision energy allows specific chemical bonds within the reactants to be broken

    Atoms rearranged

    Products formed (new chemical bonds formed)

    The angle that NO and O3 collide must be convenient Oxygen must collide with nitrogen, to allow an extra oxygen to bond to nitrogen (after detaching from O3)

    NO + O3 NO2 + O2

  • Attempt Socrative questions: 1 to 4

    Google Socrative and go to the student login

    Room name:

    City name followed by 1 or 2 (e.g. PERTH1)

    1 for 1st session of the week and 2 for 2nd session of the week

  • Part 1: Molecular collisions Chemical equations represent chemical reactions

    In a chemical reaction, the reactants on the left hand side are

    converted into the products on the right hand side of the equation,

    with the arrow representing the progression of the chemical reaction CH4 + 2O2 CO2 + 2H2O

    No atoms are created or destroyed in a chemical reaction, only rearranged to form new substances (products)

    Collisions between molecules drive chemical reactions Collisions between reactant molecules provide the energy required to

    begin the chemical reaction

    For a collision to allow a chemical reaction to begin, the collision must: Have a collision energy equal to or greater than the activation energy

    Required to break some of the chemical bonds that exist within the reactants

    Have a convenient orientation between the colliding reactants, which allows specific chemical bonds to be broken to start the chemical reaction

  • Part 2: Interpreting chemical reactions

    Chemical reaction rate

    Energy transfer in chemical reactions

    Exothermic vs endothermic reactions

  • Reaction Rate: The rate at which reactants are converted

    into products in a chemical reaction in a given time period

    Tracking how often the chemical reaction occurs

    NO2 + CO NO + CO2Reactants Products

    Chemical reaction rate

  • Chemical reaction rate

    How can the rate of a chemical reaction be determined?

    2 different ways:

    Determine how much product is being formed

    in a given period of time

    Determine how much reactant is being used up (consumed)

    in a given period of time

  • Chemical reaction rate

    Establishing the rate of a chemical reaction

    by tracking the amount of product being created

    2H2O2 2H2O + O2Hydrogen peroxide

    (liquid)Water(liquid)

    Oxygen(gas)

    Evidence that the chemical reaction has taken place is the creation of the

    oxygen gas (product)

    For example, if 600 mL of oxygen is produced in 7 minutes

    Reaction rate = 85.7 mL of oxygen produced per minute (or 1.43 mL per second)

    Chemical reaction rate =

    Change in concentration

    (amount) of product or reactant

    Time

  • Chemical reaction rate

    Establishing the rate of a chemical reaction

    by tracking the amount of reactant being used up

    2C2H5OH + 3O2 3H2O + CO2Ethanol(liquid)

    Water vapour

    (gas)

    Oxygen(gas)

    Evidence that the chemical reaction has taken place is the decrease in the

    amount of ethanol present (reactant)

    For example, if 200 mL of ethanol is used up (combusted/burnt) in 70 minutes

    Reaction rate = 2.9 mL of ethanol consumed per minute (or 0.05 mL per second)

    Chemical reaction rate =

    Change in concentration

    (amount) of product or reactant

    Time

    Carbon dioxide

    (gas)

  • Two main factors affect the rate of a chemical reaction:

    Chemical reaction rate

    N

    O O C ON

    O OC O

    Effective collision

    Collision which meets the activation energy Collision has a convenient orientation with the carbon

    (from CO) and the