chapter 8 reaction kinetics

8/12/2019 Chapter 8 Reaction Kinetics

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explain and use the terms: rate of reaction, activation energy, catalysis.

explain qualitatively, in terms of collisions, the effect of

concentration changes on the rate of a reaction

show understanding, including reference to the Boltzmann

distribution, of what is meant by the term activation energy

explain qualitatively, in terms both of the Boltzmann distribution

and of collision frequency, the effect of temperature change on the

rate of a reaction

(i) explain that, in the presence of a catalyst, a reaction has a

different mechanism, i.e. one of lower activation energy

(ii) interpret this catalytic effect in terms of the Boltzmann

distribution

describe enzymes as biological catalysts (proteins) which may have

specific activity


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Chemical kinetics is the study of the rates

of chemical reactions.

Rate of reaction is the change in

concentration of reactants or products per

unit time.


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Collision theory

a set of three statements that give the

conditions necessary for a chemical reaction to

occur.

a) Molecular collisions reactants particles

(molecules, ions or atoms) must interact(collide) with one another before any reaction

can occur


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b) The activation energy

Is the minimum energy needed for a reaction to

take place upon proper collision of reactants.


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c) A chemical reaction occurs when

Collisions between molecules have sufficient

energy to break the bonds in the reactants.

Molecules collide with the proper orientation.

Bonds between atoms of the reactants (N2and

O2) are broken, and new bonds (NO) form.


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More energy stored in product molecule bonds than in

reactant molecule bonds.


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Chemical reaction rate

The rate at which reactants are consumed or

products produced in a given time period.

Affected by these factors:

i) physical nature of the reactants

ii) reactant concentration

iii) reaction temperatureiv) presence of catalyst


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Physical nature of the reactants

Breaking a solid into smaller pieces increases the surface area

exposed to reacting chemicals in a gas or in solution.


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As the temperature of a system increases

Average kinetic energy of the reacting

molecules increases and more collisions takeplace in a given time.

Larger fraction of collision result in reaction.

Every 10o

C increase, rate of chemicalreaction doubles.


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A catalyst

Speeds up the rate of a reaction.

Is not used up during the reaction.


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The area under the curve gives the total number of molecules.

This area does not change as the temperature rises.

The peak height falls as the temperature rises and the curve spreads tothe right


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At 310 K, more molecules have enough energy to react

when they collide with other molecules.

Thus, the reaction goes faster.


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A catalyst often changes the mechanism of a reaction and makes a

reaction more productive by increasing the yield of the desired

product.

The proportion of molecules able to react increases when a catalystprovides a pathway with lower activation energy.


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Enzymesare proteins that

Catalyze nearly all the chemical reactions taking place in the cells ofthe body.

Increase the rate of reaction by providing alternative pathway withlow energy of activation.


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The function of enzymes as catalysts in biological

systems are based on the concepts of enzyme

active site and enzyme-substrate complex

formation.

The active site

Is a region within an enzyme that fits the shape of the

reacting molecule called a substrate.

Contains amino acid R groups that bind the substrate. Releases products when the reaction is complete.


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In an enzyme-catalysed

reaction

A substrate attaches to

the active site.

An enzyme-substrate

(ES) complex forms.

Reaction occurs and

products are released.

An enzyme is used over

and over.

E+ S ES E+ P


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In the lock-and-key model of enzyme action,

The active site has a rigid shape.

An enzyme only binds substrates that exactly fit the active site.

Only substrates with the matching shape can fit.

The substrate is the key that fits that lock.


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Enzymes

Are most active at an

optimum temperature

(usually 37C inhumans).

Show little activity at

low temperatures.

Lose activity at high

temperatures as

denaturation occurs.


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Enzymes

Are most active atoptimum pH.

Lose activity in lowor high pH as tertiarystructure is disruptedand denaturation

occurs.

chapter 8 reaction kinetics

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