Ch16 2/22 Halpin Lecture

Chemical Kinetics

The study of the rates of reactions and the factors that affect them.

Reaction Rate

The change of the concentrations of a reactant or product with time.

Rate of Reaction

A change in amount (of concentration of a compound/element) over an interval of time.

Rate Expression

Rate= -Delta\[A\]/Delta T

Reaction rate depends on

The concentrations of the reactants.

Initial rate

The instantaneous rate at the moment the reactants are mixed, that is, at t=0

Initial reaction rates depend only upon

Reactant concentrations and temperature

Rate Law

An equation that expresses the rate of a reaction as a function of reactant (and product) concentrations and temperature. Rate=k\[A\]^x\[B\]^y

Rate orders

The exponent of a reactant concentration in a rate law that shows how the rate is affected by changes in that concentration. (Adding the exponents give you the rate order overall)

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A rate law can only be determined from

Experimental Data

Rate constant

The proportionality constant that relates reaction rate to reactant (and product) concentrations.=K

The rate law allows us to

Predict the rate if we know the reactant concentrations.

Integrated Rate Law

A mathematical expression for reactant concentration as a function of time.

Half-life

In chemical processes, the time required for the reactant concentration to reach half of its initial value. In nuclear processes, the time required for half the initial number of nuclei in a sample to decay.

Second order kinetics depend on

Concentration

First order kinetics are

Independent of concentration

Natural logs cant have or be

Units and be a negative number

Larger the concentration

Shorter time the reaction will take

Smaller concentration

Longer time the reaction will take

Rate depends on

Concentration

First order if

When equation is linearized ln\[A\]=-kt+ln\[A\]0 and it is a straight line. If its. A curve, it could be any order…

Second order if

1/ln\[A\] is a straight line, if not then its neither first or second order

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Collision theory

Particles that are constantly moving and sometimes collide and react.

Increasing the concentration of a reactant

Increases the number of particles which increases opportunity for collision

Reaction rates will

Increase with temperature

Temperature is a measure of

The average kinetic energy of the particles that compose of a substance

Kinetic energy equation

K=1/2mu2

Faster speed doesn’t mean

More collisions and faster reaction rate (kinetic energy isn’t important ON EXAM)

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Not every collision

Leads to a reaction. They usually just bounce off each other and don’t react.

High Kinetic energy is needed to

Break bonds through collision/ through close intermolecular forces and the cause of repulsion

Activation energy (Ea)

The minimum amount of energy that the reactants must have (prior to collision) in order for reaction to take place when they collide. Energy price tag for a successful reaction.

Translational Kinetic energy

The form that the energy needs to be before kinetic energy→ Converted into potential energy