Scribs Rateof Reaction

7/31/2019 Scribs Rateof Reaction

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Rate of reaction is referred to as the change of the concentration of reactant or product withtime. Consider the reaction;

A B

The equation tells us that during the process of reaction, reactant molecules (A) are consumed

while roduct (B) are formed. As a result, concentration of the reactant decreases while

concentration of the product increases


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Reaction rate and stoichiometry

For stoichiometrically simple reaction such as,

A B

Rate = =

The minus sign indicates concentration of A decreases.

Unit: mol L-1 s-1


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In general, for the reaction

Rate =

The rate law takes the form;

Rate = k [A]x [B]y

Where: [A] = concentration of A in molar[B] = concentration of B in molark = rate constantx = order with respect to Ay = order with respect to B

x + y = reaction order

The rate law is an expression relating the rate of reaction to the rateconstant and the concentration of the reactant


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The collision theory :

Collision Theory is the theory to explain the rate of chemical reactions. It isbased on;

Rate

1- molecules must collide to react

2- molecules must possess a certain minimum kinetic energy (activationenergy) to initiate the chemical reaction.

3- molecule must collide in the right orientation in order for the

reaction to occur.


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Only effective collisions cause formation of product; collisions of

molecules with Ea and at correct orientation.

The activation energy (Ea) is the minimum energy that must be

supplied or required by collisions for a reaction to occur.


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Chemical reaction occur as a result of collision between the

reacting molecule

The number of collisions that take place per second per unitvolume of the reaction mixture is called collision frequency.

The rate of a reaction is directly proportional to the number ofcollision per second

Rate


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Molecule must collide in the correct orientation in order that the collisionwill result in a reaction


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DETERMINATION

OF REACTION

ORDER


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ReactionOrder

Zero

Order

FirstOrder

SecondOrder


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Zero Order of Reaction:


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Substituting t = 0, [A] = [A]O-[A]O = k(0) + c

C = - [A]o

[A]O [A] = kt

Unit of k for zero order reaction is M s-1


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First Oder of Reaction:


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Question: For the first order decomposition of H2O2 (aq) given

the k = 3.66 x 10^3 s-1 and [H2O2]o = 0.882 M,determine;

a) The time at which [H2O2] = 0.600 M

b) The [H2O2] after 225s.


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Second Order of Reaction


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Question:Iodine atoms combine to form molecular iodine in thegas phase

I (g) + I (g) I2 (g)

This reaction follows second order and has high rateconstant 7.0 x 10^9 M-1 s-1.

If the initial concentration of iodine was 0.086M,calculate the concentration after 2 min.


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Graphs of Order

of

Reactions


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