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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