Chemical kinetics

• Chemical kinetics definition

Chemical kinetics is a branch of chemistry which deals with the rate of chemical reaction and factor those affect them

• Definition of rate of reaction

The rate of reaction describe how rapidly the reactants are consumed or the products are formed.

• Average rate of reaction

1. Average rate of reaction= change in concentration of speci/change in time = ∆c/∆t

2. For rate of consumption it is minus sign

3. For rate off formation it is Plus sign

4. Average rate of reaction is equal to rate of formation is equal to rate of consumption.

5. Dimension is mol dm⁻³ sec⁻¹.

• Instaneous rate of reaction

1. It is used to do determine the rate of reaction for specific time interval

2. Rate consumption at any time =.-d[A]/dt.

3. With coefficients the rate of reaction is aA+bB→cC+dD

4. -1/a d[A]/dt = -1/b d[B] / dt =1/c d[C]/dt = 1/d [D].

• Definition of rate law

Rate of reaction at given temperature for a given time instant depend on concentration of reactant . Such rate concentration relation is rate law

• Rate law

1. Rate=K[A]^x[B]^y. Differential rate law

2. X and y maybe simple whole number zero OR fraction they are experimentally determined

3. For X and y = 1 , rate = k(A)(B). If concentration of x or y is double rate will be doubled

4. For x=2 &y=1 , rate =k(A)²(B). If concentration of a is doubled keeping that of B constant the rate will be increased by factor of 4.

5. X<0 the rate decrease as [A] increse

6. x=0 rate is independent of concentration of A

• Writing rate of law

2H2O2—— 2h20 + 02

If rate of reac is proportional to concentration of h2o2 rate law is

Rate =K[h2o2].

• Order of reaction

1. Addition of X and y powers.

2. Rate =K[A]^x[B]^y. , x+y.

3. K(h2)(i2) , x+y = 1+1 = 2 order of rec

4. Order of reaction is experimentally determine d

5. It can be integer or fractional.

6. If order of reaction is zero, means the rate of reaction is independent from concentration of reactant.

7. Only few reaction of third order has been found.

• Complex reaction

Complex reaction are those which constitute a series of elementary chemical reactions

• Elementary reaction

Reaction occurs in single step and cannot be broken down further into simple reactions .

• Molecularity of reaction

1. The number of molecules involves in reaction is the number of molecularity of the reaction

2. 02— O+, 1 molecurity , NO2 — two

• Order and molecularity of elementary reaction

For elementary reaction in 2N0—-2NO+O2

K[NO]². It is BIOMOLECULAR AND SECOND ORDER.

• Rate determination step

1. Some reactions are multi step reactions

2. Hence the slowest step is taken as the rate determining step .

• Reaction intermediate

1. Any compound which is formed in first step and then consumed in any step, if it is not present in overall course of reaction it is called reaction intermediate

2. It is not present in rate law

• Distinction between order and molecularity

Order

1. It is experimentally determined

2. It is sum of power of concentration of terms of reactant those appear in equation

3. Maybe an integer fraction or zero

Molecularity

1. It is theoretically identity

2. It is number of molecules or moles taking part in elementary reaction

3. It is integer.

• Definition of integrated rate law

These tells us the concentration of reactant for different time

• Integrated rate law for first order reaction in solution

1. Refer page for derivation and laws

• Units of rate constant for first order reaction

Unit of K will be s^-1, min^-1, hr^-1.

• Half life of first order reaction

Half life of a reaction is time required for the reactant concentration to fall to half of its initial value

• Half life and rate constant for first order reaction

1. Half life of first order reaction is independent of initial reactant concentration

2. Formula K=0.693/t₁/₂ , t₁/₂= 0.693/K.

3. Derivation refer page

• Integrated rate law for gas phase f reaction formula

1. Formula refer page

2. Where initial pressure of a is Pi , P is total pressure of reaction mixture at time T.

• Integrated rate law for gas phase reaction derivation

Refer page for derivation

• Zero order reaction

1. The rate of zero order reaction is independent of reactant concentration.

2. Formula - kt = (A)0-(A)t

3. Concentration of A = (A)0 at t=0 , concentration of A=(A)t at t=t

4. Unit of rate constant for zero order reaction is mol dm⁻³ t⁻¹.

5. For derivation refer page

• Half life of zero order reaction

1. The half life of zero order reaction is proportional to the initial concentration of reactant.

2. Formula t₁/₂ = [A]₀/2k. [A]₀ is initial concentration of reactant.

3. For derivation refer page

• Pseudo first order reaction

1. The reactions which are higher than first order reaction but follows the rules of first order reaction are called pseudo first order reactions.

2. It happens because one compound is present in very high concentration and amount than other so the change in concentration when added another compound is negligible.

3. For rate law refer photo

• Collision between reactant and molecules

1. Chemical reaction occur as a result of collision between reactants speci

2. Hence rate of reaction is expected to be equal to rate of collision.

3. For gas phase number of collision is far more and typically many powers of 10 compared to the observed rate.

• Activation energy

1. For reaction to occur colliding reactant must poses minimum of kinetic energy [KE] this energy is called as activation energy

2. When reactant molecules KE gets equal or greater than activation energy the reaction occurs.

• Orientation of react and molecule

1. Beside collision they should also have proper orientation to form reaction

2. Refer page for orientation.

• Activated complex

A configuration in which all three atoms are weakly connected together is called activated complex.

• Arrhenius equation

1. Arrhenius equation suggest that rate of reaction varies with temperature

2. For formula refer page

• Determination of activation energy

Refer page for formula and derivation

Abababa

Rate of reaction increases with temperature.

• Effect of catalyst on rate of reaction

1. A Catalyst is a substance added to reactant that increases rate of reaction without itself being consumed in reaction.

2. It provides alternate pathway with lower activation energy.

3. A catalyst lowers the threshold energy consequently more molecules acquire the minimum amount of energy and tend to cross the energy barriers

4. A fraction of activated molecules is greater in the catalyzed reaction .

5. Rate of reaction is larger of catalyzed reaction compared to uncatalyst reaction

**graphs.

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• Graph of Instantaneous rate

1. The tangent drawn to the curve at time t gives the rate of reaction

2. The slope gives the instantaneous rate of reaction

• Graph of half life period of first order reaction

• It shows that half life of first order reaction is independent of initial reactant concentration .

• Graphical representation of first order reaction.

• Graphical representation of first order reaction

• Graphical representation of zero order reaction

• Graphical representation of potential energy barrier

• Graphical determination of activation energy

• Graphical description of effect of temperature

• Graphical representation of potential energy barriers for catalyzed and uncatelised reaction

• Comparison of fraction of molecules for catalyzed and and catalyzed reactions