Chemical Equilibrium
-When a stress is applied to a system at equilibrium, the position of equilibrium will shift so as to minimise the stress.

Factors may affect the position of equilibrium, value of equlibrium constand and rate.

Factors

1. Concentration
When concentration of increases (by adding something), by Le Chatelier's Principle, the position equilibrium will shift to the right, to remove some added *something, thus producing more products until new equilibrium is attained. [equilibrium constant is not affected]

2. Pressure
When pressure increases (by decreasing volume / adding an unreactive gas), by Le Chatelier's Principle, it will favour the reaction that produces lesser amount of gas (forward/backward reaction), shifting towards that side (left/right). New equilibrium mixture will then contain more ________ and lesser __________. [equilibrium constant is not affected]

3. Temperature
When temperature increases, heat is added into the equilibrium mixture, by Le Chatelier's Principle, it will favour the endothermic reaction (backward/ forward reaction). Hence the position od equilibrium will shift left/right with an increase in concentration of __________. Equilibrium constant will decrease.

4. Catalyst
When added catalyst, it will increase the rate of forward and backward reaction.
No effect on position equilibrium (speeds up forward and backward reaction equally) and equilibrium constant.

Haber Process
450deg, 250atm, Finely divided iron catalyst with aluminium oxide as promoter

Temperature
With low temperature, by Le Chatelier's Principle, it will favour the exothermic reaction (forward reaction), hence the position of equilibrium will shift to the right with an increase in NH3. Thus increasing the amount of products. However rate of reaction is slow at low temperature, thus 450deg is the optimal temperature.

Pressure
With high pressure, by Le Chatelier's Principle, it will favour the foward reaction since total no of moles of products is less than reactions, thus shifting thr position of equilibrium to the right, having more NH3 and lesser N2 and H2. However too high a pressure is undesirable as stronger and more expensive pipes and vessels have to be used to withstand high pressure which increases cosr of production and maintainance

Catalyst
increase rate of reaction, equilibrium yield can be achieved in a shorter time.

Reaction kinetics

1.Concentration
When concentration increases, number of reacting paticles with energy greater than Ea increases, thus increase number of collision with correct geometry. Therefore rate of reaction increases. [gases aree measured by partial pressure]

2.Temperature
When temperature increases, the average kinetic energy of the reactant molecules increases, thus more molecules will possess energy more than Ea, which increases collisions with energy more than Ea and thus increase frequency of activated collisions.
[Boltzmann Distribution Diagram]

3. Catalyst
When there is presence of catalyst, the reaction will have a different mechanism i.e one with a lower activated energy, thus more molecules will possess energy greater than / equal to the lowered Ea, which increases frequency of activated collisions.
[Boltzmann Distribution Diagram]

Rate of reaction is defined as the change in concentration of products / reactions with time.

For Elementary reaction: mA +nB --->pC
rate equation : k[A]^m[B]^n
k: rate constant, proportionality constant
m: order of reaction wrt A
n: order of reaction wrt B
m+n: overall order of reaction.

Zero Order: independent of concentration of A / Pseudo First Order Reaction...
First Order: constant half-life....
2nd Order:....

temperature increase, Ea decrease, lead to e^(Ea/RT) decreases, hence k increases.

Catalysis
A catalyst is a substance that increase the rate of reaction and remain chemically unchanged after the end of reaction.

-heterogenous catalysis
it is one that exists in a different phase from the reactants

Adsorption Theory:
-Molecules will diffuse towards the catalyst surface, thus being adsorbed on the neighbouring active sites on catalyst surfaces. The molecules are now closer to each other and hence have a higher collision frequency. The positions of the molecules allow them to have the correct collision geometry.
-Chemisorption of molecules occurs on the catalyst surface which weakens the bonds in adsorbed molecules, this Ea is lowered.
-The adsorbed H atoms are relatively free to move over the catalyst surface and when it meet an N atom, it will form NH3.
-Once NH3 is formed, it will desorb from catalysg surface to ensure active sites are availablr for further catalytic reation.

Homogenous Catalysis
it is one that exists in the same phase as the reactants

Biological Catalysts
|