Kinetics - 6, 16

Collision Theory

Collision Theory

1. reactant particles must collide with the correct orientation

2. reactant particles must collide with sufficient E(a)

Activation Energy

Minimum amount of energy that colliding particles must require for a reaction to occur.

E(a)

energy between reactants - energy in transition state

Transition state

highest energy state on a reaction coordinate, point at which new bonds are being formed and old bonds are being broken

Maxwell-Boltzmann Distribution

In an ideal gas, the kinetic energy of the molecules is spread over a range of values

Total area under the Maxwell-Boltzmann Distribution =

Total number of particles in the sample

MBDC - When temperature increases

Curve flattens out

MBDC - When temperature decreases

curve is taller and leaner

MBDC - When lower molar mass

Higher speed, curve flattens

MBDC - When heavier molar mass

slower, taller & leaner

MBDC - Activation Energy

The lower the activation energy the more particles are eligible to take part in the reaction, shaded region larger

Find Activation Energy: Formula

lnK = (-E(a)/R) x (1/t) x lnA *divide by 1000 as R is in J

Comparing 2 conditions

ln(k1/k2) = -Ea/R (1/T2 - 1/T1)

ROR

Change in concentration or pressure of a reactant or products per unit of time.

Calculate average rate of reaction for a gaseous rxn carried out in a 2.5 dm^3 vessel if 0.04 mol of product was produced in 20 seconds.

1. c = n/v = 0.04/2.5 = 0.016

2. ROR = Δc/Δt = 0.016/20 seconds

3. average ROR = 8 x 10^-4 mol/dm^3/s

ROR =

Δc/Δt

How to calculate Instantaneous rate

1. Draw a tangent to the curve at a particular time

2. divide Δy/Δx to find gradient

Metal + Acid

Salt + H2

Metal Hydroxide + acid

Salt + water

Metal carbonate + acid

salt + CO2 + H2O

Metal Oxide + acid

Salt + water

FAROR: Concentration

1. as concentration increases

2. number of collisions increase

3. between reactant particles

4. leading to greater successful collisions

FAROR: Temperature

1. as temperature increases

2. particles gain kinetic energy

3. leading to frequent collisions

4. leading to greater successful collisions

FAROR: Surface Area

1. as surface area increases

2. more reactant particles are exposed to other reactant particles

3. leading to greater successful collisions

FAROR: Pressure

1. As pressure in a system increases

2. distance between reactant particles decreases

3. leading to more frequent collisions

4. leading to greater successful collisions

FAROR: Catalyst

1. substance that alters ROR

2. by lowering its activation energy

3. through an alternate path

4. without getting used up during the reaction

Transition Metals as catalysts

1. surface of transition metals are slightly positive due to transition metals

2. lone pairs in reactant particles are attracted to slightly positive charge.

3. temporary polar bonds formed till other reactant particles collide with it.

4. lowering activation energy

First Order Reaction, units

s^-1

Second order Reaction units

mol^-1dm^3s^-1

Third order Reaction units

mol^-2dm^6s^-1

Arhennius Factor ‘A’ =

frequency of collisions & probability that collisions are in the correct orientation.

Find Ea graphically

Graph of lnK vs 1/T where m = -Ea/R

Plausible Reaction mechanisms

1. Elementary steps must add up to give the overall balanced equation

2. Reaction mechanisms must be consistent with experimental data

Reactants - concentration/pressure vs time

Products - concentration/pressure vs time

Surface area = powder vs granules on product conc.