Chemistry - How fast? The rate of chemical change

Change in concentration of a particular reactant or product per unit time (moldm^-3s^-1

1. mass loss (gradient goes down)

2. gas production (gradient up)

3. colorimetry

1. collision frequency (number of collisions per unit time. changes with concentration, pressure, temperature, and surface area)

2. collision energy (not all collision are result in reaction, unsuccessful collisions occur when there is not enough energy to break the necessary bonds)

3. Activation energy (minimum amount of energy needed by colliding particles to react, can be changed by catalyst)

4. collision geometry (particles have to collide with the right orientation)

concentration, pressure, surface area, temperature, catalyst

higher concentration, greater number of particles colliding in given volume, higher collision frequency, higher frequency of successful collisions, increased rate of reaction

higher pressure, decreased space between particles, higher collision frequency, higher frequency of successful collisions, increased rate of reaction

increased temperature, particles moving faster, higher collision frequency, higher frequency of successful collisions, increased rate of reaction

and

increased proportion of particles have activation energy or more, increased proportion of collisions are successful

increase surface area, more particles on surface of reactants, more able collisions, higher frequency of successful collisions, increased rate of reaction

provides reactant with alternate reaction pathway which has a lower activation energy, so more successful collisions and increased rate of reaction

• reduces environmental impact

• reducing energy requirements

• reduces waste product

• increases selectivity of processes (promotes specific reactions, suppresses others)

homo: catalysts are in same phase as reactants (eg both liquids)

hetero: different phases

• shows distribution of energies at a certain temperature

• in a sample, some particles will have low, some high, and some in between energies.

• most probable energy is highest peak

• curve flattens and peak shifts to the right

• proportion of successful collisions increases

• higher proportion of particles with minimum activation energy

• peak o higher temperature is always lower and to the right

• curves only cross ones

• come from origin, never touch x axis

• tail of curve with higher temperature is higher

0 - concentration has no effect on rate of reaction

1 - concentration is directly proportional to rate of reaction

2- rate is directly proportional to square of concentration

overall order - sum of powers

• each step is called elementary step

• intermediates are products of elementary step

• rate determining step is the slowest step

• unimolecular: 1 reactant

• bimolecular: 2 reactants

• termolecular: 3 reactants

• shows relationship between rate constant and activation energy

• k = Ae^(-Ea/RT)

• k = rate constant

• A = arrhenius factor (takes into account frequency of collisions with correct orientation)

• R = gas constant

• T = temp in K

• EA = jmol^-1

• e = constant

• take natural log of both sides

• lnk = lnA - (Ea/RT)

• gradient. = Ea/R.

• Intercept = LnA

• y axis = lnK

• x axis = 1T

• A = e^yintercept