Edexcel A Level Chemistry: 16: Kinetics II

How fast reactants are converted to products

Change in concentration of products/time

Gas volume
Loss of mass
Colour change
Change in pH
Titration
Electrical conductivity

It can be collected in a syringe and the amount recorded at set intervals, and the ideal gas equation used to work out moles and then molar ratio

If a gas is given off, the system will lose mass, measured at regular intervals with a balance

Can be tracked with a colorimeter and a calibration curve plotted

If a reaction produces or used up H+, pH can be measured to determine the change in H+ concentration

Small samples can be taken at regular intervals and titrated against a standard solution, change in concentration over time

If the number of ions changes, so will the conductivity

K

Temperature

How a reactant’s concentration affects the rate

From experimental data

The sum of all the orders of reaction of the reactants

Straight line, top to bottom of Y axis

Horizontal line

Curve, top to bottom

Directly proportional

Steep curve, top to bottom

Curve, bottom to top

The time taken for half the reactant to be used up

Using the initial rates method

A clock reaction

Carrying out separate experiments using different initial concentrations of one reactant, then seeing how the change in Italy concentrations affects the rate

You measure the time taken or a set amount of product to form and how it changes as the concentrations vary

The concentration of arch reactant doesn’t change significantly over th period of the reaction
The temperature stays constant
When the end point is seen, the reaction has not proceeded too far

There’s an easily observable end point as there is a sudden increase in the concentration of a product as the limiting reactant is used up

The iodine clock reaction

H2O2 + 2I- + 2H+ ——> 2H2O + I2

Starch

To react instantaneously with any iodine that forms

The iodine becomes obvious with the indicator as it is allowed to form ithout reacting with the thiosulfate

The iodide or hydrogen peroxide

Titrations the reaction between iodine and propanone

CH3COCH3 + I2 —H+—> CH3COCH2I + H+ + I-

To stop the reaction by neutralising the acid

Rate of reaction and reactant concentrations

Rate = k[A]^m [B]^n

…the faster the reaction

The orders and rate of reaction

Rate of reaction / concentrations and orders

The slowest step in a multi-step reaction

That it features in the rate determining step

Shows the number of molecules of that reactant that are involved in or before the rate determining step

Hydroxide ions

Nucleophillic substitution

SN2

SN1

A transition state

An intermediate carbocation

SN1 or SN2

k = Ae^(-Ea/RT)

As Ea gets bigger, k gets smaller

As temperature increases, so does k

-Ea/R

By multiplying the gradient by R

In the same state as the reactant

In a different physical state to the reactants

They provide a surface for the reaction to take place on, usually as a fine mesh or powder to increase surface area

They can be easily separated from the products and leftover reactants

When a substance clings t the surface more strongly than the reactant does, preventing a catalyst from getting involved in the reaction