Factors Affecting the Rate of a Reaction

Question 1

Factors which affect the rate of a chemical reaction
During a reaction, the reactants are

Answer 1

used up and changed into the products

Question 2

The rate of a chemical reaction can be calculated using the following equation

Answer 2

change in amount of reactants and products(mol dm-3)
/
time (s)

Question 3

As a reaction proceeds, the concentration of the reactants is ………………….and the concentration of the products is…………

Answer 3

decreasing

increasing

Question 4

As a reaction proceeds, the concentration of the reactants is decreasing and the concentration of the products is increasing

Because of this, the rate of the reaction is not the same throughout the reaction but

Answer 4

changes

Question 5

A tangent will have to be drawn at a certain point on the graph, to calculate the rate at that specific time

The following graph is an example of cyclopropane being converted to propene

The concentration of cyclopropene, the reactant, is decreasing over time as the reaction progresses

Question 6

The Disappearing Cross Experiment
A simple experiment which can be done to determine how rate of reaction is affected by concentration is the disappearing cross experiment
It is set up as follows:

This experiment can be done for a number of different reactions, but taking the following reaction as an example

Answer 6

Na2S2O3 (aq) + 2HCl (aq) → 2NaCl (aq) + H2O (l) + SO2 (g) + S (s)

Question 7

In this reaction, sodium thiosulphate reacts with hydrochloric acid
The key product which allows this experiment to work, is the sulfur which is a solid, and causes the

Answer 7

solution to become opaque

Question 8

There are actually two factors which can be investigated using the disappearing cross reaction:

Answer 8

Changing the temperature
Changing the concentration of the HCl

Question 9

You can plot graphs of concentration against time if the concentration of HCl was changed, or plot 1/t against temperature if the temperature was changed

You plot 1/t because the rate is proportional to 1/time and the graph you want is rate versus temperature

Question 10

Exam Tip
The disappearing cross experiment can be used for any reaction where a solid is produced as one of the products, as this will cause the solution to become cloudy.

It does not have to be done in a conical flask, it could be done in a test tube with the cross placed underneath the test tube rack.

Watch out: this is a very simple experiment, but exam questions could try and make this seem more complicated than it is!