Chemistry Form 5: Chapter 1 - Effect of Concentration on Rate of Reaction

Chemistry Form 5: Chapter 1 - Effect of Concentration on Rate of ReactionExperiment to show the effect of concentration on reaction rate

Sodium thiosulphate solution react with dilute sulphuric acid to form a yellow precipitate of sulphur. In this experiment, the time taken for the formation of sulphur to cover the mark 'X' until it disappears from sight can be used to measure rate of reaction.

As the concentration of sulphuric acid is increased, the rate of reaction between sulphuric acid and sodium thiosulphate increases.

http://www.youtube.com/watch?v=Bm6-RgmGGoY

Explanation using collision theory

·      When the concentration of the solution of a reactant increases, the number of particles per unit volume of the solution also increases.

·      With more particles per unit volume of the solution of the reactant, the frequency of collision increases.

·      This causes the frequency of effective collision to increase. Hence, the rate of reaction increases.

Chemistry Form 5: Chapter 1 - Catalyst Affects the Rate of Reaction

Chemistry Form 5: Chapter 1 - Catalyst Affects the Rate of ReactionCatalyst is a chemical substance that change the rate of chemical reaction.

Characteristics of catalyst:

Catalyst remains chemically unchanged during reaction. Its chemical composition still the same before and after reaction.

Catalyst only change the rate of reaction. Catalyst does not change the quantity of the product formed. Catalyst is specific in its action. Only a small amount of catalyst is needed to achieve a big increase in rate of reaction.

 How catalyst increase the rate of reaction:

When a positive catalyst is used in a chemical reaction, it enables the reaction to occur through an alternative path which requires lower activation energy.

As a result, more colliding particles are able to overcome the lower activation energy. This causes the frequency of effective collision to increase. Hence, the rate of reaction increases.

Decomposition of hydrogen peroxide by catalyst of manganese (IV) oxide

http://www.youtube.com/watch?v=7_X8c2b0BB0

Chemistry Form 5: Chapter 1 - Collision Theory

Chemistry Form 5: Chapter 1 - Collision TheoryAccording to the collision theory, particles of reactant that achieve activation energy and collide with correct orientation will result in reaction.

1. Correct Orientation

Click on the diagram below to play!

2. Activation Energy

Activation energy is the minimum amount of energy that must be overcome by the colliding particles so that the reaction can occur.

Chemistry Form Five: Chapter 1 - Rate of Reaction

Chemistry Form Five: Chapter 1 - Rate of ReactionRate of reaction = change of quantity in reactant or product per unit time.

We usually use water displacement method to collect gas in school laboratory as shown below:

The reaction is fastest at the start when the reactants are at a maximum (steepest gradient)

The gradient becomes progressively less as reactants are used up and the reaction slows down.

Finally the graph levels out when one of the reactants is used up and the reaction stops.

The amount of product depends on the amount of reactants used. The initial rate of reaction is obtained by measuring the gradient at the start of the

reaction. A tangent line is drawn to measure rate of reaction at instataneous time.

Chemistry Form 4: Chapter 2 - Rutherford Atomic Model

Chemistry Form 4: Chapter 2 - Rutherford Atomic Model

The Gold Foil Experiment

Rutherford bombarded a very thin leaf of element gold with a stream of high speed positively charged particles. These positively charged particles are alpha radiation from helium nuclei. 

As expected, most alpha particles went right through the gold foil but to his amazement, a few alpha particles rebounded almost directly backwards due to same positive charge repulsion force.

Click on the diagram to play!

http://student-sc.blogspot.com/2012/12/chemistry-form-4-chapter-2-rutherford.html

This proved that:

1. the atom had a dense but very small positive nucleus2. the electrons were far away from the nucleus3. the electrons were separated from the nucleus by a lot of empty space