10.1 Rate of Reaction

 

1. Chemical reactions take place at different rates
2. A fast reaction takes a shorter time to complete whereas a slow reaction tale a longer time

 

Rate of reaction Ü       ____1_____

                                    Time taken

 

3. Rate of reaction is determined by measuring how quickly a reactant is used up or how quickly a product is produced over a period of time

 

Rate of reaction =       amount of a reactant used up

                                    Time taken

 

Rate of reaction =       _amount of a product formed

                                    Time taken

 

4. Observable change in the reaction that are monitored to measured the rate of reaction include the following:

a)     Increasing volume of gas given off

b)     Mass change of the reaction mixture

c)     Temperature change

d)     Colour change indicating concentration

e)     pH change

f)       formation of precipitation

g)     change in electrical conductivity

 

5. The rate of reaction can be measured by:

a)     The average rate of reaction over a period of time

b)     The instantaneous rate of reaction at a given time

6. In a reaction, the rate of reaction decreases with time because the reactants are used up.
7. The rate of a reaction changes as external conditions are altered.

 

10.2 Factors Affecting the Rate of Reaction

 

1. Factors that affect the rate  of reaction include:

a)     Size or total surface area of solid reactant

b)     Concentration of the reactant ( in solution)

c)     Temperature at which reaction occurs

d)     Pressure of gaseous reactant

e)     Presence of a catalyst

 

 

2. Rate of reaction increase with:

a)     Large surface area of solid reactant

b)     Higher concentration of solution

c)     Higher temperature at which the reaction occurs

d)     Higher pressure of gaseous reactant

e)     Presence of catalyst

3. Chemical reaction in industrial process are usually made faster by changing the external condition such as pressure, temperature and the use of catalyst
4. A catalyst is a substance which increase the rate of chemical reaction without itself being chemically change at the end of the reaction
5. An inhibitor is a substance which slows down the reaction.
6. Catalysts are highly specific and a little amount is enough to speed up the reaction. A catalyst not used up but may change its physical appearance at the end of the reaction. A catalyst does not increase the yield of the reaction.
7. Catalyst are very important in industrial process as the save energy, labour and time by increasing the rate of chemical reaction.

 

 

10.3 Collision Theory

 

1. According to collision theory, a collision will occur if the reacting particles
1. Possess a certain minimum amount of energy called the activation energy when they collide with each other
2. Collide at the correct orientation where the atoms are positioned as such that the formations of new bonds are possible.
2. Any external factors that increase the frequency of effective collision will result in a higher rate of reaction. These include increasing the total surface area if solid reactant, concentration of a solution, pressure of gases and temperature of the reaction and the usage of a catalyst.
3. A catalyst speed up a chemical reaction by providing an alternative path of reaction which has a low activation energy,

 

 

 

 

 

 

 

 

 

EXERCISE

 

1.      An experiment was carried out to determine the rate of reaction between sulphuric acid (H₂SO₄) and sodium thiosulphate solution (_Na2S2O3). ‘X’ mark will disappear when certain amount of sulphur precipitate was formed. Time taken for ‘X’ to disappear was record and a graph was plotted to shown the result of the experiment.

 

 

Concentration of sodium thiosulphate solution (mol dm^-3)

 

 

 

 

 

                                                                                                        Time/s

 

 

 

a.      State the factor affecting the rate of reaction in this experiment

b.      Describe an experiment to determine the factor affecting the rate of reaction in this experiment. Your description should include all precaution take

c.      Temperature is also factor that can affect the rate of reaction between sulphuric acid and sodium thiosulphate solution. With reference to the collision theory, explain this statement/

2.       

a.       

                                                  i.      state the meaning of a catalyst

                                                 ii.      give two characteristics of a catalyst

b.      Describe an experiment to investigate the effect of the amount of the catalyst , manganese (IV) oxide on the decomposition of hydrogen peroxide

c.      A catalyst is used in the Haber process to speed up the reaction to produce ammonia

                                                  i.      Name of the catalyst

                                                 ii.      Using the collision theory, explain how catalyst can affect the production of ammonia in the Haber process

3.       

a.      State the meaning of rate of reaction

b.      suggest two ways to measure the rate of reaction between hydrochloric acid and calcium carbonate

c.      describe an experiment to measure the rate of reaction between hydrochloric acid and calcium carbonate using one of the ways suggest in (b)

d.      Using the collision theory, explain why we need to store fresh milk in a refrigerator

4.       

a.      Explain

                                                  i.      activation energy

                                                 ii.      collision theory

 

                                                  i.      suggest three way to speed up the reaction between sulphuric acid and zinc

                                                 ii.      explain your answer in b(i) using the collision theory