The rate of a chemical reaction is the number of moles of reactants converted or products formed per unit time. It varies from one chemical reaction to another because some chemical reactions are faster than others. The rate at which a reaction occurs and its control are significant in industries because they are the factors that determine if the reaction will make economic sense or not.
How
to measure the rate of chemical reaction
Consider a reaction between irons and dilute
hydrochloric acid
Fe(s) + 2HCl(aq) → FeCl2(aq)
+ H2(g)
As the reaction proceeds, the iron is used up and
iron (II) chloride and hydrogen gas are formed.
The rate
of the chemical reaction between iron and the acid can be determined by:
·
Taking a given mass of iron
·
Adding an excess of hydrochloric acid
·
Noting the time taken for all the iron
to disappear or react
The rate of the chemical reaction can be calculated by:
Rate of chemical reaction = amount of iron (mole)/time
taken
Or
Rate of chemical reaction = change in
concentration of a reactant or product/time taken
Or
Rate of chemical reaction = mass of reactant/ time
taken for the reaction
Example
Questions
1)
When 20g of magnesium trioxocarbonate (IV)
oxide was added to excess dilute hydrochloric acid, carbon (IV) oxide evolved. The entire reaction took 10 minutes. Calculate the rate of the
reaction.
solution
Rate of reaction = mass of
reactant/time taken for the reaction
Mass of the reactant = 20g
Time taken = 10 minutes
Rate of reaction = 20/10 = 2g/min
Or
Mass of reactant = 20g
Time taken = 10x60 = 600s
Rate of reaction = 20/600 = 0.03g/s
2)
If the rate of chemical of calcium trioxocarbonate(IV)
with excess hydrochloric acid is 0.2g/s and the mass of calcium trioxocarbonate
(IV) which reacted with the acid is 5g, calculate the time it took for the
reaction to be completed in minutes.
Solution
Rate of reaction = 0.2g/s
Mass of reactant = 5g
Time taken for the reaction=??
Time taken = 5/0.2 = 25s
In minutes
60s = 1minute
25s = 25/60 = 0.42minutes
Factors Affecting Rate of Reaction
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