7.1	Determination of Rate of Reaction

 

Rate of Reaction

 

• Definition: Change in quantity of reactant or product per unit time.
• The rate of reaction is inversely proportional to the time of reaction.
• \(\text{Rate of reaction} ∝ \dfrac{1}{\text{Time of reaction}}\)
• The reaction with shorter time of reaction has a higher rate of reaction and vice versa.
• Examples of fast and slow reaction are as follows.

 

Fast reaction (High rate of reaction)	Slow reaction (Low rate of reaction)
The reaction of lithium and water	Rusting
Neutralisation of hydrochloric acid with sodium hydroxide	Formation of stalagmite and stalactite
Burning charcoal	Photosynthesis

 

• The rate of reaction can be measured by measuring the observable changes.
  • Reduction in the mass or concentration of reactant
  • Increase in mass or concentration of product
  • An increase in volume of gas released
  • Production of precipitate
  • Change of temperature, pH, electric conductivity or the intensity of the colour of the reacting mixture

 

The average rate of reaction

• Definition: the speed of a reaction over a time interval.

 

The instantaneous rate of reaction

• Definition: the rate of reaction that happens at any given time.
• Obtained from the gradient of the tangent on the graph of change in the amount of reactant or product against time.