7.1.1 Average Rate of Reaction – Measurable Quantities

1. During a chemical reaction, two things happen
1. The quantities of reactants reduce.
2. The quantities of products increase.
2. Therefore, the rate of the reaction can be determined by
1. measuring the decrease of the amount of the reactants over time.
2. measuring the increase in the amount of products over time.
3. However, the quantity (or change) of the reactants/product may be measurable or immeasurable.
4. The easily measured quantity changes include
1. Mass
2. Concentration (Conductivity)
3. Volume of gas

Example
The reaction between calcium carbonate and hydrochloric acid.

The rate of the reaction can be determined by

1. Measuring the reduces of the mass of the calcium carbonate (reactants) over time
   \[\begin{gathered}
   {\text{Rate or Reaction }} \hfill \\
   {\text{ = }}\frac{{{\text{Mass of CaC}}{{\text{O}}_3}}}{{{\text{Time Taken for Reaction}}}} \hfill \\
   \end{gathered} \]
2. Measuring the increases of the volume of the carbon dioxide gas produced over time.
   \[\begin{gathered}
   {\text{Rate or Reaction }} \hfill \\
   {\text{ = }}\frac{{{\text{Volume of C}}{{\text{O}}_2}{\text{ Produced}}}}{{{\text{Time Taken for Reaction}}}} \hfill \\
   \end{gathered} \]

We shall discuss the immeasurable quantity (or changes) in next section.