RATES OF REACTIONS - PUNJAB-CURRICULUM-AND-TEXTBOOK-BOARD-PCTB / 10TH-CLASS / CHEMISTRY / HISTORY-OF-CHEMISTRY-10TH-CLASS-NBF-2024 / CHEMICAL-KINETICS / RATES-OF-REACTIONS

5.1 Rates of Reactions

The rate of a chemical reaction tells us how quickly the reactants are used up or how quickly the products are formed over time. It is the change in the concentration of reactants or products in a given amount of time.

Mathematically,

Change in concentration of a substance Rate Time taken for change

As a reaction happens, the amount of reactants decreases, and the amount of products increases. For example, we measure concentration in moles per cubic decimeter (mol dm $^{- 3}$ ) and time in seconds (s). So, the unit for the rate of reaction is mol dm $^{- 3}$ s'. To better understand this, we can use a graph. (See figure 5.1)

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Figure 5.1: Graphical Representation of the rate of a chemical reaction

Diagram image pending upload by Admin.

This shows that the rate of reaction is not constant. It changes as the reaction progresses.

Average Rate of Reaction

Consider a general reaction

A ⟶ B

The rate of reaction can be expressed in terms of the rate of disappearance of reactant A or the rate of appearance of product B.

R a t e o f r e a c t i o n = \frac{d [A]}{d t}