How Does Concentration Affect The Rate of Reaction?

This article illustrates an actual Lab experiment showing How Does Concentration Affect The Rate of Reaction with outcomes.How Does Concentration Affect The Rate of Reaction

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Let’s discuss it in an easy way. To understand it better, let’s take two conical flasks A and B.

  • Flask A –  When we have put in 3 grams of zinc granules and 5 ml of 1 M hydrochloric acid in flask A, then hydrogen gas is produced gradually. We note down the volume of hydrogen gas formed after every 10 seconds by using a stopwatch.
  • Flask B – We now take another similar flat-bottomed flask B and put the same mass of 3 grams of zinc granules in it. But we now add 5 ml of 2 M hydrochloric acid into the flask (which has double the concentration than in the previous case).  The volume of hydrogen gas produced is noted after every 10 seconds by using a stopwatch.

Experiment Outcome – Concentration Affect The Rate of Reaction

We plot the graphs between time readings and the corresponding volume readings of hydrogen gas evolved for both the experiments on the same graph paper. We get two curves showing the reaction rate in the two cases.How Does Concentration Affect The Rate of Reaction?

  • The curve OA is for the reaction between 3 grams zinc and 1M hydrochloric acid whereas curve OB is for the reaction between 3 grams zinc and 2 M hydrochloric acid.
  • We can see from Figure curve OB is steeper than curve OA. This means that the reaction in flask B is faster than in flask A.
  • Since of concentration of the reactant on the rate of a flask B has the higher concentration of hydrochloric acid.

Form this we conclude that when the concentration of hydrochloric acid is increased (from 1 M to 2 M), then the rate of formation of hydrogen gas increases (or the reaction rate increases).

The rate of Reaction – Note

The volume of hydrogen gas evolved in these experiments is a measure of the rate of the two reactions (taking place in two separate flasks). So, in general, we can say that when the concentration of a reactant is increased, the reaction rate increases (the reaction goes faster). It has been found by experiments that in the reaction :

Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2(g)

If the concentration of the reactant hydrochloric acid is doubled, then the rate of evolution of hydrogen gas also gets doubled, In other words, if the concentration of hydrochloric acid is doubled, the reaction rate also gets doubled. If, however, we decrease the concentration of a reactant, then the reaction rate decreases. From this discussion, we conclude that a reaction can be made to go faster or slower by changing the concentration of reactants.

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