Temperature Change in the Reaction Involving Change of Volume or Concentration

Altering the Volume of the Solution Without Altering the Concentration

If an experiment is repeated by alter the volume without alter the concentration, the temperature change will remain the same.


Example 1:
When 50 cm³ of dilute hydrochloric acid 2 mol/dm³ is added into 50 cm³ of potassium hydroxide 2 mol/dm³, the temperature increase 13°C. What is the temperature increase if 300 cm³ of dilute hydrochloric acid 2 mol/dm³ is added into 300 cm³ of potassium hydroxide solution 2 mol/dm³ ?

Answer:
The volume of the reactants are increases by 6 times (300/50) whereas the concentration of the solution remain unchanged. Therefore the change of the temperature remain the same.

Temperature increase = 13°C


Altering the Concentration of the Solution Without Altering the Volume

If an experiment is repeated by alter the concentration by n time without alter the volume of the solution, the temperature change will be n time of the initial temperature change as well.


Example 2:
In an experiment, 50 cm³ of lead(II) nitrate solution 0.2 mol/dm³ is added into 50 cm³ of sodium carbonate solution 0.2 mol/dm³, the increase of temperature is 2.4°C. what is the increase in temperature if 50 cm³ of lead(II) nitrate solution 0.6 mol/dm³ is added into 50 cm³ of sodium carbonate solution 0.6 mol/dm³?

Answer:
The volume of the reactants remain unchanged whereas the concentration of the solution increases by 3 times (0.6/0.2). Therefore the change of the temperature

θ = 2.4°C x 3 = 7.2°C


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