Exothermic neutralisation reaction.

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Exothermic Neutralisation Reaction.


The aim of this investigation is to try to find out how concentration can effect an exothermic neutralisation reaction. I will be reacting sodium hydroxide with hydrochloric acid, which neutralises to form sodium chloride a salt with water. Sodium hydroxide is an alkali and hydrochloric acid in an acid so therefore when reacted together neutralisation occurs. In this case when both substances are reacted, thermal energy is produced hence an exothermic reaction as thermal energy is radiated out.

The reaction will look like this:

        NaOH + HCl        H2O + NaCl

The factors that might affect the results of this experiment are:

  1. Volume
  2. Concentration
  3. Type of substance used.
  4. Catalyst
  5. Pressure

Volume can affect the experiment because if it is not kept constant them results will be varied and there would be no proof that concentration can effect this exothermic neutralisation reaction, as the test would not be fair. Also if substances used were different this could affect the end result produced in this case a salt and water, as more reactive acids and alkalis can perhaps can produce a more vigorous reaction and therefore a higher temperature rise as more thermal energy is produced.

The input variable that I will change will be concentration. Concentration increases the number of collisions because there are more particles in the solution to collide with each other. So if a solution is more concentrated more particles are bumping into each other. Which makes more collisions so there are more reactions between particles, therefore more reactants that produce more water. When water is produced there bonds release energy therefore the more water produced by the reacting OH- and H+ ions the bigger the temperature rise. This is called collision theory examples of this are shown by the diagrams below.

I will record the temperature change of each experiment to find out how concentration can affect the output variable. I will keep the concentration of the alkali constant and change the concentration of the acid. I will be able to do this by recording the temperature before the start of the experiment and the temperature at the end of the experiment and then subtracting the two results away from each other. So as there will be different concentrations in different reactions this will mean different temperature changes. Therefore a different number of atoms in substances when volume is constant so different number of atoms react with each other. This means thermal energy produced by ions in different reactions will produce different temperature changes caused by formation of water.


I predict that the experiment with the highest concentration of acid used will produce the highest temperature rise once reacted with alkali. This is because there are more ions in the higher concentration acid solution than the lower concentration solution, in the same volume. The diagrams below can show this:

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2M alkali        2M acid

Complete         +        Complete


        has occurred

2M alkali        1M acid



        +                                has not occurred,

        spare OH- ion.

For example if I reacted 2 mol/l of NaOH with 2 mol/l Hydrochloric acid there will be an equal amount of ions that will react to form an exothermic neutralisation reaction likewise with 1 mol/l of each. But the 2 mol/l solution will produce the biggest temperature rise, as there will be double thermal energy produced in the volume of liquid, as the solution is more concentrated and there are more H+ and OH- ions to produce ...

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