HEAT CHANGES IN REACTIONS

EXPERIMENT 1 – NEUTRALISATION
When an acid and an alkali react together a neutralisation reaction takes place. If the acid and the alkali are both STRONG then heat energy is released and the temperature of the mixture rises. If the acid and alkali are both WEAK, then less energy is released, or energy may even be absorbed. In this case the temperature of the mixture will fall.

1) Collect two 25cm3 measuring cylinders. Label one “ACID” and the other “ALKALI”.
2) Measure out 25cm3 of 2M hydrochloric acid in the “ACID” measuring cylinder and pour it into the polystyrene cup.
3) Measure the temperature of the acid and record it in the table below.
4) Measure out 25cm3 of 2M sodium hydroxide in the “ALKALI” measuring cylinder.
5) Add the alkali quickly to the acid in the polystyrene cup. Stir and record the highest temperature reached.
6) Empty the cup, rinse with tap water and dry with paper towel.
7) Rinse the thermometer and measuring cylinders.
8) Repeat the experiment with 25cm3 each of 1M sulphuric acid and 2M potassium hydroxide.
9) Repeat the experiment with 25cm3 each of 2M ethanoic acid and 1M sodium carbonate solution.

Results HCl + NaOH
(both strong) H2SO4 + KOH
(both strong) CH3COOH + Na2CO3
(both weak)
Start temperature (OC)
Final temperature (OC)
Temperature change (OC)

EXPERIMENT 2 – DISPLACEMENT
A metal higher up in the Reactivity Series will displace a less reactive one from its compounds. Magnesium and zinc can both displace copper from a solution of copper (II) sulphate, as shown by the word equations below. Energy is released in the form of heat and the temperature of the mixture rises. magnesium (s) + copper sulphate (aq)  magnesium sulphate (aq) + copper (s) zinc (s) + copper sulphate (aq)  zinc sulphate (aq) + copper (s)

1) Measure out 25cm3 of 0.1M copper (II) sulphate solution using a clean measuring cylinder.
2) Pour the solution into the polystyrene cup and record the temperature of the solution.
3) Add a heaped spatula of magnesium powder and quickly put on the lid.
4) Stir the mixture and record the maximum temperature reached.
5) Empty the contents of the cup DIRECTLY DOWN THE PLUGHOLE of the sink and rinse it and the sink well with water (using the rubber hose on the tap to swill all the metal away so that it does not stain the sink). Dry the cup with paper towel.
6) Rinse the thermometer and dry the thermometer.
7) Repeat the experiment with a fresh 25cm3 of copper (II) sulphate solution and zinc powder.

Results MAGNESIUM ZINC
Start temperature (OC)
Final temperature (OC)
Temperature change (OC)

CALCULATIONS
It is easy to see from your temperature changes whether the reactions in experiments 1 and 2 were exothermic (gave out heat) or endothermic (took heat in) by simply looking at whether the temperature rose or dropped during the reactions.

Your teacher may want you to calculate the heat energy change for some or all of the reactions and will