Energy level diagram:
Energy transfer: A reaction that gives out energy is called n exothermic reaction. A reaction that takes in energy is alled an endothermic reaction. Exothermic reactions can feel hot as energy is taken in. Endothermic reactions can feel cold as energy is taken in. The energy change in a reaction is often given the symbol /\H. For endothermic reactions the energy change is positive , i.e heat is needed. A exothermic energy change indicates an exothermic reaction, ie heat is released.
Virtually all chemical reactions involve energy changes. Whether they are exothermic or endothermic depends on the balance between the energy needed to break bonds in the reactant, and the energy released when bonds are made in the products.
Aparatus:
3 Polystyrene beackers
3 Plastic lids
3 Thermometres (-10 - 110*C)
3 Measuring cylinders (50ml)
Hydrochloric acid (2M)
Soduim hydroxide (2M)
Distilled water
Safety:
- Always wear safety goggles as acid may splash up into your eyes.
- Wash hands after experiment.
- Always stand up when doing practical experiments.
- Were lab coats to protect your body and clothes from acid.
Pilot test:
We used polystyrene cups, due to there insulating properties. We will take the temperature of the acids and the alkalis seperately, with different thermometres, so the acids and alkalis dont mix before I want them too. Also we should wait 30 seconds before taking the temperature of each solution.
We found out that all in our pilot method would also apply for our real method, as our prediction reflected are results.
Method:
Measure 20ml of hydrochloric acid and take the temperature after leaving it for 30 seconds. Then in a seperate measuring cylinder measure out 20ml of Sodium hydroxide, pour into a polystyrene beaker, and again take the temperature after 30 seconds.
Mix both of them together and record the highest temperature. Repeat this for every temperature as shown in the table below: