We all did a trial experiment to get a feel of the layout and processes involved in the experiment and also to establish how best to perform the experiment so we knew what we were doing when it came to the real thing. Each alcohol was tested twice to check for anomalies and to give more credence to our results – more sound evidence, more reliability. Bond Energy Theory: I’m basing my results on the theory of bond energy – which is defined as the amount of energy in kilojoules associated with the breaking or making of one mole of chemical bonds in a molecular mole or compound (in this case of the alcohols).
The energy stored in the bonds is called the enthalpy and is given the symbol H. The ? H shows the change in enthalpy and is called the heat of reaction. Or so my textbook “GCSE Chemistry – B. Earl & L. D. R. Wilford” says anyhow. Bonds Made/ Bonds Broken: In an endothermic reaction, the energy level of the products will be greater than that of the reactants, as the reactants have gained energy during the reaction. In an exothermic reaction such as this one, the reactants lose their energy to their surroundings and end up with less energy in their products than at the start.
Here is an energy level diagram of an exothermic reaction: As you can see in the diagram above, the energy that the reactants possess at first is increased dramatically (in this experiment by the presence of heat in the form of a flame) so that the energy level rises high enough to penetrate the activation energy barrier and is lost to the surroundings in the form of heat. Method: 1. Obtain correct Apparatus in sufficient quantities. (I think I have listed them all more or less in the “Diagram/Apparatus” section. )
Clean the copper can of any imperfections on the surface that could influence the results. 3. Set up experiment (as shown in the Diagram/Apparatus section). 4. Check that the thermometer is suspended in the can, and not touching any of the sides. 5. Make sure the can height is constant for each experiment. 6. Making sure that the lid of the alcohol burner is fixed on top of the burner (to stop the alcohol evaporating away), weigh the burner on a set of electronic scales – making sure the figures are accurate to 2 decimal places.
Note down the starting mass of the alcohol burner. 7. Then, place 50ml of water into the copper can that is suspended directly above the alcohol burner. 8. Note down starting temperature. 9. Light the wick of the alcohol burner and quickly set up an insulation barrier of heatproof mats to block out any draughts or unnecessary heat loss. 10. When the temperature of the water has increased by 30i??
C, hastily blow out the flame that’s burning merrily atop the alcohol burner (without spilling the alcohol burner as we managed to do once…) and immediately bung the lid onto the burner and reweigh the alcohol burner on the SAME set of electronic scales to the same degree of accuracy as before. 11. When all has been completed to a reasonable level of satisfaction, breathe a sigh of relief and brace oneself for the repeat of the whole procedure for the same alcohol (do each alcohol twice to validate results) and move up the homologous series steadily using the procedure outlined above to complete the experiment.