This was done by counting the number of different bonds broken i. e. C-H and using a data table to find out the amount of energy required. Secondly, I worked out the energy released by bonds being made again by counting the bonds and using a data table. I subtracted the second number from the first to work out the energy released by the alcohol. Methanol Balanced Equation: CH3OH+1. 5O2–>CO2+2H2O Bonds Broken Energy Required for Bond Breaking (kJ/mol) Bonds Made Energy Released from Bonds Made (kJ/mol).
Total Ene Bonds Broken Energy Required for Bond Breaking (kJ/mol) Bonds Made Energy Released from Bonds Made (kJ/mol) Total Energy Used + 12383 kJ/mol Total Energy Released – 15398 kJ/mol Total Molar Energy of Combustion.
Heptanol Balanced Equation: Bonds Broken Energy Required for Bond Breaking (kJ/mol) Bonds Made Energy Released from Bonds Made (kJ/mol)Total Energy Used + 14299 kJ/mol Total Energy Released.-Bonds Broken Energy Required for Bond Breaking (kJ/mol) Bonds Made Energy Released from Bonds Made (kJ/mol) 1/mol Total Molar Energy of Combustion, ? H (kJ/mol) = +16215-20222= -4007 This data justifies my hypothesis.
More energy is released as you go up the series of alcohols therefore the water will heat up by a given temperature with less alcohol being burnt. GCSE CHEMISTRY COURSEWORK: Obtaining While obtaining evidence I took into account many safety points into consideration: Safety goggles were worn at all times I stood up so I could quickly move out of the way if there were any spillages etc. I tucked my tie in my shirt to avoid it catching fire I also made sure I took accurate readings by: Stirring the water to maintain an even temperature Closing windows that might cause a draught Keeping the tin at the same height above the flame.
Repeating anomalous results GCSE CHEMISTRY COURSEWORK: Analysing To produce a graph of ‘molecular mass’ versus ‘enthalpy of combustion’ both these values need to be calculated. Here is an example: First, the energy released has to be calculated. This can be done using the following formula: q=energy released m=mass of water (g) c=specific heat capacity of the liquid heated (4. 18J/g/i?? c for water) ?t=temperature change of water For my first piece of data this is how q would be calculated. Temperature Change: 10. 5i?? c Mass of Water: 400g (remember that water has a mass of 1g per cm3) Using the formula: q=400×4. 18×10. 5.
Second, the molar heat of combustion must be calculated. This can be done using the following formula: -q=total energy transferred to the water (negative because the reaction is exothermic) n=number of moles (weight difference/formula mass) x1000=convert J’s to kJ’s Continuing with the same example: Energy Released: 17556J (this was worked out with the first equation) Weight Change: 1. 20g Formula Mass: 32g Using the formula: ? HMy original hypothesis was that as you go up the series of alcohols, less of the alcohol will have to be burnt for the given temperature rise.
My results proved this hypothesis. The graph shows strong positive correlation proving that less alcohol is needed for the temperature rise as you go up the group. There are no anomalies, and there is hardly any scatter. When I compare my experimental data with my theoretical values I can see that although my experimental values follow the same trend, they show much less energy being given off per mole than the theoretical ones. This is because not all of the energy produced went into the water (explained in more detail in the evaluation). GCSE CHEMISTRY COURSEWORK: Evaluation.
My experimental data agreed with the theoretically predicted values. When both sets of results were plotted onto a scatter graph, I could see that they both followed the same trend. However, the line representing the theoretically predicted values was lower down on the graph showing that the experimental values were lower than the predicted ones. This is because of the experimental errors detailed below. Reliability: I believe my data to be reliable. There is hardly any scatter as the results were close to the line, and there were no anomalies.
The data was reliable enough to firmly support my conclusion. The fact that there was not much scatter shows this. However, the data was reliable but inaccurate because of the problems outlined below. If the data obtained was completely accurate then it would be on the theoretical data line. Experimental errors: It was impossible to get all the energy of the burning alcohol, using our equipment, into the can. Some inevitably escaped around the can and into the room. This explains why our results showed slightly more alcohol needing to be burned than the theoretical amount.
Sources of experimental error: Not all heat getting into the water (most escaped around the can or heated up the can) Draughts blowing in from outside Modifications: If I was to do this experiment again I might either use a different calorimeter than a tin can i. e. one that conducted heat into the water more efficiently or simply put a lid on the can and insulate it. I would also do the experiment in an environment out of the open air to stop air currents changing my results and to concentrate the heat onto the water, rather than the air around.
Further Work: I might do the same experiment but using alkanes instead of alcohols. I would investigate as to whether they produce the same trend as with alcohols and see whether they are more or less efficient. GCSE Chemistry Coursework 1 Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.