This is also backed up by the secondary data I obtained from the data book. That is as follows:
Methanol –715 kJ per mole
Ethanol –1371 kJ per mole
Propanol –2010 kJ per mole
Butanol –2673 kJ per mole
Overall I will take three recordings for ethanol, and measure the weight before and after each attempt. I will then repeat this procedure in an identical way for each other alcohol.
To make my results as accurate as possible I will be using a balance that can measure to two decimal places, and a thermometer that is capable of measuring to half a degree Celsius. To make sure my results are as reliable as possible, I will repeat each alcohol three times.
Results
Analysis
Using the above results, I am now able to work out the energy transferred per mole.
Energy required in order to heat up 100ml water by 30 degrees (using the formula ‘energy = mass * temperature change * specific heat capacity):
100ml = roughly 100g
100g * 30 degrees * 4.2 = 12600J = 12.6kJ
Using this, I can find out how much energy was transferred into the water per gram:
Energy transferred into water per gram
= 12.6kJ / Mass of alcohol burned
Methanol = 12.6kJ / 1.04g = 12.12kJ
Ethanol = 12.6kJ / 1.1g = 11.45kJ
Propanol = 12.6kJ / 1.22g = 10.33kJ
Butanol = 12.6kJ / 0.51g = 24.7kJ
Multiplying the energy given off by one gram by each alcohol’s relative molecular mass gives the energy given off per mole:
Relative molecular mass of:
Methanol = 32g
Ethanol = 46g
Propanol = 60g
Butanol = 74g
Energy released per mole:
Methanol = 12.12 * 32 = 387.4 kJ per mole
Ethanol = 11.45 * 46 = 526.7 kJ per mole
Propanol = 10.33 * 60 = 619.8 kJ per mole
Butanol = 24.7 * 74 = 1827.8kJ per mole
As you can see from the above results, and as shown in my bond energy calculations, the energy released per mole increases with the size of the molecule. This is because more bonds are formed with the surrounding oxygen (releasing energy as it does so). My evidence shows that the sequence of reactivity is: Methanol, Ethanol, Propanol, Butanol.
Evaluation
Although I tried to maintain accuracy throughout my work, undoubtedly, many factors influenced the true precision. Factors which I believe effected my results are as follows:
- Heat loss to the surroundings; therefore, energy that should have heated the water was wasted.
- Evaporation loosing water, therefore meaning there was less water present to be heated.
- Evaporation is a cooling process and therefore heat may have been lost this way.
To overcome heat loss, I did primary research and found out that a heat shield was the most beneficial way to reduce this. This, however, may have presented another problem of incomplete combustion of the alcohol due to lack of oxygen. To fix this problem, I could implement some form of oxygen pump.
The procedure itself was fine for the levels of reliability I hoped to achieve, yet, if being tested in a laboratory for professional use, more expensive equipment could be used that is beyond our means.
The evidence does support my predictions fully, and it safe to say it is sufficient to support a firm conclusion about the series of alcohols.
To expand the experiment further, I could test other alcohols and investigate the associations betwixt them.
