H - H 436kJ/mol
C = O 805kJ/mol
O = O 498kJ/mol
Bonds Broken:
1x C – C 1x +347
1x C – O 1x +360
1x O – H 1x +464
5x C – H 5x +431
3x O = O 3x +498
Total = +4730
Bonds Made:
4x C = O 4x -805
6x O – H 6x -464
Total = -6004
ΔH = 4730 – 6004
= -1274Kj/mol¯¹
Calculations:
H H
⏐ ⏐
H – C – C – OH + 3O = O ⇒ 2O = C = O + 3O
⏐ ⏐ ⏐ ⏐
H H H H
With this in mind the amount of energy the water gains will be equal to +1274. This means the number of moles lost per mole of ethanol will equal -1274.
The loss of energy in ethanol can be calculated by using the following equation:
Moles = Mass
Relative Molecular Mass
The energy given out by one gram of ethanol can be calculated as follows:
Relative Molecular Mass of Ethanol: C₂H₅OH
C: 12 x 2 =24
H: 1 x 6 = 6
O: 16 x1 = 16
Total = 46
Moles = 1 gram
46kJ/mol¯¹
Moles = 0.0217
Next multiply the result with the energy loss in kilojoules.
0.0217 X -1274 = -27.65kJ/gram
I will multiply the mass of the water, the specific heating capacity of the water and the change in temperature to figure out the amount of energy transferred to the water.
Hypothesis
I predict that as the amount of ethanol burnt increases there will also be an increase in the temperature. As the alcohol is being lit by the splint that produces heat, it will also give out oxygen and water as well as heat energy to heat the water. This will break the hydrocarbons into simpler, smaller molecules and then will later combust, making this experiment an exothermic reaction. I would expect that when the alcohol is being burnt and producing heat energy, carbon dioxide, and water will be produced meaning the alcohol would lose some mass which would evaporate into the air.
Variables
Independent Variables: I will only change the mass of ethanol I use, increasing it each time.
Dependent Variables: I shall be measuring the temperature and change in mass during this experiment.
Fixed Variables: Throughout the experiment I will make sure the volume of the water remains the same, the fuel I use will always be ethanol, the height will always be 7cm from the base of the clamp, the crucible I use weighs the same as the first one I used or that it is the same one and that I use the exact same can.
Ensuring I Carry out a Fair Test
- Repeat the experiment and work out and average.
- Use the same crucible each time as some might be thicker then others, which can cause a change in conductivity and results.
- Use the same can each time.
- Make sure the height from the bottom of the can to the base of the clamp is always the same for if it isn’t it could effect the results.
- Always ensure you are using the same amount of water each time.
Apparatus
- Clamp
- Safety Mat
- Soft Drink can (eg. Coke, Sprite, etc.)
- Measuring Cylinder
- Water
- Thermometer
- Crucible
- Ethanol
- Pipette
- Splint
- Tongs
- Digital Balance
Labelled Diagram
Risk Assessment
- Make sure you wear goggles at all times for protection.
- Always wear your lab coat tightly done up to prevent any serious accidents incase of spillages or when lighting the fuel.
- Keep your hair tied back.
- Check that your clamp is securely holding your can in place for when it contains heated water if any spills it could leave you with a burn.
- Never touch the crucible with your bare hands for it will be extremely hot once the fuel has been burnt in it. Always make sure you use tongs to carry it while moving it from one place to another to prevent burning yourself.
- Wash hands immediately if any ethanol spills on them for it is extremely flammable.
- Do not stand too close to the flame while lighting the fuel, try to stand at an arms length.
- Always have a safety mat incase of spillages or any other accidents involving flames.
- Clean any spills instantly.
Method
- Collect all your apparatus together and set it up accordingly, keeping in mind all of the safety precautions.
- Make sure the soft drink can is a height of 7 centimeters from the base of the clamp.
- Measure out 250ml of water using a measuring cylinder.
- Pour the water into the can and record the temperature.
- Next using the digital balance weigh your crucible.
- Press tare and then measure out the amount of ethanol you need with a pipette.
- Again press tare and take note of the total weight.
- Place the crucible under the can of water.
- Using your splint set the ethanol alight.
- Wait for the flame to go out before recording the temperature.
- Repeat this as many times as you think necessary.
Results
Table 1:
Table 2: