(O-H) 464 = 464
3(O=O) 3 x 498 = 1494
(C-C) 612 = 612
4993 KJ/mol
Sum of bond energies formed:
4(O=C) 4 x 805 = 3220
6(H-O) 6 x 464 = 2784 +
6004 KJ/mol
H = Sum of βE broken – sum of βE formed
= 4993 - 6004
= -1011 KJ/mol
H is negative; therefore the reaction will be exothermic
Propanol + oxygen carbon dioxide + water
C3H7OH + 4½O2 3CO2 + 4H2O
Sum of bond energies broken:
7(H-C) 7 x 413 = 2891
(C-O) 358 = 358
(O-H) 464 = 464
4½(O=O) 4½ x 498 = 2241
2(C-C) 2 x 612 = 1224 +
7178 KJ/mol
Sum of bond energies formed:
6(O=C) 6 x 805 = 4830
10(O-H) 8 x 464 = 3712 +
8542 KJ/mol
H = Sum of βE broken – sum of βE formed
= 7178 - 8542
= -1364 KJ/mol
H is negative; therefore the reaction will be exothermic
Butanol + oxygen carbon dioxide + water
C4H9OH + 6O2 4CO2 + 5H2O
Sum of bond energies broken:
9(H-C) 9 x 413 = 3717
(C-O) 358 = 358
(O-H) 464 = 464
6(O=O) 6 x 498 = 2988
3(C-C) 3 x 612 = 1836 +
9363 KJ/mol
Sum of bond energies formed:
8(C=O) 8 x 805 = 6440
10(H-O) 10 x 464 = 4640 +
11080 KJ/mol
H = Sum of βE broken – sum of βE formed
= 9363 - 11080
= -1717 KJ/mol
H is negative; therefore the reaction will be exothermic
Pentanol + Oxygen carbon dioxide + water
C5H11OH + 7½O2 5CO2 + 6H2O
Sum of bond energies broken:
11(C-H) 11 x 413 = 4543
(C-O) 358 = 358
(O-H) 464 = 464
7½(O=O) 7 x 498 = 3486
4(C-C) 4 x 612 = 2448 +
11199 KJ/mol
Sum of bond energies formed:
10(O=C) 10 x 805 = 8050
12(H-O) 12 x 464 = 5568 +
13618 KJ/mol
H = Sum of βE broken – sum of βE formed
=11199 - 13618
= -2419 KJ/mol
H is negative; therefore the reaction will be exothermic
Prediction:
My prediction for this experiment on investigating the energy produced by different alcohols is that, the longer the hydrocarbons in the chain of the alcohols, the more heat it will produce. When the alcohols are being burned, they will give out oxygen and water as well as heat energy to heat the water, which will crack the hydrocarbons into simpler molecules (smaller) and then will combust later, making this experiment an exothermic reaction. Therefore the long chains of hydrocarbons produce more energy than smaller chain molecules as the long chain breaks in to smaller hydrocarbons meaning theirs more, making the boiling point decrease, which makes them more flammable, less viscous, and more volatile. Therefore I would expect that when the alcohol's is being burned and producing heat energy, carbon dioxide, and water will be produced meaning the alcohol would lose some mass which would evaporate into the air. I therefore predict that when there is a longer chain of hydrocarbons than another alcohol, it would produce more heat than the other alcohol meaning it would have a higher reading each minute compared to a smaller chain of hydrocarbons, which could mean that the smaller hydrocarbons combust quicker then longer hydrocarbons as their less volatile.
Apparatus:
- Spirit burners containing the different alcohols
- Measuring cylinders
- Thermometer
- Balance (measuring to 2dp)
- Boiling tube
- Stop clock
- Matches
- Clamp and stand
- Water
Diagram:
Plan:
First of all; the container of the alcohol will be measured including the snuffle using a balance, and the mass will be recorded. Then I will get 23cm³ of water in a boiling tube and clamp it on the clamp stand so that the flame will just touch the bottom of the boiling tube. I will use a thermometer to measure the initial temperature of the water. Then I will start the stop clock and light the burner at the same time. I will occasionally stir the water while I am burning for three minutes. After three minutes I will extinguish the flame. I will record the final temperature of the water. The mass will then be taken of the alcohol, and the measurement of the water after being heated. I will repeat the experiment with the same alcohol twice so that I have a set of three readings and I can take the average reading so that my readings are accurate. When I have done this I will do the exact experiment for the other four alcohols to give me a more reliable set of results. To find out how much alcohol and water was burnt in the experiment. I will find the difference between the initial and final readings.
To make this a fair test I will make sure there is no other liquid or substances on the balance when I am weighing the alcohol. This will give me an accurate mass and prevent any anomalous results. When I measure the temperature I will make sure I do not touch the edge of the boiling tube with the thermometer but just the water. This is because the thermometer will read the temperature of the boiling tube and not the water. The same amount of water will be used in each of the experiments. The distance between the wick of the burner and the bottom of the boiling tube will be measured so that the distance is the same in all the experiments. The boiling tubes will be all the same size. When the stop clock has turned to 3 minutes, I will immediately extinguish the flame using the snuffle so no more water can be heated.
Safety procedures:
- I will make sure I am wearing goggles throughout the experiment
- I will make sure that I have an overall on to prevent my clothes from becoming dirty and getting in the way of lighting the alcohols.
- I will make sure that I do not sit right next to the experiment, just in case any spillages occur, for example the hot water spills all over me.
- I will make sure that the boiling tube is tightly secure in the clamp.
- Finally I will make sure that the spirit lamp it put out using the glass snuffle.
Preliminary work:
Before starting the actual experiment I carried out preliminary method to work out the appropriate measurements for the experiment. This was also done to work out the limitations and variables in the experiment. These are the results I obtained, after burning three alcohols.
Looking at my preliminary results I decided to also change the time of when I will record the temperature gained by the water, from 3 minutes, to 2.5 minutes, as the results I got in my preliminary results had a great change in temperature. I have also decided to change the distance from the wick. This is because the flame heights of the alcohols varied therefore the boiling tubes were dangerously in the flame. Therefore I decided to not keep the distance from the wick constant, and keep the boiling tube as high so that on the tip of the flame touches the boiling tube.
Method:
The alcohol was measured using a balance.
Heat given out = mass of water x 4.2 x change in temperature
