Preliminary Work
I have done some preliminary work to help me get the most accurate results for my experiment. I changed several factors. These were: Amount of water, length of time and height of water. I also measured the weight to see which combination of factors gave me greatest mass difference. From these experiments I discovered that the best amount of water was 120ml. I will be running the experiment for 3 minutes, as this is long enough to heat the water but not long enough for it to start to boil. I will also be placing the can as close to the burner as possible to prevent heat loss into the surrounding atmosphere.
Key Factors:
The key factors in my experiment are:
Amount of water – the more water the slower it heats up
Height of can away from the alcohol burner – the higher the can is away from the burner, the more heat can escape into the surrounding atmosphere.
Length of Experiment – The experiment length must be long enough for the water to be heated but not long enough for it to boil. I think 3 minutes should be about the right time for this.
Type of Alcohol – This is the factor I am going to change in order to answer my aim.
Background science:
An exothermic reaction is a reaction that gives out heat energy. The opposite to an exothermic reaction is an endothermic reaction, this takes in energy, and so is cold.
The structure of an alcohol consists of Hydrogen, Oxygen and Carbon atoms. As you go down the list of alcohols you get more carbon and hydrogen atoms. For every carbon added there are two hydrogen atoms added.
Combustion means to burn a substance in oxygen.
In a reaction you get the same amount of product out as you do reactant going in. Therefore when writing the equation you need to balance both sides equally. We do this by making sure there are equal amounts of reactants and products on each side.
Bond energy is how much energy it takes to make or break bonds between atoms.
Prediction:
Prediction:
My prediction is as follows:
I predict that the further towards the bottom of the table you go, the higher the energy released
The unbalanced equation for Propanol
C3H2OH + 02 → CO2 + H2O
The balanced equation is:
C2H5OH+3O2 → 2CO2 + 3H2O
Below is what the molecule looks like:
Here is the working out for energy per mol:
C-H bonds 7x1= 7x412= 2884
C-O bonds 1x1= 1x360= 360
O-H bonds 1x1= 1x463= 463
O=O bonds 1x3= 3x496= 1488
---------
5195 KJ/Mol
Energy change=Energy of reactants-Energy of products
5195 – 3668 = 1527
Results:
Actual Results:
My Predictions:
Analysis:
These results show me that my predictions were quite a way out. My predictions were roughly half of what the actual results were, I think that they are roughly half my predictions because there was quite a lot of interference from wind blowing the heat away, also there was some heat lost due to it not getting through the can to the water, and some also went into the atmosphere.
On the next page there is a graph showing the results of heat energy transfer per mol.
Evaluation:
My results are quite reliable in that they went in a reasonably straight graph (see above). They were not really what I predicted though. I think My predictions were off because a lot of the heat escaped into the surrounding atmosphere. To make the experiment more accurate I would have used a thinner walled can. I also would have had some kind of shroud around the burner so that wind or disturbances could not have got to the burner and blown the heat away. I would also have had exactly the same amount of fuel in each burner as I think this makes a minute contribution to the results. I would also have used a more accurate heat measuring device, such as a digital thermometer.
What I actually did in the experiment to attempt to keep it a fair test was to light the burner and blow it out exactly at the right time so that no more and no less heat energy got out. I also held the thermometer slightly away from the bottom of the tin so that it would not be directly influenced by the heat of the flame on the metal can.
The only slight anomaly was for Propanol which was a bit lower that we expected. There are a few things that could have accounted for this, such as a person walking past and disturbing the heat flow, or a fellow scientist dropping water on the burner, or putting the flame out too soon.