Data Table for Methane:
Graph of Time versus Temperature of System
Calculation for Methane:
Since we are dealing with methane which is a gas we can use the formula to calculate the actual heat energy of the system.
However, we need to calculate the mass of methane gas using the formula
We know that the density of methane gas at SATP (standard ambient temperature and pressure) is 0.717 kg/m3
Therefore,
We can now use the formula
(24.8-25.4)
= (-0.6)
=kJ
=
We are to assume that the container is not an enclosed system so heat is lost to the surroundings, therefore:
Heat lost= (theoretical heat-actual heat)
= 0.468kJ-
Therefore the percentage deviation is
=
=99.8% deviation from theoretical value.
Calculation for carbon dioxide:
Below is a graph showing change in temperature over a period of 30 minutes.
A similar process was carried out using a sample of carbon dioxide. The same light bulb was used for the same period of time meaning that the theoretical heat energy of the system is the same. In calculating the heat absorbed by the carbon dioxide, we used the same process of calculations.
We can now use the formula
The specific heat capacity of carbon dioxide at SATP is 1.006kJ/kg.C
Heat lost to the surroundings=(theoretical heat-actual heat)
=
=-18.152kJ
Therefore the percentage deviation is
=3978% deviation from theoretical value
As we can see, our heat from the carbon dioxide system had a deviation of 3978%
Calculation for Air
Below is a graph showing the change in temperature of air:
We carried a third test by using a sample of air. We used the same light bulb for the same period of time. We first have to calculate the mass of the air sample.
m= (1.184kg/L) (0.992±0.5)
m=1.174kg±0.5%
m=1.174kg±0.006kg
The specific heat capacity of air is found to be 1.006kJ/kg.C
Using,
= (1.174kg±0.006kg)(1.006)(24.5-24.0)
= (1.174kg±0.006kg) (1.006) (0.5)
=0.591kJ4.51%
=0.59kJ0.03kJ
Heat lost= (theoretical heat-actual heat)
= 0.468kJ-0.59kJ0.03kJ
=-0.1220.03kJ
Therefore the percentage deviation is
deviation from theoretical value.
Conclusion and Evaluation:
In conclusion, we can see that both greenhouse gases as well as the air sample had massive percentage deviation from the theoretical value of heat energy emitted by the bulb. All three samples of air, methane and carbon dioxide absorbed only a significant fraction of the heat emitted by the bulb leading us to various limitations and errors of this lab.
Firstly, the sealed container itself was not completely air tight as we had used plasticine to cover the hole therefore we could not consider it as a completely closed system. We could have carried the experiment out in a thermos flask which is less subject to changes in temperature from the environment.
Secondly, in our calculations, we simply assumed that the entire container was filled with the gas as we did not subtract the volume taken up by the wooden blocked nor the bulb. We could have subtracted the values; however, for example it would be impossible to measure the volume taken by the wire and so on, so it was simply assumed that the entire container was filled with the gas.
Thirdly, we had to hold the circuit together manually, so there were times where the circuit got disconnected and the bulb was off. This happened several times, reducing the overall heat energy emitted by the bulb.
More specifically, a major human error was that we had placed the temperature probe slightly too early whilst the carbon dioxide was still ice. The data would have been more accurate if we had waited for the carbon dioxide to completely sublimate into gas.
A final improvement that could be made is that we should have fixed bulb onto the lid of the container because we noticed that the temperature reader was either completely covered in the ice (regarding carbon dioxide) or either completely on the side of the bulb meaning that the temperature probe was not exposed to a balanced temperature change. This can be improved by somehow placing the bulb on the lid of the container so that there is an even distribution of heat emitted by the bulb.
Bibliography:
Light and Lighting Facts and Bits of Data! (n.d.). Retrieved from http://members.misty.com/don/
lfunfact.html
The Engineering Toolbox. (n.d.). Retrieved from http://www.engineeringtoolbox.com/methane-d_980.html
The Engineering Toolbox. (n.d.). Retrieved from http://www.engineeringtoolbox.com/
air-specific-heat-capacity-d_705.html
http://members.misty.com/don/lfunfact.html
