Determining the Enthalpy Change of A Reaction
If Calcium Carbonate, CaCO3, is heated it decomposes into Calcium
Oxide, CaO and Carbon Dioxide, CO2.
[IMAGE]CaCO3 CaO + CO2
The aim of this experiment is to determine the enthalpy change of this
reaction. To do this I will react both Calcium Carbonate and Calcium
Oxide, separately, with 2mol dm-3 Hydrochloric Acid, HCl. By recording
the temperature changes in each reaction, and using Hess's Cycle, I
will be able to work out the enthalpy change.
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Hess' Law States: "The enthalpy change for any chemical reaction is
independent of the intermediate stages, provided the initial and final
conditions are the same for each route."
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[IMAGE]
[IMAGE][IMAGE]
CaCO3 CaO + CO2
[IMAGE]
[IMAGE]
CaCl2 + CO2 + H2O
In simpler terms, the main point of Hess' Law is that the total
enthalpy change for the indirect route of a reaction is the same as
the direct route, i.e. ΔH1 = ΔH2- ΔH3.
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The diagram above represents a Hess Cycle or a Thermo chemical Cycle.
By knowing the enthalpy changes in two parts of the cycle, it is
possible to calculate the third part and complete the cycle. This is
how I carried out my experiment.
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My results were as follows: Table 1 Table 2
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Polystyrene
Glass
Mass of CaCo3 + weighing bottle
3.46
3.44
Mass of empty weighing bottle
0.94
0.92
Mass of CaCo3 used
2.52
2.52
Temperature of acid initially
20
20
Temperature of solution after mixing
22
21
Temperature change during reaction
2
1
Mass of CaO + weighing bottle
2.41
2.41
Mass of empty weighing bottle
0.92
0.92
Mass of CaO used
1.5
1.5
Temperature of acid initially
this solution we had to weigh out 5g of KHP, which is the amount needed to
used during the combustion. I can now light it and let it burn. I will
Comparing the Enthalpy Changes of Combustion of Different Alcohols Aim Combustion of alcohols is exothermic; energy is given out. Salter's Chemical storylines says, " Different fuels have different enthalpy changes". I will investigate how the carbon chain length of the alcohol affects its enthalpy of combustion. Preliminary Work ----------------
Comparing the Enthalpy Changes of Combustion of Different Alcohols. Aim: To be able to I will find the enthalpy change of combustion of a number of alcohols. so that I can investigate how and why enthalpy change is affected by molecular structure of the alcohol. Outline: I will use Methanol, Ethanol, Propanol and Butanol in the experiment.
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" This means that therefore the enthalpy change of a reaction can be measured by the calculation of 2 other reactions which relate directly to the reactants used in the first reaction and provided the same reaction conditions are used, the results will not be affected. We have the problem set by the experiment to determine the enthalpy change of the thermal decomposition of calcium carbonate. This is difficult because we cannot accurately measure how much thermal energy is taken from the surroundings and provided via thermal energy from a Bunsen flame into the reactants, due to its endothermic nature. Therefore, using the enthalpy changes obtained in reaction 1 and reaction 2 we can set up a Hess cycle.
The Enthalpy Change of Different Alcohols My aim is to compare the enthalpy change of combustion of different alcohols in relation to the structure of each molecule. The enthalpy change of combustion of a fuel is a measure of the energy transferred when one mole of the fuel burns completely. In a chemical reaction, bonds must either be made or broken, this involves an enthalpy change. The formation of bonds is exothermic, energy is lost to the surrounding; on the other hand, breaking bonds is endothermic, energy is taken in. I obtain the value for the enthalpy change of each fuel by using the formula: Energy transferred from the fuel=
NaOH(aq)Â Â Â Â Â Â Â Â +Â Â Â Â Â Â Â Â Â HCl(aq)Â Â Â Â Â Â Â Â Â Â Â Â Â Ã Â Â Â Â Â Â Â Â Â Â Â Â NaCl(aq) Â Â Â Â Â Â + Â Â Â H2O(l).
The exothermic reaction observed in this procedure is as follows ; HCL(aq) + NaOH(aq) ➡ H2O(l) + NaCL(aq) + energy. The purpose of the lab was to determine the value of ∆H of the neutralization reaction above, then compare the data to that of the accepted ∆H value of neutralization to determine the accuracy and validity of our findings. A singular trend was observed and is as follows; the decrease of ∆H indicates a reaction is exothermic, a neutralization reaction results in a (-) value ∴ the (-) value collected was congruent with the trend above, proving our results have some legitimacy at the least.
*The left side of the equation will represent the data from the experiment, and the right side represents our hypothetical calculations. By plugging in either 65°C or 0°C (depending on if were solving for the hot or cold pack), and the...
Enthalpy Changes of Combustion of Different Alcohols Aim: The aim of this experiment is to find out how the enthalpy change (total energy released when the alcohols are completely combusted in a plentiful supply of air) for 5 different alcohols is affected by the number of carbon atoms in the alcohol and other factors contributing to the molecular structure. Prediction: I predict that as the amount of carbon atoms in the alcohol increases, the higher the enthalpy of combustion will be. I have made this prediction, using the values for the enthalpy change of combustion for each alcohol, calculated using bond enthalpies and Hess' law. Methanol's molecular formula is CH3OH. This is the basic structure for all the alcohols, then to make the larger ones an extra carbon is added to the existing carbon each time and the oxygen-hydrogen molecule gets added to the atoms added to the new carbon atom When methanol combusts in air, it reacts with oxygen molecules to from water and carbon dioxide.
My most recent team experience was in Chemistry II class. We performed a group lab experiment, where we were given two unknown substances and had to figure out what they were by using different chemical reactions. With this lab, my team and I had to work together to observe the chemical reactions that the substances were making, so we could compare them to our unknown substances. My team and I observed all of these reactions together and helped each other with the color observations because one of our team members is partially color blind. In the end with all of our observations our conclusion for the two unknown substances was correct. Working with this team was an extraordinary example of what being a good teammate is all about. Good teammates
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