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The objective of this experiment was to determine the enthalpy change for the decomposition reaction of hydrogen peroxide (H2O2) under constant atmospheric pressure. The decomposition of hydrogen peroxide is represented by the following equation:
$$2text{H}_2text{O}_2(l) rightarrow 2text{H}_2text{O}(l) + text{O}_2(g)$$
This reaction is exothermic, meaning it releases heat as a product. The change in enthalpy of the system is equal to the amount of heat that is absorbed or released under constant pressure.
To increase the rate of the reaction, we used a catalyst, Iron (III) Chloride (FeCl3). The catalyst lowers the energy barrier between the reactants and products, facilitating the reaction.
In a calorimeter, some heat energy is lost or gained by the surroundings. Ideally, all heat should be either absorbed or released into the calorimeter. However, in reality, some heat exchange with the surroundings occurs (1).
The following steps were performed during the experiment:
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This experiment was repeated twice, using the same solutions. Additionally, the experiment for the Enthalpy of Decomposition of Hydrogen Peroxide was repeated twice. The same procedure was conducted for the decomposition of hydrogen peroxide, with 40ml of 6% hydrogen peroxide solution as the first solution and 10ml of 0.5 mol L-1 Iron (III) Chloride (FeCl3) solution as the second solution. The color changes of the reaction were recorded before and after the experiment (1).
The table below presents the experimental results:
| Experiment | Mass of Solution (g) | Csoltn (J K-1) | tH (J) | rH (J) | Moles H2O2 | HH2O2 (kJ mol-1) |
|---|---|---|---|---|---|---|
| 1 | 150.2 | 4.18 | 874 | -95 | 0.025 | -93.033 |
| 2 | 148.5 | 4.18 | 871 | -97 | 0.024 | -95.625 |
The aim of this experiment was to determine the enthalpy change for the decomposition of Hydrogen Peroxide, which was calculated to be -93.033 kJ mol-1. The literature value of the decomposition of hydrogen peroxide given by the lab manual is -94.6 kJ mol-1. This indicates that the experiment conducted was successful, as there was only a small percentage error of 1.66%. Nevertheless, several factors could have contributed to this small percentage error (1).
One of the main factors that may have contributed to the percentage error is the delay in placing the calorimeter lid. Heat would have been lost to the surroundings during this delay, affecting the change in temperature, ΔT. Additionally, heat exchange with the surroundings and a slight rise in heat energy due to the friction of the solution being stirred could have played a role. Human errors in reading or measuring solutions could also interfere with accurate concentration levels. To mitigate these issues in future experiments, readings and measurements should be double-checked with a lab partner, and the calorimeter lid should be replaced as quickly as possible (1).
The observed color changes during the reaction are noteworthy. The color of the iron chloride before adding it to the hydrogen peroxide solution was a light brown/orange color. Upon addition to the hydrogen peroxide, it turned dark brown/black. After the reaction was complete, the color returned to the original light brown/orange. This color change indicates that the catalyst, iron chloride, is not consumed during the reaction. During the decomposition of hydrogen peroxide, the iron in the catalyst undergoes oxidation, losing electrons. Since iron can exist in two different oxidation states, the Ferric ion (Fe3+) is reduced to the Ferrous ion (Fe2+), which is later re-oxidized into Fe3+. This explains the color changes from light brown/orange to dark brown/black and back to the original color (2).
In conclusion, despite some limitations, it can be concluded that the experiment to determine the enthalpy change of hydrogen peroxide was successful, with only a small percentage error. The results obtained were consistent with the literature value, and the color changes observed during the reaction confirmed the catalytic nature of iron chloride in the decomposition of hydrogen peroxide (1).
Enthalpy Change Experiment Report. (2024, Jan 05). Retrieved from https://studymoose.com/document/enthalpy-change-experiment-report
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