For an enthalpy lab, why would calculated value differ from the theoretical value (in percent error) for the heat reaction of Mg/HCl and MgO/HCl
The usual things like misreading thermometers, invalid calculations, poor lab technique and all of the other errors likely to be made by a student.
Mg may have not been pure, student may not have removed the oxide layer from the Mg ribbon, heat flow into or out of the calorimeter, calorimeter calibration may not have been done correctly, etc.
There are several possible reasons why the calculated value for the heat reaction of Mg/HCl and MgO/HCl might differ from the theoretical value, leading to a percent error. Here are a few potential factors to consider:
1. Incomplete reaction: The reaction may not proceed to completion due to factors like incomplete mixing, insufficient reactant quantities, or the presence of impurities. This can result in a lower calculated enthalpy value compared to the theoretical value.
2. Loss of heat: Heat can be lost to the surroundings during the experiment, reducing the measured enthalpy change. Factors like poorly insulated containers, inefficient heat transfer, or prolonged reaction times can contribute to heat loss.
3. Assumption deviations: The calculation of enthalpy change often involves simplifying assumptions, such as the assumption that the specific heat capacities of the reactants and products remain constant over the temperature range. However, these assumptions may not hold true in the actual experiment, leading to a deviation between the calculated and theoretical values.
4. Measurement error: Errors in experimental measurements, such as inaccurate temperature readings, imprecise mass measurements, or incorrect volume determinations, can introduce variations in the calculated value, resulting in a percent error when compared to the theoretical value.
5. Reaction side reactions or incomplete stoichiometry: In some cases, side reactions or incomplete stoichiometry can occur, which alter the overall enthalpy change. These deviations from the expected reaction pathway can lead to discrepancies between the calculated and theoretical values.
To minimize these discrepancies, it is important to carefully control experimental conditions, ensure complete and efficient reaction, use proper insulation techniques, and minimize measurement errors. Additionally, performing multiple trials and calculating an average value can help reduce random errors and improve the accuracy of the calculated enthalpy change.
The calculated value for the heat reaction in an enthalpy lab can differ from the theoretical value due to several factors. Here are a few possible reasons:
1. Experimental limitations: In a lab setting, it is challenging to achieve perfect conditions. Variations in temperature, pressure, and other experimental factors can introduce errors in the measurements. These errors can contribute to the difference between the calculated and theoretical values.
2. Incomplete reactions: During the course of a chemical reaction, it is possible that not all reactants are completely consumed, resulting in an incomplete reaction. This can be due to issues like insufficient mixing or the presence of impurities in the reactants. An incomplete reaction leads to a lower measured heat value compared to the theoretical value.
3. Side reactions: In some cases, side reactions may occur simultaneously with the main reaction. These side reactions can consume some of the reactants or produce additional products, affecting the overall heat of reaction. If these side reactions are not accounted for, they can lead to a discrepancy between the calculated and theoretical values.
4. Measurement errors: Errors in measuring instruments, such as thermometers or calorimeters, can introduce inaccuracies in determining the temperature changes during the reaction. Since the heat of reaction calculations depend on these temperature changes, measurement errors can impact the final calculated value.
Calculating the percent error between the calculated and theoretical values can help determine the extent of these differences. The percent error is typically calculated using the formula:
Percent error = ((|Theoretical value - Calculated value|) / Theoretical value) x 100%
By comparing the calculated and theoretical values and calculating the percent error, it is possible to evaluate the accuracy and precision of the experimental results.