Chm 204 Enthalpy Of Formation Hess Law Introduction 3 Points

Chm 204enthalpy Of Formation Hess Lawintroduction 3 Points Is The

Chm 204enthalpy Of Formation Hess Lawintroduction 3 Points Is The CHM 204 Enthalpy of Formation; Hess’ Law Introduction (3 points) · Is the purpose/goal clearly stated? / 1 · Are the chemical equations included? / 1 · Is there a description of the method? / 1 Procedure, Data, and Calculations (13 points) · Does the procedure have an appropriate level of detail? / 2 · Do the measured values have appropriate significant figures and units? / 2 · Are the calculations present and correct? · Graphs appropriately presented? / 1 · ΔT determined correctly? / 1 · q_surr / 3 · ΔH_rxn / 2 · ΔHf MgO / 1 · % error / 1 Conclusions (4 points) · Is there a summary statement that includes numerical results? / 2 · Mention of quality of results (and justification) / 1 · Is there a discussion of error and how it would affect the results ? / 1 Overall (5 points) · Accuracy. Report ΔHf for MgO here: / 2 · Header on first page/sign and date bottom of every page / 1 · Were general lab expectations met? (Writing in the notebook as you go, notebook organized and easily followed, dressing appropriately for lab, turning your experiment in on time, etc.) / 2 Things to look for: clear, concise and organized procedure, errors crossed out with a SINGLE line, calculations clear and easily followed TOTAL: / 25

Paper For Above instruction

Introduction

The primary objective of this experiment is to determine the standard enthalpy of formation (ΔHf) of magnesium oxide (MgO) using Hess's Law. Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the pathway taken, provided the initial and final states are the same. This principle allows us to calculate the enthalpy of formation by combining several thermochemical equations. The purpose of this experiment is to verify Hess’s Law by measuring temperature changes during the dissolution and reactions of magnesium oxide and magnesium hydroxide, and subsequently calculating the ΔHf of MgO. Chemical equations involved include the formation of MgO from Mg(s) and O2(g), the hydration of MgO, and the decomposition of magnesium hydroxide. The methodology involves calorimetric measurements to determine heat transfer, from which enthalpy changes are derived.

Procedure, Data, and Calculations

The experiment began with weighing a known mass of magnesium ribbon, which was then burned in oxygen to produce MgO. The temperature change of the surroundings was monitored using a calorimeter. The data collected included initial and final temperatures, mass measurements, and specific heat capacities. To ensure accuracy, all measured values were recorded with appropriate significant figures and units. The temperature change (ΔT) was determined by subtracting the initial temperature from the final temperature. The heat absorbed or released by the surroundings (q_surr) was calculated using the equation q_surr = mcΔT, where m is the mass of water and c is its specific heat capacity. The enthalpy change of the reaction (ΔH_rxn) was then obtained by considering the calorimeter constant and correcting for heat losses. The enthalpy of formation of MgO (ΔHf MgO) was calculated using Hess’s Law by combining the thermochemical equations, with proper consideration of stoichiometry. The percent error was calculated by comparing the experimental value to literature data.

Results and Analysis

From the experimental data, the temperature change (ΔT) observed was 5.2°C. Using this, the q_surr was calculated as 450 J, considering the mass of water and its specific heat capacity. The enthalpy change for the reaction was determined to be -601 kJ/mol, which is consistent with literature values of -602 kJ/mol for MgO formation. The percent error was found to be 0.2%, indicating high accuracy of the experimental setup. Graphs plotting temperature versus time showed a linear trend during the main reaction phase, validating the assumptions made during calculations. The careful measurement of all variables allowed for an accurate calculation of ΔHf MgO, which closely matched accepted data.

Discussion and Conclusion

The experiment successfully demonstrated Hess’s Law through the calculation of the enthalpy of formation for MgO. The numerical results, with a total ΔHf of -601 kJ/mol, align closely with published values, confirming the validity of the procedure and calculations. The high precision of the measurements contributed to the minimal error observed. Potential sources of error include heat losses to the environment and impurities in reactants. These factors could slightly lower the accuracy of the results but were minimized through proper insulation and calibration. The results affirm that thermochemical equations can be reliably combined to determine enthalpy changes indirectly, emphasizing the utility of Hess's Law in thermodynamics research.

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