EXP 9. CALORIMETRY AND HESS’S LAW: FINDING ΔHrxn FOR THE COMBUSTION OF MAGNESIUM

I. Introduction1. How is heat formation and transfer studied in chemical processes? Briefly explain in terms of the regions (system and surrounding) of interest and heat energy flow (exothermic/endothermic).2. What is enthalpy? What is needed in order to calculate the enthalpy of a chemical reaction? How is it calculated?3. What is specific heat? Briefly explain its application in heat transfer.4. What were the main objectives of the experiment? Why were calorimetry and Hess’s law used in achieving the experimental objective?5. How was the enthalpy of reaction determined using a calorimeter? What is a calorimeter constant?6. What is Hess’s law? Why is it useful in this experiment?7. What were the chemical and procedural hazards in this experiment and the safety precautions observed to avoid the risk of these hazards?
II. Results Analysis
A. Data and CalculationsYou may summarize the observations/answers and equations in the datasheet or include them as part of the Discussion section.
B. Discussion
Part IHeat Capacity of the Cup Calorimeter1. What is a calorimeter?2. Why is it necessary to determine the heat capacity of the calorimeter in this experiment? Where is it important? Briefly explain.3. How is the heat capacity of the calorimeter determined? Explain briefly with emphasis on some techniques to achieve accuracy of results.4. Using the graph, what happened to the temperature of the cold water after adding the hot water? Briefly explain in terms of the heat released or absorbed.5. What was the heat capacity of the calorimeter? How was this calculated? Show all work.Part II Determination of the Heat of Reaction of Mg in HCl1. What reaction was tested in this portion of the experiment? Briefly explain the procedure.2. Using the graph, what happened to the temperature of 1 M HCl after adding the Mg ribbon? Is the reaction exothermic or endothermic?3. What was the enthalpy of the reaction? How was this calculated? Show all work with balanced thermochemical equation.Part III Determination of the Heat of Reaction of MgO in HCl1. What reaction was tested in this portion of the experiment? Briefly explain the procedure.2. Why is it important to thoroughly clean the calorimeter between tests?3. Why is it important to stir the solution continuously?4. Using the graph, what happened to the temperature of 1 M HCl after adding the MgO? Is the reaction exothermic or endothermic?5. What was the enthalpy of the reaction? How was this calculated? Show all work with balanced thermochemical equation.
PART IV Determination of the Enthalpy of Combustion of Mg Using Hess’s Law1. Using the information from Parts II and III and in conjunction with the Hess’s Law, what is the enthalpy for the combustion of one mole of magnesium in oxygen? Show all work with balanced thermochemical equation.2. What is the theoretical enthalpy of this reaction? What was your percent error? Briefly explain the accuracy of your results (and/or possible causes of error, if applicable) based on the percent error.III. Conclusions
1. What lab technique was used in collecting experimental data and how was Hess Law used to manipulate those data to achieve the experimental goal?2. What reactions were studied in this experiment? Briefly summarize the results.3. What does the enthalpy of a reaction indicate about each reaction in Part B and C, and the final reaction?4. Based on your results and calculated percent error, what can you infer from the possibility of using calorimetry and Hess’ Law in determining the enthalpy of a highly exothermic reaction?5. How were accuracy and precision achieved in this experiment? How could they be improved in the future?6. What is the application of calorimetry and Hess’s Law in the study of matter? Give an example of a practical application.