Calorimetry 1: The Enthalpy of Formation of MgO Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Goals In this experiment you will determine the standard molar enthalpy of formation of magnesium oxide, MgO. This is given the symbol and is the enthalpy change for the reaction Mg(s) + 1/2 O2(g) MgO (s). You will determine the value of for one mole of MgO by using Hess's Law and the enthalpy changes of several other solution reactions that are more easily performed and observed. Having trouble viewing the slideshow? Help is here. To Learn or Review Heat, Heat Capacity, and Calorimetry Zumdahl, pp. 347-355,362-365 Enthalpy and Hess's Law Zumdahl, pp. 354-355, 369-371 Standard Enthalpy of Formation Zumdahl, pp. 372-378 Introduction Some chemical reactions are endothermic and proceed with absorption of heat while others are exothermic and proceed with an evolution of heat. The magnitude of the heat change is determined by the particular reaction of interest, as well as by the amount of reactants consumed. The change in enthalpy, H, is the heat (qp) associated with a reaction at constant pressure, in which no work is involved other than "expansion work" or "compression work", associated with volume changes of the system: qp = H The value of H is a characteristic and important property of the reaction; convenient sets of units for the molar enthalpy are kJ mol-1 or kcal mol-1. These units emphasize that enthalpy is an extensive property, which depends upon the amount of reactants consumed. Enthalpies of reaction (often called "heats of reaction") are usually tabulated for reactions occurring isothermally (at constant temperature) at, for example, 25 °C. Since enthalpy is a state function, it is not necessary for the reaction mixture to stay at constant temperature during the entire reaction. So long as the final temperature T2 equals the initial temperature T1, the H is identical to the isothermal value. Even T2 = T1 is not always an easy condition to satisfy in the laboratory. In this experiment, you will use a solution calorimeter, to determine enthalpies of reaction. Go to Chemistry and Background for more information.
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