Chem lab 9 - Experiment 9 The Heat of Ionization of a Weak...

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Experiment 9 The Heat of Ionization of a Weak Acid
Purpose In this experiment, the heat of ionization of a weak acid was investigated. According to the first law of thermodynamics, the total internal energy is equal to q, the heat energy gained by the system and w, the work done on the systemL: ∆E = q + w At constant pressure the equation becomes ∆E = q p - P∆V where q p is the change in heat content of the system at constant pressure. This is the change in enthalpy. ∆H = H final – H initial = q p = ∆E + P∆V In this experiment, a Styrofoam cup calorimeter was used to measure heats of reaction since it is a reasonably good insulator. The temperature change from a reaction inside the calorimeter can be measured, since the total heat capacity of the system (the calorimeter and its contents) are known, the change in heat content can be calculated with the formula: q p = C p ∆T where C p is the total heat capacity of the system at constant pressure and ∆T = T final - T initial The heat capacity of the calorimeter is determined experimentally to measure the temperature change resulting from mixing inside the calorimeter two known quantities of water initially at different temperatures. If there is no energy loss then, | heat lost by hot water | = | heat absorbed by cold water | + | heat absorbed by the calorimeter| . However, since the calorimeter is not perfect insulator there will be some sources of error. To correct for these errors, changes in temperature are determined graphically. In studying chemical reactions it is important for the mixing of two reacting solutions to be performed very quickly so that the temperature can be measured right away and prevent any further heat leakage. This allows for the most accurate possible results when plotting temperature versus time. In the graph, the portion of the initial period required for the system to mix

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