Lab 4 - Krista Fitzsimmons 20332134 Calorimetry: Enthalpy...

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Krista Fitzsimmons 20332134 Calorimetry: Enthalpy of Neutralization To: Jeff Sparks By: Krista Fitzsimmons 20332134 Partner: Karli Dougan Section 003
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Krista Fitzsimmons 20332134 Calorimetry: Enthalpy of Neutralization Introduction Calorimetry is simply described as the process of measuring the heat gain or loss in an isolated system and a calorimeter is the apparatus used to define this measurement. The heat that is being transferred during this laboratory is called the enthalpy (H) and q is the symbol for heat. During this laboratory, the change in enthalpy is equal to the negative heat (), therefore if the reaction is exothermic then ΔH < 0 and q is positive and if it is endothermic ΔH > 0 and q is negative. The equation for heat is (where m is the mass of the substance, c is the specific heat capacity and is the change in temperature). There are diverse ways in performing a calorimetry experiment; the most common are using a bomb calorimeter and the other, a coffee cup calorimeter. A bomb calorimeter consists of a completely isolated system placed in water (which accounts for the surroundings), a thermometer and a stirrer. Another instrument commonly used is the coffee cup calorimeter, which involves a Styrofoam cup (which is a good insulator), a Styrofoam cover/ lid, a stirrer and a thermometer. The bomb calorimeter demonstrates more accurate results and obtains constant volume whereas the coffee cup calorimeter is less accurate and obtains constant pressure; constant pressure due to the fact that the atmospheric pressure is equal to the internal pressure. Although measuring the thermometer can identify the heat transferred, this temperature will not be completely accurate considering that heat is contributing not only to the thermometer but to the walls of the Styrofoam cup and the calorimeter as well. During this laboratory, the coffee cup calorimeter is used to measure the enthalpy change since it’s easier and more realistic to perform. Once the apparatus is set up, the thermometer measures the change in heat of the acid and base mixture. Throughout the experiment, sodium hydroxide is neutralized with hydrochloric acid, nitric acid, phenol and an unknown hydrochloric acid in four separate neutralizations. Strong electrolytes, such as HCl and dissociate completely into ions whereas weak electrolytes, such as phenol dissociate partially in ions. Depending on the strength of the electrolyte, the enthalpy change will differ; it will either be smaller or larger. While performing this
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Krista Fitzsimmons 20332134 experiment and identifying the enthalpy, it can be determined which type of electrolyte transfers more energy. The purpose of this calorimetry experiment is to identify the unknown
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This note was uploaded on 02/21/2010 for the course CHEM 120L taught by Professor Sue during the Fall '09 term at Waterloo.

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Lab 4 - Krista Fitzsimmons 20332134 Calorimetry: Enthalpy...

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