Calorimetry - Experiment 10 Revision 1.1 Calorimetry and...

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Experiment 10 Revision 1.1 Calorimetry and Thermochemistry Learn how to measure Heat flow. Learn about the Specific Heat of substances. Learn about Exothermic and Endothermic chemical reactions. Learn about the Enthalpy function. In this laboratory exercise we will measure the Specific Heat of a metal and determine the Enthalpy of Reaction ( Δ H) for two solvation processes; the solvation of Magnesium Sulfate Heptahydrate and the solvation of its Anhydrous salt. These measured Enthalpy changes will allow us to determine the amount of heat required to dehydrate the hydrated salt. Each of these three experiments will require us to measure the amount of Heat (q) produced or absorbed during the process or chemical reaction. This measurement will be performed within a Calorimeter. Heat Flow (q) is generally thought of as the transfer of thermal energy from a "hot" object to a "cold" object. The warming of a soft drink on a hot day is a typical example of this transfer. The “hot” Air loses thermal energy and the “cold” soft drink gains it. However, nearly all chemical reactions involve the release or absorption of heat as well. The burning of Coal is a dramatic example of a chemical reaction in which a great deal of heat is released. C(s) + O 2 (g) CO 2 (g) + Heat Thermal energy stored in the bonds of the reactants is transferred to the cold surroundings as the reaction proceeds. Dissolving the salt Potassium Nitrate in water is an example of a chemical reaction in which heat is absorbed. As the salt dissolves, the solution becomes quite cold. KNO 3 (s) + Heat K + (aq) + NO 3 - (aq) This type of reaction is the basis for chemical cold packs used to treat minor injuries. In many instances, this transfer of Energy, measured in units of calories or Joules, can be quantified by observing the changes in temperature of the respective objects as heat flows between them. The change in temperature ( t) of a given substance as heat flows into or out of the substance will depend on the magnitude of the heat flow (q), the mass of the substance (m), and the "ability of the substance to absorb or release heat". The ability of a substance to absorb or release heat is simply the Specific Heat (sp) of the substance. Substances with large specific heats are "heat sponges" and can absorb a considerable amount of heat without a significant change in temperature. Water has a fairly high specific heat. Substances with small specific heats are "heat conductors." Metals are good conductors of heat and so have small specific heats. In terms of the temperature change, the heat flow is given as:
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q = sp x m x t (Eq. 1) Substance sp (cal/g o C) Graphite 0.170 Gold 0.0308 Water 1.00 Ethanol 0.588 Wood 0.421 Cement 0.210 Glass 0.201 The measurement of heat flows during physical and chemical processes is called Calorimetry .
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Calorimetry - Experiment 10 Revision 1.1 Calorimetry and...

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