lecture on exp 3

lecture on exp 3 - 1 Experiment #3 Thermochemistry...

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Experiment 3 Thermochemistry 1 Experiment #3 1 Thermochemistry Thermochemistry 2 Thermochemistry is the study of heat changes that take place in a change of state or a chemical reaction Heat energy is either absorbed or released Exothermic process: releases heat energy Endothermic process: absorbs heat energy Heat Flow 3 System : substance or mixture undergoing a change. Part of the universe of interest. Ex: reactants & products of a chemical reaction Surroundings : everything in vicinity of system Ex: solvent, container, atmosphere about the reaction (i.e., rest of the universe) Universe : system and surroundings together Equation describing heat flow between system and surroundings: q system = - q surroundings
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Experiment 3 Thermochemistry 2 Endothermic/Exothermic Reactions 4 Exothermic reaction : system releases heat to System Endo (into) Exo (out of) : system releases heat to surroundings, T of surroundings increases & reaction container feels warm to the touch Endothermic reaction : system absorbs heat from surroundings, T of surroundings decreases & reaction container feels cold to the touch Enthalpy of Reaction, H 5 Enthalpy (H): measure of the heat content of a substance at constant pressure Enthalpy change ( H): difference between the enthalpy of the products and the enthalpy of the reactants Exothermic reactions: H < 0 Endothermic reactions: H > 0 Calorimetry 6 In the laboratory, heat changes in physical and chemical processes are measured with a calorimeter Calorimeter: Device used to measure T changes in Thermochemistry (container that traps heat) Calorimeters must isolate the system of interest from the environment Must prevent heat transfer to outside Must not absorb heat from system (as much as possible)
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Experiment 3 Thermochemistry 3 Heat Capacity 7 The amount of heat energy required to raise the temperature of a substance by 1 K (1°C) Two types of Heat Capacity: Specific Heat Capacity (c): units are J/K g Molar Heat Capacity (C): units are J/K mol The equation for calculating the heat change (q) is given by: q = m.c. T or q = n.C. T ( m = mass, n = # moles, T = T final –T initial ) At constant pressure (as in Expt. 3):
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This note was uploaded on 07/24/2010 for the course CHEM CHEM 6BL taught by Professor Berniolles during the Summer '08 term at UCSD.

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lecture on exp 3 - 1 Experiment #3 Thermochemistry...

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