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Unformatted text preview: Uni t 7 – Thermodynamics Thermochemistry: the study of heat changes that occur during physical and chemical changes Temperature (T): a measure of the average kinetic energy of all the particles in a substance Heat (q): the sum total of all the kinetic energies of all the particles in a substance Heat flows from hot to cold Units for heat include the joule and the calorie 1 calorie = 4.184 joule 1 Calorie (food calorie) = 1000 cal or 1 kcal Calorimetry: the measurement and study of heat flow In an insulated container, the amount of heat lost by one system is equal to the amount of heat gained by the other (q lost = - q gained ) a simple ‘coffee-cup’ calorimeter All calorimeters have the following in common: insulated container: to protect the experiment from gaining heat from or losing heat to the atmosphere thermometer: to measure T initial and T final stirring mechanism: to make sure that there are no ‘hot spots’ heat absorption medium (usually water): high C p , easy to get reaction vessel: usually only used in bomb calorimeters a high-pressure ‘bomb’ calorimeter q lost = - q gained Chip Shea 1 11/5/2011 This relationship means that heat lost (produced by) the reaction in an exothermic process is gained (absorbed by) the water; in an endothermic process, the heat is lost by the surroundings (the water) and gained by the reaction. The formula used to determine heat loss or gain is q = heat absorbed or released q = mC p ∆T where m = mass of substance, g C p = specific heat capacity of substance ∆T = T final (°C)- T initial (°C) Example: How much heat must a 4110g block of aluminum at room temperature gain in order to reach the melting point of aluminum? Example: A 20.0g piece of metal at 172.8°C is plunged into 125 mL of water at 20.0°C. The temperature of the water and metal equilibrate at 23.0°C. What is the specific heat capacity of the metal? What is the metal? q lost = - q gained q metal = - q water mC p-metal ∆T = - mC p water ∆T Example: When 42.5g of ammonium nitrate is dissolved in 60.0g water in a calorimeter, the temperature drops from 25.0°C to 3.5°C. How much heat is released by the water? Phase equilibrium: a dynamic, steady-state where the rate of a phase change is equal to the rate of the reverse change During a phase change, the temperature remains constant because the kinetic energy remains constant as the potential energy changes (to form or break bonds/imf’s). Once the phase change is complete, the substance can increase (or decrease) in temperature until the next phase change is reached. A) the solid is heating, kinetic energy increases ( as temp increases), potential energy is constant B) the solid is melting, kinetic energy is constant as potential energy increases C) the liquid is heating, kinetic energy increases ( as temp increases), potential energy is constant D) The liquid is vaporizing, kinetic energy is constant as potential energy increases E) the vapor is heating, kinetic energy increases ( as temp increases), potential energy is constant Chip Shea 2 11/5/2011 E)...
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This note was uploaded on 11/05/2011 for the course ECON 101 taught by Professor Graham during the Spring '08 term at N. Colorado.
- Spring '08