Chapter 06 - Thermochemistry I

Chapter 06 - Thermochemistry I - Chapter 6 Chapter 6...

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Unformatted text preview: Chapter 6 Chapter 6 Thermochemistry: Energy Flow and Thermochemistry: Energy Flow and Chemical Change I Chemical Change I First Law of Thermodynamics First Law of Thermodynamics Law of Energy Conservation Law of Energy Conservation When a system gains energy, the surroundings loose energy When a system looses energy, the surroundings gain energy Energy can be converted from one form to another (work heat, kinetic potential, etc) But: energy cannot be created or destroyed E universe = E system + E surroundings = 0 Units of energy calorie (cal) = energy to raise temperature of 1 g of water from 14.5 o C to 15.5 o C Joule (J) = 0.239 cal food calories: Cal = 1000 cal = 1 kcal Forms of Energy Forms of Energy All energy is potential or kinetic energy (Chapter 1) Potential energy depends on distance Stone at some distance above the ground Kinetic energy depends on velocity Stone falling and hitting the ground Conversion of potential energy to kinetic energy Effect of falling stone on the ground Pebbles, dirt moving work Warming up of ground heat Other forms of energy Nuclear, chemical,electrical energy at molecular level Transfer of energy from one object to another = work + heat the surroundings A Chemical System and Its Surroundings A Chemical System and Its Surroundings System What we focus on for our energy considerations: pressure, volume, temperature, etc. Surroundings What is around the system the system System, Surroundings and Energy System, Surroundings and Energy Change in energy can be measured in the form of heat released or heat absorbed by the system- exothermic reaction releases energy increases temperature of surroundings- endothermic reaction absorbs energy decreases temperature of surroundings Thermodynamics Thermodynamics Science of energy transformation the study of energy, work, and heat the laws of thermodynamics help understand why some chemical reactions occur and others do not Dissolving NaOH in water NaOH (s) + H 2 O (l) Na + (aq) + OH- (aq) + heat T or T >0 Reaction between HCl and NaOH HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) + heat T or T >0 Dissolving NaCl in water NaCl (s) + H 2 O (l) + heat Na + (aq) + Cl- (aq) T or T <0 Reaction between N 2 and H 2 N 2 (g) + H 2 (g) + heat NH 3 (g) reaction so slow that it does not happen under standard conditions Question:- Where does the energy come from? A-B + C-D A-D + C-B These bonds must be broken: requires energy These bonds are formed: releases energy When the energy required to break bonds is less than the energy released when bonds are formed: net release of energy Exothermic reaction reaction mixtures heats up When the energy required to break bonds is more than the energy released when bonds are formed: absorption of external energy...
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This note was uploaded on 04/13/2008 for the course CHEM 1311 taught by Professor Baishakhidas,ms. during the Spring '08 term at Alamo Colleges.

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Chapter 06 - Thermochemistry I - Chapter 6 Chapter 6...

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