chapter05 - 5.1 Energy and Energy Changes Energy is...

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5.1 Energy and Energy Changes Energy is involved in all types of physical and chemical changes Energy: the capacity to do work Forms of Energy Kinetic - energy of motion – Represented by E k = 1/2 mu 2 – “m” is mass – “u” is velocity – Thermal - one form of kinetic energy associated with random motion; we measure this energy with a thermometer Forms of Energy Potential - energy of position – Chemical - energy stored within structural units of chemical substances – Electrostatic - energy resulting from interaction of charged particles – Electrostatic energy represented by: Q = charge d = size E el Θ 1 2 δ Law of Conservation of Energy • Energy may be converted from one form to another, however, the total amount of energy in the universe is constant • Example: a chemical reaction (potential) gives off heat (thermal)
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Energy Changes in Chemical Reactions • System - often the reacting vessel in the chemistry lab – A beaker of NaOH and HCl • Surroundings - the rest of the universe – When heat is given off from the beaker, the energy is transferred out of the system Thermochemistry • The study of heat (transfer of thermal energy) in chemical reactions Exothermic - transfer of heat from the system to the surroundings (Hindenburg) r H + (aq) + OH - (aq) b H 2 O (l) + energy 2H 2( g ) + O 2( g ) 2H 2 O ( l ) + energy The energy released is 285.8 KJ/mol of water formed Thermochemistry Endothermic - the transfer of heat from the surroundings to the system energy + 2HgO ( s ) 2Hg ( l ) + O 2( g ) Endothermic vs. Exothermic
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Units of Energy Joule (J) - the SI unit – The amount of energy possessed by a 2 kg mass moving at a speed of 1 m/s E k = 1/2mu 2 = 1/2(2 kg)(1 m/s) 2 = 1 kg · m 2 /s 2 = 1 joule 1 J = 1· N m (when discussing force) Units of Energy Calorie (cal) - commonly used with food labels • 1 calorie = 4.184 J • 1000 cal = 1 Calorie • Food calories are really 1000 calories in chemistry! Calculations with KE Calculate the kinetic energy of a neon atom moving at a speed of 98 m/s. It has a mass of 3.352 x 10 -26 kg E k = 1/2mu 2 = 1/2 (3.352 x 10 -26 kg)(98 m/s) 2 = 1.610 x 10 -22 J 5.2 Introduction to Thermodynamics • 3 types of systems: open (exchange of mass and energy), closed (exchange of energy) and isolated (no exchange)
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State Functions State functions depend only on initial and final states of the system and not on how the change was accomplished. • Energy (E), pressure (P), volume (V) and temperature (T) are all state functions First Law of Thermodynamics • Energy can be converted from one form to another but cannot be created or destroyed – Sound familiar? (the Law of Conservation) r Internal Energy • Demonstrate First Law by measuring the change in energy of a system between final and initial states Δ U = Δ U f - Δ U i Internal energy : 2 components Kinetic energy - molecular motion Potential energy - attractive/repulsive
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This note was uploaded on 03/03/2010 for the course CHEM CHEM400 taught by Professor Stewart during the Spring '10 term at American River.

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chapter05 - 5.1 Energy and Energy Changes Energy is...

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