Chapter-7 - CHAPTER 7 THERMOCHEMISTRY energy in chemical...

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1 CHAPTER 7 THERMOCHEMISTRY • energy in chemical reactions • thermal energy • 1 st law of thermodynamics • enthalpy change ( H rxn ) Hess’s law standard enthalpy of formation ( H f ° ) calorimetry (Lab #3)
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2 thermochemistry = study of energy/heat transfer during a chemical reaction does a reaction produce or require energy? how much ? 1 st law of thermodynamics under what conditions is a reaction possible? 2 nd law of thermodynamics (Chap. 19)
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3 • energy in chemical reactions loud quiet 2 H 2 + O 2 2 H 2 O Ag + + I - AgI emit light absorb light 2 Mg + O 2 2 MgO H 2 + Cl 2 2 HCl release heat absorb heat CH 4 + 2 O 2 CaCO 3 CaO + CO 2 CO 2 + 2 H 2 O
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4 conservation of mass and energy 3 NaN 3 (s) Na 3 N(s) + 4 N 2 (g) azide nitride N 3 - N 3- chemical energy reactants products energy release
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5 what is chemical energy ? potential + thermal (kinetic) energy energy atomic and molecular motion - depends on T attractive/repulsive interactions between atoms/ions/molecules. .. includes chemical bonds
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6 Thermal energy increases with T and amount of substance relates to physical state T (°C) 100 0 thermal energy (heat content) steam (g) water (l) ice (s) H 2 O
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7 thermal energy from molecular/atomic motion translation rotation vibration solid liquid gas T
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8 transfer of thermal energy (heat transfer) through collisions (gas, liquid) vibrations (solid) spontaneous from hot to cold T hot cold equilibrium
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9 1 st law of thermodynamics the internal energy (U) of an isolated system is constant system vs. surroundings object(s) under study “rest of the universe” isolated system: no exchange of matter or energy with surroundings
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This note was uploaded on 02/17/2011 for the course ENGINEERIN chem 1e03 taught by Professor Aaa during the Spring '11 term at McMaster University.

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Chapter-7 - CHAPTER 7 THERMOCHEMISTRY energy in chemical...

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