Chapter 06 notes S10

Chapter 06 notes S10 - Chapter Six Energy Relationships in...

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1 Chapter Six Energy Relationships in Chemical Reactions
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2 Questions and Problems: Pages 198-204 Definitions: 1-3 Energy changes in a chemical reaction: all First law of thermodynamics: 11,12 and all problems Enthalpy of chemical reactions: All as needed for understanding Calorimetry: All as needed for understanding Standard enthalpy of formation:All as needed for understanding
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3 Energy (E): Capacity to Do Work Radiant energy Energy from the sun earth’s primary energy source Thermal energy Energy associated with molecular movement Chemical energy Energy stored in chemical bonds Nuclear energy Energy stored in the nucleus of an atom Potential energy Energy available due to an object’s position
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4 Thermochemistry Study of heat change in chemical reactions System: The part of the universe being studied Closed: Only energy exchange with surroundings Isolated: No energy or matter exchange- rare Surroundings: Part of the universe not being studied
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5 Heat Transfer in a System Heat, q: Transfer of energy due to temperature difference Exothermic Reaction: System gives off heat Ex: Methane Burning: CH 4 + O 2 → CO 2 + H 2 O Bonds stronger in CO 2 and H 2 O molecules than in CH 4 + O 2 Heat goes from system to surroundings Endothermic Reaction: System gains heat Ex: Ice Melting: H 2 O (s) → H 2 O (l) Energy needed to break attractions between H 2 O molecules Heat goes from surroundings into the system
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6 Thermodynamics
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7 Thermodynamics Thermodynamics: State of a system: Describes specific conditions defined by state functions Measurement of these macroscopic properties State functions: Properties defined by Δ final - Δ initial values only Composition, temperature, pressure, energy, volume Path functions: Δ final - Δ initial values vary by how process is done Heat, work: interdependent variables
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8 State of a system: Carry a bowling ball to top of mountain Increase potential energy, can now fall back down Energy of ball at top is identical for all paths State functions: Height of mountain Path functions: Total steps taken Time to top
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9 First Law of Thermodynamics Energy can be converted from 1 form to another but cannot be created or destroyed Δ E system + Δ E surroundings =0 Internal Energy of System: E system =E kinetic + E potential Kinetic energy (molecular motion) Translational, rotational and vibrational Potential Energy (stored energy in chemical bonds) Attractions/repulsions between atoms and molecules Cannot separate two types of energy For system: Δ E system = E final - E initial For chemical reactions: Δ E reaction = E products - E reactants
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10 Work and Heat Δ E system = q + w Work (w) = force x distance = -P Δ V Negative work (-w): System loses energy to surroundings Positive work (+w): System gains energy from surroundings Work (w) = -P Δ V Δ V = V f -V i For this situation: +V -w
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This note was uploaded on 02/25/2010 for the course CHM 101 taught by Professor Geldart during the Spring '07 term at Rhode Island.

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Chapter 06 notes S10 - Chapter Six Energy Relationships in...

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