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32 Cards in this Set
- Front
- Back
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Thermodynamics
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A branch of chemistry and physics which studies changes in energy
- studies energy transfers and energy conversions |
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System
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Whatever is being studied
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Surroundings
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Everything outside of the system
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Universe
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System + Surroundings
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Chemical thermodynamics
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interested in the flow of energy between the system and the surroundings
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Standard conditions
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25 C and 100.0 kPa
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First Law of Thermodynamics
(Law of Conservation of Energy) |
In any chemical or physical change, energy isn't created or destroyed. It can be transferred or transformed into another type of energy
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Systems naturally move to a state of _________ energy.
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lower
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Entropy
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Disorder
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Second Law of Thermodynamics
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Disorder in a substance or a system is equal to the sum of the entropy of the system and the entropy of the surroundings
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Total entropy is always greater than ______.
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zero
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Natural systems move towards states of _______ disorder.
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higher
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State function
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a process whose value is independent of the path taken to reach it
- the value depends only on the initial and final values |
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Change in altitude is/is not a state function and distance is/is not a state function
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change in altitude is a state function and distance is not a state function
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Examples of state functions include:
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temperature, enthalpy, entropy, and free energy
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Enthalpy
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AH
- the heat content of a substance or a system -different chemical bonds and bond arrangement store different amounts of energy |
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What is the reference point for enthalpy?
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a free element in its most stable state at standard conditions has zero enthalpy
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Exothermic
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Heat flows from the system to the surroundings (feels warmer)
H2 + 1/2O2 --> H2O |
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Exothermic have positive/negative values for enthralpy
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negative
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Exothermic reactions tend to be spontaneous/nonspontaneous
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spontaneous
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Endothermic
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Heat flows from the surroundings into the system
H2O --> H2 + 1/2O2 |
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Endothermic have positive/negative values for enthralpy
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positive
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Endothermic reactions tend to be spontaneous/nonspontaneous
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nonspontaneous
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Heat of formation
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the change in enthalpy when 1 mole of a compound is formed from the free elements at standard conditions
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Because the elements AH is equal to zero, the AH of the reaction is the _________of the _________.
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enthalpy, compound
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Hess's Law
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the change in enthalpy for a reaction is equal to the sum of a series of reactions that add up to the overall reaction
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What is the symbol and unit for entropy?
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AS, J
-------- mol x K |
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What is the reference point for entropy?
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a substance at absolute zero
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What are the 5 factors that affect entropy?
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1. changing temp.
2. change of phase 3. assuming no change of state, # of gas particles in a reaction 4. dissolving a gas in a liquid -AS 5. dissolving a solid in a liquid +AS |
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Free energy
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-determines spontaneity
-Jason Willard Gibbs -indicated the amount of useful work we can get out of a physical or chemical process OR the amount of work required to drive a spontaneous reaction |
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characteristics of +AG
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nonspontaneous --> work is required to drive the reaction --> endergonic
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characteristics of -AG
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spontaneous --> energy is produced to do work --> exergonic
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