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Study of energy and its relationship to macroscopic properties of chemical systems.
Only valid for systems composed of large numbers of molecules. |
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| Exchange both mass and energy with surroundings. |
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| Exchange energy but not mass with the surroundings |
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| Exchange neither mass nor energy with surroundings. |
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Describe extensive and intensive properties.
Pathway independent. |
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| Proportional to the size of the system |
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| Independent of the size of the system |
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Do not describe the state of a system, but depend upon the pathway used to achieve any state.
(Ex: Work and Heat) |
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| How to transfer energy between systems |
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| Transfer of heat through molecular collisions |
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| Thermal energy transfer via fluid movements |
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| Thermal Energy transfer via EM waves. |
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At constant pressure it is equal to the product of pressure and the change in volume.
w= PΔV
If volume remains constant, no PV work is done at all. |
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| The First Law of Thermodynamics |
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Definition
Energy of a system and its surrounds are always conserved.
ΔE = q + w (work on a system)
ΔE = q - w (work done by system) |
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| Second Law of Thermodynamics |
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| Heat cannot be changed completely into work in a cylindrical process. |
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Collective energy of molecules measured on a microscopic scale (includes vibrational , rotational, translational, electronic, intermolecular potential, and rest mass energy)
All the possible forms of energy on a molecular scale. |
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| Average Kinetic Energy of a single molecule in any fluid: |
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| Virtually all physical properties change with... |
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Extra capacity to do PV work [in Joules].
H≡U+PV
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ΔH=ΔU+PΔV
Enthalpy values vary depending on the standard state. |
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| Standard state for enthalpy change |
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Definition
An element in SS is arbitrarily assigned an enthalpy value of 0J/mol
(at 25oC and 1 atm/750torr/105Pascals) |
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| Standard Enthalpy of Formation, ΔHof |
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Definition
| Change in enthalpy for a reaction that creates one mol of that compound from its raw elements in standard state. |
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The change in enthalpy from reactants to products
ΔHoreaction=ΔHfoproducts - ΔHforeactants
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| The sum of enthalpy changes for each step is equal to the total enthalpy change regardless of the path chosen. |
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| Release heat, making reaction system hot (-ΔH) |
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| Absorb heat, making the system cold (+ΔH) |
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Nature's tendancy towards disorder.
Degree of randomness.
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| Second Law of Thermodynamics |
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Entropy of a system will never decrease.
Entropy is the driving force that will determine whether or not a reaction proceeds.
If entropy of a system can decrease only if the surroundings of that system increase by an amount greater than or equal to the decrease. |
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| Entropy increases with... |
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| number, volume and temperature. |
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| Third Law of Thermodynamics |
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| Zero entropy is assigned to any pure substance at absolute zero. |
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ΔG=ΔH-TΔS
Only good for constant temperature reactions.
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