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MCAT General Chemistry Review 3
Lesson 3 - Thermodynamics
33
Chemistry
Not Applicable
06/25/2011

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Term
Thermodynamics
Definition

Study of energy and its relationship to macroscopic properties of chemical systems.

Only valid for systems composed of large numbers of molecules.

Term
Open system
Definition
Exchange both mass and energy with surroundings.
Term
Closed System
Definition
Exchange energy but not mass with the surroundings
Term
Isolated system
Definition
Exchange neither mass nor energy with surroundings.
Term
State Functions
Definition

Describe extensive and intensive properties.

Pathway independent.

Term
Extensive Properties
Definition
Proportional to the size of the system
Term
Intensive
Definition
Independent of the size of the system
Term
Path function
Definition

Do not describe the state of a system, but depend upon the pathway used to achieve any state.

(Ex: Work and Heat)

Term
How to transfer energy between systems
Definition
Heat and Work
Term
Conduction
Definition
Transfer of heat through molecular collisions
Term
Convection
Definition
Thermal energy transfer via fluid movements
Term
Radiation
Definition
Thermal Energy transfer via EM waves.
Term
PV Work
Definition

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.

Term
The First Law of Thermodynamics
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)

Term
Second Law of Thermodynamics
Definition
Heat cannot be changed completely into work in a cylindrical process.
Term
Internal Energy, U
Definition

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.

Term
Average Kinetic Energy of a single molecule in any fluid:
Definition
KEavg=(3/2)kT
Term
Virtually all physical properties change with...
Definition
Temperature
Term
Enthalpy
Definition

Extra capacity to do PV work [in Joules].

H≡U+PV

 

 

Term
Change in Enthalpy, ΔH
Definition

ΔH=ΔU+PΔV

Enthalpy values vary depending on the standard state.

Term
Standard state for enthalpy change
Definition

An element in SS is arbitrarily assigned an enthalpy value of 0J/mol

(at 25oC and 1 atm/750torr/105Pascals)

Term
Standard Enthalpy of Formation, ΔHof
Definition
Change in enthalpy for a reaction that creates one mol of that compound from its raw elements in standard state.
Term
Heat of reaction
Definition

The change in enthalpy from reactants to products

ΔHoreaction=ΔHfoproducts - ΔHforeactants

Term
Hess's law
Definition
The sum of enthalpy changes for each step is equal to the total enthalpy change regardless of the path chosen.
Term
Exothermic Reaction
Definition
Release heat, making reaction system hot (-ΔH)
Term
Endothermic Reaction
Definition
Absorb heat, making the system cold (+ΔH)
Term
Entropy, S
Definition

Nature's tendancy towards disorder.

Degree of randomness.

 

Term
Second Law of Thermodynamics
Definition

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.

Term
Entropy increases with...
Definition
number, volume and temperature.
Term
Third Law of Thermodynamics
Definition
Zero entropy is assigned to any pure substance at absolute zero.
Term
Gibbs Free Energy, ΔG
Definition

ΔG=ΔH-TΔS

Only good for constant temperature reactions.

Term

ΔG<0

Definition
Spontaneous Reaction
Term

ΔG>0

Definition
Nonspontaneous Reaction
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