Thermodynamics

Key Concepts:

Terms in this set (30)

Enthalpy
The energy involved in a reaction
Useful work
release of energy that can be obtained to cause another reaction to occur
First Law of Thermodynamics
Conservation of Energy - energy cannot be lost in a closed system (energy = q)
qsystem = -qsurroundings
In terms of enthalpy, what makes a reaction go to product formation?
Release of energy - products are more stable than the reactants (bonds formed are more stable than the bonds in the reactants)
What form of energy is released when you burn wood to warm your house?
Heat energy
What form of energy is released from batteries and mitochondria?
Electron movement
What form of energy is released from ATP losing a phosphate group to become ADP?
Mechanical deformation
Entropy
The level of disorder in a system
Examples of entropy
spilled coffee, unstructured sentence, free particles moving in a system in no set order
Second law of thermodynamics
Reactions favor an increase in entropy of the system (move towards more disorder)
Positive delta S (entropy)
Products have a higher entropy than the reactants (products are favored, more disordered)
- increase in entropy allows for useful work to be done
Gibb's Free Energy
Equation that relates enthalpy and entropy to determine the spontaneity of a reaction
- how likely is a reaction to proceed to the products
Delta G > 0
non-spontaneous reaction
Delta G < 0
spontaneous reaction
Does a system need to have a negative delta G or a positive delta G to do work?
negative delta G (spontaneous)
Is K > 1 or < 1 in a spontaneous reaction? non-spontaneous reaction
spontaneous- K>1
non-spontaneous - K<1
How do we relate equilibrium and thermodynamics?
Rayton equation
How does delta H and delta S affect delta G
Four options for reaction spontaneity and Gibbs free energy
Delta enthalpy of formation (Hf)
**Hf(products) and Hf(reactants) must be multiplied by moles (n) present on each side
Delta entropy of formation
same equation as enthalpy of reaction but use entropy of products - entropy of reactants
Delta G of formation
Freezing point depression
When solutes are present in solution, the temperature at which the solution freezes decreases (T=delta H/delta S)
- enthalpy of solutes does not change --only delta S (entropy changes)
-- larger entropy = smaller temperature for the solution to freeze

ENTROPIC EFFECT
Why do we put salt on sidewalks in the winter?
The addition of salt to the water causes a freezing point depression -- the water will freeze at a lower temperature than it typically would (prevents formation of ice if the outside temp. is higher than the NEW freezing temperature due to the ice)
Boiling point elevation
Addition of a solute to a pure solution results in an increase in entropy and a higher boiling point for the solution
-- temperature must be higher to cause the solution to enter the gas phase

liquid phase is stable longer

ENTROPIC EFFECT
Molality
(moles of substance)/mass of solvent (kg)

to calculate moles of substance - (mass of solvent/molar mass)
k
freezing point depression/boiling point elevation constant

delta T=k*molality
Increase in molality
As molality increase, the temperature of the solution increases
- Since entropy is increasing with more particles in solution, it takes more energy (temperature) to reach the boiling point
Spontaneity of oil/water mixture
- oil and mixture do not want to mix
delta H ~0, delta S- negative

-- H+ bonds surround the oil droplet restraining the movement of H2O molecules causing a decrease in entropy (less places for water molecules to move)---small droplets restrain more water and is not entropically favored
Entropy and cell membrane formation
Similar to that of oil/water mixture
-- water wants to be unorganized - pushing hydrophobic molecules away and into the membrane bilayer allows for the water to not H+ bond with the non-polar portion (remains in a disordered state because H2O molecules have more ability to move around)
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