Thermodynamics Flashcards
System
Part of the universe being studied
Surroundings
Everything else in the universe
What is the First Law of Thermodynamics?
Energy is conserved. Energy can’t be created/destroyed, only transferred from one object to another and/or transferred from one energy type to another
What is ΔH ?
Enthalpy
Define enthalpy
Total heat content of a system
If ΔH < 0 then
Reaction is Exothermic. Heat is leaving system – LOSS of heat (exo - exit)
AKA -ΔH
If ΔH > 0 then
Reaction is endothermic. Heat is entering the system. GAINING of heat.
AKA +ΔH
Spontaneous Process
Process that occurs without outside help. Has a -ΔG
Nonspontaneous Process
Process that will not occur UNLESS driven by an external source. Has a +ΔG
What is true about a reaction as it relates to spontaneity?
If going one direction in a reaction is spontaneous, then going the other way is nonspontaneous
If A + B -> C is spontaneous, then
C -> A + B is nonspontaneous
What is ΔS
Entropy
What is Entropy?
Entropy is a measure of how dispersed the system’s energy is. AKA measure of disorder.
What does an increase in entropy mean?
+ΔS , the system has become less ordered.
What does a decrease in entropy mean?
-ΔS , the system has become more ordered.
What is the equation for the ΔS of the universe?
ΔSuniverse = ΔSsystem + ΔSsurroundings
What does a spontaneous reaction do to the entropy of the universe?
+ΔSuniverse , increases the entropy of the universe, AKA increases the disorder of the universe (decreases the order)
When +ΔSuniverse , then the Tsurrounding < Tsystem
What does a nonspontaneous reaction do to the entropy of the universe?
-ΔSuniverse , decrease the entropy of the universe, AKA increase the order of the universe (decrease the disorder)
When -ΔSuniverse , then the Tsurrounding > Tsystem
Second Law of Thermodynamics
For a process to be spontaneous, the ΔSuniverse must be positive.
AKA: The entropy of the universe (composed of the entropy of the system and surroundings) must always increase during a spontaneous process.
What is the formula for estimating the ΔSsurroundings using the ΔHsystem?
ΔSuniverse = ΔSsystem - (ΔHsystem/T)
What is standard entropy?
What a molecule is at in a certain set of conditions
1 bar of pressure | 298.15 K |1 mole
How can we calculate the ΔSsystem?
xA +yB -> zC +wD
v Standard Entropy of ΔS
ΔSrxn = [zS(C) + wS(D)] - [xS(A) + yS(B)]
^Basically saying multiply the moles by the standard entropy of the product/reactant, add the reactants/products together, then do products-reactants for the ΔSsystem AKA ΔSrxn
What is ΔG
Gibbs Free Energy
What is Gibbs Free Energy
The energy available to do work. Energy we can get out of a spontaneous reaction // Energy we have to put in for a nonspontaneous reaction.
Formula for finding the ΔSuniverse using ΔG
ΔSuniverse = (-ΔG/T)
When ΔG< 0 … -ΔG … then the reation is spontaneous as the ΔSuniverse > 0
When ΔG>0 … +ΔG … then the reaction is nonspontaneous as the ΔSuniverse < 0