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
What is the formula in which ΔG, ΔH, and ΔS are related by?
ΔG = ΔHsystem - (T)(ΔSsystem)
^putting system is not a requirement as this formula will only ever use the system values, never surrounding or universe.
For the formula ΔG = ΔH - (T)(ΔS), if the values are -ΔH and +ΔS , then what will ΔG be AND what kind of reaction will occur?
ΔG will be -ΔG … Reaction will ALWAYS be spontaneous
For the formula ΔG = ΔH - (T)(ΔS), if the values are +ΔH and -ΔS , then what will ΔG be AND what kind of reaction will occur?
ΔG will be +ΔG … reaction will ALWAYS be nonspontaneous
For the formula ΔG = ΔH - (T)(ΔS), if the values are +ΔH and +ΔS , then what will ΔG be AND what kind of reaction will occur?
-ΔG IF T-value is larger = spontaneous
+ΔG if T-value is smaller = nonspontaneous
For the formula ΔG = ΔH - (T)(ΔS), if the values are -ΔH and -ΔS , then what will ΔG be AND what kind of reaction will occur?
-ΔG if T-value is smaller = spontaneous
+ΔG if T-value is larger = nonspontaneous
What is the formula for determining the T-value?
T = (ΔH)/(ΔS)
The T-value then tells us the flipping temperature for an equation to turn spontaneous/nonspontaneous.
(ΔG was set to 0, then equation was rearranged to set everything equal to T)
What equation do we use to find the ΔG if the reaction isn’t in standard conditions?
ΔG = ΔG* + (R)(T)(lnQ)
ΔG = Gibbs free energy
ΔG* = Standard Gibbs free energy
R = 8.314 J/mol*k
T = temperature (k)
Q = (products/reactants)… ([prA][prB])/([reC][reD])
