Chapter 2: 2.4 Free Energy Flashcards
When is a process in an isolated system spontaneous?
If ΔS sys > 0
When a process occurs at constant pressure and tempearture…
The heat change associated with the surroundings is given by ΔH surr
How can entropy change of the surroundings be calculated?
ΔS surr = ΔH surr / T
State the relation between:
ΔH surr and ΔH sys
(in terms of heat flow)
ΔH surr = -ΔH sys
What does the entropy change of the surroundings equal in terms of ΔH sys?
ΔS surr = -ΔH sys / T
State the formula for Gibbs free energy
G = H -TS
State the proof for:
The formula for Gibbs Free Energy
- Substituting ΔS surr = -ΔH sys/T into the formula ΔS sys + ΔS surr > 0
- Multiply both sides by -T
- Result: ΔH - TΔS < 0
Define:
Gibbs Free Energy
The amount of energy that is available (or “free”) to enable spontaneous change to occur at constant temperature and pressure
True or False:
Gibbs Free Energy is a state function
True
State the formula for:
Free energy change
ΔG = ΣG (products) - ΣG (reactants)
OR
ΔG = ΔH - TΔS
State the spontaneity of the process if:
- ΔG < 0
- ΔG = 0
- ΔG > 0
- The reaction will proceed spontaneously as written
- The system is at equilibrium (number of moles of reactans and products do not change over time)
- The reaction will not proceed spontaneously as written (the reverse process is spontaneous)
True or False:
ΔG < 0 means the reaction favours the reactants
False, ΔG < 0 means that the reaction favours the formation of the products
What does the reaction favour when ΔG > 0?
The reaction favours the reactants, with little or no products formed
Determine the sign of ΔG and what drives the reaction when:
- -ΔH
- +ΔS
-ΔG
* Enthalpically and entropically driven
Determine the sign of ΔG and what drives the reaction when:
- +ΔH
- -ΔS
+ΔG
* Reaction not spontaneous
Determine the sign of ΔG and what drives the reaction when:
- -ΔH
- -ΔS
+ΔG Or -ΔG
* Depends on temperature
* Enthalpically driven if spontaneous
Determine the sign of ΔG and what drives the reaction when:
- +ΔH
- +ΔS
+ΔG Or -ΔG
* Depends on temperature
* Entropically driven, if spontaneous
What is the sign and magnitude of ΔG affected by?
- Temperature
- Pressure
- Concentrations of reactants
- Concentrations of products
List:
Standard conditions
- 298.15 K
- 1 atm pressure
- 1 M concentration
How is free energy change under standard conditions denoted? State the formula
ΔG^o
* ΔG^o = ΔH^o - TΔS^o
True or False:
The absolute free energy of a substance can be determined
False
Define and give the notation of:
Standard Free Energy of Formation
- The standard free energy change that occurs when 1 mol of a compound is made from elements in their standard states
- ΔG^o f
What is the ΔG^o f of any element in its standard state?
Zero
State the formula for:
ΔG^o
ΔG^o = ΣΔG^o f (products) - ΣΔG^o f (reactants)
