Enthalpy/Entropy/Gibbs Free Energy Flashcards
Is bond “breaking” (or dissociation) an endothermic or exothermic process?
Endothermic
(requires energy)
Is bond “making” (or formation) an endothermic or exothermic process?
Exothermic
(produces energy)
What is the one letter abbreviation for enthalpy?
Enthalpy = (H)
What is the one letter abbreviation for Gibbs Free Energy?
Gibbs Free Energy = (G)
What is entropy (S)?
Measure of the dispersal/disorder of matter and energy.
(Entropy NEVER decreases.)
Rank solids, liquids and gases from lowest to highest entropy.
Solids < liquids < aq < gases
Gases have the highest entropy because gases are more random, have more arrangements and thus more disorder.
What does an +ΔS indicate?
(Remember S is entropy.)
An increase in entropy (more disordered).
Example: liquid → gas
What does a -ΔS indicate?
(Remember S is entropy.)
A decrease in entropy (less disordered).
Example: liquid → solid
What is the one letter abbreviation for entropy?
Entropy = (S)
What is the equation for Gibbs Free Energy (ΔG)?
ΔG = ΔH – TΔS
What is Gibbs Free Energy?
A measure of the change in enthalpy and entropy of a reaction which determines spontaneity.
[Mnemonic]
ΔG = ΔH – TΔS
Goldfish are (equals sign) Horrible without (minus sign) Tartar Sauce.
(how to remember the Gibbs Free Energy equation)
ΔG = ΔH – TΔS
Goldfish are (equals sign) Horrible without (minus sign) Tartar Sauce.
For Gibbs Free Energy, if ΔG is negative (ΔG < 0), is the reaction spontaneous or nonspontaneous?
Spontaneous
For Gibbs Free Energy, if ΔG is positive (ΔG > 0), is the reaction spontaneous or nonspontaneous?
Nonspontaneous
For Gibbs Free Energy, if ΔG is zero what does that mean?
The system is in a state of equilibrium (ΔH = TΔS).
[Mnemonic]
My negative ex-boyfriend was spontaneous.
(how to distinguish if ΔG is spontaneous or nonspontaneous)
(My negative ex-boyfriend was spontaneous.)
If ΔG is negative, the reaction is spontaneous and exergonic.
When determining the molecule with the most exothermic standard heat of combustion, what is a factor?
The larger the alkane, the more exothermic (release of heat).
Example: N-butane has a higher standard heat of combustion than ethane.
Can the spontaneity of a reaction be determined from enthalpy?
NO!
The spontaneity of a reaction can only be determined from Gibbs Free Energy!
Enthalpy (H) ≠ Spontaneity
What is the value for ΔH°f (heat of formation) of an element in its standard state?
ΔH°f of an element in its standard state = 0 (arbitrary).
Example: ΔH°f of H2 = 0
