Chemistry Basics Flashcards
G (Gibbs Free Energy)
- Energy available to do work
- ∆G = Gproducts – Greactants
- ∆G = free energy change for reaction (c-a)
- ∆G‡ = activation energy (b-a)
- ∆G = ∆H - T∆S
Enthalpy
Heat, H
∆G = ∆H - T∆S
Entropy
Disorder, S
∆G = ∆H - T∆S
Exergonic
- ∆G
Energy Released
Favour spontaneous
Endergonic
+ ∆G
Energy Absorbed
Doesn’t favour spontaneous
Exothermic
- ∆H
Heat released
Endothermic
+ ∆H
Heat absorbed
Thermodynamic Equilibrium (Keq)
aA + bB ↔ cC +dD
K_eq=(〖[C]〗_eq^c 〖[D]〗_eq^d)/(〖[A]〗_eq^a 〖[B]〗_eq^b )
Keq= equilibrium constant, position of reaction at equilibrium
Relationship between ∆G and ∆G° and equilibrium?
∆G= ∆G° + RT ln (〖[C]〗_eq^c 〖[D]〗_eq^d)/(〖[A]〗_eq^a 〖[B]〗_eq^b )
How do standard conditions differ between chemistry and biochemistry conditions?
∆G° = standard free energy change
• 298 K, 1atm, 1M conc [H+] = 1M : pH = 0
∆G’° = biochemistry standard free energy change
• pH now 7
• [H+] = 10-7
What does ∆G = 0 mean? How can ∆G = 0 be used to find the value of ∆G’°?
∆G = 0 at equilibrium (no more work)
∆G= ∆G° + RT ln (〖[C]〗_eq^c 〖[D]〗_eq^d)/(〖[A]〗_eq^a 〖[B]〗_eq^b )
0= ∆G° + RT ln (〖[C]〗_eq^c 〖[D]〗_eq^d)/(〖[A]〗_eq^a 〖[B]〗_eq^b )
∆G°=- RT ln Keq
How can unfavourable reactions be manipulated in order to go ahead?
- Remove one or more products at a rate faster than it’s produced
>Becomes kinetically driven
>In glycolysis, the next step consumes the previous steps product - Replenish one or more of the reactants at a rate faster than it is removed
>Becomes kinetically driven
>Feed reaction - Couple first unfavourable reaction to a second favourable reaction
>Utilise readily available common intermediate
Glucose + pi → Glucose 6-p + H2O
ATP + H2O → ADP + pi
Glucose + pi + ATP + H2O → Glucose 6-p + H2O + ADP + pi
What is needed for reactions to be favourable to go ahead?
∆G determines if reaction will happen spontaneously (NOT ∆G°’)
Alter initial conditions to make ∆G negative (even if ∆G’° positive)
Need to keep [products] < [reactants] so (〖[C]〗_eq^c 〖[D]〗_eq^d)/(〖[A]〗_eq^a 〖[B]〗_eq^b )<1
Smaller/bigger
Equation for pH
pH = - log[H+]
Acids
Proton donors:
AH –> A- + H+
A- is the conjugate base form of AH
