BCHM-3050 Lecture Notes - Lecture 2: Living Systems, Enthalpy, Isolated System
19 May 2018
School
Department
Course
Professor
Thermodynamic Systems
System: any part of the universe studied
Ex. Chemical reaction
○
•
Surroundings: everything else
Ex. The substance the rxn is being conducted in
○
•
Characteristics that define a system
Composition
○
Temp
○
Volume
○
Pressure
○
•
Closed system: exchange energy with surroundings BUT cannot exchange
matter
•
Open system: exchange energy AND matter with surroundings*
•
Isolated system: exchange NEITHER matter or energy w surroundings
•
*characteristic of living system. Things operate at constant temp and pressure
First law of thermodynamics and Enthalpy
1st law: Energy is conserved
Cant be created or destroyed
○
•
Closed system: energy is exchanged as work or as heat
Heat = enthalpy
○
•
Enthalpy (∆H): heat exchanged b/w system and surroundings when
system is at constant pressure
Negative ∆H: release of energy
Energy decreased within system as its transferred into
surroundings
§
○
Positive ∆H: absorption of energy
○
Typical for living systems
○
∆H: state function
Value depends on initial and final states of system
§
May be multiple ways of going about a rxn but change in heat
is the same each time
§
○
•
Measure of heat of a rxn
Calorimetry: put substance into a sealed vessel ('bomb') and explode or
burn substance
Measure exchange of energy based on the change of temperature
○
•
Temperature increase in the surroundings means energy loss in the system
•
Reversible and irreversible processes
Biochemical processes: reversible
Some are irreversible
○
•
Reversible: reaction near state of equilibrium
Equilibrium: Forward and reverse rates are equal
○
Low energy state exists
Favored over higher energy
§
The rxn is at equilibrium when this occurs
§
○
Ex. Ice melting
Can re freeze ice once it completely melts
§
○
•
Irreversible: far from equilibrium
Process drives toward state of equilibrium
○
Ex. Burning paper
Cant remake the paper
§
○
Spontaneous process
○
•
Standard state conditions (STP):
Temp: 273.15 K
○
Pressure: 1 atm
○
Concentration: 1 M
○
•
2nd law of thermodynamics and Entropy
2nd law: Entropy of isolate system will increase to max value
Favorable
○
Basically: if things are left on their own, they will not just become
ordered
○
•
Entropy (∆S): state function
Measure of degree of randomness
Natural tendency of molecules
§
○
Ex. Dissolution and phase change
○
•
Entropy will decrease with input of energy
•
Increase of entropy (left to right)
Solids < liquids < gas
Free energy: 2nd law in open system
Open system: entropy and enthalpy
•
Free energy (∆G): tells whether a process will require energy or release
energy
•
∆G =∆H - T(∆S)
∆G: energy change available to do work at constant temperature and
pressure
•
If ∆G is.. If free E is.. Process is
- Available Exergonic (favorable)
+ Required Endergonic (unfavorable)
0 Zero equilibrium
Exergonic: lose energy
The reaction occurred spontaneously
○
•
Endergonic: gain energy
Rxn occurs because energy is inputted
○
•
Criteria for a favorable process in a nonisolated system is that ∆G is
negative
At constant temp and pressure
○
•
Ex 1. is it energetically favorable for ice to melt at 263 K, where ∆H is +5.63
kj/mol and ∆S is +20.6 j/K*mol?
∆G =∆H - T(∆S)
∆G =5630 - 263(20.6)
∆G = + 212.2
UNFAVORABLE
Ex 2. favorable for ice to melt at 283 K, ∆H is +6.77 kj/mol and ∆S is +24.7
J/K*mol?
∆G =∆H - T(∆S)
∆G =6.77- 283(24.7)
∆G = -220.1
FAVORABLE
∆H∆SLow T High T
++∆G + ∆G -
+ - ∆G + ∆G +
- + ∆G -∆G -
--∆G -∆G +
Free energy, chemical reactions and equilibrium
K = equilibrium constant
K< 1 favors reactants
○
K> 1 favors products
○
•
Use Q when rxn is not at equilibrium (opposite of K)
Q < 1 favors products
○
Q > 1 favors reactants
○
•
∆G = ∆G˚ + RTlnQ*
*for systems not at equilibrium
R= 8.314 j/mol*k
T = 273.15
∆G˚ = free energy of rxn at STP
Free energy change of chemical rxn (∆G) depends on:
∆G˚
○
Initial concentration of reactants and products
○
•
Even if ∆G˚ is + , under proper concentration ∆G˚ can become -
•
When system is at equilibrium
Q = K
○
∆G = 0
○
•
Equilibrium v homeostasis
Both: concentration of product and reactants is constant
•
Homeostatic conditions: far from equilibrium
Energy is required maintain
○
Controlled system
○
Q far from K
○
•
Equilibrium = concentrations of products and reactants are equal
•
Value of Q Value of ∆G Favored direction
< K < 0 forward
>K >0 reverse
K = Q 0 neither
Coupling, water, buffered solns, and biochem stp
Coupling: meshing of rxns that will not go in the forward direction and
rxn that will go in the forward direction to make the unfavorable rxns
become favorable
Living systems use this
○
•
Living systems = aqueous
Buffered
○
•
Stp of biochem:
T = 273.15
○
R = 1 atm
○
Concentration = 1 M
For H+ = 10^-7 M
§
○
•
ATP
ATP: common energy currency
Large energy in phosphodiester bonds
○
•
ATP to ADP = favorable process
•
Why are certain compounds so energy rich?
Resonance stabilization of products
•
Charge repulsion in reactants
•
Tautomerization of products
•
∆G˚' for redox rxns
Reductant: electron donor
Becomes oxidized
○
Has been reduced and has a bunch of electrons
○
•
Oxidant: electron aceptor
Becomes reduced
○
Has lost its electrons and has no electrons
○
•
Standard reduction potential (E˚): tendency of specie gaining e-
Large E˚ = larger tendency of e- carrier to become reduced
○
Positive E˚ is favorable
○
•
∆G˚= -nF∆E˚
∆E˚ = [E˚ reduction + E˚ Oxidation]
N = # e- transferred (usually 1 or 2)
F = 96.5 kj/mol*V
Chapter 3: Thermodynamics
Friday, May 18, 2018
4:02 PM
Thermodynamic Systems
System: any part of the universe studied
Ex. Chemical reaction
○
•
Surroundings: everything else
Ex. The substance the rxn is being conducted in
○
•
Characteristics that define a system
Composition
○
Temp
○
Volume
○
Pressure
○
•
Closed system: exchange energy with surroundings BUT cannot exchange
matter
•
Open system: exchange energy AND matter with surroundings*
•
Isolated system: exchange NEITHER matter or energy w surroundings
•
*characteristic of living system. Things operate at constant temp and pressure
First law of thermodynamics and Enthalpy
1st law: Energy is conserved
Cant be created or destroyed
○
•
Closed system: energy is exchanged as work or as heat
Heat = enthalpy
○
•
Enthalpy (∆H): heat exchanged b/w system and surroundings when
system is at constant pressure
Negative ∆H: release of energy
Energy decreased within system as its transferred into
surroundings
§
○
Positive ∆H: absorption of energy
○
Typical for living systems
○
∆H: state function
Value depends on initial and final states of system
§
May be multiple ways of going about a rxn but change in heat
is the same each time
§
○
•
Measure of heat of a rxn
Calorimetry: put substance into a sealed vessel ('bomb') and explode or
burn substance
Measure exchange of energy based on the change of temperature
○
•
Temperature increase in the surroundings means energy loss in the system
•
Reversible and irreversible processes
Biochemical processes: reversible
Some are irreversible
○
•
Reversible: reaction near state of equilibrium
Equilibrium: Forward and reverse rates are equal
○
Low energy state exists
Favored over higher energy
§
The rxn is at equilibrium when this occurs
§
○
Ex. Ice melting
Can re freeze ice once it completely melts
§
○
•
Irreversible: far from equilibrium
Process drives toward state of equilibrium
○
Ex. Burning paper
Cant remake the paper
§
○
Spontaneous process
○
•
Standard state conditions (STP):
Temp: 273.15 K
○
Pressure: 1 atm
○
Concentration: 1 M
○
•
2nd law of thermodynamics and Entropy
2nd law: Entropy of isolate system will increase to max value
Favorable
○
Basically: if things are left on their own, they will not just become
ordered
○
•
Entropy (∆S): state function
Measure of degree of randomness
Natural tendency of molecules
§
○
Ex. Dissolution and phase change
○
•
Entropy will decrease with input of energy
•
Increase of entropy (left to right)
Solids < liquids < gas
Free energy: 2nd law in open system
Open system: entropy and enthalpy
•
Free energy (∆G): tells whether a process will require energy or release
energy
•
∆G =∆H - T(∆S)
∆G: energy change available to do work at constant temperature and
pressure
•
If ∆G is.. If free E is.. Process is
- Available Exergonic (favorable)
+ Required Endergonic (unfavorable)
0 Zero equilibrium
Exergonic: lose energy
The reaction occurred spontaneously
○
•
Endergonic: gain energy
Rxn occurs because energy is inputted
○
•
Criteria for a favorable process in a nonisolated system is that ∆G is
negative
At constant temp and pressure
○
•
Ex 1. is it energetically favorable for ice to melt at 263 K, where ∆H is +5.63
kj/mol and ∆S is +20.6 j/K*mol?
∆G =∆H - T(∆S)
∆G =5630 - 263(20.6)
∆G = + 212.2
UNFAVORABLE
Ex 2. favorable for ice to melt at 283 K, ∆H is +6.77 kj/mol and ∆S is +24.7
J/K*mol?
∆G =∆H - T(∆S)
∆G =6.77- 283(24.7)
∆G = -220.1
FAVORABLE
∆H∆SLow T High T
++∆G + ∆G -
+ - ∆G + ∆G +
- + ∆G -∆G -
--∆G -∆G +
Free energy, chemical reactions and equilibrium
K = equilibrium constant
K< 1 favors reactants
○
K> 1 favors products
○
•
Use Q when rxn is not at equilibrium (opposite of K)
Q < 1 favors products
○
Q > 1 favors reactants
○
•
∆G = ∆G˚ + RTlnQ*
*for systems not at equilibrium
R= 8.314 j/mol*k
T = 273.15
∆G˚ = free energy of rxn at STP
Free energy change of chemical rxn (∆G) depends on:
∆G˚
○
Initial concentration of reactants and products
○
•
Even if ∆G˚ is + , under proper concentration ∆G˚ can become -
•
When system is at equilibrium
Q = K
○
∆G = 0
○
•
Equilibrium v homeostasis
Both: concentration of product and reactants is constant
•
Homeostatic conditions: far from equilibrium
Energy is required maintain
○
Controlled system
○
Q far from K
○
•
Equilibrium = concentrations of products and reactants are equal
•
Value of Q Value of ∆G Favored direction
< K < 0 forward
>K >0 reverse
K = Q 0 neither
Coupling, water, buffered solns, and biochem stp
Coupling: meshing of rxns that will not go in the forward direction and
rxn that will go in the forward direction to make the unfavorable rxns
become favorable
Living systems use this
○
•
Living systems = aqueous
Buffered
○
•
Stp of biochem:
T = 273.15
○
R = 1 atm
○
Concentration = 1 M
For H+ = 10^-7 M
§
○
•
ATP
ATP: common energy currency
Large energy in phosphodiester bonds
○
•
ATP to ADP = favorable process
•
Why are certain compounds so energy rich?
Resonance stabilization of products
•
Charge repulsion in reactants
•
Tautomerization of products
•
∆G˚' for redox rxns
Reductant: electron donor
Becomes oxidized
○
Has been reduced and has a bunch of electrons
○
•
Oxidant: electron aceptor
Becomes reduced
○
Has lost its electrons and has no electrons
○
•
Standard reduction potential (E˚): tendency of specie gaining e-
Large E˚ = larger tendency of e- carrier to become reduced
○
Positive E˚ is favorable
○
•
∆G˚= -nF∆E˚
∆E˚ = [E˚ reduction + E˚ Oxidation]
N = # e- transferred (usually 1 or 2)
F = 96.5 kj/mol*V
Chapter 3: Thermodynamics
Friday, May 18, 2018 4:02 PM
Document Summary
The substance the rxn is being conducted in. Closed system: exchange energy with surroundings but cannot exchange matter. Open system: exchange energy and matter with surroundings* Isolated system: exchange neither matter or energy w surroundings. Closed system: energy is exchanged as work or as heat. Enthalpy ( h): heat exchanged b/w system and surroundings when system is at constant pressure. Energy decreased within system as its transferred into surroundings. Value depends on initial and final states of system. May be multiple ways of going about a rxn but change in heat is the same each time. Calorimetry: put substance into a sealed vessel ("bomb") and explode or burn substance. Measure exchange of energy based on the change of temperature. Temperature increase in the surroundings means energy loss in the system. The rxn is at equilibrium when this occurs. Can re freeze ice once it completely melts. 2nd law: entropy of isolate system will increase to max value.
