Thermodynamics
-
Upload
kyle-dennis -
Category
Documents
-
view
38 -
download
1
description
Transcript of Thermodynamics
Thermodynamics
Chemical reactions proceed according to the rules of thermodynamics
• The law of conservation of energy – energy can be converted from one form to another but the total amount of energy is constant
• Entropy – the universe is becoming more chaotic
ACK!
Some constants
Gas constant: R = 8.315 Joules/K* mol or
1.9872 cal/K.mol
Faradays constant: F = 96485 Joules/Volt.mol or
23062 cal/Volt* mol
Thermodynamics
Energy: definitions
Energy – ability to do work
Energetics – energy transfer
Types of energy
• Potential – trapped energy
• Kinetic – energy of movement
Energy Categories: more definitions• Radiant energy – energy released from one
object to another• Mechanical energy – energy to move objects
from place to place• Electrical energy – energy that results from the
movement of charged particles down a charge gradient
• Thermal energy – reflected in the movement of particles and serves to increase temperature
• Chemical energy – energy that is held within chemical bonds
Energy Categories, Cont.
Animals rely on all five types of energy, which are interconvertible
Food Webs are Transfers of Energy
Figure 2.3
Free Energy (G)
1. Change in free Energy (ΔG)
ΔG = Products – ReactantsΔG negative – reaction will proceed forward →
ΔG positive – reaction will proceed backward ←
ΔG zero – reaction at equilibrium ↔
2. Standard free Energy – ΔGo: 298 K (25oC), 1 atm pressure, pH 7.0 and 1M [initial] for all reactants and products
Thermodynamics in a biological setting
Thermal Energy
Thermal energy movement of molecules
Most chemical reactions involve changes in thermal energy• Exothermic reactions – release heat• Endothermic reactions – absorb heat
Chemical Reactions and Thermal EnergyEnthalpy
Enthalpy – average thermal energy of a collection of molecules i.e. bond energy
Change in enthalpy (H) = Hproducts – Hsubstrates
• Exothermic: H is negative i.e. C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
• Endothermic: H is positive i.e. ADP + Pi → ATP
Chemical Reactions and Thermal EnergyEnthalpy and Entropy together
Entropy (S) – measure of randomness or disorder
Exothermic: H is negative, increase in S → reaction will occur spontaneously – negative G
Endothermic: H is positive, S is positive → reaction will occur spontaneously. It has to overcome the positive H
Free Energy: calculations
Free energy changes of reactions are additive (coupled reactions):Consider the phosphorylation of glucose to glucose 6-phosphate:
Go: glucose + Pi ↔ glucose-6-phosphate + H2O = 3.3 kcal/mol
Go: ATP + H2O ↔ ADP + Pi = -7.3 kcal/mol
Summing these reactions together:ATP + glucose ↔ ADP + glucose 6-phosphate
G° = +3.3 + (-7.3) = - 4kcal/mol (favourable)
Biological reactions
G = Go + RTln ([products]/[reactants])Where R = gas constant, T = temperature in Kelvin
Example:
glucose + ATP ↔ glucose-6-phosphte + ADP
Go: glucose + Pi ↔ glucose-6-phosphate + H2O = 3.3 kcal/mol
Go: ATP + H2O ↔ ADP + Pi = -7.3 kcal/mol
Glucose: [5mM]; ATP: [2mM]; ADP: [0.15mM]; glucose-6-phosphate: [0.05mM]
So, G = - 4.0 kcal/mol + 1.9872cal/K mol)(298K)ln((0.05*0.15)/(5*2))
= -8.26kcal/mol
ΔG for reactions that don’t make or break bonds
Go is zero
- Examples: glucose transport, ion transport across membranes
G = RTln ([inside]/[outside])Or for charged ions:
G = RTln ([inside]/[outside]) + zFEmwhere z = valence of the ion; F = Faraday constant and Em = membrane potential
G = RTln ([inside]/[outside]) + zFEmwhere z = valence of the ion; F = Faraday constant and Em
= membrane potential
Example: Diffusion of Cl- from out to in
Cl- outside cell: 120mM; Cl- inside cell: 10mM; Em = -80mV
G = (1.987cal/K mol)(298K)(ln(10/120) + (-1)(23062 cal/V mol)(-0.08V) =
376 cal/mol
Transport across membranes