Thermodynamics

• Thermodynamics is a set of principles that apply to all physical and biological processes and governs the conditions under which they can occur
• 1st law of thermodynamics states that the total amount of energy within a system and its surrounding is constant

  Energy can neither be created nor destroyed, only interconverted between forms
• 2nd law of thermodynamics states that the total entropy of a system and its surrounding always increase
• The 2 types of systems are open and closed

  Closed systems cannot exchange matter across boundaries (some energy can pass through)

  Open systems can pass matter across boundaries

  Cells are open systems
• Enthalpy is the heat storage capacity of a system

  Formula: Enthalpy = internal energy +(pressure x volume), H = E + (pv)

  Measured in J/mol
• Exothermic reaction is the release of heat during a reaction

  Endothermic reaction where heat is absorbed during a reaction
• Entropy refers to the level of disorder in a system, it always increases spontaneously
• Solids have high order = low entropy

  Gases have low order = high entropy
• Gibbs Free Energy (G) is the amount of available energy to do work, indicates if a biochemical process will occur spontaneously
• Gibbs Free Energy equation: ΔG = ΔH - TΔS

  ΔG - change in gibbs free energy, in kJ/mol

  ΔH - change in enthalpy, in kJ

  T - temperature, in K

  ΔS - change in entropy, in J/K
• Conversion of celsius to kelvin is +273 ie. 0ºC is 273K
• If ΔG is less than 0 it is a spontaneous process, if ΔG is more than 0 it is not a spontaneous process
• Standard biological conditions are represented as ΔGº' (delta G nought prime), where temperature is 310K and pH is 7
• An exergonic reaction is one that is spontaneous and is energetically favourable
• When ΔS (change in entropy) is less than 0 it is ordered, when ΔS is more than 0, it is disordered
• A disordered and exothermic reaction will be spontaneous/exergonic, meaning the system loses energy
• An ordered and endothermic reaction will be non-spontaneous/endergonic, meaning the system gains energy
• An ordered exothermic reaction will be spontaneous at low temperatures

  A disordered endothermic reaction will be spontaneous at high temperatures
• 5 important rules of ∆G

  1. Spontaneous reaction in ∆G is less than 0
  2. Non-spontaneous reaction ∆G is more than 0, requires energy
  3. At equilibrium ∆G = 0
  4. ∆G depends on free energy of reactants and product but is independent in its path
  5. Doesn't provide information on rate of reaction
• An endergonic reaction is one that is not spontaneous and is energetically unfavourable