energy - capacity to do work 

• kinetic energy - energy of motion
• potential energy - stored energy in objects not actively moving but w/ capacity to do so
• all energy can be converted into heat
• thermodynamics - "heat changes"; study of energy
• kilocalorie - unit of heat
  • equal to 1000 calories
  • 1 calorie needed to raise temperature of 1g water by 1 degree C
  • 0.239 calorie = 1 joule

oxidation-reduction - energy stored as potential energy in covalent bonds 

• strength of covalent bond measured by amount of energy needed to break it
• energy in bonds can transfer to new bonds during reactions
• oxidation - loss of an electron; oxygen (most common electron acceptor) takes the electron away
• reduction - gain of an electron
• redox reactions - chemical reactions w/ oxidation/reduction
  • oxidation/reduction must take place together
  • reduced form has higher energy level than oxidized form
  • reducing power - ability of organisms to store energy by transferring electrons
• energy of electrons depends on how far it's from the nucleus and how strongly the nucleus attracts it
• atoms release energy when electrons return to original energy level from a higher energy level

laws of thermodynamics - 2 laws that govern all energy changes 

• 1st Law of Thermodynamics - energy cannot be created/destroyed, only changed
  • total amount of energy in the universe stays the same
  • w/ every energy conversion, some energy escapes into the environment as heat
  • heat - measure of random motion of particles; can only be used to do work w/ a heat gradient
  • energy available for work decreases as more energy converts to heat
• 2nd Law of Thermodynamics - disorder in the universe increases continuously
  • energy spontaneously converts from more ordered, less stable form to less ordered, more stable form
  • entropy - measure of disorder in a system
  • largest amount of potential energy availabe when universe originally formed
  • every energy exchange increases disorder

free energy - energy available to do work in a system 

• heat energy makes it easier for atoms to pull apart, increasing disorder
• chemical bonding decreases disorder
• Gibbs' free energy = enthalpy (energy in chemical bonds) - temperature(K) * entropy
  • G = H - TS
  • change in G = change in H - T * change in S
• endergonic - describes reaction needing an input of energy; has a positive change in free energy, where there's more energy in products than in reactants
• exergonic - describes spontaneous reactions that release excess free energy as heat; has a negative change in free energy

activation energy - extra energy needed to start a chemical reaction 

• old bonds must first be broken for new bonds to form
• rate of exergonic reactions depend on amount of activation energy needed
• catalysis - process that lowers the activation energy needed; cannot make endergonic reactions start spontaneously