BIO Lecture 1: Thermodynamics

The MCAT tests our knowledge on thermodynamics in terms of how it relates to chemical reactions.  Therefore, there are 2 forms of energy in chemistry that we need to know: HEAT ENERGY and POTENTIAL ENERGY.  Heat energy refers to movement of molecules and potential energy refers to energy stored in chemical bonds (i.e. ATP).  

1st Law of Thermodynamics: energy in the universe is constant (conservation of energy - therefore if we lose energy in a "system" the energy of the rest of the universe must increase)

2nd Law of Thermodynamics: entropy (disorder or randomness) of the universe tends to increase over time (in terms of chemistry: a reaction will occur spontaneously--without input of energy--if it increases the disorder of the universe)

Gibbs Free Energy: we can't discuss thermodynamics without touching on this formula.  DeltaG = DeltaH - TDeltaS.  The change in Gibbs free energy determines whether the reaction is favorable (spontaneous) or unfavorable (nonspontaneous)

T = Temperature (in Kelvin) 

H = Enthalpy 

S = Entropy

-if DeltaG is negative the reaction is spontaneous and exergonic (energy exits the system)

-if DeltaG is positive the reaction is non spontaneous and endergonic (energy must be added)

NOTE: the value of DeltaG depends on the concentrations of the reactants and products

NOTE: spontaneous means that a reaction may proceed without additional energy input, but it says NOTHING about the rate of the reaction. Thus, DeltaG is only a measure of the difference in free energy between reactants and products 

-if DeltaH is negative then the reaction is exothermic (liberates heat)

-if DeltaH is positive then the reaction is endothermic (requires input of heat)