Thermodynamics relationship between heat and work tells us what processes are possible. Determines the equilibrium state of a system. Predicts product/reactant proportions at tells us if a process can take place unassisted equilibrium. Describes the distribution of energy in a system. Free energy (g) relates enthalpy and entropy to spontaneity can also be related to equilibrium constants. Determines the pathway to get to equilibrium and how fast it is reached. Spontaneous process : can occur in a system left to itself, no continuous external action is necessary to make it happen, does not refer to how fast a process occurs. If a process is spontaneous, the reverse process is nonspontaneous. Nonspontaneous process : cannot take place in a system left to itself. A high activation energy (ea) can effectively block a thermodynamically favored reaction. At 25 c: many exothermic processes are spontaneous, many endothermic processes are nonspontaneous, enthalpy change (cid:894) h(cid:895) is not a sufficient criterion for predicting spontaneous change.