CHAPTER 5 EQUILIBRIA AND FREE ENERGY Investigate the concept of an equilibrium constant Keq defines the relationship between reactant concentrations and product concentrations under the condition of equilibrium Concept of Chemical Equilibrium State of delicate balance poised between forward and reverse reactions that appear macroscopically to be at rest Expressed as an arbitrary chemical process aA bB cC dD Reactants go to products but equally products go back to reactants Reaction proceed to the point where G Gp GR 0 Dynamic equilibrium state aA bB cC dD o At this point the equilibrium condition is satisfied and change ceases from macroscopic view Natural world there are only two options o The system is in equilibrium and will remain that way unless disturbed by outside influence o System is out of equilibrium and will in time achieve equilibrium The Equilibrium Constant Reaction quotient ignore the little c on Q Q Keq T AT EQUILIBRIUM Q is defined for all conditions equilibrium or otherwise Equilibrium for a specific temperature Refers back to concentrations at certain temperatures If Qc Keq then the reaction will shift from left to right If Qc Keq then the reaction will shift from right to left Qc Keq equilibrium Even if concentrations at equilibrium may vary experiment by experiment for a particular reaction the equilibrium constant will always remain the same o As long as concentration is raised to the power of its individual stoichiometric coefficient Manipulation of the Equilibrium Constant Equilibrium constant expressed in concentration units Kc C H 3 OH CO o Example When you reverse the chemical equation expressing the equilibrium relation between the left hand and right hand species we invert the function form of the equilibrium constant 1 K c K c If you multiple the stoichiometric coefficients in the balanced chemical reaction by a common fact then the equilibrium constant is raised to the power of the multiplier When reactions are summed together to form a net reaction the equilibrium constants are multiply together to form the resultant equilibrium constant Equilibrium Constant in Concentration vs Pressure Units Kp Kc RT n Stressed Equilibria The Haber process process for the formation of ammonia from nitrogen and hydrogen at high pressure and temperature over an iron catalyst o Developed this method for fixing nitrogen by breaking the N2 bond to make nitrogen available for the use by plants o Process was used to develop nitrate explosives used in WWI Increase in partial pressures of each pushes reaction towards the products to side with the least amount of moles release stress o Le Ch telier s principle Raising the temp of an equilibrium mixture shits the equilibrium condition in the direction of the endothermic reaction Shift in equilibrium aims to reduce the magnitude of the change G 0 when Q Keq G G RT ln Q G RT Keq e