Announcements Exams will be handed back in lab next week. Weekly quizzes for the rest of the semester.

The value of the equilibrium constant can be determined from concentration data

The reaction quotient is calculated from non-equilibrium concentrations to determine if a system is at equilibrium

How to solve equilibrium problems Write the equilibrium expression Determine Q if Q = K, it’s at equilibrium if Q < K, reactants go to form products if Q > K, products go to form reactants Call the amount reacting “x” Solve for x in the equilibrium expression Use x to determine equilibrium concentrations

Determining equilibrium concentrations when a system does not start at equilibrium Given these initial concentrations, what will the final concentrations be when equilibrium is reached? From last time: K=0.11, Q=7.25 Since Q>K, reaction goes in reverse to get to equilibrium C2H5OH CH3CO2H CH3CO2C2H5 Initial Change Equilibrium

Equilibrium constants can also be written in terms of gas pressure KP is not necessarily the same number as KC 2 NH3(g) N2(g) + 3 H2(g) Kc = 5.8 x 105 Kp =

An equilibrium will shift in response to change in the system or its environment LeChatelier’s Principle

The effect of concentration changes on equilibria Add product [C] Remove reactant [A] Remove all of reactant [B] and product [D]

The effect of volume changes on equilibria Equilibrium will shift to side with fewer moles of gas

If we decrease the volume of this reaction, the equilibrium will… Shift left Shift right Remain the same

The effect of temperature changes on equilibria Endothermic reactions Exothermic reactions

LeChatelier’s Principle- Quantitative 1-Liter flask contains 0.50 mol butane and 1.25 mol isobutane (at equilibrium). We then add 0.50 mol and butane. What happens and what are the final concentrations of isobutane and butane?