SCH 4U What happens when we disturb chemical systems at equilibrium? [Co(H2O)6]Cl2 + heat pink [ CoCl2(H2O)2] + 4 H2O blue When a chemical system at equilibrium is disturbed by a change in a property, the systems adjusts in a way that opposes the change ...eventually establishing a new equilibrium! 1. Concentration Change 2. Temperature Change 3. Total Pressure Change aA + bB cC + dD Adding a reactant = more available to react = favours forward rxn (“equil shifts right”) With time, product concentration(s) increase Eventually new equilibrium established... ... with different reactant/product concentrations from initial equilibrium NOTE: Initial and final K values are the same! aA + bB cC + dD Removing (decreasing conc of) a product also favours forward rxn (shifts equil right) Remember: system shifts to try to counteract the disturbance! e.g. 2 CO2(g) 2 CO(g) + O2(g) aA + bB cC + dD What about... ....decreasing a reactant concentration? ....increasing a product concentration? Add an ion to solution that already contains that ...equilibrium shifts away ion... from added ion 3 NO2(g) + H2O(l) 2 HNO3(aq) + NO(g) desired product what about removing water? remove Hb(aq) + O2 Decreases Increases as asblood blood circulates goes into through lungs body HbO2(aq) Endothermic: Exothermic: reactants + E products reactants products + E If we heat/ cool the system, equilibrium shifts to minimize the change... If we cool the system... Equilibrium shifts in direction that produces heat (favours exothermic) If we heat up the system... Equilibrium shifts in direction that absorbs heat (favours endothermic) NOTE: The value of K changes with temp. (only constant at specific temperature) Predict how K will change if... ...we heat up an endothermic (fwd) rxn? → Equil. shifts right, K increases ...we cool down an endothermic rxn? → Equil. shifts left, K decreases And what about exothermic (fwd) reaction? N2O4(g) + energy 2 NO2(g) Recall Boyle’s Law: Remember, pressure is caused by gas molecules striking the walls of a container, so you change pressure by changing the number of collisions (change volume) ONLY affects GASES! Increasing total pressure of system shifts equilibrium to side of balanced equation showing fewest number of gas molecules If P (↑), then V (↓) and concentrations change (i.e. increase) If both sides of the equation have the same number of molecules of gas, any change in pressure or volume will have no effect on equilibrium i.e. H2(g) + I2(g) 2 HI(g) Addition of a catalyst A catalyst speeds up the rate of a reaction Lower the activation energy, which increases the rate of reaction, of both the forward and reverse reactions Catalysts do NOT affect position of equilibrium, only time taken Adding Inert Gases Inert gases do NOT react with other gases (i.e. NOT part of the equilibrium system) Presence of inert gas changes the probability of successful collisions for both the reactants and products equally, resulting in NO shift in equilibrium Pg 457 #1 – 4 Pg 459 #2 – 4 Read pgs 461 – 462 on the Haber Process Haha, just kidding!