Presentation on theme: "Chemical Equilibrium A B + A + C + B D A + B C + D 1. 4."— Presentation transcript:
1 Chemical Equilibrium 1. 2. 3. 4. A B + A + C + B D A + B C + D 1. 4. Reaction begins.No products yet formed.High rate of collisions between A & B.Rate of forward reaction HIGH.2 & 3Products formedCollisions between reactants decrease.Rate of forward reaction DECREASESReverse reaction begins.Rate of forward reaction EQUAL to rate of reverse reaction.Dynamic equilibrium established.Concentrations constant.
2 EQUILIBRIM REACTIONS e.g. N2(g) + 3H2(g) 2NH3(g) Most reactions DO NOT go to completion.Reactions that do not go to completion are REVERSIBLE.Reversible reactions exist in a state of EQUILIBRIUM.Equilibrium is reached when the rate of the forward reaction equals the rate of the reverse reaction.The reaction proceeding from L R as the equation is written is known as the forward reaction.e.g. N2(g) + 3H2(g) NH3(g)
3 Chemical Equilibrium A + B A + C + B D A + B C + D …………… ……………… …………… …………..………………………………………………………………………………………….
4 Chemical Equilibrium A + B A + C + B D A + C + B D DYNAMIC CHEMICAL EQUILIBRIUMReactantsConcentrationProductstimeForwardReaction RateReverse
5 Equilibrium Position - Left The equilibrium reaction does not mean the amounts of products and reactants are equal.If the products react more easily than the reactants but BOTH RATES are very slow.We say the Equilibrium is shifted to the LEFT.There will be higher concentration of reactants.A+C+BDtimeReactantsProductsConcentrationRatio of: ProductsReactantsWould be LESS than one.< 1
6 Equilibrium Position Middle If the reactants and the products both have similar reaction rates.The Equilibrium position will lie in the middle.There will be the same concentration of reactants & Products.A+C+BDReactantsConcentrationRatio of:ProductsReactantsWould be EQUAL TO one.Productstime= 1ProductsReactants= 1
7 Equilibrium Position - Right If the reactants react ……… ………… than the products.The Equilibrium is ………….. to the ……………….There will be higher concentration of ………….A+BC+D……………Ratio of:ProductsReactantsWould be ………………. than ONE.Conc…………….1time
8 Equilibrium Position - Right If the reactants react more easily than the products.The Equilibrium is shifted to the RIGHT.There will be higher concentration of Products.A+BC+DProductsRatio of:ProductsReactantsWould be GREATER than one.ConcReactants> 1time
9 Equilibrium Position SHIFT To …………A+C+BDTo ………Concentrationtime…………………………….ReactantsConcentrationConcentration……………….ProductstimetimeProductsReactants> 1ProductsReactants< 1ProductsReactants= 1
10 Equilibrium Position SHIFT A+C+SHIFTED To LeftBDTo rightConcentrationtimeReactantsProductsReactantsReactantsConcentrationConcentrationProductsProductstimetimeProductsReactants> 1ProductsReactants< 1ProductsReactants= 1
11 Adding Reactants Conc reactants products A + C + B D time More …………………….addedReactant concentration ……………………Forward reaction rate …………………..Reactant concentration ………………/Product concentration ………….Reverse reaction rate ……………………….New equilibrium established - ………….. ratio of PRODUCTS/REACTANTS - equilibrium shifted to …………………
12 Adding Reactants reactants Conc. products A + C + B D time Reactant addedreactantsEquilibrium ShiftsNew equilibriumestablishedConc.productsA+C+BDtimeMore Reactant addedReactant concentration increases & Forward reaction rate increasesProduct concentration decreases & Reverse reaction rate decreasesReactant concentration decreases as reactants used up.Product concentration increases as new products formed.New equilibrium established - higher ratio of PRODUCTS/REACTANTS - equilibrium shifted to RIGHT
13 Adding Products Eqm. Shifts New Equilibrium Reactants Conc Products A Product addedA+C+BDtimeMore PRODUCT addedPRODUCT concentration increases (Instantly - Reactant decreases )3. REVERSE reaction rate increases (fast then slower)4. PRODUCT concentration decreases, REACTANT concentration increases (fast then slower)5. Forward reaction rate increases6. New equilibrium established - lower ratio of PRODUCTS/REACTANTS - equilibrium shifted to LEFT.
14 Conditions of an equilibrium At equilibrium both reactions continue to occur - the system is DYNAMIC.The system is CLOSED – nothing added or removed.The concentrations of reactants and of products remain constant.Rate of the forward reaction equals rate of the back reaction.Equilibrium can be obtained from either side.
15 Reminder of dynamic equilibrium Dynamic equilibrium animation
16 Chemical Equilibrium Equilibrium is reached when the rate of the forward reaction equals the rate of thereverse reaction.H2(g) + I2(g)2HI(g)(H = -13kJ/mol)The H value always refers to the forward reaction. 13 kJ of energy is liberated for every mole of HI formed.For the whole reaction:H2(g) + I2(g)2HI(g)(H = -26kJ)
17 Chemical Equilibrium Reaction Rate H2 + I2 2 HI 2 HI H2 + I2 H2 + I2 Explanation P1422 HIH2 + I2Time
18 Chemical Equilibrium Reaction Rate H2 + I2 2 HI 2 HI H2 + I2 H2 + I2 Explanation P1422 HIH2 + I2Time
19 At equilibrium the concentration of all sub- Equilibrium ConstantAt equilibrium the concentration of all sub-stances are constant at a fixed temperature.Each equilibrium has a constant e.g. forH2(g) + I2(g)2HI(g)Kc =[H2] means conc. of ...N.BKc is only determined by the concentrations of solutions and gases. Pure liquids & solids are not included in the equation – their concentrations are constant.
20 Equilibrium Constant In General: aA + bB cC + dD [C]c [D]d Kc = When Kc has a high value, there will be more PRODUCTS – (on the RIGHT) - we say the equilibrium lies to The RIGHT (vice versa for a low value).
21 Equilibrium Constant Calculations 1. The balanced equation must be known.The concentration of a solid or liquid remains constant - these are not included in the equation.3. The concentration of the solvent is constant and not included in the equation.examples: PP4. The value of Kc is given without units.
22 Kc Calculation Examples Write expressions for Kc for each of the following reactions:C3H8(g) O2(g) 3CO2(g) H2O(g)Ca(s) + 2H2O(ℓ) Ca(OH)2(aq) H2(g)AgNO3(aq) NaCℓ(s) AgCℓ(s)+ NaNO3(aq)D. Na2CO3(s) HCℓ (aq) 2NaCℓ(aq) + H2O(ℓ) CO2(g)
23 Kc Calculation Examples Write expressions for Kc for each of the following reactions:C3H8(g) O2(g) 3CO2(g) H2O(g)Ca(s) + 2H2O(ℓ) Ca(OH)2(aq) H2(g)AgNO3(aq) NaCℓ(s) AgCℓ(s)+ NaNO3(aq)D. Na2CO3(s) HCℓ (aq) 2NaCℓ(aq) + H2O(ℓ) CO2(g)[CO2]3[H2O]4[C3H8] [O2 ]5Kc =Kc =[Ca(OH)2][H2][NaNO3][AgNO3]Kc =[NaCl]2[CO2][HCl]2Kc =
25 Calculating KGiven: N2(g) + 3H2(g) ↔ 2NH3(g) At equilibrium: [N2] = 0.30 M [H2] = 0.10 M [NH3] = 0.20 M
26 Calculating Concentrations at Equilibrium Methane gas reacts with water vapour to produce carbon monoxide gas and hydrogen gas according to this equation:CH4(g) + H2O(g) ↔ CO(g) H2(g)At equilibrium: [CO] = M [H2] = M [CH4] = M. If K is 5.67, calculate the concentration of water vapourHomework: complete the worksheet: Equilibrium Exercise 1
27 Carbon monoxide is a primary starting material in the synthesis of many organic compounds, including methanol, CH3OH(l). At C, K is 6.4 x 10 −7 for the decomposition of carbon dioxide into carbon monoxide and oxygen. Calculate the concentrations of all entities at equilibrium if mol of CO2(g) is placed in a closed container heated at C.
28 If 0. 50 mol N2O4(g) is placed in a 1 If 0.50 mol N2O4(g) is placed in a 1.0 L closed container at 150 0C, what will be the concentrations of N2O4(g) and NO2(g) at equilibrium? (K=4.50)When hydrogen and iodine are placed in a closed container at 440 0C, they react to form hydrogen iodide. At this temperature, the equilibrium constant, K is Determine the concentrations of all entities at equilibrium if 4.00 mol of hydrogen and 2.00 mol of iodine are placed in a 2.00 –L reaction vessel.H2(g) I2(g) ↔ HI(g)
29 The following reaction has an equilibrium constant of 25.0 1100 K. H2(g) I2(g) ↔ HI(g)If 2.00 mol of hydrogen gas, H2(g) and 3.00 mol of iodine gas, I2(g) are placed in a 1.00 L reaction vessel at 1100K, what is the equilibrium concentration of each gas?
30 Changing Equilibrium Conditions Predicting the effectLe Chatelier’s PrincipleIf the conditions of an equilibrium system are changed, a process takes place which tends to oppose or cancel the effect of the change.
31 Changing Equilibrium Conditions 2. The equilibrium constantN2(g) + 3H2(g) NH3(g) (H < 0)Kc =When the concentration of the N2 is increased, the ratio (Kc) will be smaller.To restore the value of Kc and the equilibrium,more N2 will have to react with H2This will diminish the concentrations of reactants.
32 N2(g) + 3H2(g) 2NH3(g) (H < 0) Adding ReactantsN2(g) + 3H2(g) NH3(g) (H < 0)When the concentration of the N2 is increased:the concentration of reactants increases instantaneouslyThe ratio Kc (momentarily) decreasesForward reaction rate increases and the concentrations of REACTANTS is LOWERED whilst the concentration of NH3 INCREASES.The reverse reaction rate INCREASES as more NH3 forms.A new equilibrium is established which has shifted to the RIGHT.The value of the ratio Kc is restored to its original valueKc =Overall Kc UNCHANGED!Kctime
33 N2(g) + 3H2(g) 2NH3(g) (H < 0) Effect of TemperatureN2(g) + 3H2(g) NH3(g) (H < 0)Kc =Increasing the temperaturewill favour the ENDOTHERMIC reaction.The REVERSE reaction will be favouredMore REACTANTS producedthe reaction shift to the LEFT.KctimeThe ratio (Kc) will therefore DECREASE.
34 Effect of Pressure Kc = N2(g) + 3H2(g) 2NH3(g) (H < 0) Increasing the PRESSUREEquilibrium will shift to REDUCE pressure.Reaction will favour the side with the LEAST number of MOLES of GAS – RHS NH3.More NH3 produced.Kc goes go up (this eg)!Kc =KctimeThe ratio (Kc) will therefore INCREASE.
35 Effect of a Catalyst Ea Ea E reactE prodPotential EnergyPotential EnergyE reactE prodA CATALYST lowers the ACTIVATION ENERGY of the reaction by providing a different reaction pathway.Activation Energy is lowered for BOTH FORWARD AND REVERSE REACTIONS.BOTH rates are therefore increased by the same amount and so the EQUILIBRIUM DOES NOT SHIFT!!!!
36 Industrial Preparation N2(g) + 3H2(g) NH3(g) (H < 0)Favorable conditions:HighLOWIn practice a ……………………. Temperature is used. Too ………………… will slow the reaction down.Kc =Kctime
37 Industrial Preparation N2(g) + 3H2(g) NH3(g) (H < 0)Favourable conditions:High [N2] & [H2]High PressureLOW TemperatureLOW [NH3]In practice a compromise temperature is used. Too low will slow the reaction down.Kc =Kctime
39 Equilibrium Disturbance 2SO2(g) + O2(g) --> 2SO3(g)Conc of O2 is increasedTemperature is increasedPressure is increased
40 Equilibrium in solutions Heterogeneous equilibriumDepending on circumstances, a solution may be:Under saturated – forward rate greater than reverse (salt dissolving)Over saturated – reverse greater than forward – salt precipitatesSaturated – forward & reverse the same rate (equilibrium)
41 Equilibrium in solutions Heterogeneous equilibriumDepending on circumstances, a solution may be:Under saturated – forward rate greater than reverse (salt dissolving)Over saturated – reverse greater than forward – salt precipitatesSaturated – forward & reverse the same rate (equilibrium)
42 Solubility of salts All nitrates are soluble All alkali metal & ammonium salts are solubleChlorides, bromides & iodides are soluble - except Ag, Hg, Cu & PbSulphates are soluble – except Pb, Ca, Ag &HgCarbonates, phosphates & sulphates of alkali metals & ammonium are solubleHydroxides of alkali metals, ammonium & barium are solubleSulphides of alkali metals, alkaline earth metals and ammonium are soluble
43 Equilibrium in solutions The equation for the equilibrium reactionof a saturated salt solution can be representedas follows:AB (s) A+ (aq) + B- (aq)
44 Equilibrium in solutions The equilibrium constant is called thesolubility product and is calculated asfollows:Ca(OH)2(s) Ca2+(aq) OH-(aq)Ksp = [Ca2+][OH-] 2
45 Equilibrium in solutions Temperature Change:Solubility curves show us that solubility's of most salts increase with increase in temperature.
46 Equilibrium in solutions Change in concentration :NaCl (s) Na+(aq) + Cl-(aq)Adding HCl to the above equilibrium, causesthe equilibrium to shift to the left. NaCl istherefore precipitated until the equilibriumis restored.Disturbance of the equilibrium by increas-ing the concentration of one kind of ion iscalled the common ion effect.
47 Equilibrium in solutions Take note that the common ion effect isnot restricted to solubility equilibriaonly.NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)Adding a few drops of indicator and NH4Clwill show that the equilibrium will shift to theleft - Explain.