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Cheat Sheet for Chemical Equilibrium, Cheat Sheet of Chemical Principles

Ksp is equilibrium constant of solubility

Typology: Cheat Sheet

2020/2021

Uploaded on 04/23/2021

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Cheat&Sheet&for&Chemical&Equilibrium:&
Equilibrium&
Rates&are&equal.&
Concentrations&remain&constant.&&
&
Finding&Keq&&
Keq&=&products&
&&&&&&&&&&&&&&&&&&&&&&&&&reactants&
You&can&have&Kc,&Kp,&Ksp,&Ka,&Kb&&These&are&the&same&as&Keq.&They&just&describe&specific&types&
of&reactions.&
Given:&&Concentrations.&&Asked&for&Keq,&solve&for:&&Kc.&
Given:&&Pressures.&Asked&for&Keq,&solve&for:&&Kp.&
Given:&Grams.&Asked&for&Keq&and&it&is&not&clear&which&to&use…&&
o If&you&have&a&reaction&of&gases,&solve&for:&Kp.&
o If&you&are&a&reaction&with&aqueous&solutions,&solve&for:&Kc.&
Sometimes&you&are&asked&to&solve&for&Kc&and&then&relate&to&Kp.&You&use&Kp&=&Kc(RT)∆n&
&
Finding&Keq&when&the&reaction&is&changed:&
When&a&reaction&is&reversed,&the&new&Keq&=&(1&/&Keq)&
When&a&reaction&is&multiplied,&the&new&Keq&=&(Keq)n&where&n=&the&number&the&equation&is&
multiplied&by&
When&more&than&one&reaction&is&added&together&(like&a&Hess’s&Law&problem),&your&Keq&for&each&
reaction&will&be&MULTIPLIED&together.&New&Keq&=&(K1)*(K2)&
&
Determining&The&Direction&a&Reaction&Proceeds&
K&>&1:&Production&of&the&products&is&favored.&Equilibrium&lies&to&the&right.&
K&<&1:&Production&of&the&reactants&is&favored.&Equilibrium&lies&to&the&left.&
Reaction&Quotient,&Q,&for&non‐equilibrium&conditions&
o Q&=&K,&System&is&at&equilibrium&
o Q&>&K,&Too&many&products,&system&shifts&to&the&Left&to&increase&production&of&reactants&
o Q&<&K,&Too&many&reactants,&system&shifts&to&the&Right&to&increase&production&of&products&
&
ICE&Charts&
Completed&using&Concentrations&or&sometimes,&Partial&Pressures&
Given:&Initial&Concentration&of&Reactants&only‐&Products&will&be&zero.&Determine&the&change&by&
subtracting&“x”&from&reactants&and&adding&“x”&to&products.&
Given:&Initial&Concentrations&of&Products&only‐&Reactants&will&be&zero.&Determine&the&change&by&
subtracting&“x”&from&the&products&and&adding&“x”&to&reactants.&
Given:&Initial&Concentration&of&a&species&and&Equilibrium&concentration&of&a&species:&Determine&
the&change&by&subtracting&equilibrium&concentration&and&initial&concentration.&Fill&in&table&as&
appropriate.&
Don’t&forget&to&consider&mole&ratios&when&determining&the&change&of&other&species.&
Keq&is&determined&from&equilibrium&values.&
All&ICE&charts&you&see&on&the&AP&exam&follow&the&5%&rule.&That&means&when&you&subtract&“x”&
or&add&“x”&from&a&concentration&other&than&0,&you&can&ignore&it!&
&
&
&
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Cheat Sheet for Chemical Equilibrium: Equilibrium

  • Rates are equal.
  • Concentrations remain constant. Finding Keq
  • Keq = products reactants
  • You can have Kc, Kp, Ksp, Ka, Kb  These are the same as Keq. They just describe specific types of reactions.
  • Given: Concentrations. Asked for Keq, solve for: Kc.
  • Given: Pressures. Asked for Keq, solve for: Kp.
  • Given: Grams. Asked for Keq and it is not clear which to use… o If you have a reaction of gases, solve for: Kp. o If you are a reaction with aqueous solutions, solve for : Kc.
  • Sometimes you are asked to solve for Kc and then relate to Kp. You use Kp = Kc(RT)∆n Finding Keq when the reaction is changed :
  • When a reaction is reversed, the new Keq = (1 / Keq)
  • When a reaction is multiplied, the new Keq = (Keq)n^ where n= the number the equation is multiplied by
  • When more than one reaction is added together (like a Hess’s Law problem), your Keq for each reaction will be MULTIPLIED together. New Keq = (K 1 )(K 2 ) Determining The Direction a Reaction Proceeds*
  • K > 1 : Production of the products is favored. Equilibrium lies to the right.
  • K < 1 : Production of the reactants is favored. Equilibrium lies to the left.
  • Reaction Quotient, Q, for non‐equilibrium conditions o Q = K , System is at equilibrium o Q > K , Too many products, system shifts to the Left to increase production of reactants o Q < K, Too many reactants, system shifts to the Right to increase production of products ICE Charts
  • Completed using Concentrations or sometimes, Partial Pressures
  • Given: Initial Concentration of Reactants only‐ Products will be zero. Determine the change by subtracting “x” from reactants and adding “x” to products.
  • Given: Initial Concentrations of Products only‐ Reactants will be zero. Determine the change by subtracting “x” from the products and adding “x” to reactants.
  • Given: Initial Concentration of a species and Equilibrium concentration of a species: Determine the change by subtracting equilibrium concentration and initial concentration. Fill in table as appropriate.
  • Don’t forget to consider mole ratios when determining the change of other species.
  • Keq is determined from equilibrium values.
  • All ICE charts you see on the AP exam follow the 5% rule. That means when you subtract “x” or add “x” from a concentration other than 0, you can ignore it!

Equilibrium Constant of Solubility

  • The equilibrium constant for these problems is called the solubility product while the solubility is the concentration that is actually dissolved or “x”.
  • The way to show the dissolving of the solid is AgI Ag+^ + Cl‐
  • Since the reactants are solids, the equilibrium expression would be Ksp= [product#1][product#2]
  • Given: Solubility: Determine the Ksp by setting up an ICE chart to properly deal with mole ratios.
  • Given: Ksp: Determine the solubility by writing an ICE chart and solving for “x”.
  • Given: Initial Concentrations and asked whether a precipitate will form: Calculate Q (no ICE chart needed) and compare with Ksp: o Q>Ksp , precipitate will form o Q=Ksp , at equilibrium o Q<Ksp , no precipitate formed
  • Selective precipitation is the process by which metal ions are separated based on different Ksp values. They therefore need different concentrations of one anion for precipitation to occur.
  • ∆G = ∆G° + RTlnQ ‐ formula used to relate Gibbs Free Energy at standard and non‐standard conditions.
  • At equilibrium: ∆G° = ‐RTlnKeq Le Châtelier’s Principle:
  • If a system is disturbed by a change in temperature, pressure, or concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance.
  • Change in Concentration: o Increase Concentration‐ system will shift away from addition by consuming added substance. o Decrease Concentration‐ system will shift to increase the concentration of that substance.
  • Change in Volume/Pressure (FOR GASES ONLY) o Increase Pressure/Decrease Volume‐ shift towards side with fewer moles of gas. o Decrease Pressure/Increase Volume‐ shift towards side with more moles of gas.
  • Change in Temperature: o Increase Temperature‐ system will shift in the direction to consume heat (Just like concentration rule!). o Decrease Temperature‐ system will shift in the direction to produce heat (Just like concentration rule!)
  • Common Ion Effect‐ The addition of an ion already involved will cause a shift away from this addition. Specifically, it will decrease the solubility of a compound.
  • Addition of a Catalyst‐ will increase forward and reverse rates by lowering activation energy, but will have no effect on the concentrations at equilibrium. Keq NOT affected.