Cheat Sheet for Chemical Equilibrium | Cheat Sheet Chemical Principles

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.

Cheat Sheet for Chemical Equilibrium, Cheat Sheet of Chemical Principles

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