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¬&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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