CHEMICAL EQUILIBRIUM Flashcards
Kc
Equilibrium concentration (units: mol/L)
Kp
Equilibrium pressure (units: bar)
Which equilibrium constant do I use?
K/Keq always refer to Kc. If asked SPECIFICALLY for Kp then use that
Relating Kc & Kp formula
Kc = Kp (RT)^-∆n
Equilibrium constant equation format
[Products]/[Reactants] but DO NOT include pure liquids or solids, only solutions and gas
If equation is all gas phase
Use Kp and find pressure
If equation has gas and aq phase
Use Kc cause aq is present
Homogenous equilibria
Reaction with all the same phase (Kc/Kp)
Heterogenous equilibria
Reaction with more than one phase (activity a)
Activity (a)
Used in heterogenous equilibria that is unites and measures effective concentration relative to standard state
Standard states (3)
- Solutions (C) = 1 mol/L
- Gas (P) = 1 bar
- Activity for pure liquid/solid = 1
Why is the activity of a pure liquid or solid 1 and unites
Because pure liquid and solids do not impact equilibria so they have a constant reactivity of 1
K
Expresses relationship between reactants and products
Direction of K
- When K>1: Forward reaction (products) are favored
- When K<2: Reverse reaction (reactants) are favored
- When K = 2: Neither reaction is favored
Rules for manipulating K
- If reaction is reversed, equilibrium constant is inverted
- If equation is multiplied, factor k is raised by the power of that factor
- If 2 individual equilibrium equations are adde, the product of K is the equilibrium constant of the equation
ICE table
Change = equilibrium - initial, in I row, either reactants or products should have a concentration and the other is 0, in C row, use coefficient of equation +/-x, E is everything added
Quadratic formula
x = -b +/ sqrt b^2-4ac/2a or use calculator lol
Small x approximation
- Use when there is small k but large initial concentration by 1000x difference. You are just ignoring/omitting added or subtracted x in an equation
- eg. x^2/0.250-x –> x^2/0.250. Check if equilibrium constant is less than 5% of initial concentration by x/initial change
Reaction quotient
Measures how far reaction is from equilibrium (same equation format is k with products/reactants
Q and K relation (3)
- Q<K: Reaction proceed to products to reach equilibrium
- Q = K: Reaction at equilibrium
- Q>K: Reaction proceed to reactants to reach equilibrium
Le Chatelier’s principle
Tells us that if equilibrium is disturbed, it will shift to minimize or counteract change
Affect of concentration in gaseous phase reaction
Adding or removing gas thats not an inert gas causes equilibrium to shift to side with fewer gas molecules
Affect of pressure in gaseous phase reaction
If total pressure is increased, equilibrium will shift to side with fewer gas molecules unless its an inert gas (noble gas)
If volume of container increases
- Pressure decreases
- Equilibrium shifts to side with more gas
If volume of container decreases
- Pressure increases
- Equilibrium shifts to side with fewer gas
When temperature increases
Heat is added to system
When temperature decreases
Heat removed from system
+∆H (H>0)
Endothermic (absorb heat)
-∆H (H<0)
Exothermic (release heat)
If container of exothermic reaction cooled
Moves to right
If container of exothermic reaction heated
Moves to left
If container of endothermic reaction cooled
Moves to left
If container of endothermic reaction heated
Moves to right
Affect of catalyst in equilibrium
No effect since it increases rate both forward and reverse reactions at the same time
