EQUILIBRIUM

Chemical reaction occurs when

• collisions between molecules make enough energy to break the bonds

• molecules collide with proper orientation

• bonds between atoms in reactants break and new bonds form

Proper orientation for collisions

Chemical reaction does NOT occur when

• collisions between reacting molecules do not provide sufficient energy to break the bonds

• wrong orientation

activation energy

minimum energy needed for reaction to take place (with proper collision of reactants)

reaction rate

• speed which reactant is used up

• speed which product forms

Increase in reaction rate caused by

• faster molecules → temperature rises → more colliding molecules with activation energy

• increase in concentration

Increase in concentration of reactant causes

• increase in collisions

• increase in reaction rate

catalyst

• speeds up reaction rate

• lowers activation energy

• not used up during reaction

denatures catalyst

• temperature

• pH

reversible reaction

there are both forward and reverse:

• reactants initially present and collide, forward begins

• as products form they collide, reverse begins forming reactants

equilibrium

• rate of forward = rate of reverse

• no further change in amounts of reactants and products, remain constant (NOT NECESSARILY THE SAME)

equilibrium constant expression

Kc = [products]^b / [reactants]^a

M

mol/L represented by brackets in K_c equation

heterogeneous equilibrium

• gases, solids, liquids part of reaction

• solids and liquids are constant

• cancel solids and liquids to write K_c expression

K <<< 1

favors reactants, little of forward reaction has occurred then equilibrium

K = 1

equal

K >>> 1

favors products, most of forward reaction occurs then equilibrium

large K_c at equilibrium

• large amounts of products

• little reactant left

• favors products

small K_c at equilibrium

• small amount of products

• favors reactants

calculating equilibrium concentration

1. Write K_c expression

2. Substitute values

3. Solve for missing

Le Châtelier’s principle

• change in equilibrium conditions changes system’s equilibrium

• system at equilibrium under stress will shift

• rate of forward or reverse reaction will change to return system to equilibrium

adding reactant

• upsets equilibrium

• increase in collisions

• shifts products

• forward rate increases to equal K_c

adding product

• increase in collisions

• increase in reverse rate

• forms more reactants

• shifts equilibrium to reactants

removing reactant

• decreases reactant collisions

• decreases forward rate

• shifts equilibrium to reactants

removing product

• decreases reverse rate

• greater forward rate

• shits equilibrium to product

decrease volume

• increases concentration

• shifts equilibrium to lesser moles

volume increase

• decreases concentration

• shifts equilibrium to greater moles

heat and exothermic

• decrease in temperature → shifts to products

• increase in temperature → shifts to reactants

heat and endothermic

• decrease in temperature → shifts to reactants

• increase in temperature → shift to products

catalyst

equal increase in rates, NO EFFECT

saturated solution

• max dissolved solute

• solid solute

• equilibrium → dissolving rate = recrystallization rate

solubility product expression

Ksp = [ ^charge]^a[ ^charge]^b

• NO SOLID, solid is constant

calculating K_sp

1. K_sp= [product][product]

2. put any products with coefficients to that power

molar solubility

moles of solute dissolve in 1L of solution

calculating molar solubilit

1. [given Ksp] = [x][x]

2. solve, likely by square rooting [x][x] and [given Ksp]