Chemical Equilibria Flashcards
When do chemical reactions become reversible?
When both the reactants and products in a reaction are of similar stability the reaction can go in either way
How long will forward/reverse reactions occur for?
until the concentrations of both reactants and products undergo no further change
What is equilibrium?
the state in which both reactants and products are present in concentrations which have no further tendency to change with time
What is the formula for equilibrium?
K =[concentration of products]^coefficients/{concentration of reactants]^coefficients
How do you identify how much product/reactant is present?
K < 0.001 = only reactants present
K between 0.001-1 = more reactant that product
K between 1-1000 = more product than reactant
K >1000 = only products present
What is Le Chatelier’s Principle?
When a stress is applied to a system at equilibrium, the equilibrium shifts to relieve the stress and restore an equilibrium
What is an acid/base? are these reactions equilibrium reactions?
acids are proton donors and must contain a H in its formula
Bases are proton acceptors and must have a lone pair of electrons
Acid/Base reactions are ALWAYS equilibrium reactions
What is the difference between strong and weak acids?
Strong acids and bases dissociate completely and weak acids and bases do not
Thus there is no reverse reaction
How can the pH be determined and what is the pOH?
pH = a figure expressing the acidity of a solution pH=-log10 [H3O+]
pOH = a scale used for basic solutions pOH=-log10[OH-]
What is Kw?
the relationship between [H3O+] and [OH_], it is true for any aqueous environment
Kw= [H3O+] X [OH-] = 1x10^-14 at 25degrees C
What is pH + pOH?
14
What is Ka?
Ka is the dissociation constant for weak acids pKA = -log10 (Ka)
When Ka is large, pKA is small (giving a strong acid)
For bases pKb= -log10(Kb)
How can acid strength be determined
This can be determined via titration
How is a titration curve read?
the area of gradual increase = the buffer zone
the inflection within the graph = equivalence with pKa
What are buffer solutions?
- Generally they are a mixture of a weak acid and its conjugate base
- these solutions maintain the pH and make it approximately constant
