Equilibrium -physical Flashcards
Equilibrium definition
A chemical reaction where reactant and products concentrations remain constant
Rate equation for equilibrium
K= [C]^c [D]d/[A]a [B]b
Where a,b,c,d
If the equilibrium position lies to the left
Products < reactants
K<1
More reactants than products
If the equilibrium position lies to the right
Products >reactants
K>1
Equilibrium constant rules
Not affected by concentration and pressure
When temperature increases the value of K increases for the endothermic reaction
When temperature decreases the value for K increases for the exothermic reaction
Endothermic enthalpy change
Positive
Exothermic enthalpy change
Negative
Water equilibrium
H2O +H2O —> H3O+ +OH-
Kw formula
Kw = [H3O+] [OH-]
=1.01x10^-14
Kw rules
Affected by temperature
pH formula
pH = -log[H+]
H+ concentration formula
10^-pH
Concentration calculation and pH calculation tips
Always write out the dissociation equation
Strong acids
Acids that completely dissociate into ions in aqueous solution
Strong bases
Bases that completely dissociate into ions
Weak acids
Acids which partially dissociate into ions in aqueous solution
Weak bases
Bases which partially dissociate into ions in aqueous solution
Strong acids examples
Hydrochloric, nitric and sulphuric.
Weak acids examples
Ethanoic, sulphurous and carbonic
Strong bases examples
Metal hydroxides and oxides
Weak bases examples
Ammonia and amines
Brønsted-Lowry acids definition
A proton donator since H+ ions are protons
Brønsted-Lowry bases definition
A proton acceptor since H+ ions are protons
Conjugate acid
The proton donator in the reverse reaction
Conjugate base
The proton acceptor in the reverse reaction
Amphoteric
Where a substance can act as an acid and base
Weak acids properties
Higher pH
Lower conductivity
Slower rate of reaction
Strong acids properties
Lower pH
Higher conductivity
Faster rate of reaction
Strong bases properties
Higher pH
Higher conductivity
Faster rate of reaction
Weak acids properties
Lower pH
Lower conductivity
Slower rate of reaction
Rules for neutralising strong and weak acids and bases
The quantities of acid and bases used in a reaction are based on the balanced equation, not in acid strength.
Ka formula
[Products] / [reactants]
Unique rule for Ka
Don’t put water into the equation
pKa formula
-logKa
PKa scale
The lower the pKa the stronger the acid
Why is PKa better than pH
It isn’t affected by the dilution of water since all species are diluted by the same factor
Ka scale
The higher the Ka the stronger the acid
Weak acid and strong base salt pH
More than 7
Strong acid and weak base salt pH
Less than 7
Strong acid and base salt pH
7
Explanation of strong base and weak acid salt pH
The the conjugate base ions will react with hydronium ions supplied by water equilibrium, the water equilibrium will shift to replace the hydronium ions producing an excess of hydroxide ions.
Weak base and strong acid salt pH explanation
The conjugate acid ions will react with the hydroxide ions supplied by the water equilibrium, the water equilibrium will shift to replace the hydroxide ions producing an excess of hydronium ions.
pH of weak acids formula
pH = 1/2pKa - 1/2logc
Buffer solutions def
A solution where the pH remains constant on addition of small amounts of acid or base
Acid buffer composition
A weak acid
The salt of a weak acid and strong base
pH of buffer solution
pH = pKa - log[acid]/[salt]
Indicator dissociation
HIn + H2O —> H30+ + OH-
Dissociation constant of indications (Kin)
[H3O+] [In-]/[HIn]
Titration graph rules
pH changes quickly around the endpoint of reaction
The endpoint is the middle of the vertical line.
Weak acid strong base indicator
Change colour between 7 and 11
Strong acid weak base indicator
Change colour between 3 and 7
Colour change of indicator
When H+ concentration is equal to Kin
Colour change pH range explanation
The colour change is distinguishable when [Hin] and [in-] are within factor of ten therefore pH =Kin +/-1
