Physical Chemistry Flashcards
Equilibrium constant
K. A measure of the ratio of the concentration of products to reactants at equilibrium– the position of the equilibrium
Increasing/ decreasing K
The only thing that affects K is temperature
Definition of an acid
It donates H+ ions
Definition of a base
It accepts H+ ions
Conjugate acid/ base
What is formed on the other side of the reaction e.g. acid is conjugate base. The stronger the acid, the weaker the conjugate base
H+ ions
Just a proton. Forms a cluster in water, simplest being H30+, or hydronium (dative covalent bond between H+ and H2O)
PKw
14
Strength of acid/ base depends on?
How well they dissociate in water
Strong acids
Dissociate completely into ions. Have a higher conductivity, lower pH and faster reaction rate due to higher H+ concentration
Weak acids
Don’t completely dissociate into ions
Examples of strong acids
HCL, HNO3, H2SO4
Examples of weak acids
Ethanoic acid, methanoic acid, carbonic acid, and sulphurous acid
Ka
acid dissociation constant. The larger the Ka, the more the acid breaks down, so the stronger it is
PH
Depends on Ka, concentration of acid and salt
Strong bases examples
Sodium hydroxide, potassium hydroxide, lithium hydroxide
Weak bases examples
Basically anything with Amm in it e.g. ammonia
PH of a salt solution
Depends on strength of the acid and base from which it was formed (pH depends on which one is strongest)
Equilibrium of when a solvent is soluble in two different solvents
K= [solute] in solvent A divided by
[solute] in solvent B
Soap
Salt formed from a fatty acid (weak) and Na or K hydroxide
Amphoteric substance
Can act as acids or bases e.g. water
Ka of dissociated ions
Ka= [H+] [A]
—————-
[HA]
Buffer solutions
Has a pH which remains constant (ish) despite the addition of small amounts of H+ or OH- ions
Base added to buffer solutions
H+ ions are removed and excess x molecules break up to replace them
Equilibrium in a chemical reaction
when the composition of the reactants and the products remains constant indefinitely
Endothermic reactions and K
a rise in temperature causes an increase in K and the yield of the product is increased
Exothermic reactions and K
a rise in temperature causes a decrease in K and the yield of the product is decreased
catalyst and K
a catalyst does not affect the value of K
indicators
weak acids
standard enthalpy of formation
the enthalpy change when one mole of a substance is formed from its elements in their standard states
positive S
the greater the degree of disorder, the greater the entropy
second laws of thermodynamics
the total entropy of a reaction system and its surroundings always increases for a spontaneous process
exothermic reactions and entropy
heat energy released increases the entropy
endothermic reactions and entropy
heat energy absorbed decreases the entropy
the third law of thermodynamics
the entropy of a perfect crystal at 0K is zero
– Gibb’s
the reaction is feasible
order of a reaction
can only be determined through experimental data
rate determining step
the slowest step of the reaction, which the rate of the reaction is dependent on
reaction feasibility for reversible reactions
equilibrium will lie to the left
reaction feasibility for non-reversible reactions
equilibrium will lie to the right
