Reaction Feasibility + Chemical Equillibrium for some reason Flashcards
What is the standard enthalpy of formation?
The enthalpy change when 1 mole of a substance is formed from its elements in their standard states
standard enthalpy equation?
ΔH°= ΣΔHf (products) – ΣΔHf (reactants)
What is entropy(S)?
A measure of the degree of disorder
What does the second law of thermodynamics state?
the total entropy of a reaction system and its surroundings always increases for a spontaneous reaction
Heat energy absorbed by the reaction system from the surroundings
decreases the entropy of the surroundings
an increase in temperature increases
entropy
What does the third law of thermodynamics state?
The entropy of a perfect crystal at 0K is zero
Gibbs equation?
ΔG° = ΔH° - TΔS°
negative ΔH°
positive ΔS°
ΔG° is negative, reaction is always feasible
positive ΔH°
negative ΔS°
ΔG° is positive, reaction is never feasible
negative ΔH°
negative ΔS°
Reaction is only feasible at low temperatures
positive ΔH°
positive ΔS°
Reaction is only feasible at high temperatures
To calculate the temperature let
ΔG°=0
K depends on the reaction
temperature
K>1 means
the equillibrium lies to the right (more products than reactants)
K<1 means
the equillibrium lies to the left (more reactants than products)
K=
[C][D] /[A][B] (products on the numerator, reactants on the denominator) (raise each to the number of moles)
What is the equillibrium constant? (K)
characterises the equillibrium composition of the reaction mixture
The concentrations of pure liquids and solids is
1
For endothermic reactions, a rise in temperature causes an _________ in K and the yield of the product is ____________
increase, increased
What does amphoterric mean?
can act as both an acid and a base
pH equation?
pH= -log[H+]
What is Kw?
dissociation constant
Kw equation?
Kw=[H+][OH-]
H+ equation?
[H+]=10^-pH
How to calculate the concentration of one ion if the other ion is known?
use Kw or pH+pOH=14
Bronsted-Lowry definition of an acid?
A proton donor
Bronsted-Lowry definition of a base?
a proton acceptor
What does Ka represent?
The acid dissociation constant
pKa equation? (strong acid pH equation)
pKa=-logKa
weak acid pH equation?
pH=1/2pKa-1/2logc
A soluble salt of a strong acid + strong base=
neutral solution
A soluble salt of a weak acid + strong base=
alkaline solution
A soluble salt of a strong acid + weak base=
acidic solution
What is a buffer solution?
one in which the pH remains approximately constant when small amounts of acid, base or water are added
What is a buffer made up of?
A weak acid/base and the salt of that weak acid/base
Describe an acid buffer solution
In an acid buffer solution, the weak acid provides hydrogen ions when these are removed by the addition of a small amount of base. The salt of the weak acid provides the conjugate base, which can absorb excess hydrogen ions when these are produced by the addition of a small amount of acid
Describe a basic buffer solution
In a basic buffer solution the weak base removes excess hydrogen ions, and the conjugate acid provided by the salt supplies hydrogen ions when these are removed.
pH of acid buffer solution equation
pH=pKa-log x [acid]/[salt]
At 25C the value of Kw is
1 x 10^-14
