Physical chemistry Flashcards
What is equilibrium?
When the composition of reactants and products are constant indefinitely
What does the equilibrium constant, k, indicate?
The position of equilibirum
What are the concentrations of pure solids and liquids at equilibirum?
1
For endothermic reactions, a rise in temperature causes an…?
increase in K and the yield of
the product is increased.
For exothermic reactions, a rise in temperature causes a…?
decrease in K and the yield of
the product is decreased.
What value is kw at 25 cel
1x10-14
What is the conc of H+ and OH- in both water and aqeuous solutions with a pH of 7 at 298K?
both 7 x10-7 mol/L
The Brønsted-Lowry definitions of acids and bases
an acid is a proton donor and
a base is a proton acceptor
What is a buffer solution?
the pH remains approximately constant when small amounts of acid, base or water are added.
What does an acid buffer consist of?
An acid buffer consists of a solution of a weak acid and one of its salts made from a strong base.
How does an acidic buffer work?
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 produced by the addition of a small amount of acid
What does a basic buffer consist of?
A basic buffer consists of a solution of a weak base and one of its salts.
How does a basic buffer work?
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.
what is the theoretical point at which colour change occurs using an indicator
[H3O+] = KIn
What is the standard enthalpy of formation?
the enthalpy change when one mole of a
substance is formed from its elements in their standard states.
What is entropy, s?
The entropy (S) of a system is a measure of the degree of disorder of the system. The greater the degree of disorder, the greater the entropy.
The relationship between entropy, mp and bps?
There is a rapid increase in entropy at the melting point of a substance and an even more rapid and larger change in entropy at the boiling point.
The 2nd law of thermodynamics
states that the total entropy of a reaction system and its surroundings always increases for a spontaneous process.
What happens when heat energy is released by a reaction system into its surroundings?
increases the entropy of the surroundings
The 3rd law of thermodynamics
entropy of a perfect crystal at 0 K is zero
What is the standard entropy of a substance?
the entropy value for the substance in its standard state.
What happens when the value of G is negative?
G = negative, reaction is feasible and can occur
What does a feasible reaction mean?
A feasible reaction is one that tends
towards the products rather than the reactants. This does not give any indication of the rate of the reaction
At equilibrium, G = ?
0
A reversible reaction will proceed spontaneously until…
the composition is reached where
∆ G = 0 .
What does the rate of a chemical reaction depend on?
The rate of a chemical reaction normally depends on the concentrations of the reactants.
What is zero order?
changing the concentration of a reactant A has no effect on the rate of the reaction
What is first order?
doubling the concentration of a reactant A doubles the rate of the reaction
What is second order?
doubling the concentration of a reactant A increases the rate of the reaction fourfold
What can only be determined from experimental data?
The order of a reaction
What is the rate reaction dependant on?
the slowest step, which is called the ‘rate determining step’.
