Chemical Equili Flashcards
When is a chemical reaction equilibrium ?
A chemical reaction is in equilibrium when the composition of the reactants and products remains constant indefinitely.
What is K ?
-The equilibrium constant ( K ) characterises the equilibrium composition of the reaction mixture.
-The value of an equilibrium constant indicates the position of equilibrium
-K gives no indication of the rate at which equilibrium is established
-Equilibrium constants have no units
What influences the value of K
-The numerical value of the equilibrium constant depends on the reaction temperature and is independent of concentration and/or pressure
-The presence of a catalyst does not affect the value of the equilibrium constant.
Some stuff about water
-H3O+ (aq) represents a hydronium ion, a hydrated proton. A shorthand representation of H3O+ (aq) is H+ (aq)
-Water is amphoteric (can react as an acid and a base).
-The dissociation constant for the ionisation of water is known as the ionic product and is represented by Kw
dissociation constant (KD) is a specific type of equilibrium constant
What are acids and bases, and their conjugates ?
-The Brønsted-Lowry definitions of acids and bases state that an acid is a proton donor and a base is a proton acceptor.
-For every acid there is a conjugate base, formed by the loss of a proton.
-For every base there is a conjugate acid, formed by the gain of a proton.
What are strong and weak acids and bases, and their examples
-Strong acids and strong bases are completely dissociated into ions in aqueous solution.
-Weak acids and weak bases are only partially dissociated into ions in aqueous solution.
-Strong acids include: hydrochloric acid, sulfuric acid and nitric acid, while weak acids include: ethanoic acid, carbonic acid and sulfurous acid
-Solutions of metal hydroxides are strong bases. Ammonia and amines are examples of weak bases.
What is a buffer solution ?
-A buffer solution is one in which the pH remains approximately constant when small amounts of acid, base or water are added.
What is an acid buffer ?
-An acid buffer consists of a solution of a weak acid and one of its salts made from a strong base.
-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 is a basic buffer ?
-A basic buffer consists of a solution of a weak base and one of its salts.
-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 are indicators ?
-Indicators are weak acids
-In aqueous solution the colour of an acid indicator is distinctly different from that of its conjugate base.
What determines a colour change in an indicator ?
-The colour of the indicator is determined by the ratio of [HIn] to [In-]
-The theoretical point at which colour change occurs is when [H3O+] = KIn
-The colour change is assumed to be distinguishable when [HIn] and [In-] differ by a factor of 10.
-The pH range over which a colour change occurs can be estimated by the expression: pH = pKIn +/- 1
What is KIn
The acid indicator dissociation constant
