physical chem flash - blue Flashcards
what is equilibrium constant
the equilibrium constant has the symbol k, (k has no units). the general equation for k is
aA + bB ->
difference between homogeneous equilibrium and a heterogeneous mixture
homogeneous equi: all species in equation are same state
heterogeneous equi: species in equation are different states
how do you write an expression for k when it is a heterogeneous equilibrium
when writing an expression for k in a heterogenous equilibrium, pure solids and liquids are emitted as their concentration is taken as constant and given value 1
what does the value of k tell us about the position of equilibrium
if k=1 neither products/reactants are favoured k>1 => products are favoured, k<1 => reactants are favoured
what effect does pressure have on k
this will change equilibrium position, the value of k does not change
what effect does a catalyst have on k
not change equilibrium position. value of k does not change
what effect does temp have on k
if endothermic, an increase in temp products, and product/ reactant ratio increases. therefore k increases
- if exothermic, increase in temperature favours reactants and so ratio product/reactant decreases. therefore k decreases
what effect does concentration have on k
it will change equilibrium position, however value of k does not change
equation for parts per million
ppm=grams of solution x 1,000,000
what is 1ppm equal to
1ppm=1mgkg-1.
1ppm=1mgl-1
What is equivalence point
The equivalence point is when the consent number of moles of base is added to neutralise the number of moles of an acid, the equivalence point is when gradient of titration curve is at its steepest
What is a buffer solution
a solution that remains approximately constant when a little bit of acid or base is added to it
How does an acid buffer work
The weak acid provides H+ which reacts with the addition of small amounts of a base, the salt of the weak acid provides the conjugate base, which can absorb excess H+ ions produced when small amounts of an acid are added. The removal of OH- by reaction with H+ will cause equilibrium to shift to RHS, so PH remains constant
What does a basic buffer consist of
A basic buffer consists of a solution of a weak base and one of its salts ie ammonia and ammonium chloride
How does a basic buffer work
The weak base removes excess H+ ions from addition of an acid and the conjugate acid produced by the salt supplies H+ ions when there are removed, the removal of H+ ions by reaction with OH- will cause equilibrium to shift to the RHS, so PH remains constant
General formula for indicators
Acid-base indicators are used in acid base titrations as they change colour at the end point of the reactions in acid base reactions. The equivalence point is the end point. Indicators are weak acids in which the colour of the acid is different from that of the conjugate base
When will the indicator change colour
The colour of an indicator at any time during a titration depends on the relative concentration of non ionised molecules and conjugate base (use book for rest of this)
How is an appropriate indicator for a titration experiment solutions
The appropriate indicator for a titration must be chosen so that the colour change occurs over the Ph range when the Ph is changing very rapidly. It isn’t possible to choose a suitable indicator for weak acid/weak base titration ionise Ph so it doesn’t change rapidly enough at end-point.
K<1 equ lies left
K=1 equ equal
K>1 equ lies right
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A system is in equilibrium when concentrations of reactants and products are constant. In equilibrium forward and backward reaction rates are equal
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In equilibrium pure solids and liquids given value 1
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Only T affects Kc
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At higher temps, products favoured so K increase
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At lower temp, reactants favoured so k decrease
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Catalysts speed up a reaction and lower the activation energy
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Bronsted lowry acid is a proton donor and a bronsted lowry base is a proton acceptor
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An acid buffer:
weak acid and one of its salts
A basic buffer is a weak base and one of its salts
is a weak base and one of its salts
