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CFE - Advanced Higher Chemistry > 5) Unit 1 - Chemical Equilibrium > Flashcards

5) Unit 1 - Chemical Equilibrium Flashcards

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1
Q

when is a reaction said to be in equilibrium

A

when the rate of the forward reaction is equal to the rate of the of the backward reaction

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2
Q

name 3 things that alter the position of quilibrium

A
  • altering the concentrations of products or reactants
  • altering the temperature
  • altering pressure when their are different number of moles on product and reactant sides
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3
Q

when writing the equilibrium constant K if there are pure solids or liquids what do you take their concentration as?

A

1

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4
Q

describe why altering concentrations of products or reactants does not affect K

A
  • only affects the position of equilibrium but not K
  • Adding more products will shift the equilibrium to the left. The system reacts to make more reactants therefore the ratio of products to reactants will be the same
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5
Q

describe why pressure does not effect k

A
  • only affects the position and not the k value
  • if pressure increases the equilibrium shifts to the side with the fewest gases moles
  • therefore the equilibrium reacts to restore the same ratio as product to reactants
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6
Q

describe why changes in emperature does affect k

A
  • K is temperature dependent
  • if the forward reaction is endothermic, decreasing the temperature favours the formation of products
  • If the forward reaction is endothermic, increases in temperature favours the formation of products
  • Therefore the ratio of products to reactants is not the same as before, therefore altering the value of k
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7
Q

when would you use the ionic product of water.

A

•when you need to calculate the pH/pOH when given a concentration or pOH/pH of acid or base

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8
Q

what 2 formulas should you remember for the ionic product of water

A

H+ x OH- = 1x10-14

pH + pOH = 14

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9
Q

according to bronstead lowry’s definition of an acid and a base, what is an acid and what is a base

A 
ACID = ELECTRON DONOR
BASE = ELECTRON ACCEPTOR
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10
Q

what is a conjugate acid and a conjugate base

A

conjugate acid = species left when a base accepts an electron

conjugate base = species left when an acid donates an electron

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11
Q

strong acids and bases completely _______ in solution.

weak acids and bases partially _______ and form an _________ which lies mostly to the left.

A

strong acids and bases completely dissociates in solution.

weak acids and bases partially dissociate and form an equilibrium which lies mostly to the left.

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12
Q

what is the general Ka, for weak acids

A

ka = [H3O+][A-]/[HA]

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13
Q

the ______ the Ka, the stronger the acid

the ______ the pKA, the stronger the acid

A

the larger the ka, the stronger the acid

the smaller the pKa, the stronger the acid

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14
Q

formula used to work out the pH of a weak acid

A

pH = 1/2pKa - 1/2logc

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15
Q

what salt does a strong base and strong acid make and why

A

Neutral salt.

  • Water exists in equilibrium producing H+ and Oh- ions.
  • When the salt of a strong acid and strong base dissociates it will not react with the H+ or OH- ions in solution
  • Therefore the concentrations of H+ and OH- are equal, making it neutral
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16
Q

what salt does a strong base and weak acid make and why

A

BASIC

  • Water exists in equilibrium producing H+ and Oh- ions.
  • When the salt of a weak acid and strong base dissociates, one of its ions will react H+, removing them out of the equilibrium
  • This decreases the concentration of H+ in solution meaning OH-> H+. BASIC
17
Q

what salt does a weak base and strong acid make and why

A

ACIDIC

  • Water exists in equilibrium producing H+ and OH- ions
  • When the salt of a strong acid and a weak base dissociates, OH ions are removed because one of the salts ions reacts with it
  • This decreases the OH- ion concentration in solution meaning H+> OH. ACIDIC
18
Q

indicators are usually weak acids?

true or false

A

true

19
Q

what is the acid dissociation constant for an indicator ‘HIn’

A

Kin = [H3O+][In-]/[HIn]

20
Q

the colour of the acid molecule HIn, is the same as the colour of the conjugate base in indicators.

True or false

A

false.

They are different colours

21
Q

what formula is used to work out the pH of an indicator

A

pH = pKin + log[In-]/[HIn]

22
Q

how much greater does the In- concentration have to be compared to the HIn, for colour to dominate (colour change)

A

10x greater

23
Q

what is the equivalence point

A

the exact point when the exact amount of alkali has been added to neutralise an acid H+=OH-

24
Q

what is a buffer solution

A

solution which the pH remains the same even on the addition of small amounts of acid or alkali or water.

25
Q

What is an acid buffer

and give an example

A

solution of weak acid and one of its salt

e.g. sodium ethanoate and ethanoic acid

26
Q

how do acid buffers work on the addition of H+

A
  • H+ will react with the negative ion of dissociated salt

* the H+ are removed meaning the concentration of H+ remain the same

27
Q

how do acid buffers work on the addition of OH-

A
  • OH- will react with the H+ ion of the dissociated weak acid
  • H+ ions will remain the same, because the equilibrium will react to produce more/ replace them from the large supply of the reactant (weak acid)
28
Q

What is a basic buffer

and give an example

A

solution of weak base and one of its salts

e.g. ammonia solution and ammonium chloride

29
Q

how do basic buffers work on the addition of H+

A
  • H+ will react with OH- of dissociated weak acid
  • OH- ions will remain the same, because the equilibrium will react to produce more / replace them from the large supply of the weak acid
30
Q

how do basic buffers work on the addition of OH-

A
  • OH- will react with the positive ion of the dissociated salt.
  • The OH- ions are removed meaning the concentration of H+ and OH remain the same
31
Q

one tip should use when calculating the pH of buffer solution

A

Put in the concentrations of acid and salt, in the NEW VOLUME. (x ratio stuff)

32
Q

formula for calculating the pH of buffer solution

A

pH = pKa - log([acid]/[salt])

CFE - Advanced Higher Chemistry (10 decks)

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