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Chemistry > 7 Equilibria > Flashcards

7 Equilibria Flashcards

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1
Q

Reversible reaction

A

the products can react to reform the original reactants

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2
Q

Dynamic equilibrium

A

the rate of the forward reaction is equal to the rate of the backward reaction in a closed system and the concentrations of the reactants and products remain constant

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3
Q

La Chateliers principle

A

if a change is made to a system at dynamic equilibrium, the position of equilibrium moves to minimise the change

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4
Q

An increase in concentration

A

equilibrium shifts to the right to reduce the effect of an increase in the concentration of a reactant

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5
Q

Decrease in concentration

A

Shifts to the left to reduce the effect of a decrease in reactant (or an increase in the concentration of product)

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6
Q

What effect does water have on equilibrium when it is added to an equilibrium mixture?

A

it has no effect on the position of equilibrium as the water dilutes all the ions equally so there is no change in the ratio of reactants to products

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7
Q

An increase in pressure

A

Shifts in the direction that produces the smaller number of molecules of gas to decrease the pressure again

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8
Q

Decrease in pressure

A

Shifts to the direction that produces the larger number of molecules of gas to increase the pressure again

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9
Q

Increase in temperature

A

Moves in the endothermic direction to reverse the change

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10
Q

Decrease in temperature

A

Moves in the exothermic direction to reverse the change

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11
Q

What is a catalyst and its effect on equilibrium?

A
  • a substance that increases the rate of a chemical reaction
  • only causes a reaction to reach equilibrium faster
  • therefore have no effect on the position of equilibrium
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12
Q

Kc

A
  • Solids are ignored in equilibrium expressions
  • The Kc of a reaction is specific and only changes if the temperature of the reaction changes
  • The concentration of reactants and products=number of moles/volume
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13
Q

Partial pressure of a gas

A
  • the pressure that the gas would have if it was in the container all by itself.
  • Partial pressure=mole fraction x total pressure
  • sum of the partial pressures should add up to the total pressure
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14
Q

Total pressure

A
  • sum of the partial pressures
  • sum of the mole fraction should add up to 1,00
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15
Q

Mole fraction of a gas

A
  • the ratio of moles of a particular gas to the number of moles of gas present.
  • Mole fraction= number of moles of a particular gas/total number of moles if all the gases in the mixture
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16
Q

Changes that affect the equilibrium constant

A
  • only temperature changes the equilibrium constant
  • pressure changes the position
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17
Q

Changes in concentration

A

If all other conditions stay the same, the equilibrium constant Kc is not affected by any changes in concentration of reactants or products

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18
Q

Changes in pressure

A
  • A change in pressure only changes the position of equilibrium
  • If all other conditions stay the same, the equilibrium constant Kc is not affected by any changes in pressure of the reactants or products
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19
Q

Changes in temperature

A
  • Changes in temperature change the equilibrium constant Kc

Eg) 2HI ( g ) ⇌ H2 ( g ) + I2 ( g ) (endothermic reaction)
- An increase in temp causes H2 and I2 to increase, but HI decreases therefore Kc increases

Eg) 2SO2 (g) + O2 (g) ⇌ 2SO3 (g) (exothermic)
- An increase in temp causes SO3 to decrease and SO2 and O2 to increase therefore Kc decreases

20
Q

Presence of a catalyst

A
  • If all other conditions stay the same, the equilibrium constant Kc is not affected by the presence of a catalyst
  • A catalyst speeds up both the forward and reverse reaction at the same rate so the ratio of products to reactants remains unchanged
21
Q

Haber process: Synthesis of ammonia:

A

N2 (g) + 3H2 (g) ⇌ 2NH3 (g) ΔHr= -92 kJ mol/-1

22
Q

Maximizing the ammonia yield: pressure
(favors high pressure as it produces a higher yield of ammonia, but that is expensive to do therefore compromise of 200 atm is used)

A
  • An increase in pressure will cause equilibrium to shift towards the right (fewest moles of gas to reduce pressure) therefore yield of ammonia increases
  • An increase in pressure will cause the particles to be closer together and therefore increasing the number of successful collisions leading to an increased reaction rate
  • Very high pressures are expensive to produce, therefore a compromise pressure of 200 atm is chosen
23
Q

Maximizing the ammonia yield: temperature
(favors a low temperature as the reaction is exothermic and will move to the right which increases the yield of ammonia, but the temperature can’t be too low otherwise particles won’t have enough kinetic energy to reach equilibrium therefore compromise of 400-450 is used)

A
  • To get the maximum yield of ammonia the position of equilibrium should be shifted to the right
  • The Haber process is exothermic and this will shift to the right if the temperature is lowered, however a decrease in temperature will decrease the energy of the surroundings so the reaction will go in one direction in which energy is released to counteract this and since the reaction is exothermic the equilibrium shifts to the right
  • However at low temperatures the gases won’t have enough kinetic energy to collide and react and equilibrium would not be reached, therefore a compromise temperature of 400-450 degrees Celsius is used
  • A heat exchanger can be used which warms the gas mixture to give molecules more kinetic energy
24
Q

Removing ammonia

A
  • Removing ammonia by condensing it to a liquid causes the equilibrium to shift to the right to replace the ammonia causing more ammonia to be formed from hydrogen and nitrogen
  • The removed ammonia is stored at very low temperatures and there is no catalyst present with the stored ammonia so the decomposition reaction of ammonia to decompose back into hydrogen and nitrogen will be too slow
25
Q

Catalyst for Haber process

A
  • In the absence of a catalyst the reaction is very slow and hardly anything happens in a reasonable time
  • Therefore an iron catalyst is used
26
Q

Contact process: Synthesis of sulfuric acid

A

2SO2 (g) + O2 (g) ⇌ 2SO3 (g) ΔHr= -197 kJ mol/-1

27
Q

Maximizing the sulfuric acid yield: Pressure

A
  • An increase in pressure will result in the equilibrium shifts towards the right (fewest moles of gas formed to reduce the pressure) therefore yield of sulfuric acid increases
  • In practice the reaction is carried out at only 1 atm and this is because Kp for this reaction is already very high therefore the position of equilibrium is already far over to the right
  • Higher pressures than 1 atm will be unnecessary and expensive
28
Q

Maximizing the sulfuric acid yield: Temperature

A

Same as Haber, a compromise temperature of 450 degrees Celsius is used

29
Q

Removing sulfuric acid

A
  • SO3 is removed by absorbing it in 98% sulfuric acid
  • The SO3 reacts with the solution and more H2SO4 is formed
30
Q

Catalystfor Contact process

A

Uses vanadium (V) oxide

31
Q

Common acids (names and formulae)
Common alkalis (names and formulae)

A

in notes

32
Q

Bronsted-Lowry theory of acids and bases

A

defines acids and bases in terms of proton transfer between chemical compounds

33
Q

A Bronsted-Lowry acid

A

a species that gives away a proton (H+)

34
Q

A Bronsted-Lowry base

A

a species that accepts a proton (H+) using its lone pair of electrons

35
Q

Amphoteric

A

species that can act both as acids and bases (water is an example)

36
Q

Strong acids and bases

A

fully dissociate in aqueous solutions

37
Q

Weak acids and bases

A

partially dissociate in aqueous solutions

38
Q

Strong and weak acids can be distinguished from each other by their:

A

pH value (using pH meter or universal indicator)

39
Q

pH meter

A

The pH meter is connected to the pH electrode which shows the pH value of the solution

40
Q

Universal indicator

A
  • Less accurate method
  • The universal indicator paper is dipped into a solution of acid upon which the paper changes colour
  • The colour is then compared to those on a colour chart
41
Q

Electrical conductivity

A
  • Since a stronger acid has a higher concentration of H+ ions it conducts electricity better
  • The electrical conductivity can be determined by using a conductivity meter which is connected to an electrode and the conductivity can be read off the meter
42
Q

Reactivity

A

The greater the H+ concentration, the more H2 gas is produced

43
Q

The differences in behavior between strong and weak acids using:

A
  • pH value
  • Electrical conductivity
  • Reactions with a reactive metal (reactivity)
44
Q

2 common reactions:

A

Mg (s) + 2HCI (aq) → MgCl2 (aq) + H2 (g)
- Reaction produces a lot of bubbles and hydrogen gas due to high concentration of H+ present in solution

Mg (s) + 2CH3COOH (aq) → Mg(CH3COO)2 (aq) + H2 (g)
- Reaction produces less bubbles and hydrogen gas due to lower concentration of H+ present in solution

45
Q

Neutralisation reactions

A

Acid + base → salt + water
- H+ (aq) + OH- (aq) → H20 (l)
the spectator ions which are not involved in the formation of water, form the salt
Eg) HCI + NaOH → HOH + NaCl

Acid + metal carbonate → salt + water + carbon dioxide

  • Hydrochloric acid- forms a chloride
  • Nitric acid- forms a nitrate
  • Sulfuric acid- forms a sulfate
46
Q

Indicators

A

substances that change colour when they are added to acidic or alkaline

47
Q

2 most common indicators used in titrations:

A

methyl orange (3.1 - 4.4 range) and phenolphthalein (8.3 - 10)

Chemistry (19 decks)

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