Equilibria Flashcards
Le Chatelier’s principle states that
Le Chatelier’s principle states that when a change is imposed on an equilibrium, the equilibrium position will shift to oppose the change.
The change Le Chatelier refers to can be as a result of:
The change Le Chatelier refers to can be as a result of:
Change in temperature.
Change in pressure.
Change in concentration.
What happens when an exothermic reversible reaction is cooled down?
1
Decide which way releases heat
2
Decide which reaction increases
3
Decide where the equilibrium position goes
What happens when an exothermic reversible reaction is cooled down?
1
Decide which way releases heat
The forward reaction releases heat in this example
2
Decide which reaction increases
You want more heat, so the rate of the forward reaction increases
3
Decide where the equilibrium position goes
It shifts to the right because more products are formed by a faster forwards reaction
At equilibrium, both forward and backward reactions still happen, but the ..
So we describe the equilibrium as
At equilibrium, both forward and backward reactions still happen, but the concentrations of reactants and products remain constant. So we describe the equilibrium as dynamic
What are the conditions used in the synthesis of ethanol?
300° c
65 atm
n equilibrium constant greater than one indicates that
An equilibrium constant less than one indicates that
n equilibrium constant greater than one indicates that the forward reaction dominates.
An equilibrium constant less than one indicates that the backward reaction dominates.
Whats dynamic equilibrium
At dynamic equilibrium concentrations of reactants and products are constant and the forwards reaction in the backwards reaction are going at the same rate
What conditions are needed for dynamic equilibrium to be established
For a dynamic equilibrium to be established it must be a closed system and the temperature must be constant
How does the addition of a catalyst affect the position of equilibrium in a reversible reaction
The addition of a catalyst has no affect on the position of the equilibrium in a reversible reaction
An industrial process uses the following reversible reaction
A + 2B (reverse signs) C + D
Change in enthalpy = -189Kjmol-1
Explain the effect of increasing the concentration of a on the position of equilibrium
Shift the equilibrium to the right favouring the forward reaction in order to get rid of the EXcess a
An industrial process uses the following reversible reaction
A + 2B (reverse signs) C + D
Change in enthalpy = -189Kjmol-1
Explain the effect of increasing the pressure on the position of equilibrium
There are three moles on the left and only two on the right increasing the pressure will shift the equilibrium to the right in order to reduce the number of moles to reduce the pressure again
An industrial process uses the following reversible reaction
A + 2B (reverse signs) C + D
Change in enthalpy = -189Kjmol-1
Explain the effect of increasing the temperature on the position of equilibrium
The fourth reaction is exothermic so the backwards reaction must be endothermic increasing the temperature will shift the equilibrium to the left in order to remove the extra heat
What will be the effect of increasing the pressure on the position of equilibrium of the following reaction they both have two molecules on either side of the reaction
There are the same number of moles on either side of the reaction increase increasing the pressure favours the reaction producing the fewest moles but since both reactions are equal in this respect increasing the pressure will not shift the position of equilibrium
In the production of ethanol from Ethene and steam using low temperature and high-pressure favours the forward reaction and gives a better yield
given that this is the case explain why a moderate temperature and pressure are used when making ethanol and Industrially
The temperature and pressure used in the industrial production of ethanol or a compromise
using a low temperature increases the yield of the reaction
but at a low temperature of the reaction rate becomes much slower so moderate temperature is used as a compromise
between a good yield and a fast reaction using a high-pressure also increases the yield of the reaction but high pressures are expensive to produce you need stronger pipes and containers to withstand high pressure so moderate pressure is used as compromise between maximum yield and minimum expense
Why does changing the concentration of a reagents doesn’t affect Kc
If the concentration of a reagent is changed equilibrium will shift and the concentration of other reagents will also change so Kc will stay the same
How does adding a catalyst affect the equilibrium constant
Doesn’t change Kc but it decreases the time taken to reach equilibrium
What is petroleum
A mixture that consists mainly of alkane hydrocarbons
Why are alkanes described as saturated hydrocarbons
they only contain carbon and hydrogen atoms
each of the carbon is forms four single bonds they are no carbon carbon double bonds present
Fractional distillation separates hydrocarbons what property are they separated by
Boiling point
Explain why some fractions are drawn off higher up the fractional distillation column than others
Some fractions have lower boiling points than others this means they can dance further up the columns so are drawn off higher up
What is cracking
Cracking is breaking long chain alkanes into smaller hydrocarbons
Why do we crack heavier petroleum fractions
There is more demand for later petroleum factions Sol to meet the demand the heavier fractions are cracked into lighter fractions
Why does using a catalyst for catalytic cracking cut costs
Because the reaction can be done at a lower temperature and pressure and at an increased speed
Write the equation for the complete combustion of pentane
Cnnc
Give three pollutants produced by vehicle exhausts
Nitrogen oxides carbon monoxide soot unburnedhydrocarbons carbon dioxide
What can be used to remove pollutants from vehicle exhausts
Catalytic converter
Explain how acid rain is caused by burning fossil fuels containing sulphurz
The sulphur burns to produce sulphur dioxide gas
if sulphur dioxide gas enters the atmosphere it can dissolve in the moisture and form sulphuric acid
Describe one method for removing sulphur dioxide from fluegases
Powdered calcium carbonate can be mixed with water to make an alkaline slurry
when the fluegases mix with the alkaline slurry that acidic sulphur dioxide gas reacts with the calcium compounds to form a harmless salt
What’s a photochemical reaction
U
Write an equation for the initiation step of the synthesis of chloromethane by photochemical reaction
G
Describe what takes place in the termination step of a free radical substitution mechanism
G
Why is ozone in the atmosphere beneficial
H
Describe how chlorine free radicals are formed in the upper atmosphere
T
Right to equations to show how chlorine atoms catalyse the decomposition of ozone
Y
Explain why CFCs were banned from use as solvents and refrigerants
G
