Chemical Equilibria Flashcards
Le Chatelier’s principle suggests that a high pressure will produce a low yield of hydrogen in this first stage.
Explain, in terms of the behaviour of particles, why a high operating pressure is used in industry.
The reaction gets to equilibrium faster
High pressure leads to more molecules in a given volume so more successful collisions IN A GIVEN TIME
A nickel catalyst is used in the first stage.
Explain why the catalyst is more effective when coated onto an unreactive honeycomb.
Increase in surface area
Increase in MORE successful collisions
State the effect, if any, of using a smaller flask on the amount of sulfur trioxide at equilibrium.
Explain your answer.
Increase in SO3
Fewer moles on RHS equilibrium shifts to reduce the pressure and keep Kc constant
A student added a solution containing 0.50 mol of (aq) to a solution containing 0.50 mol of (aq) and shook the mixture.
After 30 seconds, there was no further change in colour.
The amount of Z(aq) at equilibrium was 0.20 mol.
The student added a few drops of Y(aq) to the equilibrium mixture of Xaq), Y(aq) and Z(aq) in part (c).
Suggest how the colour of the mixture changed. Give a reason for your answer.
Darkened/went more orange
The equilibrium moved to the right
To oppose the increased conc of Y
Reaction 2 is exothermic. A typical compromise temperature of 200 °C is used industrially for this reaction.
Explain the effect of a change of temperature on both the position of equilibrium and the rate of reaction, and justify why a compromise temperature is used industrially.
Calculate the value for K, for the reaction of ethanoic acid and ethanol at 20 °C
Give your answer to the appropriate number of significant figures.
Suggest how, using the same mass of ethanoic acid, the experiment could be improved to reduce the percentage uncertainty.
Use a lower concentration of NaOH
So that a larger titre is required (reduces percentage uncertainty in titre)
A
Award mark for X on the time axis at the point where the lines just become horizontal
Give the meaning of the term dynamic in the context of a dynamic equilibrium.
The forward and reverse reactions occur at the same time
Concentrations stay constant
The total pressure on the system is increased at constant temperature.
State and explain the effect, if any, of this change on the time taken to reach this equilibrium.
No effect
Equal moles on both sides
The mixture in part (C) reached equilibrium in a container of 1.5 dm-3
Decrease
More moles on LHS
Equilib shifts to LHS to oppose reduction in pressure
T1
Reaction is exothermic
Equilib shifts to oppose reduction in temp at T2
Equilib shifts to oppose increase in temp at T1
Write an equation for the reaction that has an enthalpy change that is the standard enthalpy of formation of ethanol.
square root Kc = 0.086
State le chatliers principle
ii shorter/decreases
iii none
State the meaning of carbon neutral
An activity which has no net carbon emissions to the atmosphere
Kc for this equilibrium has no units.
State why the units cancel in the expression for K.
Equal number of moles on each side of the equation
Explain why a catalyst has no effect on the position of an equilibrium.
Catalysts increase/speed up the rate of the forward and backward reactions
In crease in rate is the same
The yield increases
There are more moles of the left
Equilibrium shifts to oppose the increase in pressure
(ii Use the diagram to state the effect of an increase in temperature at constant
pressure on the yield of ammonia. Use Le Chatelier’s principle to explain this effect.
Yield decreases
The forward reaction is ecorthermic
Equilibrium shifts to the left to oppose the increase in temp
(i)
State why industry uses a pressure lower than 35 MPa.
Do not include references to safety.
Less electrical pumping cost
Use lower pressure equipment
Uses less expensive equipment
Less acid present
Equilibrium shift to the right
State why it is necessary to maintain a constant temperature in an experiment to measure an equilibrium constant.
Kc constant is temperature dependent
State what the . represents in Cl.
Unpaired electron
Decrease
Fossil fuels used
CO2/H2O produced which are greenhouse gases
B
C
Suggest two reasons why the operation of this process at a pressure much higher than
5 MPa would be very expensive.
Pumping
Strong pressure quipent
High maintenance cost
If a catalyst were not used in this process, the operating temperature would have to be greater than 700 K. Suggest why an increased temperature would be required.
To speed up rate of reaction
C
V cancels in Kc expression
Explain why 800 K is referred to as a compromise temperature.
Balance between rate and yield
Show how combining the equations from these two methods can lead to the 1:2 mol ratio of carbon monoxide to hydrogen required for this synthesis of methanol.
Explain why the equilibrium yield is unchanged when a catalyst is introduced.
(iv) Both forward and backward rates changed / increased (1)
by equal amount (same proportion)
D
D
Give one advantage and one disadvantage of preparing ethyl ethanoate by
Reaction 2 rather than by Reaction 1.
Reaction goes to completion
Reaction is vigorous/dangerous as HCL is toxic
Write a general expression for the partial pressure of a gas in a mixture of gases in terms of the total pressure.
D
