equilibrium
When a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate.
Explain how a catalyst increases the rate of a reaction
lowers activation energy
provides different reaction pathway
A pressure of 100 atmospheres is used instead of atmospheric pressure. The higher pressure gives a greater yield of methanol and an increased rate of reaction. Explain why.
equilibrium moves to the product side because fewer molecules
more collisions per unit time because more molecules per unit volume
A pressure of 285 atmospheres is not used in the Haber process instead of 200 atmospheres. Give one reason why
higher energy costs
Explain why a low pressure is used in stage 1. Give your answer in terms of equilibrium
higher yield
fewer molecules on the left hand side
The rate of reaction is different when manganese dioxide is used as a fine powder rather than coarse lumps. Explain why. You should answer in terms of collision theory.
surface area greater
more collisions per unit time
C2H4 (g) + H2O (g) → C2H5OH (g)
Explain how increasing the pressure of the reactants will affect the amount of ethanol produced at equilibrium.
more ethanol produced
system moves to fewer molecules
The forward reaction is exothermic. Use Le Chatelier’s Principle to predict the effect of increasing temperature on the amount of ethanol produced at equilibrium.
amount decrease because equilibrium moves to the left
A few drops of a colourless solution containing a high concentration of thiocyanate ions (SCN–) are added to the orange equilibrium mixture.
Explain the colour change observed.
becomes more red
equilibrium moves to the right
the concentration of thiocyanate is reduced
A water bath is set up at a temperature above room temperature.
When a test tube containing the orange equilibrium mixture is placed in the water bath, the mixture becomes more yellow.
Explain what this shows about the energy change for the forward reaction.
the equilibrium moves to the left
the temperature is reduced
therefore the forward reaction is exothermic
Plan a method to investigate the effect of changing the mass of sodium carbonate powder on the highest temperature reached.
measure volume of hcl with a measuring cylinder
pour hcl into a polystyrene cup
measure initial temperature with a thermometer
add a known mass of sodium carbonate measured with a balance and stri
measure the highest temperature reached
repeat with different masses of sodium carbonate
repeat the whole investigation
use the same starting temperature
use the same volume of hcl
use the same concentration of hcl
Give three conclusions that can be drawn about the rate of reaction between magnesium and dilute hydrochloric acid in this investigation.
Use data from the graph and the table above.
rate decreases
rate decreases more slowly as time increases
rate becomes 0 at 60s
rate is greatest at the start
then rate decreases
then the reaction stops
collect gas in a gas syringe
measure the volume of gas produced
acid particles are used up so concentration decreases
therefore there are less frequent collision so rate decreases
discard anomalies
find a mean
Which two statements are correct when the reaction reaches equilibrium?
the mass of each substance does not change
the rates of the forward reaction and reverse reaction are equal
The student compares the rates of the reaction of zinc carbonate with:
• 0.01 mol/dm3 methanoic acid
• 0.01 mol/dm3 ethanoic acid.
The rate of the reaction with methanoic acid is greater than the rate of the reaction with ethanoic acid. Explain why.
You should refer to ions in your answer. Use the table above.
methanoic acid has a lower pH
methanoic acid has a higher concentration of hydrogen ions
more collisions per unit time
Plan an investigation to show how the concentration of the sodium thiosulfate solution affects the rate of the reaction with dilute hydrochloric acid.
Your plan should give valid results
measure 10cm3 of sodium thiosulfate
place in conical flask
measure 10 cm3 of hcl
place conical flask on a cross
add hcl to flask
swirl
start stopclock
measure time for cross to become no longer visible
repeat and find mean
repeat for diff concentration of sodium thiosulfate
control
conc of hcl
volume of hcl and sodium thiosulfate