Dynamic Equillibrium + Chemical/fuel cells (PAPER ONE) Flashcards
What is meant by dynamic equillibrium?
The point at which the forward and backward reactions are still occurring at the same rate but the percentages of the reactants and products are no longer changing.
Describe the formation of ammonia
a reversible reaction between…
- nitrogen (extracted from the air)
and
- hydrogen (obtained from natural gas)
it can reach a dynamic equilibrium
What conditions are required for the Haber process? - why?
Temperature - 450’C (Has a lower yield of ammonia than lower temperatures, but produces it at a faster rate)
Pressure - 200 atmospheres (Position of equilibrium moves towards the side with fewer molecules of reacting gas - very high pressures are too expensive to maintain)
Catalyst - Iron (doesn’t change position of equilibrium but does increase the rate of reaction)
What’s a closed system?
A system where only energy can be transferred/exchanged between the system and its surroundings.
(dynamic equilibrium occurs in a closed system)
What happens to the position of equilibrium when the temperature increases/decreases
Increases - shifts in the endothermic direction
Decreases - shifts in the exothermic direction
What happens to the position of equilibrium when the gas pressure increases/decreases
Increases - shifts in the direction that forms fewer gas molecules (as this reduces pressure)
Decreases - shifts in the direction that forms more gas molecules (as this increases pressure)
What happens to the position of equilibrium when the concentration increases/decreases
Increases - Shifts in the direction that uses up the substance that has been added
Decreases - Shifts in the direction that forms more of the substance that has been removed
What’s the Haber process?
A reversible reaction between nitrogen and hydrogen to form ammonia
How is the time taken to reach equilibrium affected by an increase in temperature?
Speeds up time taken (position shifts in endothermic direction)
How is the time taken to reach equilibrium affected by an increase in gas pressure?
Reaches position faster
- Because gas molecules are more concentrated
- So, there are more frequent collisions
How is the time taken to reach equilibrium affected by an increase in concentration of a reacting substance?
Reaches position faster (position of equilibrium moves away from the
reacting substance in the balanced equation)
What do fertilisers contain?
Nitrogen, phosphorus and potassium compounds to promote plant growth
How long does a chemical cell produce a voltage for?
A chemical cell produces a voltage until one of the reactants is used up
What happens in a hydrogen-oxygen fuel cell?
Hydrogen and oxygen are used to produce a voltage with water as the only product
What are the strengths and weaknesses of fuel cells?
Strengths:
- They produce a voltage for as long
as reactants are supplied.
- Water is the only product (no greenhouse gases produced such as CO2)
- Quieter and lower maintenance than a petrol/diesel engine
Weaknesses:
- Most hydrogen manufactured releases carbon dioxide as a by-product
- Hydrogen needs to be stored in a tank
Heat energy is needed to convert hydrated copper sulfate to anhydrous copper sulfate. This is a reversible reaction.
Devise an experiment to show that this is a reversible reaction. [4 marks]
- Heat the hydrated solid
- Would observe steam/solid turns white
- Add water which should react with anhydrous solid
- Solid goes blue again (as heat is released)
What source of hydrogen is used in the Haber process?
Obtained from natural gas
Haber process balanced equation
N₂ + 3H₂ ⇌ 2NH₃
