C3 Topic 4 - Gases, Reversible Reactions And Ammonia Flashcards
Using Avogadro’s Law, how can the volume of any gas be calculated?
Volume = No. of moles x 24 Dm^3 = M x 24 dm^3
OR
Volume = (Mass of gas / RFM of gas) x 24 Dm^3 = (g/M) x 24 dm^3
What is Avogadro’s Law?
One mole of any gas always occupies 24dm^3 (=24,000 cm^3) at room temperature and atmospheric pressure (RTP - 25°C and 1 atmosphere)
How would you find the mass of a compound in a reaction, using Avogadro’s Law?
- Find the reacting mass of a known compound.
- Write down the RFM of both the known and unknown compounds.
- Divide the RFMs by the RFM of the known compound.
- Multiply by the mass of the known compound, this gives you the mass of the unknown gas.
- Now use the formula for working out the volume of the gas. Divide by the RFM and multiply by 24.
- This gives you the volume of the unknown compound.
What is a reversible reaction?
A reversible reaction is one where the products can themselves react to produce the original reactants.
A + B C + D
Wheat is dynamic equilibrium, in a reversible reaction?
The dynamic equilibrium of a reversible reaction, is where both the reactants and the products are still reacting to make each other but the net reaction rate is zero as they are the same in both directions.
How does pressure affect the dynamic equilibrium?
If you RAISE the pressure, the equilibrium favours the side with the LOWER volume/FEWER molecules.
If you LOWER the pressure, the equilibrium favours the side with the HIGHEST volume/more molecules.
How does temperature affect the dynamic equilibrium?
If you RAISE the temperature, the ENDOTHERMIC side is favoured as it USES UP the extra heat.
If you LOWER the temperature, the EXOTHERMIC side is favoured as it GIVES OUT more heat to compensate.
How does a catalyst affect a reversible reaction?
A catalyst speeds up both sides of the reaction, both forwards and backwards, by the same amount. Therefore, adding a catalyst causes the reaction to reach an equilibrium faster though it doesn’t affect the position of the equilibrium.
What is the Haber process?
N2(g) + 3H2(g) 2NH3(g)
Nitrogen - taken from air
Hydrogen - taken from natural gas
What compromises have to be made so that the Haber process is safe yet efficient?
Pressure: 200 atm
There are more molecules on the LHS so the reaction favours the side with ammonia. While a higher pressure would produce more ammonia, the equipment would need to be more expensive to prevent an explosion.
Temperature: 450°C
A higher temperature would actually move the equilibrium to the nitrogen and hydrogen side as it is endothermic, but lowering the temperature lowers the rate of reaction.
Catalyst: Iron
Iron speeds up the rate of reaction but does not affect the yield.
What is ammonia used for?
Fertilisers use ammonia because the nitrogen helps to increase plant growth.
If fertilisers enter a river or lake, they can cause eutrophication which you should know from biology…
Algae grow, taking light from underwater plants, they die and decomposers break them down, using up all the oxygen in the water, causing fish and other animals to die.
