C2e - Manufacturing chemicals: making ammonia Flashcards
Describe how different factors affect the cost of making a new substance (6)
higher temperature leads to higher energy cost
unreacted materials recycled leads to lower costs
the more workers needed (labour-intensive processes), the higher the labour costs
-automation reduces wages bill
complex machinery/higher pressure leads to higher plant cost
catalysts increases rate of chemical reaction, therefore reducing time & costs
Explain how economic considerations determine the conditions used in the manufacture of chemicals (3)
rate and %yield must be high enough to give a sufficient daily yield of product
a low % yield can be accepted if the reaction can be repeated many times w/ recycled starting materials
optimum conditions used that give the lowest production cost rather than the fastest reaction or highest % yield
Conditions in the Haber process (4)
iron catalyst
high pressure (200 atm)
high temperature (~450C)
unreacted nitrogen and hydrogen are recycled
Word equation for the Haber process
nitrogen + hydrogen ⇌ammonia
Symbol equation for the Haber process
N2 + 3H2 ⇌ 2NH3
What is a reversible reaction
reaction that can go either way so that the products of the forward reaction act as the reactants of the opposite, backward reaction
Explain the conditions used in the Haber process (4)
high pressure increases the percentage yield of
ammonia as higher pressure favours the forward reaction
high temperature decreases the percentage yield of ammonia but gives a high rate of reaction
-450°C is an optimum temperature to give a fast
reaction with a sufficiently high percentage yield
catalyst increases the rate of reaction but does not change the percentage yield
How is ammonia important to world food production
Ammonia can be used to manufacture fertilisers, without which crop yields would be much smaller
