C7.4 Introducing dynamic equilibrium Flashcards
- What is the symbol for reversible reactions?
↔
- What is a reversible reaction?
-a reaction where the products can react to produce the reactants
- What happens if a reversible reaction takes place in a closed system?
-the reversible reaction can reach a state of equilibrium
- In what conditions can a reversible reaction reach a state of equilibrium?
-in a closed system
none of the reactants or products can escape
- What does the term ‘closed system’ mean?
-none of the reactants or products can escape
- What does equilibrium mean?
-the relative (%) quantities of reactants and products will reach a certain balance and stay there
- What is a dynamic equilibrium?
- reactions are still taking place in both directions AT THE SAME RATE
- reactions both ways cancel each other out= no overall effect
- What are the feedstocks for the Haber process?
- nitrogen
- hydrogen
- How are the feedstocks for the Haber process obtained?
- nitrogen: the air (78% nitrogen)
- hydrogen: cracking of chemicals in natural gas using steam
- What are the industrial conditions for the Haber process?
- pressure= 200 atmospheres
- temperature= 450⁰
- catalyst= iron
- What is the symbol equation for the Haber process?
N2 + 3H2 ↔ 2NH3 (+heat)
- What is the word equation for the Haber process?
-nitrogen + hydrogen ↔ ammonia (+heat)
- What is the reaction between hydrogen and nitrogen to form ammonia in the Haber process?
-a reversible reaction
- What does the Haber process being reversible cause?
-not all nitrogen and hydrogen will convert into ammonia
- How is the yield of ammonia increased in the Haber process?
- by recycling unreacted hydrogen and nitrogen, so nothing is wasted
- (more product produced using the same amount of reactant)
- What is the effect of changing pressure on the yield of ammonia at equilibrium in the Haber process?
-high pressures favour the forward reaction (because four molecules of gas on left and 2 on right)= increase yield
- What is the effect of changing temperature on the yield of ammonia at equilibrium in the Haber process?
- lower temperatures= increase yield
- as forward reaction is exothermic so increasing temp would move equilibrium the wrong way
- Do gases in the Haber process reach equilibrium?
-gases do not stay in the reactor long enough to reach equilibrium
- What is used to increase the rate of reaction in the Haber process?
-an iron catalyst
=increase rate of reaction= ammonia produced faster
- How are conditions in the Haber process a compromise to produce an economically viable yield of ammonia?
- pressure: high as possible to increase % yield/ without being too expensive to build= 200 atmospheres
- temperature: compromise between maximum yield and rate of reaction- decrease temp to increase rate of reaction/ increase temp to increase speed of reaction= 450⁰
- What living organisms ‘fix’ nitrogen at room temperature and pressure using enzymes as catalysts?
-Nitrogen-fixing bacteria
- How does a nitrogen-fixing bacterium ‘fix’ nitrogen?
-‘fix’ nitrogen at room temperature and pressure using enzymes as biological catalysts
- What is an example of a biological catalyst?
-enzymes
- Under what conditions is the Haber process done?
-high temperatures and pressures turn nitrogen and hydrogen into ammonia
- What catalyst is used in the Haber process and why?
- iron catalyst speeds up making ammonia
- without it the temperature would have to be raised= decrease percentage yield
- Why are chemists interested in producing new catalysts that mimic natural enzymes?
-so processes like the Haber process could be at room temperature and pressure
= cheaper and more efficient
- What are the uses of nitrogen fixation (e.g. from the Haber process)?
- ammonia used for fertilisers = increase crop yield= increase world food production
- ammonia used in industry (make plastics, explosives, pharmaceuticals)
- What is the negative impact on the environment of the large scale manufacture of ammonia and the widespread use of fertilisers made from it?
-large amount so fertilisers pollute water supplies and cause eutrophication (algae growth causing death of plants and animals)
- What is eutrophication?
-fertilisers leach into lakes and rivers =rapid algae growth =blocks out light to other plants =microorganisms feed on dead plans using oxygen =fish die from lack of oxygen =everything dies
- How sustainable is the nitrogen fixation processes?
1- whether or not the feedstock is renewable: hydrogen non-renewable as from fossil fuels, nitrogen renewable as from air
2- the atom economy: all H2 and N2 makes ammonia= amazing atom economy
3- the nature and amount of by-products or wastes and what happens to them: no waste as chemicals all recycled
4- the energy inputs or outputs: lots of energy needed for high temperatures (450⁰)
5- the environmental impact: fertilisers from NH3 (ammonia)= water pollution
6- the health and safety risks: high pressure/temperatures= dangerous
7- the social and economic benefits: very profitable
- Why is fixing nitrogen by the Haber process important?
-the nitrogen in plants would normally be returned to the soil when it had died, however we harvest the crops so the nitrogen is not returned to soil= we need fertilisers with nitrogen for plants to grow so we don’t starve
- What can the efficiency of the Haber process be improved by?
-by using a different catalyst (to mimic natural enzymes)
=be produced at room temperature and pressure
=cheaper and more efficient
