4.2.1 - Chemical Synthesis Flashcards
what is chemical synthesis and what are the aims?
selection of particular reagents to form a product with specific properties
1. economically viable
2. safe as possible
3. least wastage
how can yield and rate be optimised?
- recycle reactants not used
- removing products when formed
- using catalysts
- choosing suitable temperature
- choosing suitable pressure
what are the 6 steps in calculating the limiting reagents?
- limit the most expensive reactants
1. write the balanced equation (if not provided)
2. calculate the moles of each of the reactants
3. divide the moles by the coefficient in the balanced equation
4. the smaller number if the limiting reagent
5. use the moles of the limiting regent to determine the moles of the product
6. determine the mass of the product
how do you calculate the yield?
- determine the moles of the reactant (calculating theoretical yield)
- n = m / MM - determine the moles of the product (calculating the theoretical yield)
- n = n of reactant x (unknown coefficient/known coefficient) - determine the mass of the product (calculating the theoretical yield)
- mass = n X MM - determine the percentage yield
- % yield = experimental/theoretical X 100
what is the haber process and how does it work?
conditions to optimise yield and rate for ammonia production
1. reactants added
2. pressure at 200 atm
3. pressurised at 200 atm
4. pressurised gases heated to 450 degrees and passed through an iron catalyst
5. reaction cooled to liquefy ammonia to remove it
6. unreacted nitrogen and hydrogen are recycled
what is the contact process?
- conditions to optimise yield and rate for sulfuric acid production
- temperature: forward reaction is exothermicm therefore a lower temp is needed
- but a low temp means slow production rate (moderate temp of 450 degrees is used)
what is fuel synthesis?
- a chemical that when it reacts can release energy
what are fuels made from?
either:
1. fossil fuels through either fractional distillation or catalytic cracking
2. all fuels made from crude oil are hydrocarbons and are non-renewable
what are biofuels made from?
- renewable sources such as plants, algae or animal waste
- eg. ethanol and biodiesel
what are the requirements for a carboxylic acid and alcohol condensation reaction?
- strong acid catalyst and heat
- esterification, ester functional group
- reversible reaction
how are lipids formed?
- a condensation reaction
- ester bonds are formed between the three fatty acids and glycerol
what is biodiesel synthesis?
- transesterification reactions of plant or animal fats
what are the conditions of biodiesel synthesis (base catalyzed) to optimise yield and rate?
- must be kept dry
- low temperature
- low pressure
what is saponification?
- triglycerides react with NaOH/KOH to produce a glycerol and fatty acid salt called a ‘soap’
- base hydrolysis
what conditions are required for saponification to occur?
- NaOH
- water
- heat
what are the conditions of biodiesel synthesis (lipase catalyzed) to optimise yield and rate?
- low temperature
- low pressure
- note: slow and expensive
why is it beneficial to use lipase catalyzed biodiesel synthesis?
- no soap formed (purity and yield)
- recycle glycerol
- safer (lower temperature and toxicity)
- biodegradable
what is ethanol synthesis (fermentation)?
requirements:
- suitable grain/fruit
- yeast
- air excluded
- 37 degrees
what are the advantages to ethanol synthesis?
- renewable feedstock
- safer (lower temp and pressure)
- biodegradable
what are the disadvantages to ethanol synthesis?
- slow reaction
- impure ethanol
- batch processing
what does the ethanol synthesis of crude oil involve?
- addition reaction: hydration of ethane (oxidation)
what are the requirements of ethanol synthesis (crude oil)?
- heat
- pressure
- a strong acid catalyst
what is the problem with ethanol synthesis (crude oil)?
- ethene is formed by catalytic cracking of crude oil making this form of ethanol NOT a biofuel
explain to 5 step process of how fuel cells work (electrochemical device)?
- oxygen flows through front intake grill and is supplied to the fuel cell stack
- hydrogen stored in the tanks (yellow cylinder) is supplied to the fuel cell stack
- hydrogen and oxygen react inside the fuel-cell stack, generating electricity and water
- the generated electricity is supplied to the electric motor, which propels the vehicle
- the only by-product of creating electricity in the fuel stack is water, which is emitted through the tailpipe
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