Flashcards in Chemistry Deck (77):
What's a reversible reaction?
One where the products of the reaction can themselves react to produce the original reactants
Give two examples of reversible reactions and explain one.
1- the dehydration of copper (2) sulfate
2- the thermal decomposition of ammonium chloride. It is a white solid and when heated it breaks down into the gases ammonia and hydrogen chloride
What does equilibrium mean?
Happens in a closed system: where the relative (%) quantities if reactants and products reach a certain balance and stay there.
What's a dynamic equilibrium?
Where the reactions are taking place in both directions but the overall effect is nil because the forward and reverse reactions cancel each other out. They are taking place at exactly the same rate in both directions
What reaction is favoured by an increase in temperature and why?
The endothermic reaction will increase to use up the extra heat
Which reaction is favoured by a decrease in temperature?
The exothermic reaction will increase to give out more heat
What does a greater volume mean on one side of a reaction?
Means there are more molecules
What reaction will be encouraged if the pressure is raised?
The reaction which produces less volume
What reaction will be encouraged if the pressure is lowered?
The reaction which produces more volume
What is a metal ore?
A compound containing a metal that is worthwhile extracting
What's the reaction called that separates a metal from the oxygen in it's oxide?
A reduction reaction
What happens in a reduction reaction?
Is the gain if electrons
In a reduction reaction, what is the substance called that reduces the metal and is oxidised?
The reducing agent
What's the most common type of reducing agent used in reduction reactions?
How are metals that are more reactive that carbon extracted?
How are metals that are less reactive than carbon extracted?
By heating with carbon monoxide
What's the main ore of aluminium?
After mining and purifying bauxite what is left?
A white powder of pure aluminium oxide, Al2O3
What catalyst is used in aluminium oxide extraction and why?
It's dissolved in molten cryolite as Al2O3 has a very high melting point of over 2000 degrees which brings the temperature down to about 900 degrees which makes it cheaper and easier
What are the electrodes in aluminium extraction made from and why?
Graphite because it's a good conductor of electricity
Why does molten aluminium oxide conduct electricity?
Because it contains free ions
What type of reaction is aluminium oxide?
What happens at the cathode of the electrolysis of Al3O2?
Al3+ +3e- ---> Al
The positive al3+ ions are attracted to the negative electrode where they pick up electrons and turn into aluminium atoms. They sink to the bottom. This is a reduction- gain of electrons
What happens at the anode of the electrolysis of Al3O2?
2O2- ---> O2 + 4e-
The negative oxygen ions are attracted to the positive electrode where they lose electrons. The oxygen atoms will then react together to form 02 or with the carbon anode to form co2. It's an oxidation reaction- loss of electrons
Why is electrolysis expensive?
1) uses a lot of electricity
2) energy is also needed to heat the electrolyte mixture to 900 degrees
3) the disappearing positive electrodes need frequent replacement
What is iron extracted from ?
What are the raw materials used in extracting iron?
1) iron ore contains iron
2) coke is almost pure carbon- reduces the iron oxide to iron metal
3) the limestone takes away impurities in the form of slag
What are the 5 stages of reducing iron ore to iron?
1) hot air is blasted into the furnace, making the coke burn much faster than normal. This raises the temperature to about 1500 degrees Celsius
2) the coke burns and produces carbon dioxide
3) the carbon dioxide then reacts with un burnt coke to form carbon monoxide
CO2 + C --> 2CO
4) the carbon monoxide the reduces the iron ore to iron
3CO + Fe2O3 --> 3CO2 + 2Fe
5) the iron is molten at this temperature and very dense so it runs straight to the bottom of the furnace where it's tapped off
How are impurities in iron removed?
1) the main impurity is sand (silicon dioxide). This is still solid at 1500 degrees Celsius and tends to stay mixed in with the iron- the limestone removes it
2) the limestone is decomposed by the heat into calcium oxide and carbon dioxide
CaCO3 --> CaO + CO2
3) the calcium oxide then reacts with the sand to form calcium silicate or slag which is molten and can be tapped off
CaO + SiO2 --> CaSiO3 ( molten slag)
What is the cooled slag used for?
Road-building and fertiliser
What do iron and aluminium have in common?
1) dense and lustrous(shiny)
2) high melting points -iron 1538 aluminium 660
3) high tensile strength- strong and hard to break
4) they are malleable
5) good conductors of electricity and heat
What is wrought iron used for?
Almost completely pure iron- It's malleable so used for making ornamental gates and railings
What is an alloy?
a metal made by combining two or more metallic elements
What is cast iron a mixture of and what is it used for?
It's a mixture of iron, carbon and silicon.
It's very hard and brittle so used for manhole covers and some cooking pans
What is steel made of? And why is it more useful than iron? What is used for?
Made of iron, carbon and some other metals.
It's harder than pure iron and can still be hammered easily into sheets and welded together.
It's great for making car bodies and girders for construction
What's the main problem with iron?
It corrodes easily
What's an allow of iron that does t rust? What is it used for?
Stainless steel made of iron and chromium m. Used for knives and forks and cooking pans
What are the uses of aluminium?
It doesn't corrode so useful in water contact products like drinks cans
Less dense than iron so it's light weight is useful when weight is important like bicycle frames and aeroplanes
Why doesn't aluminium corrode easily?
Because it reacts very quickly with oxygen in the air to form aluminium oxide. A nice protective layer of aluminium oxide sticks firmly to the aluminium below and stops any further reaction taking place
How is crude oil formed?
Over millions of years, high temperatures and pressures cause the buried remains of plants and animals into crude oil
What is crude oil a mixture of
How is crude oil separated into different hydrocarbon fractions?
By fractional distillation
1) the oil is heated until most of it has turned into gas. The gases renter a fractionating column and the liquid but BITUMEN is drained off at the bottom
2) there's a temperature gradient- hot at the bottom and gradually cooler as you go up. When the substances that make up crude oil reach a part of the column where the temperature is lower than their boiling point they condense
3) the longer hydrocarbons have high boiling points so condense and drain out if the column early on near the bottom
4) the shorter hydrocarbons have lower boiling points so condense higher up near the top of the column where it's cooler
5) bubble caps in the fractionating column stop the separated Liquids from running back down the column and remixing. You end up with the crude oil mixture separated out into different fractions. Each fraction contains a mixture of hydrocarbons with similar boiling points
What's the order of hydrocarbon fractions from lowest boiling point to highest?
1) refinery gases
4) kerosene (paraffin)
6) fuel oil
What are the uses of refinery gases?
Bottles gas; heating; used in pottery and glass manufacture
What is gasoline used for?
Fuel for cars
What's naphtha used for?0
Used in the chemical industry as 'feedstock' to make: plastics, dyes, drugs, explosives and paints
What is kerosene used for?
Jet engines; domestic heating; paint solvent
What is diesel used for?
Fuel for Diesel engines in cars, trucks, trains, boats
What is fuel oil used for?
Domestic central heating; fuel for big ships
What is bitumen used for?
Road surfacing and asphalt for roofs
What is fractional distillation an example of?
A physical process- there are no chemical reactions
What are pollutants produced from burning Fuels ?
Carbon monoxide, nitrogen oxides and sultry dioxide
How is carbon monoxide produced? why is it poisonous?
From incomplete combustion
1) CO is poisonous- it can stop your blood doing it's proper job of carrying oxygen around the body.
2) it combines irreversibly with haemoglobin in blood cells meaning the blood can carry less oxygen
3) lack of O2 in blood can lead to fainting, a coma or death
where do nitrogen oxides and sulfur dioxide come from?
from burning fuel
the sulfur dioxide comes from sulfur impurities in the fossil fuels
nitrogen oxides are created when the temperature is high enough for the nitrogen and oxygen in the air to react. this often happens in car engines. nitrogen oxides include NITROGEN MONOXIDE (NO) & NITROGEN DIOXIDE (NO2)
what is acid rain caused by and what are the equations?
sulfur dioxide and nitrogen oxides
1) all is rain is slightly acidic because carbon dioxide in the air reacts with water to produce a slightly acidic solution CO2 + H2O --> H2CO3 (carbonic acid)
2) when sulfur dioxide mixes with cloud it forms dilute sulfuric acid, which is much more acidic 2SO2 + 02 + 2H2O --> 2H2SO4
3) nitrogen oxides from nitric acid in clouds and the rain that falls is acid rain
what are the effects of acid rain on the environment?
- causes lakes to become acidic and many plants and animals die as a result as can't adapt to these conditions
- kills trees and damages limestone buildings and ruins stone statures
-links between acid rain and health problems have been suggested
what is cracking?
splitting up long-chain hydrocarbons into short-chain which have a higher demand
why are short-chain hydrocarbons demanded more than high ones?
lower boiling points and much thinner - high ones a viscous
what is cracking a form of?
thermal decomposition- breaking molecules down into simpler molecules by heating them
in industry, what are the conditions for cracking?
vaporised hydrocarbons are passed over a powered catalyst
-powered catalyst: Silica (SiO2) and alumina (Al2O3)
how do you crack paraffin in the lab?
1) put mineral wool soaked in paraffin in one end of a boiling tube with a catalyst in the centre. The tube has a delivery tube to a glass jar collected over water
2) heat the paraffin, after a few seconds move the Bunsen burner to heat the silica or alumina catalyst- alternate between the two until the paraffin vaporises and the catalyst glows red
3) the heated paraffin vapour cracks as it passes over the heated catalyst
4) small alkanes collect at the end of the boiling tube, while alkene gases travel down the delivery tybe
5) the alkenes are he collected through water using a glass jar
what does the long-chain alkane - dodecane (found in paraffin) crack into?
octane- shorter alkane molecules (useful for petrol) and ethene- alkenes (for making plastics)
how are polymers made?
when lots of small molecules called monomers join together
what are addition polymers?
the monomers that make up addition polymers have a carbon-carbon double bond- alkenes
what conditions do addition polymers need?
high pressure and a catalyst- small molecules will open the double bonds and polymerise to form very long saturated chains -polymers e.g. ethene becomes poly(ethene)
what are some uses of polymers?
1) poly(ethene) is light and stretchable so ideal for packaging- plastic bags, bottles and other containers
2) poly(propene) is very tough but relatively flexible and resistant, used for making kettles, food containers and carpets.
why are most polymers hard to get rid of?
-because most are inert- don't react easily so the c-c bonds are very strong and aren't easily broken
-which means it takes a really long time for addition polymers to biodegrade
-burning plastics can release toxic gases
- best to reuse and recycle than dispose
what is the Haber process?
the production of ammonia NH3 - used for fertilisers
what is the reversible reaction in the Haber process ? where are reactants obtained from?
N2 + 3H2 ---> <---2NH3 (+heat)
nitrogen from the air and hydrogen form natural gas or from cracking hydrocarbons
what are the industrial conditions need in the Haber process?
pressure: 200 atmospheres
why does higher pressure favour the forward reaction in the Haber process? and why is it set as high as possible?
because there are 4 molecules of gas on the left for every 2 on the right so set as high as possible to give the best % yield, without making the plant too expensive to build
in the Haber process is the forward reaction exothermic or endothermic?
exothermic which means that increasing the temp will move the equilibrium the wrong way- towards the reactants- so the yield of ammonia would be greater at a lower temperature
whats the problem with lower temperature?
slower rate of reaction so temp is increased#
what is 450 a compromise between?
maximum yield and speed of reaction
how is ammonia formed in the Haber process?
formed as a gas but as it cools in the condenser it liquefies and is removed, the unused hydrogen and nitrogen are recycled so nothing is wasted
what does the iron catalyst do?
makes the reaction go faster, but doesn't affect the % yield