so let's try and go through everything that you need to know for gcse chemistry paper 2. we're going to be covering rates of reactions organic chemistry chemical analysis atmospheric chemistry and using resources and here are the timestamps if you want to skip ahead you can download the pdf of this from scienceshorts.net link in description the rate of a reaction is how quickly it happens any rate is a measurement of an amount of something divided by time it's always something per second or something per minute etc now more often than not the something that we measure is the volume of gas that's made from a reaction the quicker the gas is made the faster the rate of reaction we can also do color change or turbidity that's how cloudy it gets now for two molecules or atoms to react with each other they need to collide with each other successfully there are a few factors that can change how often this happens and that affects the rate of reaction first one is surface area if reactants are ground up then there are more particles exposed to the other reactant so that means that there are going to be more frequent collisions between the reactants concentration or pressure for a gas that's the same as well more frequent collisions temperature is the biggest one it makes the particles move faster that not only makes them collide more frequently but because they also have more energy that means that these collisions are more likely to be successful too and last but not least we have a catalyst this is a substance that acts as a sort of middleman for the reactants but it's not used up in the reaction it just helps the reactants meet as it were what this does is lowers the activation energy remember that from paper one so that means that collisions again are more likely to be successful they don't need as much energy to react now for measuring volume of gas then we can collect the gas in a gas syringe i'll write that on there in a few minutes that's nice and easy but there's another experiment where we have sodium thiosulfate and hydrochloric acid and when these react they make a product that is cloudy and so what we do is make different concentrations of hydrochloric acid so let's say we're given 0.2 moles per decimeter cubed we might call that 0.2 molar for short and you have to know how to do this we're going to make different concentrations let's say that we want 20 40 60 80 and 100 of the hydrochloric acid that we have to begin with so we're going to make let's say 10 milliliters every single time but 20 of that is going to be hydrochloric acid 80 is going to be distilled water and that gives us a concentration of 0.04 molar that's just 20 of that 0.2 we have the sodium thiosulfate in a conical flask with a piece of paper underneath with a cross drawn in it we add the acid start the timer and we time how long it takes for the cross to disappear because the solution goes cloudy like we said turbidity is another word for cloudiness reversible reactions can be a little bit confusing but these are just reactions that go both ways but if we have a closed system that means that stuff nor energy can get in or out the system will reach equilibrium that means that the rate of the forward reaction is the same as the rate of the reverse reaction or backward reaction that means the amount of everything involved in the reaction is staying the same so basically the reaction stopped so we need to know le chatelier's principle if an equilibrium we say dynamic equilibrium is disturbed by changing conditions the reaction moves to counteract the change in other words it will always try to reach equilibrium let's say we add more reactants on the left that means the equilibrium will shift to the right in other words the rate of the forward reaction will increase so that means the reactance gets used quicker more product is made but eventually it will reach equilibrium again the same can be achieved by removing product and that's actually what we do in say the harbor process changing pressure can also shift the equilibrium higher pressure means the equilibrium shifts to the size with the fewest molecules so let's have a look at the prime example of a reversible reaction the harbor process this is what we use to make ammonia for let's say fertilizer so we have nitrogen n2 going in plus three h2 hydrogen makes two nh3 now you can see on the left we have four molecules n2 and three lots of h2 on the right we only have two so you can probably see that if we increase the pressure that means we're going to increase the amount of ammonia made because that's the side with the fewest molecules so high pressure gives you a high yield a lot of ammonia is made and a fast rate as well but it's very very expensive to maintain so we have a compromised pressure of 200 atmospheres low temperature gives you a high yield as well because more energy generally means that things are broken apart not put together but a low temperature gives you a slow rate so that's not ideal either so we have a compromise temperature of 450 degrees celsius to make it a lot better though we have an iron catalyst that helps increase the rate of the forward reaction by decreasing the activation energy and you can see a graph here of gas volume being made against time for a reaction you can see at the start we have a fast rate because the gradient of the graph is steep but eventually it levels out to zero and we can see that the reaction has stopped as soon as the line is actually level okay let's go into organic chemistry lots here especially for triple organic chemistry is all about carbon-based molecules like hydrocarbons hydrocarbons are molecules that only have carbon and hydrogen in nothing else but you also have things like alcohols and esters etc we'll talk about those in a minute they have more than just carbon and hydrogen in but sticking with hydrocarbons crude oil is a mixture of different length hydrocarbons generally alkanes what we do is fractional distillation we're going to split the crude oil into different bits so we put the crude oil in the bottom of this fractionating column we heat it and it evaporates well apart from the very longest anyway the evaporated crude oil rises and the tower is cooler as we go higher up and because they have different boiling points that means that the gases recondense at different heights we have the shortest ones at the top and the longest ones at the bottom the fraction with the shortest hydrocarbons is lpg or liquid petroleum gas next we have petrol going down we have paraffin then diesel then fuel oil below that then we have bitumen at the bottom that's what goes into tarfall roads everything else apart from bitumen is basically used as a fuel but we can do more with them as well as we'll see crude oil is a mixture of generally alkanes if we change the carbons going up to 50 60 long etc but let's just look at a few of the very shortest ones here we have methane that's just one carbon myth means one and ain means that it's an alkane can't have any other type actually eth means two so ethane it's an alkane with two carbons in and you can see the carbons are bonded to as many hydrogens as they possibly can be prop means three butte means four so we can have propane and butane two and then it goes pentane hexane septa and octane they're all fairly self-explanatory after that like we said most of these are used as fuel so we burn them that means they undergo combustion so we react them with oxygen let's take methane ch4 that reacts with o2 it makes h2o just water weird isn't it fire makes water and we can make co2 as well let's balance it real quick four hydrogens on the left so that means we have to have four on the right two so let's double up water and then we have four oxygens on the right so that means we have to double up the o2 on the left water is always made but carbon dioxide is only made if there's lots of oxygen available we call that complete combustion if there's not a lot available carbon monoxide co or just carbon which is soot is made instead carbon monoxide is deadly because it binds to the hemoglobin in your red blood cells stopping the oxygen getting into your blood so we've seen alkanes but now we're on to alkenes because we have a double e that means a double bond alkenes always have at least one double bond let's take ethene heath two carbons but we can see that we have a double bond in between so the carbons aren't bonded to as many hydrogens as they could be so we say it's unsaturated it's not full as it were however atoms can come in and saturate the alkene so they can come in and make a something alkane so let's say bromine comes along it can react with the ethene to break that double bond and the bromine's bond to it to make a bromo alkane this can work for other things as well and actually this is the test for an alkene if you don't know if something is an alkane or alkene we can mix it with bromine water and if the bromine water goes from orange to colorless that means that it is an alkene because the bromine is reacting and is making a bromo alkane which are colorless now we can make alkenes from alkanes by doing cracking or catalytic cracking let's say that we have an alkane let's go with butane now what we can do is crack this literally split it into we use a catalyst and a high temperature of about 550 degrees c now any one of these carbon-carbon bonds can be broken but let's say that the one in the middle is broken so that leaves us with ethane c2h6 but the other product can't be an alkane it has to be an alkene c2h4 so we've made ethane and ethene from butane so kraken an alkane always gives you a shorter alkane and an alkene too and this is very useful for two reasons one it gives you alkenes and you can do polymerization with those second one is though that we can make shorter arcanes and more often than not we need lots of shorter alkanes for fuel rather than the longer ones so we can crack the longer alkanes to meet the demand for shorter ones sadly for organic chemistry there's just a lot of reactions that you have to remember more often than not just for triple like we said an alkene is unsaturated if you react it with just hydrogen then we make an alkane it becomes saturated alkene and a halogen like bromine makes that halogen alkane bromoalkane chloroalkane etc react an alkene with water and we end up with an alcohol an alcohol is a molecule with an o h group or a hydroxide group and here we can see ethene reacting with water and that makes ethanol it's ethane but with an oh on one end that's the all bit that's what makes it ethanol an alcohol can react with sodium and it makes sodium ethoxide and hydrogen now if we have an alcohol like ethanol sorry i've drawn ethane by accident there don't worry fixed on the pdf if it comes in contact with an oxidizing agent then it can make a carboxylic acid like ethanol being made into ethanoic acid carboxylic acids have that cooh group incidentally carboxylic acids have high boiling points higher than water anyway and they're weak acids this one's a bit complicated if we react a carboxylic acid with an alcohol like ethanoic acid and ethanol it makes an ester because two h's in a node disappear from between them and they join together to make an ester and this one would be called ethyl ethanoate esters have a nice smell like pear drops if we react to carboxylic acid with a metal we make salt and hydrogen if we react it with a hydroxide we make a salt and water much like any other acid did a bit of polymers in paper one they're big molecules made from smaller molecules we call them monomers the main type of making them is addition polymerization like we saw we can turn lots of ethenes into polyethylene but there are other things that can be polymerized as well like amino acids amino acids can join together to make peptides they can then join together to make polypeptides and they're the basis of proteins which make up living matter amino acids are a carboxylic acid in a way but they have the nh2 group on the other end from the cooh end in biology nucleotides can join together to make polynucleotides and that's the basis of dna carbohydrates are another polymer starch is basically a polymer of glucose that's why it takes longer to break down in your body we have another type as well condensation polymerization this is when we joined together two different molecules with different functional groups you know we've seen ohc and h2 those are functional groups so if we have a monomer it can be any carbon chain length but it has oh on both ends and similarly for another monomer that has cooh on both ends it's almost like an ester on steroids we're just doing the above reaction over and over again and we end up with a polyester okay i'm going to jump over to using resources we use resources for warmth shelter food and water and transport there are two main types finite or non-renewable resources that means they can't be replaced once used at least not very quickly or easily like fossil fuels renewables can like wind sunlight and trees question mark if you want a great documentary that looks at this question mark check out planets of the humans on youtube potable or potable water is water that is safe to drink it doesn't mean that you can put it in a pot it comes from the french word potable desalination is the removal of salt from say seawater which you have to do to make it safe to drink one way you can do this is with distillation we can evaporate the water and recondense it and it leaves all the salt behind but we don't do that without drinking water because it's horrendously expensive so instead we treat our water not from the sea with a few ways first one is filtration that removes big insoluble particles like sand etc and secondly we want to sterilize it to kill microbes nasties that can make us ill and we do that with chlorine or ultraviolet light an lca is a life cycle assessment this assesses the impact of a product that you want to make over its whole lifetime first raw materials what impact on the world does getting the raw materials have manufacturing how much energy is needed distribution how are you gonna get it into people's hands that can have a big impact use and then disposal very important and we can limit these impacts by doing the whole reduce reuse recycle thing all of these conserves resources that means that you're not using as much as you would otherwise recycling material sometimes reduces energy required all of these means that you also have less waste in landfill sites alloys are a mixture of metals this can also be carbon and the metal like carbon and iron make steel gold that's used in jewelry is not pure gold because pure gold is too soft so we have in it gold silver copper and zinc bronze is an alloy of copper and tin corrosion happens to any metal when it reacts with oxygen or water and it makes a metal oxide rust however is the word that's reserved just for iron when it corrodes and it makes iron oxide most glass that we use is soda lime glass ceramics are brittle but they usually make good insulators hdpe and ldpe denotes high or low density polyethylene high density is when you need a stiff plastic say for bottles and low density for things like bags thermo setting plastics are polymers that harden when they're heated and that's because cross links are made between the polymers which makes it very strong and this is permanent thermoplastic on the other hand is when a polymer softens when heated that's most plastics that we have composites are what we call basically non-metal alloys like fiberglass and they can be very light and strong in order to have metals we need to extract them from ore from the ground we can use reduction reactants to get it out and we can use electrolysis to purify it we can use displacement reactions to get a metal from scrap as well there's a couple of weird ways that we can get metal as well new ways bio leaching what we do is have bacteria that produce leachate they contain metal compounds and then we just basically gather it up phyto mining plants instead what they do is absorb metals through their roots then we harvest and we burn it and we get the metals from the ash what about the atmosphere then well we think that the early atmosphere had a lot of hydrogen and helium in but then that escaped fairly quickly however i put a question mark there because that would require other gases to push them out they wouldn't escape just by themselves because of something called escape velocity anyway whatever volcanoes then when they erupt they make water carbon dioxide methane ammonia plants then they turned co2 into o2 c absorbs lots of co2 as well and then carbon can be locked away in carbonates as well you know rocks etc nowadays the composition of the atmosphere is about 78 nitrogen 21 oxygen tiny percentage of co2 0.04 percent and argon is about 1 what's not accounted for here is water vapor but people don't tend to talk about that as a gas in the atmosphere which is kind of weird the greenhouse effect is when short wavelengths from the sun they go through the atmosphere through the greenhouse gases but they're reflected off the ground and things on the ground as a longer wavelength these longer wavelengths like infrared get absorbed by the greenhouse gases and that keeps the planet nice and warm as with most things though too much of a good thing can be a bad thing so some people like to talk about something called carbon footprint this is the net amount of carbon dioxide that you emit and they say that you can offset this by say planting trees or plants so it's the amount of carbon dioxide you put into the atmosphere take away the amount that you've removed from the atmosphere okay back to chemical analysis then a formulation is any mixture that has a specific purpose like petrol diesel very precise amounts of chemicals to make sure that your car runs smoothly there's a number of ways that we can identify compounds or elements in a mixture we can use chromatography and we've seen this in paper one there are a few simple tests that we can do for gases hydrogen pops with a lit splint a squeaky pop oxygen re-lights a glowing splint carbon dioxide turns lime water cloudy and chlorine turns damp blue litmus paper white we can identify metal ions using flame tests if we have a compound that we think has a metal in we can burn it and it has a pale green color we have barium in it orange red that's calcium green a little bit of blue that's copper lithium is crimson red sodium would give you an orange flame and potassium is a lovely lilac color sort of soft purple we can also identify them using precipitate reactions what we do is add excess sodium hydroxide and a solid insoluble precipitate can be formed in the test tube aluminium magnesium and calcium ions will give you a white precipitate iron two plus will give you a green precipitate iron three plus brown and put them the wrong way around here but they're fixed on the pdf there are a few tests that we can do for non-metal ions carbonate ions co3 two minus if we add any acid bubbles will be made and that's carbon dioxide so we know there's a carbonate ion there halogen ions chloride bromide iodide ions what we do is add nitric acid then silver nitrate we get a white precipitate formed if it's cl minus present cream precipitate for a bromide ion and yellow for an iodide ion however in the big leagues they have far more accurate ways of identifying atoms or ions with very expensive equipment or instruments spectroscopy what we do is measure what wavelengths of light or infrared are absorbed by a compound and if a certain wavelength is absorbed we have a certain molecule or certain bond there and we also have flame emission spectroscopy what we do is burn the compound and particles in the flame are excited by an em radiation source and then they re-emit radiation and we can see what characteristic wavelengths are emitted and that can tell us what's being burned so i hope you found that helpful if you think i've missed anything then pop it in a comment down below and i'll add it to the mind map all the best for your exams see you next time