[Music] so in today's video we're going to look at the reactions of alkenes which we can class as unsaturated hydrocarbons the unsaturated part means that they contain at least one carbon-carbon double bond which is their functional group meanwhile the hydrocarbon part means that they only contain hydrogen and carbon atoms now the key point to this video is that the fact that alkenes have a double bond allows them to undergo addition reactions this is because the carbon-carbon double bond can open up and allow the two carbons to bond to atoms of another molecule so this basically allows us to add another molecule to our alkene hence the name addition reaction in this video we'll cover three types of addition reactions those with hydrogen with water and with halogens let's start with hydrogen the alkene we have here is propine because it's a three carbon chain if we add hydrogen gas and supply a catalyst the double bond between the carbon atoms will break apart and the hydrogen atoms will then be able to bond to those carbons the product here that we formed is propane and importantly it doesn't have a double bond anymore so it's now saturated and so it's classed as an alkane rather than an alkene next up we have the reaction of an alkene with water and this time we have ethene as our alkene the conditions for this reaction are the presence of a catalyst at high temperatures so that our water will actually be in the form of water vapor or steam when they react the double bond on the alkene opens up again and the water molecule will split into a hydrogen atom and an o h group which can then both go and bond to those carbon atoms the product this time is called ethanol which because it has this oh group is a type of alcohol and ethanol is actually the same alkyl as we use in alcoholic drinks and some industrial processes this means that we do this reaction quite a lot in industry once the reaction has taken place though we somehow have to separate the ethanol which is what we want from any unreacted ethene and water the ethene is easy to separate because it has a relatively low boiling point and so if we cool down the mixture the ethene will stay as a gas while the water and ethanol will condense into liquid form to separate the water and ethanol though we need to use fractional distillation if you remember from one of our much earlier videos this works by taking the mixture of ethanol and water and placing it in a round bottom heating flask then as we heat it up perhaps with a bunsen burner the ethanol will boil first because it has a slightly lower boiling point than water does and so we'll evaporate up through the fractionating column and then condense into a separate beaker whereas our water will remain in the heating flask because it didn't evaporate the last example we need to cover is the reaction of alkenes with halogens this is basically the same as the reaction with hydrogen that we saw earlier but importantly it doesn't require any catalyst the most common example you'll see is with bromine for example if we add some bromine which has an orange color to some ethene and we give it a little shake then they'll react to form dibromoethane and because this uses up all of the bromine the orange color would disappear this is actually the main test that we use to distinguish alkenes from alkanes because alkenes have double bonds they're more reactive and can react with the bromine to decolorize it in contrast alkanes are saturated so they don't have any double bonds for the bromine to be added to which means that if we add bromine water to a solution of alkanes the solution will remain orange because the bromine won't react so to summarize alkenes can decolorize bromine water from orange to colorless whereas alkanes can't anyway that's everything for this video so hope you enjoyed it if you did then please do tell your friends about us and otherwise cheers for watching