[Music] hi and welcome back to three sighs lessons Cole you K by the end of this video you should be able to describe how hydrocarbons can be used as fuels you should then be able to write balanced equations for the complete combustion of hydrocarbons in the last video we looked at how the properties of hydrocarbons depend on the size of the molecule we saw that short chain hydrocarbons are highly flammable and they have low boiling points as the hydrocarbon molecules get larger they become less flammable and the boiling point increases also longer chain hydrocarbons have a higher viscosity in other words they tend to flow more slowly now in this video we're looking how hydrocarbons can be used as fuels and I'm showing you some examples here ships planes and cars all run on hydrocarbon fuels and there were lots of other cases where hydrocarbons are used as fuels here's a first key fact that you need to learn hydrocarbon fuels release energy when they're combusted and remember that combustor just means burned during combustion the carbon and hydrogen atoms in the fuel react with oxygen in other words the carbon and hydrogen are oxidized now if the oxygen is unlimited then this reaction produces carbon dioxide and water and scientists call this complete combustion so in this video we're going to look at how to write chemical equations for complete combustion I'm showing you here the equation for the complete combustion of methane as you can see this equation is not balanced so how do we balance it well we start by balancing the carbon atoms we've got one carbon atom in the methane we also have one carbon atom in the carbon dioxide this means that the carbon atoms are balanced now we need to bounce the hydrogen atoms we've got four hydrogen atoms in the methane but there were only two hydrogen atoms in the water so the Hajin atoms are not balanced we need to get four hydrogen atoms on the right hand side and to do that we put a large two in front of the water like this now we have four hydrogen atoms and hydrogens balanced finally we need to bounce the oxygen atoms on the right hand side we've got two atoms of oxygen in the carbon dioxide we've also got two atoms of oxygen in the water so that means that we've got four atoms of oxygen in total on the right-hand side on the left hand side we've got two atoms of oxygen so as you can see the oxygen atoms are not balanced we need to get four oxygen atoms on the left-hand side and to do that we place a large two in front of the o2 like this and now the equation is fully balanced here's a combustion equation for you to try pause the video now and balance this equation okay so we start by balancing the carbon atoms on the left-hand side we've got three carbon atoms and on the right-hand side we've got one carbon atom so we need to get three carbon atoms on the right-hand side and to do that we place a large three in front of the co2 like this we now have three carbon atoms on the right-hand side so the carbon atoms are balanced next we need to bounce the hydrogen atoms on the left-hand side we've got eight atoms of hydrogen on the right-hand side we've only got two atoms of hydrogen so we need to get eight hydrogen atoms on the right-hand side and to do that we place a large number four in front of the water like this now we have eight hydrogen atoms on the right-hand side and the hydrogens are balanced finally we need to bounce the oxygen atoms on the right hand side we have six oxygen atoms in the carbon dioxide and we have four oxygen atoms in the water this gives us a total of ten oxygen atoms on the left-hand side we've got two oxygen atoms so the oxygen atoms are not balanced we need to get ten oxygen atoms on the left-hand side to do that we need to place a large five in front of the oxygen like this and now the equations balanced remember you'll find plenty of questions on combustion in my vision workbook and you can get that by clicking on the link above [Music]