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How to Calculate Atom Economy
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- in this video we're going to look at how to calculate the atom economy which is required by GCSE chemistry and is also useful in your understanding of
- quantitative chemistry as it allows you to assess how efficient a reactant addition is in producing desired products so let's start by looking at
- the formula so atom economy as a percentage is equal to the molecular mass of the desired products divided by the total molecular mass of all of the
- reactants and you multiply that by 100 so we'll look at a generic reaction we can see how we can extract those pieces of information so say we've got reacted
- 1 and reacted two reacting together they form a desired product which were interested in and then they form another product or perhaps products and we can
- ignore those we only focus on the desired product so let's see how this matches together so what we would do is we'd find the total molecular mass of
- both of the reactants that would go in the bottom of our equation and then the desired products molecular mass would go on the top of that fraction and then we
- multiply that by 100 and that would give us a percentage at an economy and for some students writing this out in words could be quite helpful so if you pause
- the video pick which way makes most sense to you and taken over that so in words you would say you find the molecular mass of the desired product
- then divide it by the total mass of all reactants and lastly you would multiply that by 100 and that would give you the percentage you've got a clear recipe
- then you step by step through exactly how to do the calculation and now let's do a worked example to see that in practice our work example is what is the
- Atem economy of producing carbon dioxide by burning propane so we have a combustion reaction here we've got propane reacting with oxygen that's of
- course combustion and it's producing carbon dioxide plus water and the water is a not useful product that we're now interested in the question tells us
- producing carbon dioxide we're looking at so we can identify our desired product I've just highlighted that there so our desired product is a 3 co2 and
- I've put on the other side all of the data that we require forget the relative atomic mass of each of those atoms that appear in our
- equation let's start by finding the two things that we need to substitute into our equation so start with the mass of the desired product we've got three Co
- twos so if we find the molecular mass of co2 we have to multiply that by three so that's why I've got a big three up front the molecular so the relative atomic
- mass of carbon is 12 so that's why we have a 12 there and then we've got a 2 because you've got two oxygens multiply that by 16 which the relative dome of
- atomic mass of oxygen stick that in the calculator and we get 132 then we need to work out the tool of all of the reactants we've got propane and we've
- got the oxygens we have to do all of that so we're doing 3 times 12 which were 3 carbons carbon is 12 plus 8 times 1 so the 8 hydrogens hydrogen is
- relative that massive one then we do the same thing we did in the previous one with a big 5 out front because we have 5 ol twos and we work out what 102 is so
- 82 times 16 and we multiply that all by 5 that gives us 204 we've now got the two things we need to substitute into the equation we put that in the equation
- so we've got the molecular mass of the desired product 132 that goes on the top molecular mass of all the reactants we've added it all up getting 204 we
- substitute that in multiply that by a hundred and that will give us the answer so we can see the atom economy is sixty four point seven percent and that is our
- final answer so take a minute to pause the video go back through it in your head write some notes make sure you follow each and
- every step and if you're not sure and something rewind it and you'll see the explanation again lastly just quickly check that you've got the idea of an
- economy here is a slightly crafty question some people be able to solve it straight away by looking at if you really understand it or you can go
- through the procedure calculate and you may come up with a quite obvious answer when you see it and I'll put the answer in the bottom in the description
- of this video so hopefully that's been helpful to you and you know calculate Assam economy thank you for watching
Zum Nachlesen
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