GCSE Chemistry - Atom Economy - Calculations | Why it's Important (2027/28 exams)
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https://www.youtube.com/watch?v=eZCtGJwns0Q

Transkript (automatisch erstellt)

0:07 When you're making chemicals commercially, the reactions usually make multiple products. However, there's normally only one or
0:15 maybe two that are actually useful. For example, in this reaction, the aim is only to make hydrogen. So, the other product, in this case,
0:26 carbon dioxide, is basically waste. This production of waste products happens a lot in industrial processes and so it's helpful for companies to be
0:36 able to quantify it and know exactly how much of the reactants are actually going to form the useful products that they want.
0:46 So in this case that would be what percentage of the carbon oxide and water is actually going to form hydrogen. We call this value the atom economy
0:59 and the official equation for it looks like this. So we have to take the relative formula mass of the desired product or products
1:09 if there are more than one and divide it by the total relative formula masses of all the reactants and then we multiply all by 100 to turn
1:20 it into a percentage. As the aim of this reaction is to create hydrogen, that's our desired product. And it mr would be 2 * 1, so two.
1:34 For our reactants, we have carbon monoxide, which has an MR of 28, and water, which has an MR of 18. So to get the total MR of all our
1:46 reactants, we just add 28 and 18 together to get 46. So to find the atom economy of this reaction, we take our MR of hydrogen
1:58 because that's our desired product and divide it by the 46 because that's the MR of all of our reactants.
2:08 Then finally, we multiply the whole thing by 100 to turn it into a percentage, giving us an atom economy of 4.35%.
2:20 4.35% is actually a pretty low atom economy because it means that only 4.35% of the reactants are being turned into the
2:31 useful product that we want whereas the other 95.65% is being given off as waste. In general, atom economies are usually
2:43 much higher than this, but they can also be even lower. As an example of a reaction with a very high atom economy, let's take a look at
2:55 this one where we have nitrogen and hydrogen reacting together to form ammonia. Because the desired product ammonia is
3:05 the only product here, the atom economy would be 100%. Because all of the reactants are being used to make ammonia, there aren't any
3:15 other products that could be considered waste. Next, we need to cover the main reasons why it's important to consider atom
3:25 economy. Number one is that raw materials are expensive and so if they're mostly being converted
3:33 into waste products, the process is generally going to be less profitable. Reason two is that it's less sustainable to use large quantities of reactants to
3:44 make tiny amounts of products. And three, waste products themselves can be expensive to get rid of and can damage the environment.
3:57 The best solutions to these problems are to either use a more efficient reaction or to find a use for the waste products so that they become a useful byproducts
4:08 instead of waste. And even if they can't sell these useful byproducts for very much money, it's still much better than paying to dispose
4:18 of the waste. The last thing to cover are that there are lots of other important factors to
4:26 consider when you're thinking about how profitable a reaction is. For example, the percentage yield, the cost of the raw materials,
4:36 the position of the equilibrium, the rate of reaction, and the cost of maintaining the right conditions like the temperature and the pressure.
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