# Atom economy/Percentage yield question help please

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#1
Explain why a reaction can have a high percentage yield but low atom economy? [3]

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#2
?????
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3 years ago
#3
For example lets take the Haber Process.

You have the following reaction: N2+3H2 ----> 2NH3 (reversible reaction)

This reaction has 100% atom economy because only 1 product is formed. However the yield is altered by changes in temp and pressure. So basically since this reaction is exothermic, a lower temp is favoured due to Le Chatelier's principle, but a lower temp means a slower rate of reaction etc.
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3 years ago
#4
(Original post by shohaib712)
Explain why a reaction can have a high percentage yield but low atom economy? [3]

I think the answer here is actually that

Yield is the Actual Yield/Theoretical Yield (1)
Atom Economy is the Mass of desired product/Sum of all masses (1)

Therefore, a reaction with 100% yield could still have a low atom economy if a lot of the reactants end up as waste byproducts. (1)

Explanation here is that yield calculates how you much you make from what you are expecting to make, whereas atom economy assesses the efficiency of the actual reaction

edit: I realise that may still be unclear. I can try reword it if you want to pm for clarification
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#5
(Original post by floatationdevice)
I think the answer here is actually that

Yield is the Actual Yield/Theoretical Yield (1)
Atom Economy is the Mass of desired product/Sum of all masses (1)

Therefore, a reaction with 100% yield could still have a low atom economy if a lot of the reactants end up as waste byproducts. (1)

Explanation here is that yield calculates how you much you make from what you are expecting to make, whereas atom economy assesses the efficiency of the actual reaction

edit: I realise that may still be unclear. I can try reword it if you want to pm for clarification
No no this is an amazing explanation thank you!
Could I ask these questions if you dont mind?

- Do you need to know the definitions of %yield and atom economy?
- what does the spec mean by: "benefits for sustainability of developing chem processes with a high atom economy"?
- What does sustainability mean?
- and if you where to evaluate the sustainability/efficiency of a reaction do you need to take both atom econ and %yield into consideration?
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3 years ago
#6
(Original post by shohaib712)
No no this is an amazing explanation thank you!
Could I ask these questions if you dont mind?

- Do you need to know the definitions of %yield and atom economy?
- what does the spec mean by: "benefits for sustainability of developing chem processes with a high atom economy"?
- What does sustainability mean?
- and if you where to evaluate the sustainability/efficiency of a reaction do you need to take both atom econ and %yield into consideration?
I'm guessing you are edexcel, since I don't think I studied sustainability at AS

You most likely would not be asked to define either separately as a 1 or 2 mark q, but it's likely to come up as part of a bigger question, so definitely do remember the definitions.

I can only guess these

The internet defines it as:
The less waste there is, the higher the atom economy, the less materials are wasted, less energy used, so making the process more economic, 'greener' and sustainable.

Do you have a textbook? This should all be explained in one

Edit:

rest of extract

Reactions with a low atom economy are very wasteful and use up resources at faster rate than high atom economy reactions. They are less sustainable in the long run and the cost of raw materials will increase over time.
The less waste there is, the higher the atom economy, the less materials are wasted, less energy used, so making the process more economic, 'greener' and sustainable.
Quite simply, the larger the atom economy of a reaction, the less waste products are produced and hopeful the waste is easy and cheap to deal with, or even better, some use can be found for these 'by-products'.
source: http://www.docbrown.info/page04/4_73calcs14other2b.htm
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#7
(Original post by floatationdevice)
I'm guessing you are edexcel, since I don't think I studied sustainability at AS

You most likely would not be asked to define either separately as a 1 or 2 mark q, but it's likely to come up as part of a bigger question, so definitely do remember the definitions.

I can only guess these

The internet defines it as:
The less waste there is, the higher the atom economy, the less materials are wasted, less energy used, so making the process more economic, 'greener' and sustainable.

Do you have a textbook? This should all be explained in one

Edit:

rest of extract

Reactions with a low atom economy are very wasteful and use up resources at faster rate than high atom economy reactions. They are less sustainable in the long run and the cost of raw materials will increase over time.
The less waste there is, the higher the atom economy, the less materials are wasted, less energy used, so making the process more economic, 'greener' and sustainable.
Quite simply, the larger the atom economy of a reaction, the less waste products are produced and hopeful the waste is easy and cheap to deal with, or even better, some use can be found for these 'by-products'.
source: http://www.docbrown.info/page04/4_73calcs14other2b.htm
Yes but i'm finding it confusing to understand.

e.g. theres a question that says:
"Comment on the percentage yield and atom economy of this process in terms of sustainability"

but the mak scheme says:

Any two from:low atom economy gives a poor sustainability a use for the aqueous calcium hydroxide needs to be developed to increase atom economy

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3 years ago
#8
(Original post by shohaib712)
Yes but i'm finding it confusing to understand.

e.g. theres a question that says:
"Comment on the percentage yield and atom economy of this process in terms of sustainability"

but the mak scheme says:

Any two from:low atom economy gives a poor sustainability a use for the aqueous calcium hydroxide needs to be developed to increase atom economy

As mentioned before, I haven't studied this board. I think that the answer here is that sustainability is mainly concerned about atom economy, as for any given reaction, yield can be altered by changing reaction conditions or using more sophisticated equipment etc.
On the other hand, a reaction's atom economy cannot be changed without changing the reaction itself.

Tbh not really sure here. Try look online to double check. Hope this helps
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3 years ago
#9
are u taking the piss why u ignoring my reply, u know how much effort it took to do that bhenjodh
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3 years ago
#10
(Original post by DneepSingh)
u know how much effort it took to do that bhenjodh
Very little?
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3 years ago
#11
(Original post by alow)
Very little?
smd blud
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#12
(Original post by DneepSingh)
For example lets take the Haber Process.

You have the following reaction: N2+3H2 ----> 2NH3 (reversible reaction)

This reaction has 100% atom economy because only 1 product is formed. However the yield is altered by changes in temp and pressure. So basically since this reaction is exothermic, a lower temp is favoured due to Le Chatelier's principle, but a lower temp means a slower rate of reaction etc.
Thanks!
TBH I didn't notice your answer but Flotationdevice explained it better tho

Would a side reaction between products e.g. (soluble gas,CO2 dissolving in water) be a reason for loss of % yield?

My textbook doesn't mention reversible reactions as a limiting factor, (i will add it in my notes though) :/

Are you doing OCR?
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#13
(Original post by floatationdevice)
As mentioned before, I haven't studied this board. I think that the answer here is that sustainability is mainly concerned about atom economy, as for any given reaction, yield can be altered by changing reaction conditions or using more sophisticated equipment etc.
On the other hand, a reaction's atom economy cannot be changed without changing the reaction itself.

Tbh not really sure here. Try look online to double check. Hope this helps
Would a side reaction between products e.g. (soluble gas,CO2 dissolving in water) be a reason for loss of % yield?
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