How to Calculate Atom Economy?

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To calculate atom economy, one must find the total molar mass (Mr) of the desired products and divide it by the total molar mass of the reactants, then multiply by 100. It is crucial to only consider the mass of products that are in their elemental form, such as O2 gas, rather than those still in compounds. A common mistake is to include the entire mass of oxygen from compounds, which can lead to erroneous percentages exceeding 100%. The correct approach involves using the appropriate coefficients for reactants and products in the calculation. Understanding these principles ensures accurate assessment of reaction efficiency.
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To work out the answer to this question, do I just find the total Mr of the products and divide it by the total Mr of the reactants (and then multiply by 100, and pick the biggest percentage?)

Cheers
 
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influx said:
atomecon.png


To work out the answer to this question, do I just find the total Mr of the products and divide it by the total Mr of the reactants (and then multiply by 100, and pick the biggest percentage?)

Cheers

If you did that, you would get %100 every time. Otherwise, you would be violating conservation of mass.

If you want to know the effency of producing Oxygen from your reactants, which product mass do you want to use in your equation?
 
flatmaster said:
If you did that, you would get %100 every time. Otherwise, you would be violating conservation of mass.

If you want to know the efficiency of producing Oxygen from your reactants, which product mass do you want to use in your equation?

If you do it for A, you get 118 %... (so I am doing something wrong?)

Mr of (NaNO2 + (1/2)O2) = 101
Mr of (NaNO3) = 85

(101/85)*100 = 118.8%

For A, wouldn't we use both products, since both products contain Oxygen?
 
Mr of (NaNO2 + (1/2)O2) = 101
You did this one wrong. You forgot to take 1/2 the mass of o2
For A, wouldn't we use both products, since both products contain Oxygen?No. We're only concerned with O2 as Oxygen gas. If the Oxygen is still in a compound, you haven't made oxygen.
 
flatmaster said:
If you did that, you would get %100 every time. Otherwise, you would be violating conservation of mass.

If you want to know the effency of producing Oxygen from your reactants, which product mass do you want to use in your equation?

flatmaster said:
Mr of (NaNO2 + (1/2)O2) = 101



You did this one wrong. You forgot to take 1/2 the mass of o2



For A, wouldn't we use both products, since both products contain Oxygen?


No. We're only concerned with O2 as Oxygen gas. If the Oxygen is still in a compound, you haven't made oxygen.


Oh, I always thought that when calculating the Mr, you do not consider the coefficients. Thanks for clearing that up..

So would this be a correct calculation (for A):

Mr of (1/2)O2 = 16
Mr of NaNO3 = 85

so 16/85 x 100 = 18.8%
 

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