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# Atom economy and percentage yield help watch

1. Struggling with part b of this question:

1,2-dichloroethane undergoes thermal cracking to give chloroethene.
CH2ClCH2Cl → CH2=CHCl + HCl

a. Calculate the percentage yield of this process if 10.0 tonnes of the 1,2-dichloroethane yield 2.0 tonnes of chloroethene.
I've done this - it's 31.7%.

b. Use the percentage yield and atom economy of this reaction to calculate how much in tonnes of the 1,2-dichloroethane is actually converted into chloroethene.
The book's answer to this is 0.4 tonnes but I'm not sure how you get there.
2. (Original post by uselessdoctor)
Struggling with part b of this question:

1,2-dichloroethane undergoes thermal cracking to give chloroethene.
CH2ClCH2Cl → CH2=CHCl + HCl

a. Calculate the percentage yield of this process if 10.0 tonnes of the 1,2-dichloroethane yield 2.0 tonnes of chloroethene.
I've done this - it's 31.7%.

b. Use the percentage yield and atom economy of this reaction to calculate how much in tonnes of the 1,2-dichloroethane is actually converted into chloroethene.
The book's answer to this is 0.4 tonnes but I'm not sure how you get there.
Something is wrong here.

10 tonnes of C2H4Cl2 = 1x107/99.0 = 1.01x105 mol
which theoretically could produce 1.01x105 mol of C2H4.
which is 1.01x105 x 28 = 0.283 tonnes
%age yield = 100 x 0.2 / 0.283 = 71%

Part b makes no sense. There is no reference to initial quantities and atom economy isn't needed for a calculation like this.

Are you sure you have copied it correctly and included all of the information in the Q?
3. (Original post by Pigster)
Something is wrong here.

10 tonnes of C2H4Cl2 = 1x107/99.0 = 1.01x105 mol
which theoretically could produce 1.01x105 mol of C2H4.
which is 1.01x105 x 28 = 0.283 tonnes
%age yield = 100 x 0.2 / 0.283 = 71%

Part b makes no sense. There is no reference to initial quantities and atom economy isn't needed for a calculation like this.

Are you sure you have copied it correctly and included all of the information in the Q?
This would be correct if the product were ethene, but the question asks for chloroethene ...

... in which case the OP was correct.
4. (Original post by charco)
This would be correct if the product were ethene, but the question asks for chloroethene ...

... in which case the OP was correct.
In which case, I need new glasses.

The 0.4 tonnes still makes no sense, though.

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