# Homework Help: Atom economy question

1. May 14, 2012

### influx

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

2. May 14, 2012

### flatmaster

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?

3. May 14, 2012

### influx

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?

4. May 14, 2012

### flatmaster

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.

5. May 14, 2012

### influx

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%