Question

A compound $X$ decomposes by reactions done independently under different reaction conditions as follows:
$X\to 2Y+Z\dots \dots \text{(i)}$
$3X\to 4W+2V\dots \dots \text{(ii)}$
Assume the percentage yield of reaction (i) to be 40 % and that of reaction (ii) to be 75%. If 3 moles of Y were formed and a total of 15 moles of X were taken initially, the moles of W formed will be:

• A. 11.25
• B. 7.23
• C. 15.64
• D. 20.25

Answer 1

The correct option is A 11.25

Let us assume that ‘a’ mol of X was taken in reaction (i).
As per stoichiometry,
1 mol of X gives 2 mol of Y
a mol of X gives 2a mol of Y
But, as the yield is 40 %, number of moles of Y obtained = $\frac{40}{100}\times 2a$
Actual yield of Y is given as 3.
So, $\frac{40}{100}\times 2a=3$
On solving, a = 3.75 mol
Moles of X taken in reaction (ii) $=15–3.75=11.25$ mol
In reaction (ii),
3 mol of X gives 4 mol of W
11.25 mol of X will give $=\frac{4}{3}\times 11.25=15$ mol of W
But, the yield given is 75 %
Actual number of moles of W obtained $=0.75\times 15=11.25$ mol