Question

How many moles of potassium chlorate were necessary to produce eight moles of oxygen?
 $ 2KCl{O_3}{\text{ }} \to {\text{ 2KCl + 3}}{{\text{O}}_2} $

Answer 1

Hint: We are given the decomposition reaction of potassium chlorate. Since it is a balanced decomposition reaction we will find the number of moles of oxygen produced on decomposition of one mole of potassium chlorate. Thus we will find the number of moles of potassium chlorate needed to produce eight moles of oxygen.

Complete answer:
The decomposition reaction of potassium chlorate is given as:
 $ 2KCl{O_3}{\text{ }} \to {\text{ 2KCl + 3}}{{\text{O}}_2} $
Since it is a balanced decomposition reaction, we can find the number of moles of oxygen produced on decomposition of one mole of potassium chlorate. On observing the above we can say that two moles of potassium chlorate produce three moles of oxygen. Therefore we can write as:
Since,
Two moles of $ KCl{O_3} $ will produce number of mole oxygen $ = 3 $
One mole of $ KCl{O_3} $ will produce number of mole of oxygen $ = \dfrac{3}{2} $
Since the ratio of moles is constant for each compound, we can find the moles of potassium chlorate needed for producing eight moles of oxygen as:
 $ \Rightarrow \dfrac{2}{3}{\text{ }} \times {\text{ 8}} $
 $ \Rightarrow \dfrac{{16}}{3} $
 $ \Rightarrow 5.33 $
Therefore we need $ 5.33 $ moles of potassium chlorate to produce eight moles of oxygen. Also we can say that the number of moles needed to produce eight moles of oxygen are $ \dfrac{{16}}{3} $ moles.

Note:
For a balanced chemical reaction the ratio of moles of each compound is constant. Thus with the help of the ratio of moles we can find the moles of potassium chlorate. This follows the law of conservation of mass for a balanced chemical reaction. The method which we used to find moles of potassium chlorate is known as the unitary method.