Question

2B + 3H2 2BH3 How many moles of BH3 are synthesized when 27.0 moles of H2 completely react?

Answer 1

Answer: 18.0 moles of $BH_3$ will be produced when 27.0 moles of $H_2$ completely react.

Explanation:

The balanced chemical equation is:

$2B+3H_2\rightarrow 2BH_3$  

According to stoichiometry :

3 moles of $H_2$ produce = 2 moles of $BH_3$

Thus 27.0 moles of $H_2$ will produce=$\frac{2}{3}\times 27.0=18.0 moles$  of $BH_3$

Thus 18.0 moles of $BH_3$ will be produced when 27.0 moles of $H_2$ completely react.