What is the maximum mass of PH3 that can be formed when 62.0g of phosphorus reacts with 4.00g of hydrogen?

Question

 

P_4(g) + 6H_2(g) = 4PH_3(g)

Answer 1

The atomic mass of phosphorus is 30.9738, so the molecular mass of P₄ is 4 x 30.9738 = 123.90 g

So you have 62 / 123.90 = 0.50 moles of P₄

Atomic mass of hydrogen is 1.0079, so molecular mass is 2 x 1.0079 = 2.0159, so you have

4 / 2.0159 = 1.98 moles of H₂

From the equation for 0.50 moles of P₄ you need 3 moles of H₂ to react (you only have 1.98).

So all the phosphorus can't react, so we need to look at the hydrogen

You have 1.98 moles of H₂, that means 1.98 / 6 moles of P₄ can react with this, giving 4 x 1.98 / 6 moles of PH_3. The molecular mass of PH₃ is 33.9975, so mass is 33.9975 x 4 x 1.98 / 6 = 44.88 g

Mike