Question

how many grams of H3PO4 are poduced when 10.0 moles of water react with an excess P4O10

Answer 1

Start by writing a balanced equation for the reaction.
\[\text{H}_2\text{O} + \text{P}_4\text{O}_{10} \longrightarrow \text{H}_3\text{PO}_4\]
Balance the equation.

Then look at the mole ratio: \[\text{H}_2\text{O} : \text{H}_3\text{PO}_4\]
Once you have determined how many moles of product should be obtained, convert that number of moles to mass by multiplying by the molar mass.