Question

For the reaction 2 Na + 2 H2O -------> 2 NaOH + H2, how many grams of hydrogen gas are produced when 133.6 g of water are reacted?

I am soooo confused in chemistry. Please help.

Answer 1

First calculate molecular masses of

M_H2 = (2*1.008) and
M_H2O = (2*1.008+15.999)

Then
mass of hydrogen produced
=mass of water *(M_H2/(2M_H2O))

Note the factor 2 in the denominator comes from the stoichiometric coefficient of H2O.