posted by Payton .
In the reaction Mg(s) + 2HCl(aq) d H¿(g) + MgCl¿(aq), how many moles of hydrogen gas will be produced from 250.0 milliliters of a 3.0 M HCl in an excess of Mg?
I can't decipher the funny symbols. I assume you meant to write
Mg + 2HCl ==> H2 + MgCl2.
mols HCl = M x L = 3.0 x 0.250 = ?
mols H2 = 1/2 that (from the coefficients)