How properties before and after a chemical reaction can be used to determine if a chemical reaction occurred

If 16.00g of hydrogen gas reacts with 126.73g of oxygen, how many grams of water are yielded? (both reactants are completely consumed in the reaction.)

Which one of the following bonds would you expect to be the most polar? a) b–h b) n–h c) p–h d) al–h e) c–h

Calculate the concentration of all species in a 0.165 m solution of h2co3.