Question

how many grams of water are produced when 2.50 mol oxygen reacts with hydrogen?

Answer 1

According to reaction below, when one mol of oxygen reacts with two mol of hydrogen, two mol of water is produced. Thus, when 2.5 mol of oxygen reacted with hydrogen, 2 * 2.5 mol = 5 mol of water is produced. The molar mass of water is 18 g/mol. One mol of water weighs 18 g. 5 mol of water weights 5 * 18 = 90 g.
O2 + 2 H2 = 2 H2O
Answer: 90 g.