Question: how many moles of hydrogen gas are needed to react with 15.1 grams of chlorine gas?
Answer: Thenwe divide the given mass by this molar mass to get moles: 15.1g/(70.9) = 0.21298 moles. Now we can use the mole-to-mole ratio of hydrogen to chlorine. Notice in the reaction how the coefficient of both H2and Cl2 is 1, so the amount of hydrogen is equal tochlorine, so we have 0.21298 moles of hydrogen as well.