Law of conservation

Question

If 20 grams of magnesium reacts with 175 grams of chlorine to form magnesium chloride, and no magnesium is left after the reaction, but 23 grams of chlorine remained unreacted. How any grams of aluminum bromide were formed?

Answer 1

First write the balanced equation ...

Mg + Cl₂ ==> MgCl₂

Next, we determine the limiting reactant ...

mol Mg = 20 g x 1 mol/12 g = 1.67 mol

mol Cl₂ = 175 g - 23 g = 152 g x 1 mol/71 g = 2.14 mol

Since the Mg and Cl₂ react in a 1:1 mol ratio, Mg is limiting

Finally, calculate g of MgCl₂ ...

1.67 mol Mg x 1 mol MgCl₂/mol Mg x 83 g/mol = 139 g