Solid magnesium metal reacts with chlorine gas according to the following equation:

Question

Mg + Cl2 --> MgCl2

What mass of magnesium chloride is formed in the reaction between 7 g of Mg and 13.2 g of Cl2

Answer 1

This is a limiting reagent problem. You know that when BOTH reactants are given.

Convert 7 g Mg to moles. moles = grams/molar mass
Convert 13.2 grams Cl2 to moles.

Using the coefficients in the balanced equation, convert mole Mg to moles MgCl2.
Same process, convert moles Cl2 to moles MgCl2.
The answers to moles MgCl2 will be different; obviously, one of them is wrong. In limiting reagent problems, the correct answer is ALWAYS the smaller one and the reactant producing that value is the limiting reagent.

Now use the smaller value and convert moles MgCl2 to grams. g = moles x molar mass.
Post your work if you get stuck.