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

Mg + Cl2 --> MgCl2

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

is this correct
7 g+13.2 g = 20.2 grams ?

No. This is a limiting reagent problem. You know that because the problem gives BOTH the reactants.

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

Convert moles Mg to moles MgCl2.
Convert moles Cl2 to moles MgClw.
It is likely that the number of moles calculated each way will not be the same which means one of them is wrong. In limiting reagent problems, the smaller answer is ALWAYS the correct one and the reactant producing that value is the limiting reagent.

Take the smaller value and convert moles MgCl2 to grams. g = moles x molar mass.

To determine the mass of magnesium chloride formed in the reaction, you need to first find the limiting reactant. The limiting reactant is the one that will be completely consumed and determine the maximum amount of product that can be formed.

To find the limiting reactant, you can use the concept of stoichiometry, which relates the amount (in moles) of each reactant to the amount of product produced.

First, convert the masses of both magnesium (Mg) and chlorine gas (Cl2) to moles using their respective molar masses. The molar mass of magnesium is 24.31 g/mol, and the molar mass of chlorine is 70.90 g/mol.

For magnesium:
7 g of Mg * (1 mol Mg / 24.31 g Mg) ≈ 0.287 mol Mg

For chlorine gas:
13.2 g of Cl2 * (1 mol Cl2 / 70.90 g Cl2) ≈ 0.186 mol Cl2

Next, look at the balanced chemical equation:
Mg + Cl2 → MgCl2

From the balanced equation, you can see that the ratio of moles between magnesium and chlorine gas is 1:1. This means that for every 1 mole of magnesium, 1 mole of chlorine gas is required to form 1 mole of magnesium chloride.

Since both reactants have a 1:1 ratio, the limiting reactant will be the one with the smaller number of moles. In this case, the limiting reactant is chlorine gas because it has fewer moles (0.186 mol) compared to magnesium (0.287 mol).

Now, you can use the moles of the limiting reactant (chlorine gas) to calculate the moles of magnesium chloride formed. According to the balanced equation, 1 mole of chlorine gas reacts to form 1 mole of magnesium chloride.

0.186 mol Cl2 * (1 mol MgCl2 / 1 mol Cl2) = 0.186 mol MgCl2

Finally, convert the moles of magnesium chloride to grams using its molar mass. The molar mass of magnesium chloride (MgCl2) is 95.21 g/mol.

0.186 mol MgCl2 * (95.21 g MgCl2 / 1 mol MgCl2) ≈ 17.7 g MgCl2

Therefore, the correct mass of magnesium chloride formed in the reaction between 7 g of Mg and 13.2 g of Cl2 is approximately 17.7 grams, not 20.2 grams.