Determining Limiting and Excess Reactants in the Reaction between Magnesium and Oxygen

In chemical reactions, the determination of limiting and excess reactants is crucial for understanding the reaction process and ensuring that one reactant is completely consumed before the others. This article will guide you through the process of identifying the limiting and excess reactants when 2.2 grams of magnesium (Mg) is reacted with 6.43 grams of oxygen (O?). We will also cover the importance of stoichiometry, molar ratios, and the calculation of moles to solve this problem.

Understanding Stoichiometry and Molar Ratios

The balanced chemical equation for the reaction between magnesium and oxygen to form magnesium oxide is:

2 Mg O? → 2 MgO

The stoichiometric ratio of Mg to O? is 2:1, meaning that 2 moles of Mg react with 1 mole of O? to produce 2 moles of MgO.

Calculating Moles of Reactants

To determine the limiting and excess reactants, we first need to calculate the moles of each reactant involved in the reaction.

Calculating Moles of Magnesium (Mg)

The molar mass of Mg is 24.31 g/mol.

[ text{Moles of Mg} frac{2.2 text{ g}}{24.31 text{ g/mol}} approx 0.0905 text{ moles} ]

Calculating Moles of Oxygen (O?)

The molar mass of O? is 32.00 g/mol.

[ text{Moles of O}_{2} frac{6.43 text{ g}}{32.00 text{ g/mol}} approx 0.201 text{ moles} ]

Determining Stoichiometric Requirements

From the balanced equation, 2 moles of Mg react with 1 mole of O?. This gives us the stoichiometric ratio of 2:1.

Finding the Required Amount of Oxygen (O?)

Using the moles of Mg calculated, we can determine the required amount of O? to react with all the available Mg:

[ text{Moles of O}_2 text{ required} frac{0.0905 text{ moles Mg}}{2} approx 0.04525 text{ moles O}_2 ]

Comparing Available Oxygen with Required Oxygen

Available O?: 0.201 moles Required O? for 0.0905 moles of Mg: 0.04525 moles Since we have more O? available than required, O? is in excess.

Determining the Limiting Reactant

Since we need 0.04525 moles of O? to react with all the available Mg, and we have 0.201 moles of O?, Mg will be the limiting reactant. This is because only 0.09 moles of Mg is available, and not enough O? is required to fully react with it.

Conclusion

Limiting Reactant: Magnesium (Mg) Excess Reactant: Oxygen (O?)

The determination of the limiting and excess reactants is essential for predicting the outcome of a chemical reaction and maximizing yield. In this case, understanding the molar ratio, calculating moles, and comparing reactant quantities allowed us to identify the limiting reactant (Mg) and the excess reactant (O?).