When magnesium metal is burned in air (Figure 3.5), two products are produced. One is magnesium oxide, MgO. The other is the product of the reaction of Mg with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. d. Magnesium nitride can also be formed by reaction of the metal with ammonia at high temperature. Write a balanced equation for this reaction. If a 6.3-g Mg ribbon reacts with 2.57 g NH3(𝑔) and the reaction goes to completion, which component is the limiting reactant? What mass of H2(𝑔) is formed in the reaction?

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Step 1: Write the balanced chemical equation for the reaction of magnesium with ammonia. The reaction is: 3Mg + 2NH_3 \rightarrow Mg_3N_2 + 3H_2.

Step 2: Calculate the moles of Mg and NH_3. Use the molar mass of Mg (24.31 g/mol) and NH_3 (17.03 g/mol) to convert the given masses to moles.

Step 3: Determine the limiting reactant by comparing the mole ratio from the balanced equation with the calculated moles of each reactant. The reactant that produces the least amount of product is the limiting reactant.

Step 4: Use the stoichiometry of the balanced equation to calculate the moles of H_2 produced, based on the moles of the limiting reactant.

Step 5: Convert the moles of H_2 to grams using the molar mass of H_2 (2.02 g/mol) to find the mass of hydrogen gas formed.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Balancing Chemical Equations

Balancing chemical equations is essential for accurately representing the conservation of mass in a chemical reaction. Each side of the equation must have the same number of atoms for each element involved. This ensures that the reactants and products are correctly accounted for, allowing for the determination of stoichiometric relationships and the identification of limiting reactants.

Limiting Reactants

The limiting reactant is the substance that is completely consumed first in a chemical reaction, thus determining the maximum amount of product that can be formed. To identify the limiting reactant, one must compare the mole ratios of the reactants based on the balanced equation and the initial amounts available. This concept is crucial for calculating the theoretical yield of products.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on their molar relationships. It allows chemists to predict the quantities of substances consumed and produced in a reaction. Understanding stoichiometry is vital for solving problems related to mass, moles, and the yields of products, especially when determining the amount of gas produced in reactions.

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Textbook Question

When magnesium metal is burned in air (Figure 3.5), two products are produced. One is magnesium oxide, MgO. The other is the product of the reaction of Mg with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. c. In an experiment, a piece of magnesium ribbon is burned in air in a crucible. The mass of the mixture of MgO and magnesium nitride after burning is 0.470 g. Water is added to the crucible, further reaction occurs, and the crucible is heated to dryness until the final product is 0.486 g of MgO. What was the mass percentage of magnesium nitride in the mixture obtained after the initial burning?

Textbook Question

hen magnesium metal is burned in air (Figure 3.5), two products are produced. One is magnesium oxide, MgO. The other is the product of the reaction of Mg with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. e. The standard enthalpy of formation of solid magnesium nitride is −461.08 kJ/mol. Calculate the standard enthalpy change for the reaction between magnesium metal and ammon