Consider the following reagents: zinc, copper, mercury (density 13.6 \(\mathrm{g} / \mathrm{mL}\) , silver nitrate solution, nitric acid solution. (a) Given a 500 -mL Erlenmeyer flask and a balloon, can you combine two or more of the foregoing reagents to initiate a chemical reaction that will inflate the balloon? Write a balanced chemical equation to represent this process. What is the identity of the substance that inflates the balloon? (b) What is the theoretical yield of the substance that fills the balloon? (c) Can you combine two or more of the foregoing reagents to initiate a chemical reaction that will produce metallic silver? Write a balanced chemical equation to represent this process. What ions are left behind in solution? (d) What is the theoretical yield of silver?

Chemical reactions are processes in which substances, known as reactants, transform into new substances called products. In the exercise, two separate reactions are considered. The first involves zinc reacting with nitric acid, producing hydrogen gas, which can inflate a balloon. This is represented by the balanced chemical equation:

def:chemical_equation1In the exercise, zinc (Zn) and nitric acid (2HNO_{3}) are the reactants, while zinc nitrate (Zn(NO_{3})_{2}) and hydrogen gas (H_{2}) are the products. The second reaction features copper and silver nitrate, leading to the formation of copper nitrate and metallic silver as follows:

def:chemical_equation2These reactions follow the law of conservation of mass, where the total mass of the reactants equals the total mass of the products. The equations are balanced to reflect this, with equal numbers of each atom on both sides of the reaction.

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It is a key concept to understand when determining the theoretical yield in chemistry. In the exercise, the stoichiometry of the reactions is determined by the coefficients in the balanced equations, which represent the molar ratios of the reactants and products. For instance, in the reaction between zinc and nitric acid, the stoichiometric ratio is 1:2, meaning one mole of zinc requires two moles of nitric acid to complete the reaction.

With the knowledge of stoichiometry and the balanced chemical equations, one can calculate the theoretical yield, which is the maximum amount of product that can be obtained from a given amount of reactants under ideal conditions. In the exercise, the stoichiometry allows students to determine the theoretical yield of hydrogen gas and metallic silver by using the molar ratios from the equations:

def:stoichiometric_calculation1and

def:stoichiometric_calculation2In both reactions analyzed, the stoichiometric ratios match the amounts provided, suggesting no limiting reagent. Understanding stoichiometry is crucial for predicting the outcomes of chemical reactions and optimizing the use of reactants.

The limiting reagent in a chemical reaction is the reactant that is completely consumed first, thereby limiting the amount of products formed. It dictates the theoretical yield of the reaction. Identifying the limiting reagent is vital for accurately calculating the theoretical yield.

In the exercise provided, students must analyze the molar amounts of reactants in the reactions to determine if there is a limiting reagent. As the stoichiometry reveals, both reactions under consideration do not have a limiting reagent since the reactants are present in amounts that perfectly match the stoichiometric ratios required for the reactions to proceed:

def:limiting_reagent_analysis1and

def:limiting_reagent_analysis2However, in real-world scenarios, it's common to have a limiting reagent due to non-ideal conditions or discrepancies in reactant amounts. Therefore, understanding how to identify the limiting reagent is essential for both theoretical calculations and practical applications in the laboratory.