Question

4Which of the following statements is true for the reaction of nitrogen gas with hydrogen gas to produce ammonia \(\left(\mathrm{NH}_{3}\right){ }^{7}\) Choose the best answer. a. Subscripts can be changed to balance this equation, just as they can be changed to balance the charges when writing the formula for an ionic compound. b. The nitrogen and hydrogen will not react until you have added the correct mole ratios. c. The mole ratio of nitrogen to hydrogen in the balanced equation is 1: 2 . A Ammonia will not form unless 1 mole of nitrogen and 3 moles of hydrogen have been added. c. The balanced cquation allows you to predict how much ammonia you will make based on the amount of nitrogen and hydrogen present.

Short answer

The correct statement is option e: The balanced chemical equation allows you to predict the amount of ammonia you will make based on the amount of nitrogen and hydrogen present. This is possible due to the stoichiometric coefficients and mole ratios in the balanced equation.

Step-by-step solution

Write down the unbalanced chemical equation

First, we need to write down the unbalanced chemical equation for the given reaction, which is the formation of ammonia from nitrogen gas and hydrogen gas: \[ \text{N}_{2}+\text{H}_{2}\rightarrow\text{NH}_{3} \]

Balance the chemical equation

Next, we need to balance the chemical equation by adjusting the coefficients in front of each molecule. This is done in order to ensure that the number of atoms on the reactant side matches the number of atoms on the product side for each element present in the reaction. The balanced chemical equation is: \[ \text{N}_{2}+3\text{H}_{2}\rightarrow2\text{NH}_{3} \] This indicates that 1 mole of nitrogen gas reacts with 3 moles of hydrogen gas to produce 2 moles of ammonia.

Analyze each statement and choose the correct option

Now that we have a balanced chemical equation, we can analyze each of the given statements and select the correct answer. a. False. Subscripts must not be changed to balance a chemical equation. Instead, coefficients are used for this purpose. b. False. The reaction can proceed even if the mole ratios in the reactants are not exactly matched. However, the amount of product formed is limited by the reactant present in the smaller proportion, called the limiting reactant. c. False. The mole ratio of nitrogen to hydrogen in the balanced equation is 1:3, not 1:2. d. False. Ammonia will form as long as nitrogen and hydrogen are present in any proportion. However, having 1 mole of nitrogen and 3 moles of hydrogen available matches the stoichiometry of the balanced equation, which will lead to the efficient formation of ammonia. e. True. The balanced chemical equation allows us to predict the amount of ammonia that will form based on the amount of nitrogen and hydrogen present. This is possible due to the stoichiometric coefficients and mole ratios in the balanced equation. Based on the analysis, the correct statement is option e.

Key concepts

Stoichiometry

Stoichiometry lies at the heart of the science of chemistry, providing a methodical way to predict the quantities of reactants consumed and products formed in a chemical reaction. It involves calculations derived from the balanced chemical equation, reflecting the law of conservation of mass where the total mass of reactants equals the total mass of products.

Understanding stoichiometry begins with mastering the skill of chemical equation balancing. It's a process analogous to a recipe in cooking where ingredients must be mixed in certain proportions to achieve the desired result. In chemical terms, these proportions are based on the mole concept and Avogadro's number, allowing chemists to quantify atoms, ions, and molecules in bulk matter to facilitate these calculations.

When performing stoichiometric computations, we utilize the mole ratio from the balanced equation to convert between moles of different substances in the reaction. This enables us to predict the outcome of a chemical process at a macroscopic level, from the amounts of each reactant used to the quantity of product one can expect to obtain. This predictive power makes stoichiometry invaluable, particularly in industrial applications where efficiency and cost-effectiveness are king.

Limiting Reactant

The concept of a limiting reactant in chemistry is an extension of the basic principles of stoichiometry. It's about identifying which reactant in a chemical reaction will run out first, hence 'limiting' the amount of product that can be formed. Similar to when a builder runs out of bricks and can't complete a wall, a chemical reaction halts when one of the reactants is entirely consumed.

In the example of synthesizing ammonia (NH₃), once we have the balanced equation (N₂ + 3H₂ → 2NH₃), stoichiometry tells us that nitrogen (N₂) and hydrogen (H₂) react in a 1:3 mole ratio. If we start with equal moles of nitrogen and hydrogen, hydrogen will become the limiting reactant because we need three times as much hydrogen as nitrogen to continue the reaction until all the nitrogen is consumed.

Determining the limiting reactant is crucial for calculating theoretical yields, minimizing waste, and optimizing economic efficiency in chemical manufacturing processes. It also underscores the practical implications of balanced reactions beyond the laboratory, affecting how materials are sourced and used in real-world settings.

Mole Ratio

Mole ratio is the bridge that links the microscopic world of atoms and molecules to the quantifiable macroscopic chemical phenomena we can observe. This ratio comes directly from the coefficients found in the balanced chemical equation and serves as a conversion factor between the amounts (in moles) of different reactants and products.

For instance, the balanced equation for forming ammonia provides a clear mole ratio: one mole of nitrogen gas (N₂) reacts with three moles of hydrogen gas (H₂) to produce two moles of ammonia (NH₃). This translates to mole ratios of 1:3 for nitrogen to hydrogen and 1:2 for nitrogen to ammonia.

When conducting chemical reactions, this proportionality is key to measuring and mixing reactants properly. It's important to stress to students that mole ratios are based on stoichiometry and cannot be arbitrarily changed to satisfy the balanced equation – they are defined by the inherent properties of the chemical reaction studied. Whether scaling up for industrial manufacturing or performing a classroom experiment, the mole ratio is an indispensable part of chemistry that ensures the reaction occurs as expected.