Question

Nitrogen can be obtained by (a) passing ammonia over red-hot copper(II) oxide and (b) heating ammonium dichromate [one of the products is \(\mathrm{Cr}(\mathrm{III})\) oxide]. Write a balanced equation for each preparation.

Short answer

(a) \(2 \text{NH}_3 + 3 \text{CuO} \rightarrow \text{N}_2 + 3 \text{Cu} + 3 \text{H}_2\text{O}\); (b) \((\text{NH}_4)_2\text{Cr}_2\text{O}_7 \rightarrow \text{N}_2 + \text{Cr}_2\text{O}_3 + 4 \text{H}_2\text{O}\).

Step-by-step solution

Write the Chemical Reaction for Method (a)

Identify the reactants and products in the reaction where ammonia (NH₃) is passed over red-hot copper(II) oxide (CuO). The products are nitrogen gas (N₂), copper (Cu), and water (H₂O).The unbalanced chemical reaction is:\[ \text{NH}_3 + \text{CuO} \rightarrow \text{N}_2 + \text{Cu} + \text{H}_2\text{O} \]

Balance the Equation for Method (a)

Balance the number of each type of atom on both sides of the reaction. Start by balancing the nitrogen atoms first, then hydrogen, and finally the oxygen and copper atoms.Balanced equation:\[ 2 \text{NH}_3 + 3 \text{CuO} \rightarrow \text{N}_2 + 3 \text{Cu} + 3 \text{H}_2\text{O} \]

Write the Chemical Reaction for Method (b)

Identify the reactants and products in the reaction where ammonium dichromate \((\text{(NH}_4\text{)}_2\text{Cr}_2\text{O}_7)\) is heated. The products are nitrogen gas (N₂), chromium(III) oxide (Cr₂O₃), and water vapor (H₂O).The unbalanced chemical equation is:\[ \text{(NH}_4\text{)}_2\text{Cr}_2\text{O}_7 \rightarrow \text{N}_2 + \text{Cr}_2\text{O}_3 + \text{H}_2\text{O} \]

Balance the Equation for Method (b)

Balance the chemical equation by ensuring the number of each type of atom is the same on both sides. Begin with nitrogen, then chromium, and lastly balance the hydrogen and oxygen atoms.Balanced equation:\[ \text{(NH}_4\text{)}_2\text{Cr}_2\text{O}_7 \rightarrow \text{N}_2 + \text{Cr}_2\text{O}_3 + 4 \text{H}_2\text{O} \]

Key concepts

Balancing Chemical Equations

Balancing chemical equations is essential because it ensures the law of conservation of mass is obeyed. This principle states that matter cannot be created or destroyed within a chemical reaction. Thus, the number of atoms for each element must be the same on both sides of the equation.
To balance equations, follow these basic steps:

• Write down the unbalanced equation with the correct chemical formulas for reactants and products.
• Count the number of atoms for each element on both sides of the equation.
• Adjust coefficients (the numbers before substances) to balance each type of atom, one at a time.
• Tip: It often helps to start with elements that appear in only one reactant and one product, such as N and H in the given reactions.

Remember, you cannot change the actual subscripts within a chemical formula, only the coefficients.
This practice not only helps in understanding and solving chemical reactions but also solidifies fundamental chemistry principles.

Nitrogen Preparation

Nitrogen is a crucial element in both nature and industry, making its preparation an important process. Two methods for nitrogen preparation are through ammonia and ammonium dichromate reactions. For Method (a), when ammonia is passed over red-hot copper(II) oxide, nitrogen gas is produced along with copper and water.
The balanced chemical equation is:\[2 \text{NH}_3 + 3 \text{CuO} \rightarrow \text{N}_2 + 3 \text{Cu} + 3 \text{H}_2\text{O}\]In Method (b), heating ammonium dichromate results in the formation of nitrogen gas, chromium(III) oxide, and water vapor. This reaction also exhibits significant gas release and is sometimes used in demonstration because of its dramatic nature.
The balanced chemical equation is:\[\text{(NH}_4\text{)}_2\text{Cr}_2\text{O}_7 \rightarrow \text{N}_2 + \text{Cr}_2\text{O}_3 + 4 \text{H}_2\text{O}\]Both of these methods emphasize the versatility of nitrogen and its compounds in chemistry and industrial applications.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They display both reactants (things that start the reaction) and products (things that result from the reaction). Understanding how to interpret and write these equations is foundational in chemistry.
Here's a basic rundown of the elements in a chemical equation:

• Reactants: Substances present before the reaction takes place. They are listed on the left side.
• Products: Substances produced by the reaction. They are shown on the right side.
• Coefficients: Numbers placed before substances to balance the equation, indicating the number of molecules or moles.
• Subscripts: Numbers within chemical formulas that indicate the number of atoms of an element in a molecule.

Within the context of the exercise, understanding the nature of the reactants and anticipating the products helps to handily balance the equation. Each component plays a critical role in ensuring the chemical reaction is correctly and clearly described in symbolic form.