Question

Write a balanced equation for each of the following combination reactions: (a) Chromium is heated with oxygen to give chromium(III) oxide. (b) Chromium is heated with nitrogen to give chromium(III) nitride.

Short answer

(a) \( 4 \text{Cr} + 3 \text{O}_2 \rightarrow 2 \text{Cr}_2\text{O}_3 \); (b) \( 2 \text{Cr} + \text{N}_2 \rightarrow 2 \text{CrN} \).

Step-by-step solution

Write Unbalanced Reaction for (a)

We start with identifying the reactants and product for the reaction of chromium and oxygen to form chromium(III) oxide. The unbalanced chemical equation is: \ \( \text{Cr} + \text{O}_2 \rightarrow \text{Cr}_2\text{O}_3 \).

Balance the Chromium Atoms for (a)

In the product \( \text{Cr}_2\text{O}_3 \), there are 2 chromium atoms. Therefore, we need 2 chromium atoms on the reactant side as well. Adjust the equation: \ \( 2 \text{Cr} + \text{O}_2 \rightarrow \text{Cr}_2\text{O}_3 \).

Balance the Oxygen Atoms for (a)

There are 3 oxygen atoms in \( \text{Cr}_2\text{O}_3 \), but \( \text{O}_2 \) yields only 2 oxygen atoms. Use a coefficient to balance the oxygens: \ \( 2 \text{Cr} + \dfrac{3}{2} \text{O}_2 \rightarrow \text{Cr}_2\text{O}_3 \). \( \dfrac{3}{2} \) simplifies to multiplying the whole equation, giving: \ \( 4 \text{Cr} + 3 \text{O}_2 \rightarrow 2 \text{Cr}_2\text{O}_3 \).

Write Unbalanced Reaction for (b)

For chromium reacting with nitrogen, we write the unbalanced equation for forming chromium(III) nitride: \ \( \text{Cr} + \text{N}_2 \rightarrow \text{CrN} \).

Balance the Chromium and Nitrogen Atoms for (b)

In the product (\( \text{CrN} \), you need to balance both chromium and nitrogen. Each \( \text{CrN} \) unit takes one Cr and half \( \text{N}_2 \). To balance, write: \[ 2 \text{Cr} + \text{N}_2 \rightarrow 2 \text{CrN} \].

Key concepts

Combination Reactions

In chemistry, combination reactions are fascinating processes where two or more substances come together to form a single product. These reactions are straightforward yet vital. They demonstrate how new compounds can be formed from simpler substances. For example, when chromium is heated with oxygen, they combine to form chromium(III) oxide. This type of reaction is practically useful for synthesizing compounds in both industrial and laboratory settings. You can identify a combination reaction by observing that multiple reactants merge to create one product.
Let's breakdown how these reactions occur step by step:

• Identify the reactants involved in the reaction. In our exercise, these were chromium and oxygen or nitrogen.
• Write the unbalanced chemical equation showing the reactants turning into the product.
• Balance the chemical equation. This involves ensuring that there are equal numbers of each type of atom on both sides of the equation.

Understanding combination reactions helps us grasp the basics of how different elements interact to form new substances.

Stoichiometry

Stoichiometry is a critical concept in chemistry, referring to the calculation of reactants and products in chemical reactions. It involves using balanced chemical equations to determine the amounts of substances involved in a reaction. In the exercise, unbalanced equations were initially written for both reactions of chromium with oxygen and nitrogen. Stoichiometry was then employed to balance these equations. The balancing process ensures that the same number of each type of atom appears on the reactant side as on the product side. Here's how stoichiometry was applied in the given problem:

• For reaction (a) with oxygen, we started by balancing chromium atoms, followed by the oxygen atoms.
• This involved adding coefficients to the reactants and products, such as adding a coefficient of 4 to chromium on the reactant side and 2 on the product side.

Stoichiometry helps us understand the proportional relationships between different substances in a reaction, enabling us to predict the quantities needed or produced. This is essential for both laboratory experiments and large-scale industrial chemical processes.

Chemical Reactions

Chemical reactions are the processes that allow substances to transform into new substances with different chemical properties. They are fundamental to chemistry and occur everywhere around us—from digestion to combustion, and even photosynthesis. In our exercise, we explored two specific reactions involving chromium: - The heating of chromium with oxygen to produce chromium(III) oxide. - The heating of chromium with nitrogen to produce chromium(III) nitride. These are examples of combination reactions, where two elements or compounds form a single product. For these reactions to be properly understood, we need to ensure that they are represented with balanced chemical equations. A balanced chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. Thus, every atom present in the reactants must also appear in the products. This balancing act is achieved by adjusting coefficients before chemical formulas, as seen in the given exercise. By comprehending these chemical reactions and their balanced equations, we gain insight into how different substances interact and the new products that result from these interactions.