Question

Challenge Solid iron reacts with chlorine gas to form solid iron(lil chloride (FeCl,). Write the balanced equation and the equilibrium constant expression for the reaction.

Short answer

Balanced equation: \(2 \: Fe (s) + 3 \: Cl_2 (g) \rightarrow 2 \: FeCl_3 (s)\) Equilibrium constant expression: \(K = [Cl_2]^3\)

Step-by-step solution

Write the unbalanced equation

To write the unbalanced chemical equation, we write the reactants and products involved in the reaction: Fe (s) + Cl2 (g) → FeCl3 (s)

Balance the chemical equation

To balance the chemical equation, we need to ensure that there are an equal number of atoms of each element on both sides of the equation: 2 Fe (s) + 3 Cl2 (g) → 2 FeCl3 (s)

Write the equilibrium constant expression

For a heterogeneous reaction containing a mixture of solids and gases, only the concentrations of the gases are considered in the equilibrium constant expression. Since the concentration of solids remains constant throughout the reaction, they are not included in the expression. In this case, the equilibrium constant expression (K) will only involve the concentration of chlorine gas, and can be written as: K = [Cl2]^3 That's the final answer, so we have: Balanced equation: 2 Fe (s) + 3 Cl2 (g) → 2 FeCl3 (s) Equilibrium constant expression: K = [Cl2]^3

Key concepts

Balancing Chemical Equations

Balancing chemical equations is a fundamental skill required in chemistry. It ensures that the law of conservation of mass is obeyed during a chemical reaction. This means that the same number of each type of atom must appear on both sides of the equation. To balance a chemical equation, follow these steps:

• Write down the unbalanced equation by representing the reactants and products in their chemical form.
• Count the number of atoms of each element on both sides of the equation.
• Use coefficients (the numbers in front of the molecules) to adjust the number of atoms, ensuring both sides have equal numbers.

For example, in the reaction of iron with chlorine gas to produce iron(III) chloride, the unbalanced equation is:
Fe (s) + Cl_2 (g) → FeCl_3 (s)
By assessing the number of atoms, we see that two chlorine atoms on the reactant side balance with three chloride ions in the product. Thus, the balanced equation becomes:
2 Fe (s) + 3 Cl_2 (g) → 2 FeCl_3 (s).
Balancing chemical equations might seem tricky at first, but with practice, it becomes an intuitive process.

Equilibrium Constant Expression

In chemical reactions, especially those that occur in closed systems, equilibrium can be established where the rate of forward and reverse reactions become equal. The equilibrium constant (K) is a value that expresses the ratio of concentrations of products to reactants at equilibrium for a given reaction. It indicates the relative amounts of products and reactants.

• The general form for an equilibrium constant expression depends on whether the reactants and products are in the gas phase, aqueous solution, or solid state.
• For reactions involving gases, the equilibrium constant expression is written in terms of partial pressures.
• Solid substances are not included in the equilibrium constant expression because their concentrations remain constant.

For the reaction:
2 Fe (s) + 3 Cl_2 (g) → 2 FeCl_3 (s),
Only gaseous chlorine affects the equilibrium state, yielding the expression:
K = \[ \text{[Cl}_2\text{]}^3 \],
where [Cl_2] represents the concentration of chlorine gas in moles per liter at equilibrium. This expression helps predict the direction of the reaction under different conditions.

Chemical Reactions

Chemical reactions describe the process by which substances interact to form new products. These reactions can result in the combination, decomposition, or rearrangement of atoms. Understanding chemical reactions involves several key steps:

• Identifying reactants and products: Reactants are the starting substances, while products are the substances formed as a result of the reaction.
• Representing reactions with chemical equations that show the transformation from reactants to products.
• Observing changes that indicate a reaction has occurred, such as color change, temperature change, gas production, or precipitate formation.

In the provided example, solid iron reacts with chlorine gas to form iron(III) chloride. This specific reaction demonstrates a synthesis reaction, where two or more reactants combine to form a single product. The chemical equation for this reaction, when balanced, is:
2 Fe (s) + 3 Cl_2 (g) → 2 FeCl_3 (s).
Each element’s transformation is unique and comprehending their individual changes enriches our understanding of chemical behavior.