Problem 1 - Chemistry and Chemical Reactivity

Question

The equation for the oxidation of phosphorus in air is \(\mathrm{P}_{4}(\mathrm{s})+5 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s}) .\) Identify the reactants and products and the stoichiometric coefficients. To what do the designations s and g refer?

Step-by-Step Solution

Answer

Reactants: \(\mathrm{P}_{4}(s)\), \(5\mathrm{O}_{2}(g)\); Product: \(\mathrm{P}_{4}\mathrm{O}_{10}(s)\); Coefficients: 1, 5, 1; (s) solid, (g) gas.

Step 1: Identify the Reactants

In a chemical reaction, the substances that are present at the beginning and undergo change are called reactants. For the given equation \(\mathrm{P}_{4}(\mathrm{s})+5 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\), the reactants are \(\mathrm{P}_{4}(\mathrm{s})\) and \(5\mathrm{O}_{2}(\mathrm{g})\).

Step 2: Identify the Products

Products are the substances that are formed from the chemical reaction. In the equation \(\mathrm{P}_{4}(\mathrm{s})+5 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\), the product is \(\mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\).

Step 3: Determine Stoichiometric Coefficients

Stoichiometric coefficients are the numbers that appear before the formulas in a balanced chemical equation, indicating the ratio of moles of each substance involved. In this reaction, the coefficients are 1 for \(\mathrm{P}_{4}\), 5 for \(\mathrm{O}_{2}\), and 1 for \(\mathrm{P}_{4} \mathrm{O}_{10}\).

Step 4: Understand State Symbols

In a chemical equation, the designations (s), (g), (l), and (aq) indicate the physical state of the substances: (s) for solid, (g) for gas, (l) for liquid, and (aq) for aqueous solution. In this equation, \(\mathrm{P}_{4}(\mathrm{s})\) and \(\mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\) refer to solids, and \(\mathrm{O}_{2}(\mathrm{g})\) indicates a gas.

Key Concepts

Oxidation Reaction

In the realm of chemistry, an oxidation reaction is a crucial type of chemical reaction. It involves the transfer of electrons between substances, leading to a change in their oxidation states. Oxidation also commonly involves the combination of a substance with oxygen. In everyday life, the rusting of iron and the browning of an apple are examples of oxidation reactions. In the given exercise, we have the oxidation of phosphorus where phosphorus combines with oxygen molecules in the air to form phosphorus pentoxide (\(\mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\)).
This process is considered an oxidation reaction for the following reasons:

• Phosphorus (\(\mathrm{P}_{4}\)) gains oxygen to form \(\mathrm{P}_{4} \mathrm{O}_{10}\).
• Electrons are transferred as phosphorus atoms increase their oxidation state by gaining oxygen.

Understanding oxidation reactions is important as it underpins a lot of chemical processes in nature and industry.

Reactants and Products Identification

In any chemical reaction, it's essential to correctly identify reactants and products as they represent the substances interacting in the reaction. Reactants are the starting substances that undergo a chemical change, and products are the new substances formed as a result of the reaction.
Examining the equation \(\mathrm{P}_{4}(\mathrm{s})+5 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\), we can identify:

• Reactants: These are \(\mathrm{P}_{4}(\mathrm{s})\) and \(5\mathrm{O}_{2}(\mathrm{g})\).
  Phosphorus and oxygen in gaseous form start the reaction.
• Product: This is \(\mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\), a solid compound resulting from the reaction of the reactants.

Identifying reactants and products is crucial for understanding how chemical reactions proceed and for balancing chemical equations correctly, following stoichiometric principles.

State Symbols in Chemical Equations

State symbols in chemical equations provide valuable information about the physical state of the substances involved in a reaction.
These symbols include:

• (s) for solids
• (g) for gases
• (l) for liquids
• (aq) for aqueous solutions, which are substances dissolved in water

In the chemical equation from the exercise, the state symbols are particularly informative:

• \(\mathrm{P}_{4}(\mathrm{s})\): The subscript 's' signifies that phosphorus begins as a solid.
• \(5\mathrm{O}_{2}(\mathrm{g})\): The 'g' denotes that oxygen is a gas, appropriate considering how it exists under typical atmospheric conditions.
• \(\mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\): The product remains a solid after the reaction.

Understanding these state symbols is foundational for predicting reaction conditions and behaviors, which can affect reaction rates and equilibria.