Problem 142 - Introductory Chemistry Atoms First

Question

When you strike a match, trace amounts of white phosphorus \(\left(\mathrm{P}_{4}\right)\) are converted into an oxide of phosphorus, \(\mathrm{P}_{4} \mathrm{O}_{10}\). This conversion releases sufficient heat to ignite the match head. Write a balanced reaction for this conversion, and classify the reaction type(s).

Step-by-Step Solution

Answer

The balanced equation for the conversion of white phosphorus (P4) into an oxide of phosphorus (P4O10) is \( \mathrm{P}_4 + 5\mathrm{O}_2 \rightarrow \mathrm{P}_4\mathrm{O}_{10} \). The reaction type is Synthesis (Combination).

Step 1: Write down the unbalanced chemical equation

Firstly, write the unbalanced chemical equation for the given conversion: \[ \mathrm{P}_4 + \mathrm{O}_2 \rightarrow \mathrm{P}_4\mathrm{O}_{10} \]

Step 2: Balance the chemical equation

In order to balance the chemical equation, we need to make sure that the number of atoms for each element is the same on both sides of the equation. We can see that there are 10 oxygen atoms in P4O10 on the right side of the equation, so we need 5 molecules of O2 to balance the oxygen atoms: \[ \mathrm{P}_4 + 5\mathrm{O}_2 \rightarrow \mathrm{P}_4\mathrm{O}_{10} \] Now the equation is balanced because there are 4 atoms of phosphorus and 10 atoms of oxygen on both sides.

Step 3: Classify the reaction type(s)

This reaction is a combination of two elements, phosphorus and oxygen, to form a compound, P4O10. Therefore, this is a synthesis (combination) reaction. Combining the steps, we can conclude: Balanced equation: \( \mathrm{P}_4 + 5\mathrm{O}_2 \rightarrow \mathrm{P}_4\mathrm{O}_{10} \) Reaction type: Synthesis (Combination)

Key Concepts

Synthesis Reaction

A synthesis reaction is a type of chemical reaction where two or more simple substances combine to form a more complex product. In the context of our exercise, white phosphorus (\( \mathrm{P}_{4} \)) reacts with oxygen (\( \mathrm{O}_2 \)) to form tetraphosphorus decoxide (\( \mathrm{P}_4\mathrm{O}_{10} \)). This is a classic example of a synthesis reaction.

• In a synthesis reaction, the reactants are typically elements or simple compounds.
• The product is usually a more complex compound.
• These reactions are also called combination reactions.

Synthesis reactions are quite common and can involve the formation of a wide range of complex compounds including salts, oxides, and hydrocarbons. The general form of a synthesis reaction can be written as:\[ A + B \rightarrow AB \]Where A and B are the reactants that combine to form the product AB.

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into new substances. This transformation is the result of the rearrangement of atoms. It’s important to understand a few key aspects:

• In a chemical reaction, the substances you start with are called "reactants," and the new substances formed are called "products."
• The bonds between atoms in the reactants are broken, and new bonds are formed to create the products.
• In the equation \( \mathrm{P}_4 + 5\mathrm{O}_2 \rightarrow \mathrm{P}_4\mathrm{O}_{10} \), phosphorus and oxygen are reactants, while tetraphosphorus decoxide is the product.

To ensure the reaction obeys the law of conservation of mass, which states that matter cannot be created or destroyed, the number of each type of atom must be the same on both sides of the chemical equation. This is achieved by balancing the reaction.

Oxidation

Oxidation is a part of many chemical reactions and involves the loss of electrons by a molecule, atom, or ion. In our exercise, the oxidation process occurs as phosphorus gains oxygen to form an oxide.

• Oxidation does not necessarily involve oxygen; it is more generally defined in terms of electron transfer.
• In our reaction, oxidation is part of the synthesis process as phosphorus (\( \mathrm{P}_4 \)) combines with oxygen, forming an oxide (\( \mathrm{P}_4\mathrm{O}_{10} \)).
• This oxidation releases energy, which is why this reaction supplies the heat needed to ignite a match head.

Oxidation is always part of a coupled process where another substance gains the electrons lost by the oxidized species. This partner process is called reduction, and together they form redox reactions.