Question

Write a balanced equationfor each of the following reactions: (a) hydrolysis of \(\mathrm{PCl}_{5}\), (b) dehydration of phosphoric acid (also called orthophosphoric acid) to form pyrophosphoric acid, (c) reaction of \(\mathrm{P}_{4} \mathrm{O}_{10}\) with water.

Short answer

(a) Hydrolysis of PCl5: \(PCl_{5} + 4H_{2}O \rightarrow H_{3}PO_{4} + 5HCl\) (b) Dehydration of phosphoric acid to form pyrophosphoric acid: \(2H_{3}PO_{4} \rightarrow H_{4}P_{2}O_{7} + H_{2}O\) (c) Reaction of P4O10 with water: \(P_{4}O_{10} + 6H_{2}O \rightarrow 4H_{3}PO_{4}\)

Step-by-step solution

(a) Hydrolysis of PCl5

First, let's write the reactants and the products of the hydrolysis of PCl5. In hydrolysis, the compound reacts with water to break down into new compounds. The products of the hydrolysis of PCl5 are phosphoric acid (H3PO4) and hydrochloric acid (HCl). The balanced equation is as follows: \[PCl_{5} + 4H_{2}O \rightarrow H_{3}PO_{4} + 5HCl\]

(b) Dehydration of phosphoric acid to form pyrophosphoric acid

Now, let's write the reactants and products of the dehydration of phosphoric acid to form pyrophosphoric acid. In dehydration, water molecules are removed from the reactants to form new compounds. For this reaction, two molecules of phosphoric acid lose a water molecule to form a molecule of pyrophosphoric acid. The balanced equation is as follows: \[2H_{3}PO_{4} \rightarrow H_{4}P_{2}O_{7} + H_{2}O\]

(c) Reaction of P4O10 with water

Finally, let's write the reactants and products of the reaction of P4O10 with water. In this reaction, P4O10 reacts with water to form phosphoric acid. The balanced equation is as follows: \[P_{4}O_{10} + 6H_{2}O \rightarrow 4H_{3}PO_{4}\]

Key concepts

Hydrolysis

Hydrolysis is a chemical reaction where water is used to break down a compound. In the case of \(\mathrm{PCl}_{5}\), when it goes through hydrolysis, it reacts with water molecules to produce phosphoric acid (\(H_{3}PO_{4}\)) and hydrochloric acid (\(HCl\)). This process essentially involves breaking the bonds in \(\mathrm{PCl}_{5}\) and inserting the components of the water molecules.\
The balanced equation representing this hydrolysis can be written as:\ \[PCl_{5} + 4H_{2}O \rightarrow H_{3}PO_{4} + 5HCl\] \
Here, you can see that each \(PCl_5\) molecule is using four water molecules to undergo the transformation. Thus, hydrolysis is a vital reaction, helping transform compounds by altering chemical structures with the help of water.

Dehydration

Dehydration is another important chemical process. Unlike hydrolysis, which adds water, dehydration reactions involve removing water molecules from the reactants. When discussing phosphoric acid (\(H_{3}PO_{4}\)), it can undergo dehydration to form pyrophosphoric acid. In this specific reaction, two phosphoric acid molecules lose a single water molecule to form a new compound called pyrophosphoric acid (\(H_{4}P_{2}O_{7}\)).\
The balanced chemical equation representing this dehydration is:\ \[2H_{3}PO_{4} \rightarrow H_{4}P_{2}O_{7} + H_{2}O\] \
Notice how two molecules combine and expel water. This rearrangement illustrates how dehydration helps synthesize complex molecules from simpler ones by removing water. Such reactions are crucial in both biological processes and industrial applications.

Balanced Equations

A balanced equation is a fundamental aspect of any chemical reaction, ensuring that the same number of each type of atom appears on both sides of the equation. This reflects the law of conservation of mass. Consider the reaction of \(\mathrm{P}_{4}O_{10}\) with water, where the product is phosphoric acid. The equation is balanced as follows:\
\[P_{4}O_{10} + 6H_{2}O \rightarrow 4H_{3}PO_{4}\] \
Here, four phosphorus atoms on the reactant side are matched by four phosphorus atoms in the product. Similarly, ten oxygen atoms from \(\mathrm{P}_{4}O_{10}\) and six oxygen atoms from water result in a total of sixteen oxygen atoms on both sides. The balance in reactants and products exemplifies the need for equilibrium in chemical equations. Balancing ensures that the chemical transformation respects the fundamental principle of atom conservation, making it a critical skill for understanding and applying chemistry principles.