Question

Write a proper formation reaction for each substance. a) \(\mathrm{O}_{3}(\mathrm{~g})\) b) \(\mathrm{Na}_{2} \mathrm{O}_{2}(\mathrm{~s})\) c) \(\mathrm{PCl}_{5}(\mathrm{~g})\)

Short answer

Formation reactions: (a) \(3/2 \, \mathrm{O}_{2}(g) \rightarrow \mathrm{O}_{3}(g)\) (b) \(2 \, \mathrm{Na}(s) + \mathrm{O}_{2}(g) \rightarrow \mathrm{Na}_{2}\mathrm{O}_{2}(s)\) (c) \(1/4 \, \mathrm{P}_{4}(s) + 5/2 \, \mathrm{Cl}_{2}(g) \rightarrow \mathrm{PCl}_{5}(g)\).

Step-by-step solution

Understanding Formation Reactions

Formation reactions involve creating one mole of a compound from its elements in their standard states. For each of the given substances, we need to write chemical equations showing this process.

Write Formation Reaction for \\ \(\mathrm{O}_{3}(\mathrm{~g})\\)

Ozone, \(\mathrm{O}_3\), is composed of the element oxygen. The standard state of oxygen is \(\mathrm{O}_2(\mathrm{~g})\), so the formation reaction is: \[3/2 \, \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{O}_{3}(\mathrm{~g})\].

Write Formation Reaction for \\ \(\mathrm{Na}_{2} \mathrm{O}_{2}(\mathrm{~s})\\)

Sodium peroxide, \(\mathrm{Na}_{2}\mathrm{O}_{2}\), is formed from sodium and oxygen. Sodium in its standard state is \(\mathrm{Na}(s)\), and oxygen is \(\mathrm{O}_{2}(\mathrm{~g})\). The reaction is: \[2 \, \mathrm{Na}(s) + \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{Na}_{2}\mathrm{O}_{2}(s)\].

Write Formation Reaction for \\ \(\mathrm{PCl}_{5}(\mathrm{~g})\\)

Phosphorus pentachloride, \(\mathrm{PCl}_{5}\), involves phosphorus and chlorine. Phosphorus can be in several allotropes; we use white phosphorus, \(\mathrm{P}_4(s)\), the most stable form, and chlorine is \(\mathrm{Cl}_{2}(\mathrm{~g})\). The formation reaction is: \[\frac{1}{4} \, \mathrm{P}_4(s) + \frac{5}{2} \, \mathrm{Cl}_2(\mathrm{~g}) \rightarrow \mathrm{PCl}_{5}(\mathrm{~g})\].

Key concepts

Chemical Equations

A chemical equation represents the symbolic representation of a chemical reaction. It shows the reactants and the products involved in the reaction in a concise way. Every chemical equation must be balanced, meaning the number of atoms for each element is the same on both sides of the equation.
This ensures that no atoms are lost or gained in the process. Consider a formation reaction where compounds are formed from their basic elements.

This is often used to describe the formation of chemical compounds from their most stable forms, called standard states.
In the steps given, each formation reaction is carefully balanced to ensure the law of conservation of mass is adhered to, making these equations crucial for understanding chemical processes.

Standard States

The standard state of an element refers to its most stable form under standard conditions, which are 1 atm pressure and a specified temperature, usually 298.15 K (25 °C).
This concept is important because it provides a reference point for thermodynamic calculations and chemical reactions.

For example, in the formation reaction of ozone, the element oxygen is in its standard state as \(\mathrm{O}_{2}(\mathrm{~g})\), which is its most stable form at room temperature and atmospheric pressure.
Similarly, sodium in its formation reaction is presented as \(\mathrm{Na}(s)\) while chlorine appears as \(\mathrm{Cl}_{2}(\mathrm{~g})\) in its gaseous state, all reflecting their most stable conditions.

Ozone Formation

Ozone (\mathrm{O}_{3}) plays a vital role in atmospheric chemistry, absorbing harmful ultraviolet radiation.
However, its formation can also be explored in a controlled manner, showing the transition of oxygen in its standard state.

In its formation reaction, \(\mathrm{O}_{3}\), gaseous oxygen molecules (\(\mathrm{O}_{2}(\mathrm{~g})\)) are the reactants.
The chemical equation: \(\frac{3}{2} \, \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{O}_{3}(\mathrm{~g})\) illustrates the combination of oxygen molecules to form ozone by implying the existence of intermediate steps involving radical reactions. This highlights the dynamic transformation from a more stable to a somewhat less stable form, critical in chemical kinetics.

Sodium Peroxide

Sodium peroxide (\mathrm{Na}_{2} \mathrm{O}_{2}), a compound formed from sodium (\mathrm{Na}) and oxygen (\mathrm{O}_{2}), serves as an example of an oxidizing agent. It finds usage in applications like pulp bleaching and as an oxygen source in breathing devices.
In chemical form, it represents a solid at room temperature.

Its formation reaction is: \(2 \, \mathrm{Na}(s) + \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{Na}_{2}\mathrm{O}_{2}(s)\).
Here, sodium's transition from its metallic form to part of the compound alongside diatomic oxygen reflects the change in atomic structure and energy states.

Phosphorus Pentachloride

Phosphorus pentachloride (\mathrm{PCl}_{5}), a compound derived from phosphorus and chlorine, is used in the preparation of organic compounds and as a chlorinating agent.
Understanding its formation reaction provides insight into the molecular assembly from its basic elements.

The reaction: \(\frac{1}{4} \, \mathrm{P}_4(s) + \frac{5}{2} \, \mathrm{Cl}_2(\mathrm{~g}) \rightarrow \mathrm{PCl}_{5}(\mathrm{~g})\) shows phosphorus in its standard form, white phosphorus \(\mathrm{P}_4(s)\), combining with chlorine gas \(\mathrm{Cl}_{2}(\mathrm{~g})\).
This balanced equation not only represents the stoichiometry but also adjusts the basic units of reactants, ensuring accuracy in chemical synthesis.