Question

Write equations for reactions that could be used to release each of the following elements from their compounds. (a) \(\mathrm{O}_{2}\) (b) \(\mathrm{H}_{2}\) (c) \(\mathrm{Cl}_{2}\)

Short answer

The equations are: (a) \(2 \mathrm{KClO}_{3}(s) \rightarrow 2 \mathrm{KCl}(s) + 3 \mathrm{O}_{2}(g)\), (b) \(\mathrm{Zn}(s) + 2\mathrm{HCl}(aq) \rightarrow \mathrm{ZnCl}_{2}(aq) + \mathrm{H}_{2}(g)\), (c) \(2 \mathrm{NaCl}(aq) \rightarrow 2 \mathrm{Na}^{+}(aq) + \mathrm{Cl}_{2}(g) + \mathrm{H}_{2}(g)\)

Step-by-step solution

Release of Oxygen, \( \mathrm{O}_{2} \)

An example of a chemical reaction that releases oxygen is the decomposition of potassium chlorate (\( \mathrm{KClO}_{3} \)) into potassium chloride (\( \mathrm{KCl} \)) and oxygen gas. This can be written as:\[ 2 \mathrm{KClO}_{3}(s) \rightarrow 2 \mathrm{KCl}(s) + 3 \mathrm{O}_{2}(g) \]

Release of Hydrogen, \( \mathrm{H}_{2} \)

Hydrogen gas can be produced when an acid reacts with a metal. For example, when hydrochloric acid (\( \mathrm{HCl} \)) reacts with zinc (\( \mathrm{Zn} \)), zinc chloride (\( \mathrm{ZnCl}_{2} \)) is formed, and hydrogen gas is released. This can be written as: \[ \mathrm{Zn}(s) + 2\mathrm{HCl}(aq) \rightarrow \mathrm{ZnCl}_{2}(aq) + \mathrm{H}_{2}(g) \]

Release of Chlorine, \( \mathrm{Cl}_{2} \)

An example of a reaction releasing chlorine is the electrolysis of sodium chloride (\( \mathrm{NaCl} \)) in water. When electricity is applied, sodium chloride separates into sodium ions, chlorine gas, and hydrogen gas. The simplified equation for this process is: \[ 2 \mathrm{NaCl}(aq) \rightarrow 2 \mathrm{Na}^{+}(aq) + \mathrm{Cl}_{2}(g) + \mathrm{H}_{2}(g) \]

Key concepts

Decomposition Reaction

Decomposition reactions are types of chemical reactions where a single compound breaks down into two or more simpler substances. These reactions generally require an input of energy in the form of heat, light, or electricity. In the classroom or laboratory, decomposition reactions demonstrate the principle that compounds are held together by bonds that can be broken to form new substances.

For instance, a common decomposition reaction taught in chemistry classes is the breakdown of potassium chlorate \(\mathrm{KClO}_{3}\) to form potassium chloride \(\mathrm{KCl}\) and oxygen gas \(\mathrm{O}_{2}\). Here's the process in a simplified manner:
\[ 2 \mathrm{KClO}_{3}(s) \rightarrow 2 \mathrm{KCl}(s) + 3 \mathrm{O}_{2}(g) \]
Through this reaction, students can observe the release of oxygen, a gas necessary for many forms of life. This is a classic example of how decomposition reactions are essential to understanding chemical processes in nature and industry.

Acid-Metal Reaction

Acid-metal reactions are a subset of chemical reactions that involve an acid and a metal. The result of such a reaction usually includes the release of hydrogen gas \(\mathrm{H}_{2}\) and the formation of a salt. In the classroom, these reactions can be quite spectacular, as they often produce effervescence or fizzing as the hydrogen gas escapes.

An example of an acid-metal reaction occurs when hydrochloric acid \(\mathrm{HCl}\) interacts with zinc \(\mathrm{Zn}\), yielding zinc chloride \(\mathrm{ZnCl}_{2}\) and hydrogen gas \(\mathrm{H}_{2}\). The balanced chemical equation for this reaction is:
\[ \mathrm{Zn}(s) + 2\mathrm{HCl}(aq) \rightarrow \mathrm{ZnCl}_{2}(aq) + \mathrm{H}_{2}(g) \]
This type of reaction not only illustrates the concept of reactivity series—in which metals have different reactivity with acids—but also the practical usage in hydrogen gas production.

Electrolysis of Sodium Chloride

Electrolysis is a method of using an electric current to drive a non-spontaneous chemical reaction. The electrolysis of sodium chloride \(\mathrm{NaCl}\), commonly known as table salt, involves passing an electric current through molten or dissolved salt to produce sodium metal and chlorine gas. This process is widely used in industry to obtain these substances for various uses.

During the electrolysis of aqueous sodium chloride, chlorine gas \(\mathrm{Cl}_{2}\), hydrogen gas \(\mathrm{H}_{2}\), and sodium hydroxide \(\mathrm{NaOH}\) are produced when electricity is applied. The simplified overall reaction is as follows:
\[ 2 \mathrm{NaCl}(aq) + 2 \mathrm{H}_{2}\mathrm{O}(l) \rightarrow 2 \mathrm{NaOH}(aq) + \mathrm{Cl}_{2}(g) + \mathrm{H}_{2}(g) \]
Not only is this an excellent example for studying electrolytic processes, but it is also a crucial industrial reaction for producing elemental chlorine and sodium hydroxide, which are key ingredients in many products. The reaction also emphasizes the migration of ions towards electrodes and the selective discharge of ions, which are foundational principles in electrochemistry.