Write and balance each of the following equations, and then identify each equation by type. $$ \begin{array}{c}{\text { a. hydrogen }+\text { iodine } \rightarrow \text { hydrogen iodide }} \\ {\text { b. lithium + water } \longrightarrow} \\\ {\text { lithium hydroxide + hydrogen }} \\ {\text { c. mercury(II) oxide } \longrightarrow \text { mercury + oxygen }} \\ {\text { d. copper + chlorine } \rightarrow \text { copper(II) chloride }}\end{array} $$

A synthesis reaction, one of the fundamental types of chemical reactions, occurs when multiple reactants come together to form a single product. The general form of a synthesis reaction is represented as \textbf{A + B \rightarrow AB}. These reactions are often exothermic, meaning they release energy in the form of heat or light.

For example, in the provided exercise, when hydrogen gas (\textbf{H\(_2\)}) combines with iodine (\textbf{I\(_2\)}), they form hydrogen iodide (\textbf{HI}), as shown in Step 1 of the solution: \textbf{H\(_2\) + I\(_2\) \rightarrow 2HI}. To master synthesis reactions, it's critical to focus on identifying the reactants that come together and ensuring the resulting product is a compound made from these initial substances.

In a single-displacement reaction, an element reacts with a compound and takes the place of another element within that compound, creating a new element and a new compound in the process. The generic formula is \textbf{A + BC \rightarrow B + AC}, where \textbf{A} replaces \textbf{B} in the compound. These reactions usually occur when \textbf{A} is more reactive than \textbf{B}.

As seen in Step 2 of the solution, lithium (\textbf{Li}) reacts with water (\textbf{H\(_2\)O)} to form lithium hydroxide (\textbf{LiOH}) and hydrogen gas (\textbf{H\(_2\)}), represented by the balanced equation \textbf{2Li + 2H\(_2\)O \rightarrow 2LiOH + H\(_2\)}. When studying single-displacement reactions, focus on the reactivity series and the ability of the displacing element to take the place of another within a compound.

Contrary to synthesis reactions, decomposition reactions break down compounds into two or more simpler substances. The general form of a decomposition reaction is \textbf{AB \rightarrow A + B}. These reactions can occur naturally over time or can be induced by factors like heating, radiation, or electricity, known as electrolysis.

For illustration, as demonstrated in Step 3, mercury(II) oxide (\textbf{HgO}) decomposes to form mercury (\textbf{Hg}) and oxygen gas (\textbf{O\(_2\)}), depicted by the balanced equation \textbf{2HgO \rightarrow 2Hg + O\(_2\)}. To understand decomposition reactions, it's important to identify the original compound and recognize the conditions under which it decomposes into simpler elements or compounds.

Chemical reactions can be classified into various types based on the reactants involved and the changes they undergo to produce products. The primary types include synthesis, decomposition, single-displacement, double-displacement, and combustion reactions. Each type has distinctive characteristics and follows specific patterns.

• Synthesis reactions combine elements or compounds.
• Decomposition reactions break down compounds.
• In single-displacement and double-displacement reactions, elements or ions get exchanged between compounds.
• Combustion reactions typically involve a hydrocarbon reacting with oxygen to produce carbon dioxide and water.

By familiarizing themselves with these categories, students can better predict and balance chemical equations as exhibited in the exercise solution. Capable of determining reaction types aids in the comprehension of chemical processes and reactions encountered in both academic studies and real-world applications.