91Ó°ÊÓ

Combustion reactions are chemical reactions that occur between a fuel and an oxidizer, typically oxygen, releasing energy in the form of heat and light. These reactions are common in everyday life and are essential for processes like burning wood, gasoline, and even organic solvents like acetone. For acetone, a common organic solvent represented chemically as \( ext{C}_3 ext{H}_6 ext{O}\), complete combustion occurs when acetone reacts with oxygen to form carbon dioxide and water.

To balance the combustion reaction of acetone, the primary task is to ensure that the number of atoms for each element is the same on both sides of the equation. Here’s how to balance it:

• Start with carbon: each acetone molecule has three carbon atoms, which means you will need three \( ext{CO}_2\) molecules to balance the carbon atoms.
• Next, balance the hydrogen by using water molecules. Acetone contains six hydrogen atoms, so three \( ext{H}_2 ext{O}\) molecules are required.
• Finally, consider the oxygen. The balanced equation requires nine oxygen atoms, where one comes from acetone and the rest from \( ext{O}_2\). Therefore, four \( ext{O}_2\) molecules are used.

Bearing this in mind, the balanced equation is:

\[\text{C}_3\text{H}_6\text{O} + 4\text{O}_2 \rightarrow 3\text{CO}_2 + 3\text{H}_2\text{O}\]This reaction highlights the principles of combustion, emphasizing efficient energy conversion and the production of carbon dioxide and water.

Decomposition reactions break down a single compound into two or more simpler substances. These reactions are integral to understanding processes like the breakdown of mercury (I) carbonate. The decomposition of mercury (I) carbonate, or \(\text{Hg}_2\text{CO}_3\), involves it breaking down into carbon dioxide gas, elemental mercury, and mercury oxide.

Let’s explore how to balance the decomposition reaction:

• Start with the reactant, mercury (I) carbonate. It is made of two mercury atoms, one carbon atom, and three oxygen atoms.
• In the products, you will have one \(\text{CO}_2\), which uses the single carbon and two of the oxygen atoms from \(\text{Hg}_2\text{CO}_3\).
• After accounting for carbon and some of the oxygen, focus on mercury. Since \(\text{Hg}_2\text{CO}_3\) splits into \(\text{Hg}\) and \(\text{HgO}\), ensure you have one mercury (\(\text{Hg}\)) and one mercury oxide (\(\text{HgO}\)).

The balanced equation is:

\[\text{Hg}_2\text{CO}_3 \rightarrow \text{CO}_2 + \text{Hg} + \text{HgO}\]This decomposition reaction shows the release of gases and formation of solids, illustrating the diversity and dynamism of chemical reactions.

Combination reactions occur when two or more substances react to form a single product. These are straightforward types of reactions that often involve simpler balancing. An example is the chemical reaction between sulfur dioxide (\(\text{SO}_2\)) and water (\(\text{H}_2\text{O}\)) to produce sulfurous acid (\(\text{H}_2\text{SO}_3\)).

This reaction is a classic example of a gas reacting with a liquid to form an acid. To balance this combination reaction:

• Start by writing the unbalanced equation as: \(\text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3\).
• Check all the atoms: you have one sulfur, three oxygens, and two hydrogens both in reactants and in the product.
• Since each element is already balanced with this setup, no further modification is needed.

Thus, the balanced equation is:

\[\text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3\]

This simplicity in combination reactions makes them a perfect introduction to balancing chemical equations and understanding the formation of new substances from reactants.