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A combination reaction, also known as a synthesis reaction, involves two or more substances reacting to form a single new product. These reactions are one of the simplest types of chemical reactions. An example from the exercise is the reaction of calcium metal with oxygen gas to form calcium oxide.

To write the balanced equation for this reaction, we start with the substances involved:

• Calcium (Ca) - the metal reactant.
• Oxygen (O鈧�) - the gaseous reactant.
• Calcium Oxide (CaO) - the product.

The unbalanced equation may look like this:\[\text{Ca} + \text{O鈧倉 \rightarrow \text{CaO}\]
To balance the equation, count the atoms on each side and adjust the coefficients accordingly. In this case, balance the oxygen by placing a 2 in front of CaO, making it:\[\text{Ca} + \text{O鈧倉 \rightarrow 2\text{CaO}\]
Further adjust the... by placing a 2 in front of Ca, resulting in:\[2\text{Ca} + \text{O鈧倉 \rightarrow 2\text{CaO}\]This equation is now balanced, with equal numbers of Ca and O on both sides.

Combination reactions often release energy, making them exothermic. These reactions are common in forming compounds in nature.

Decomposition reactions are the opposite of combination reactions. In decomposition reactions, a single compound breaks down into two or more simpler substances. This type of reaction usually requires energy input, like heat, to occur.

An informative example from the given exercise is the decomposition of copper(II) hydroxide. When heated, it decomposes into copper(II) oxide and water.

• Copper(II) Hydroxide (Cu(OH)鈧�) - the compound undergoing decomposition.
• Copper(II) Oxide (CuO) - one of the products.
• Water (H鈧侽) - another product.

The initial unbalanced equation is:\[\text{Cu(OH)鈧倉 \rightarrow \text{CuO} + \text{H鈧侽}\]
In this equation, notice the number of atoms for each element on both sides of the equation:

• 1 Copper atom on each side.
• 2 Oxygen atoms from Cu(OH)鈧� turning into one CuO and one H鈧侽, totaling two Oxygen atoms.
• 2 Hydrogen atoms in the water molecule, matching the 2 from the hydroxide groups.

This equation is already balanced as is. Decomposition reactions are crucial in various applications, including recycling and the breakdown of organic materials.

Combustion reactions are usually the burning of substances in the presence of oxygen. They generate heat and light, making them exothermic processes. In combustion, organic compounds often convert into carbon dioxide and water.

An example from the exercise is the combustion of heptane. Heptane, a hydrocarbon, reacts with oxygen to form carbon dioxide and water.

• Heptane (C鈧嘓鈧佲倖) - the hydrocarbon fuel.
• Oxygen (O鈧�) - the oxidizing agent causing the burn.
• Carbon Dioxide (CO鈧�) and Water (H鈧侽) - the products resulting from complete combustion.

The unbalanced reaction is:\[\text{C鈧嘓鈧佲倖} + \text{O鈧倉 \rightarrow \text{CO鈧倉 + \text{H鈧侽}\]
To balance it, adjust the carbon and hydrogen atoms first:\[\text{C鈧嘓鈧佲倖} + \text{O鈧倉 \rightarrow 7\text{CO鈧倉 + 8\text{H鈧侽}\]
Then, ensure there are enough oxygen molecules by placing an 11 in front of O鈧�:\[\text{C鈧嘓鈧佲倖} + 11\text{O鈧倉 \rightarrow 7\text{CO鈧倉 + 8\text{H鈧侽}\]
Finally, your equation is balanced! Combustion reactions are vital for energy production in engines as well as cooking and heating processes. Proper balancing ensures an understanding of the stoichiometry involved, which is crucial for efficient energy use.