Write a balanced equation for each reaction: (a) "Slaking" of lime (treatment with water) (b) Combustion of calcium in air

Slaking of lime is a common process in construction and industrial applications. It involves the reaction between calcium oxide (also known as quicklime) and water to produce calcium hydroxide, commonly referred to as slaked lime.

Calcium oxide (CaO) is a white, caustic, alkaline substance derived from the thermal decomposition of limestone. When water is added to calcium oxide, a highly exothermic reaction occurs, releasing a significant amount of heat and forming calcium hydroxide \text{Ca(OH)}_{2}.

This reaction can be represented as:
\[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \]

To ensure that the chemical equation is balanced, we compare the number of each type of atom on both sides of the equation. In this case:

• 1 calcium atom on both sides
• 2 hydrogen atoms on both sides
• 2 oxygen atoms on both sides

The balanced equation is:
\[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \]

Slaked lime has various uses, such as in mortar for building construction, in water treatment to soften water, and in agriculture to neutralize acidic soils.

Combustion reactions are types of chemical reactions where a substance combines with oxygen, releasing energy in the form of light and heat. In the case of calcium, combustion involves the reaction of calcium metal with oxygen from the air.

Initially, the unbalanced equation for the combustion of calcium can be written as:
\[ \text{Ca} + \text{O}_2 \rightarrow \text{CaO} \]

To balance this equation, we need to ensure that the number of atoms of each element is the same on both sides. Since \text{O}_2 provides two oxygen atoms, we need two calcium oxide (CaO) molecules to balance the oxygen atoms. This gives the balanced equation:
\[ 2 \text{Ca} + \text{O}_2 \rightarrow 2 \text{CaO} \]

This means that two moles of calcium react with one mole of oxygen to yield two moles of calcium oxide. Combustion of calcium is a highly exothermic reaction, meaning it releases a lot of heat and can produce a bright white light. It’s a good example of a metal reacting with oxygen to form an oxide.

Calcium is an alkaline earth metal, commonly found in compounds like limestone (\text{CaCO}_3). It readily reacts with various substances, resulting in important industrial and biological compounds.

Here are some notable reactions involving calcium:

• With water: Calcium reacts slowly with cold water to form calcium hydroxide and hydrogen gas. This reaction is less vigorous compared to its reaction with acids:
  \[ \text{Ca} + 2 \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2 \]
• With acids: Calcium reacts with acids to produce a salt and release hydrogen gas. For example, with hydrochloric acid (HCl), the reaction is:
  \[ \text{Ca} + 2 \text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2 \]
• With oxygen: As covered in the combustion reaction, calcium reacts with oxygen to form calcium oxide.

Calcium compounds, such as calcium carbonate (\text{CaCO}_3), calcium sulfate (\text{CaSO}_4), and calcium phosphate (\text{Ca}_3(\text{PO}_4)_2), play crucial roles in various fields. For example, \text{CaCO}_3 is a primary component of cement and lime, used widely in construction, while calcium ions are essential in biological systems, especially for bone health and cellular functions.