1.2. Types of Chemical Reactions

Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat (1.13)

In this reaction, calcium oxide and water combine to form a single product, calcium hydroxide. Such a reaction in which a single product is formed from two or more reactants is known as a combination reaction.

Combination reactions are those in which two or more reactants combine to form a single product. This process can often release heat, which is a characteristic of such reactions. Here, calcium oxide (CaO) combines with water (H₂O) to form slaked lime (calcium hydroxide), demonstrating how elements or compounds come together to create something new.

Think of combination reactions like making a smoothie. You take various fruits, blend them together, and end up with a delicious drink, which is a new product created from the combination of different ingredients.

In this reaction you can observe that a single reactant breaks down to give simpler products. This is a decomposition reaction.

2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g) (1.19)

Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. CaCO₃(s) → CaO(s) + CO₂(g) (1.20)

Decomposition reactions occur when a single substance breaks down into two or more simpler products. This process usually requires some form of energy input, such as heat. For example, heating ferrous sulfate (FeSO₄) causes it to decompose into ferric oxide (Fe₂O₃) and gases like sulfur dioxide and sulfur trioxide. Another common example is the decomposition of calcium carbonate (CaCO₃) to form calcium oxide (CaO) and carbon dioxide (CO₂), which is important in construction.

Imagine a plant rotting away. As it breaks down, it transforms into simpler organic materials. This is akin to how a molecular compound, like calcium carbonate, decomposes into smaller parts when heated.

In this reaction, iron has displaced or removed another element, copper, from copper sulfate solution. This reaction is known as displacement reaction.

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s) (1.24)

Displacement reactions happen when one element displaces another from a compound. In the reaction between iron and copper sulfate, iron replaces copper because it is more reactive. The result is iron sulfate and elemental copper. This reaction shows how different metals can interact based on their reactivity.

Think of it like a game of musical chairs. When the music stops, a more popular player (iron) takes the seat (copper) from the less popular one (copper sulfate), showing that in chemistry, one substance can push another out of its position.

Formation of barium sulphate and sodium chloride: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq) (1.27).

In double displacement reactions, two compounds exchange ions to form two new compounds. For example, when sodium sulfate and barium chloride are mixed, barium sulfate precipitates out of the solution, while sodium chloride remains dissolved. This precipitation indicates a chemical change has occurred, often visible as a solid forming in a liquid.

Imagine a swap meet where two vendors trade their items. Just as items change hands to form new collections, ions in a chemical reaction swap places to create new compounds.

If a substance gains oxygen during a reaction, it is said to be oxidised. If a substance loses oxygen during a reaction, it is said to be reduced.

Oxidation and reduction reactions, collectively known as redox reactions, involve the transfer of oxygen or hydrogen. Oxidation refers to the addition of oxygen or loss of hydrogen, while reduction refers to the loss of oxygen or gain of hydrogen. This process is critical in various reactions including combustion and respiration.

Think of oxidation like a car gaining fuel (oxygen) and getting ready to go, while reduction is like the car returning home after dropping off the passengers (losing oxidized substances).

--