When the bonds of reactant molecules are broken to form new bonds in the products, it results in new substances, this is called a chemical reaction. Chemical reactions are constantly happening around us. From food metabolism in our body to the sunlight ,they are all either chemical reactions or a result of chemical reactions. Thus it is important to understand the concept of chemical and physical changes.
A burning candle is probably the best illustration of both physical and substance change. You can observe that, when it burns for a while, the candle turns into wax, which is a physical change. The light energy that we get is the result of chemical change. The chemical reaction can either form a new substance, allow the energy to be absorbed or just give it off. Most often chemical changes are followed by some physical changes.
As there are several chemical reactions happening constantly around us, a convenient nomenclature called chemical equation was evolved to simplify the way we express a chemical reaction.
A chemical equation is a mathematical statement that symbolizes the formation of a product from reactants while stating the conditions that help the reaction to happen.
In a chemical equation, the reactants are the elements written on the left-hand side while the products formed are added on the right-hand. The sides of the equation are connected by one-headed or two-headed arrows, as applicable.
A + B → C + D
Here, the reactants A and B react with each other to form the products C and D. In an actual chemical equation, the chemical formula of the reactants is used. To ensure that the law of conservation of mass is followed, a chemical equation must be balanced i.e. the number of elements on either side should be equal. This is called the balancing of the equation.
There are different chemical reactions based on the product formed, the changes that occur in the reactants, the type of reactants involved and so on. Different types of reactions are explained here,
A combustion reaction happens when a combustible material reacts with oxygen resulting in the generation of heat and light energy. Examples of this type of reaction are, fireworks explosion, combustion of fuel in vehicles, lighting up a matchstick, cooking, gas usage, etc.
A decomposition reaction is a reaction where a chemical compound is broken down into two or more products with the generation of energy in the form of heat, light and/or electricity. Here the chemical bonds are broken down and new bonds are formed. Examples of chemical change under this reaction category include the formation of fossil fuels, electrolysis of water, decomposition process of potassium chlorate by heat, etc.
A neutralization reaction often occurs between a strong acid and a strong base resulting in formation of salt and water. The water molecule is formed by combining OH– and H+ ions. When a neutralization process occurs the overall pH of the products changes to 7. For example, the reaction between HCl and NaOH gives out NaCl and water.
A redox reaction is where both reduction and oxidation reactions occur simultaneously. One reactant undergoes a reduction reaction while the other reactant is oxidised. Eg. The redox reaction happens between Zinc molecules and copper. Zinc ion is the oxidised product and copper is the reduced product.
Zn+Cu2+= Zn2+ + Cu
Here the resultant reactions lead to the precipitation of the products where the elements in the reactants will switch their places or undergo displacement reactions to form new products. Eg. The reaction between silver nitrate and sodium chloride leads to the formation of silver chloride and sodium nitrate.
A synthesis reaction is one where two reactants react with each other to form an entirely new product. It can happen between multiple reactants leading to the formation of more than one product as well. Eg, Glucose formation by photosynthesis.
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