Representing Chemical Reactions

A chemical reaction involves a process that leads to the transformation of one set of substances to another.
Each chemical reaction is depicted using a chemical equation. The starting substances are called reactants and the end substances are called products.
In a chemical equation, reactants are always written on the left-hand side whereas products are on the right-hand side. The arrow (‘->’) points towards the products, indicating the direction of the reaction.
The law of conservation of mass states that matter cannot be created or destroyed. It means a balanced chemical equation must have the same number of atoms of each element on both sides.
In balancing chemical equations, you can only change the coefficients (numbers placed ahead of substances), not the subscript (the small number right after an atom in a chemical formula).
An important type of reaction is Combination (or Synthesis) reaction. Here, two or more reactants combine to form a single product. An example is the combination of hydrogen and oxygen to make water.
Decomposition reaction is another important type of reaction. It involves breaking down a single reactant into two or more products. An example is the decomposition of water into hydrogen and oxygen.
Displacement reaction involves an element in a solution being displaced by another element, leading to a new product. Importantly, an element can only displace another if it’s more reactive.
In exothermic reactions, heat energy is released, often causing a rise in temperature in the surrounding environment. Combustion reactions are a common example of exothermic reactions.
In contrast, endothermic reactions absorb heat energy from their environment, often resulting in a temperature decrease in the surroundings. The process of photosynthesis is an example of an endothermic reaction.
Catalysts are substances that speed up the rate of a chemical reaction but are not used up in the reaction. They provide an alternate pathway for the reaction that requires less activation energy.
In reversible reactions, the reactants can combine to form products and the products can also decompose back to form reactants. This occurs until an equilibrium is reached where the rates of the forward and the reverse reactions are equal.