1. Physical And Chemical Changes

Matter undergoes two main types of changes: physical changes and chemical changes. Physical changes alter the form or appearance of a substance but not its chemical composition, such as melting ice or dissolving salt in water. Chemical changes, however, result in the formation of new substances with different properties, often involving the breaking and forming of chemical bonds, like the burning of wood or the rusting of iron. Recognizing the difference is fundamental to understanding chemical processes.

2. Chemical Equations and Balancing

A chemical equation is a symbolic representation of a chemical reaction, showing the reactants and products. For example, the formation of water from hydrogen and oxygen is written as $2H_2 + O_2 \rightarrow 2H_2O$. Balancing a chemical equation ensures that the law of conservation of mass is obeyed, meaning the number of atoms of each element is the same on both sides of the equation. This involves adjusting stoichiometric coefficients to represent the correct ratios of reactants and products involved in a reaction.

3. Types Of Chemical Reactions

Chemical reactions can be broadly classified into several types. Combination reactions involve two or more reactants forming a single product. Decomposition reactions are the opposite, where a single compound breaks down into simpler substances. Displacement reactions occur when one element replaces another in a compound. Double displacement reactions involve the exchange of ions between two compounds. Additionally, reactions are classified as redox reactions (involving changes in oxidation states) and others like acid-base reactions and precipitation reactions.