Chemical Reactions and Equations - 1.31.3 1.31.3 HAHAHA

A chemical reaction is a process where the internal structure of substances changes to form new substances with different properties. It is represented by a chemical equation such as $A + B \rightarrow C + D$.

Balanced Chemical Equation: Based on the Law of Conservation of Mass, the total number of atoms of each element must remain the same before and after a chemical reaction. For example, $2H_2 + O_2 \rightarrow 2H_2O$.

Combination Reaction: A reaction in which a single product is formed from two or more reactants. Example: $CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat}$.

Decomposition Reaction: A single reactant breaks down into two or more simpler products. This requires energy in the form of heat (Thermal), light (Photolytic), or electricity (Electrolytic).

Displacement Reaction: A more reactive element displaces a less reactive element from its compound. Example: $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$.

Double Displacement Reaction: A reaction where there is an exchange of ions between the reactants to form new compounds, often resulting in a precipitate. Example: $Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) \downarrow + 2NaCl(aq)$.

Redox Reactions: Reactions involving both Oxidation (addition of oxygen or removal of hydrogen) and Reduction (removal of oxygen or addition of hydrogen).

Exothermic and Endothermic Reactions: Exothermic reactions release energy to the surroundings ($CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + \text{Energy}$), while endothermic reactions absorb energy ($2AgCl \xrightarrow{\text{Sunlight}} 2Ag + Cl_2$).