Chemical Reactions & Equations

A chemical reaction is a process where reactants are transformed into products by breaking and forming chemical bonds. Energy is either released or absorbed during this process.

The main types are combination, decomposition, single displacement, double displacement, combustion, neutralization, and redox reactions.

Chemical reactions play a crucial role in cooking, cleaning, manufacturing, medicine, and energy production. Digestion, photosynthesis, and burning fuel are everyday examples.

Adjust the coefficients (not subscripts) so the number of atoms of each element is equal on both sides of the equation. This follows the law of conservation of mass.

An exothermic reaction releases heat energy to the surroundings. Examples include combustion, rusting of iron, and the reaction of acids with bases.

An endothermic reaction absorbs heat from the surroundings. Examples include decomposition of calcium carbonate, photosynthesis, and electrolysis of water.

A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. It lowers the activation energy. Example: MnO₂ in decomposition of H₂O₂.

Higher temperatures increase the kinetic energy of molecules, increasing collision frequency and energy — generally increasing reaction rates. A 10°C rise roughly doubles the rate for many reactions.

A redox (reduction-oxidation) reaction involves simultaneous transfer of electrons. One species is oxidized (loses electrons) and another is reduced (gains electrons). Example: Zn + CuSO₄ → ZnSO₄ + Cu.

Combustion of fuels, photosynthesis in plants, rusting of iron, baking of bread (CO₂ from baking soda), and cooking food all involve everyday chemical reactions.

Reactions can cause pollution (combustion producing CO₂, NOx) or benefit the environment (photosynthesis removing CO₂, green energy production). Understanding them helps control environmental damage.

Organic reactions involve carbon-based compounds (hydrocarbons, alcohols, esters), while inorganic reactions involve minerals, metals, salts, and non-carbon-based compounds.

Chemical equilibrium is the state where the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant. It is a dynamic, not static, state.

Observable signs include: color change, temperature change (hot or cold), gas production (bubbles), precipitate formation, change in smell, and emission of light.

Pressure mainly affects gaseous reactions. Increasing pressure increases the concentration of gases, raising collision frequency and reaction rate. It can also shift equilibrium (Le Chatelier's principle).