Chemical Equations

• Chemistry is the study of matter and its properties as well as how matter changes.
• A chemical reaction is a process that involves rearrangement of atoms and molecules to form new substances.
• Chemical reactions are represented by chemical equations.
• A chemical equation is a symbolic representation of a chemical reaction using chemical formulas and symbols.

Chemical Equations

• A chemical equation includes reactants, products, and an arrow indicating the direction of the reaction.
• Reactants are the substances that participate in a chemical reaction and are written on the left side of the arrow.
• Products are the substances formed as a result of a chemical reaction and are written on the right side of the arrow.
• The arrow (→) indicates the direction of the reaction, pointing from reactants to products.
• Plus signs (+) are used to separate multiple reactants or products.
• State symbols indicate the physical state of substances: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous (dissolved in water).

Balancing Chemical Equations

• Balancing a chemical equation involves adjusting the coefficients of the reactants and products to ensure the number of atoms of each element is the same on both sides of the equation.
• The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction, hence the need for balancing.
• Only coefficients should be changed when balancing equations, not subscripts in chemical formulas.
• Balancing typically starts with the most complex molecule and proceeds element by element.
• Fractional coefficients can be used temporarily, but the final equation should have whole number coefficients.

Types of Chemical Reactions

• Combination reaction: Two or more substances combine to form a single product.
• Decomposition reaction: A single substance breaks down into two or more simpler substances.
• Displacement reaction: An element reacts with a compound, displacing another element from it.
• Double-displacement reaction: Two compounds react by exchanging ions to form two new compounds.
• Redox reaction: Involves both reduction and oxidation processes.

Combination Reactions

• Also known as synthesis reactions.
• Example: 2Mg(s) + O2(g) → 2MgO(s), where magnesium combines with oxygen to form magnesium oxide.
• Typically exothermic, releasing heat.

Decomposition Reactions

• Often require energy in the form of heat, light, or electricity to proceed.
• Example: CaCO3(s) → CaO(s) + CO2(g), where calcium carbonate decomposes into calcium oxide and carbon dioxide upon heating.

Displacement Reactions

• Involve a more reactive element displacing a less reactive element from its compound.
• Can be single displacement or double displacement.
• Example: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s), where zinc displaces copper from copper sulfate.

Double-Displacement Reactions

• Involve the exchange of ions between two reacting compounds.
• Often result in the formation of a precipitate, gas, or water.
• Also known as metathesis reactions.
• Example: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq), where silver nitrate reacts with sodium chloride to form silver chloride precipitate and sodium nitrate.

Redox Reactions

• Involve the transfer of electrons between reactants.
• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• The substance that loses electrons is oxidized and acts as a reducing agent.
• The substance that gains electrons is reduced and acts as an oxidizing agent.
• Example: 2Na(s) + Cl2(g) → 2NaCl(s), where sodium is oxidized and chlorine is reduced.

Oxidation and Reduction

• Oxidation is the process where a substance loses electrons.
• Reduction is the process where a substance gains electrons.
• Oxidation and reduction always occur together, hence the term redox reaction.
• Oxidizing agents help in oxidation by accepting electrons.
• Reducing agents help in reduction by donating electrons.

Corrosion

• Corrosion is the process by which a metal is degraded due to chemical reactions with its environment.
• Rusting of iron is a common example of corrosion.
• Requires the presence of oxygen and water.
• Can be prevented by coating the metal surface with paint, oil, or another metal (galvanization).

Rancidity

• Rancidity is the oxidation of fats and oils in food, resulting in unpleasant taste and odor.
• Caused by exposure to air, light, or moisture.
• Can be slowed down by storing food in airtight containers, refrigeration, or adding antioxidants.

Factors Influencing Reaction Rates

• Temperature: Reaction rates generally increase with increasing temperature.
• Concentration: Higher concentrations of reactants usually lead to faster reaction rates.
• Surface Area: Increased surface area of solid reactants can increase reaction rate.
• Catalysts: Substances that speed up a reaction without being consumed in the process.

Catalysts

• Catalysts provide an alternative reaction pathway with a lower activation energy.
• They remain chemically unchanged at the end of the reaction.
• Can be homogeneous (in the same phase as reactants) or heterogeneous (in a different phase).
• Enzymes are biological catalysts.