Mi a kémia? A kémia alapjai

• Chemistry is the study of matter and its properties, as well as how matter changes
• Matter is anything that has mass and takes up space
• Chemistry is known as the "central science" because it connects other natural sciences like physics, geology, and biology
• Chemistry seeks to understand the composition, structure, properties, and reactions of matter

Branches of Chemistry

• Analytical Chemistry: Identifies and quantifies the components of matter
• Biochemistry: Studies chemical processes in living organisms
• Inorganic Chemistry: Studies properties and reactions of inorganic compounds
• Organic Chemistry: Studies carbon-containing compounds
• Physical Chemistry: Applies physics to the study of chemical systems

Matter

• Matter exists in different states: solid, liquid, gas, and plasma
• Solids have fixed shape and volume
• Liquids have fixed volume but take the shape of their container
• Gases have neither fixed shape nor volume
• Plasma is an ionized gas, often found at high temperatures

Elements and Compounds

• Elements are substances that cannot be broken down into simpler substances by chemical means
• Compounds are substances composed of two or more elements chemically combined in fixed proportions
• Mixtures are combinations of substances that are not chemically combined and can be separated by physical means
• Homogeneous mixtures have uniform composition throughout (e.g., saltwater)
• Heterogeneous mixtures have non-uniform composition (e.g., sand and water)

Atoms

• Atoms are the smallest unit of an element that retains the chemical properties of that element
• Atoms are composed of protons, neutrons, and electrons
• Protons have a positive charge and are located in the nucleus
• Neutrons have no charge and are located in the nucleus
• Electrons have a negative charge and orbit the nucleus

Atomic Number and Mass Number

• The atomic number (Z) is the number of protons in the nucleus of an atom, which determines the element's identity
• The mass number (A) is the total number of protons and neutrons in the nucleus
• Isotopes are atoms of the same element with different numbers of neutrons, thus different mass numbers

Ions

• Ions are atoms or molecules that have gained or lost electrons, resulting in a net electrical charge
• Cations are positively charged ions, formed by losing electrons
• Anions are negatively charged ions, formed by gaining electrons

Molecules

• Molecules are two or more atoms held together by chemical bonds
• Chemical formulas represent the number and type of atoms in a molecule (e.g., H2O)
• Molecular compounds are formed from nonmetal atoms
• Ionic compounds are formed from ions (metal and nonmetal)

Chemical Bonds

• Ionic bonds are formed by the transfer of electrons between atoms, resulting in electrostatic attraction between ions
• Covalent bonds are formed by the sharing of electrons between atoms
• Metallic bonds are formed by the delocalization of electrons among a lattice of metal atoms

Chemical Reactions

• Chemical reactions involve the rearrangement of atoms and molecules to form new substances
• Reactants are the starting materials in a chemical reaction
• Products are the substances formed in a chemical reaction
• Chemical equations represent chemical reactions using chemical formulas and symbols
• Balancing chemical equations ensures that the number of atoms of each element is the same on both sides of the equation, following the law of conservation of mass

Mole Concept

• The mole (mol) is the SI unit for the amount of substance
• One mole contains Avogadro's number (6.022 x 10^23) of particles (atoms, molecules, ions, etc.)
• Molar mass is the mass of one mole of a substance, usually expressed in grams per mole (g/mol) and numerically equal to the atomic or molecular weight in atomic mass units (amu)

Stoichiometry

• Stoichiometry deals with the quantitative relationships between reactants and products in chemical reactions
• Stoichiometric coefficients in a balanced chemical equation represent the mole ratios between reactants and products
• Limiting reactant is the reactant that is completely consumed in a reaction, determining the maximum amount of product that can be formed
• Percent yield is the ratio of the actual yield (amount of product obtained) to the theoretical yield (amount of product calculated based on stoichiometry), expressed as a percentage

Solutions

• A solution is a homogeneous mixture of two or more substances
• The solute is the substance being dissolved
• The solvent is the substance doing the dissolving
• Concentration is the amount of solute present in a given amount of solvent or solution

Acids and Bases

• Acids are substances that donate protons (H+) or accept electrons
• Bases are substances that accept protons or donate electrons
• pH is a measure of the acidity or basicity of a solution, ranging from 0 to 14
• pH < 7 indicates an acidic solution
• pH = 7 indicates a neutral solution
• pH > 7 indicates a basic solution
• Neutralization is the reaction between an acid and a base, forming a salt and water

Oxidation-Reduction Reactions

• Oxidation is the loss of electrons
• Reduction is the gain of electrons
• Oxidizing agents cause oxidation by accepting electrons
• Reducing agents cause reduction by donating electrons
• Redox reactions involve the transfer of electrons between species

Chemical Kinetics

• Chemical kinetics studies the rates of chemical reactions
• Reaction rate is the change in concentration of reactants or products per unit time
• Factors affecting reaction rates include temperature, concentration, surface area, and catalysts
• Catalysts are substances that speed up a reaction without being consumed in the reaction

Chemical Equilibrium

• Chemical equilibrium is the state where the rates of the forward and reverse reactions are equal
• At equilibrium, the concentrations of reactants and products remain constant
• Le Chatelier's principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress
• Common stresses include changes in concentration, temperature, and pressure

Thermodynamics

• Thermodynamics is the study of energy and its transformations
• Energy is the capacity to do work or transfer heat
• The first law of thermodynamics states that energy is conserved
• Enthalpy (H) is a measure of the heat content of a system
• Exothermic reactions release heat (ΔH < 0)
• Endothermic reactions absorb heat (ΔH > 0)
• Entropy (S) is a measure of the disorder or randomness of a system
• The second law of thermodynamics states that the entropy of the universe is always increasing
• Gibbs free energy (G) is a measure of the spontaneity of a reaction
• Spontaneous reactions have a negative change in Gibbs free energy (ΔG < 0)