v2-10-chemistry (1)

Mass and energy cannot be created or destroyed; the total mass of reactants equals the total mass of products in a chemical reaction.

Repeatability: obtaining the same result under the same conditions and same setup. Reproducibility: obtaining the same or similar result under different conditions, labs, or methods.

Peer review ensures the accuracy, reliability, and clarity of scientific work by having experts check experiments, data, and conclusions before publication.

A set of ideas, methods, and rules that guide scientists' research and interpretation of data; paradigms can change when new evidence challenges them.

Phlogiston theory proposed combustible materials contained 'phlogiston' released during burning. It was replaced by Lavoisier's oxygen theory of combustion (oxidation).

Mendeleev organised elements by atomic mass and properties and predicted undiscovered elements based on patterns; modern tables use atomic numbers and electron configurations. [pages 2–3]

It indicates we are 95% sure the true value lies within the stated range (e.g., 0.48–0.52 M for a concentration).

A p-value estimates the probability that an observed result is due to random chance; a low p-value (e.g., 0.01) suggests the result is unlikely to be random.

Bayesian probability updates the likelihood of a hypothesis by combining prior belief with new evidence, changing confidence as data accumulates.

Melting: particles in a solid gain potential energy (not kinetic) to overcome intermolecular forces; temperature remains constant during the phase change.

Boiling occurs throughout a liquid at its boiling point with bubble formation; evaporation is a surface process that can occur at any temperature below the boiling point. [pages 10–11]

Added or removed energy is used to change potential energy (overcome or form intermolecular forces) rather than changing kinetic energy, so temperature stays constant during the phase change. [pages 8–9]

A heating curve plots temperature vs. time: temperature rises in solid/liquid/gas regions and plateaus during melting (latent heat of fusion) and boiling (latent heat of vaporisation).

Sublimation: direct transition from solid to gas without a liquid phase. Examples: dry ice (CO₂) sublimating; solid air fresheners releasing fragrance. p.9, 15

Boyle's Law: for a fixed amount of gas at constant temperature, volume is inversely proportional to pressure. Mathematically: PV = constant.

Charles's Law: for a fixed amount of gas at constant pressure, volume is directly proportional to absolute temperature. Mathematically: V/T = constant. [pages 12–13]

Avogadro's Law: at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles (V ∝ n).

Higher external pressure raises the boiling point (makes boiling occur at higher temperature); lower pressure lowers the boiling point, so boiling occurs at lower temperatures (e.g., high altitudes).

Number of moles (n), volume (V), pressure (P), and temperature (T).

Diffusion: random motion causes particles to spread from high to low concentration until uniform. Example: perfume spreading through a room.

Rate of diffusion ∝ 1/√molar mass. Lighter gases diffuse faster than heavier ones at the same temperature.

Higher temperature increases kinetic energy and molecular velocity, accelerating diffusion.

They determine how quickly drugs spread through tissues and reach targets; controlled-release formulations adjust diffusion rates for sustained effects. [pages 15–16]

A mole is the amount of substance whose mass in grams equals its relative formula mass (e.g., 1 mol O = 16 g).

At RTP (25°C and 1 atm), 1 mole of gas occupies 24 dm³.

Use stoichiometric coefficients to convert moles of reactants to moles of products (e.g., 2H₂ + O₂ → 2H₂O means 2 mol H₂ yields 2 mol H₂O).

The limiting reactant is the reactant completely consumed that produces the least moles of product; it determines the theoretical yield.

Percentage yield = (Actual yield / Theoretical yield) × 100.

Convert percentages to moles, divide each by the smallest mole value, and use the resulting ratio as subscripts for the empirical formula.

Calculate molar mass of empirical formula, divide compound's molar mass by it to get n, then multiply subscripts by n.

Percentage purity = (mass of pure compound / total mass of sample) × 100.

Molarity is moles of solute per dm³ of solution (mol/dm³).

Moles = mass / molar mass; Molarity = moles / volume (dm³). Example: 5.6 g KOH in 1 dm³ → 5.6/56 = 0.1 M.

M1V1 = M2V2. Use it to calculate volumes or concentrations when diluting solutions (e.g., 12 M HCl to 0.1 M, for 250 cm³ requires 2.08 cm³ concentrated acid).

React known-volume standard solution with unknown concentration using indicator; use M1V1/n1 = M2V2/n2 and concordant readings to calculate molarity of the unknown. [page 34–35]

Strength = mass of solute (g) / volume of solution (dm³). Example: 20 g in 2 dm³ → 10 g/dm³.

1 g/dm³ = 0.001 g/cm³, so 50 g/dm³ = 0.05 g/cm³.

Mass per dm³ = molarity × molar mass (g/mol). Example: 0.25 M NaOH → 0.25 × 40 = 10 g/dm³.

Side reactions, reversible reactions, mechanical loss during separation (filtration, distillation), incomplete reactions.

Use 24 dm³ per mole at RTP: 2.5 × 24 = 60 dm³.

Use M1V1 = M2V2 → V1 = (0.1 × 250) / 12 = 2.08 cm³ concentrated HCl, dilute to 250 cm³.

Decreasing volume reduces space for particles, increasing collision frequency with container walls, which raises pressure; temperature (kinetic energy) remains constant.

At constant T and P, adding more moles increases the number of particles and collisions; to keep pressure constant, volume increases proportionally (V ∝ n).

Plum pudding (electrons in positive 'soup'), Rutherford (nucleus with orbiting electrons), Bohr (quantised energy levels), Quantum model (probability clouds/electron orbitals).