Chemistry: Physical, Inorganic and Organic Essentials for AEEE
AEEE Chemistry spans physical chemistry (mole concept, thermodynamics, equilibrium, kinetics, electrochemistry, solutions), inorganic chemistry (periodic trends, chemical bonding, coordination compounds, p- and d-block elements) and organic chemistry (general organic chemistry, hydrocarbons, functional groups, isomerism, biomolecules and polymers). Questions reward precise definitions and clean stoichiometry more than long derivations.
Core rules
- Mole concept: moles = mass/molar mass = volume at STP/22.4 L = molarity × volume in litres.
- Periodic trends: atomic radius decreases across a period and increases down a group; ionisation energy and electronegativity follow the opposite pattern.
- Hybridisation from steric number: 2 → sp, 3 → sp², 4 → sp³; lone pairs occupy hybrid orbitals and compress bond angles.
- Aromaticity requires a planar cyclic system with 4n + 2 π electrons.
- Le Chatelier: raising pressure shifts equilibrium towards the side with fewer gaseous moles.
Worked example
4 g of H₂ reacts with 32 g of O₂ to form water. Find the mass of water produced. Moles of H₂ = 4/2 = 2 mol; moles of O₂ = 32/32 = 1 mol. The equation 2H₂ + O₂ → 2H₂O requires H₂ and O₂ in a 2:1 ratio, and the reactants are present in exactly that ratio, so neither is limiting. Water formed = 2 mol × 18 g/mol = 36 g. Had the O₂ been 0.5 mol, oxygen would have been limiting and water would be 1 mol = 18 g.
Traps that cost marks
- Comparing masses instead of moles when identifying the limiting reagent.
- Forgetting that molarity changes with temperature because volume expands.
- Assigning tetrahedral geometry to molecules with lone pairs without adjusting the bond angle (NH₃ is 107°, H₂O is 104.5°).
- Confusing oxidation and reduction in electrochemistry: oxidation is loss of electrons at the anode.
- Ignoring stereochemistry when a question asks for the number of isomers.