Flashcards · 9701 · AS Topic 4

States of matter (AS Level) flashcards

11 cards on AS Topic 4, subtopics 4.1 to 4.2. Pick a subtopic or study them all.

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The ideal gas equation, with units: pV = nRT p in Pa, V in m³, n in mol, T in K, R = 8.31 J K⁻¹ mol⁻¹. Convert: kPa × 1000, cm³ ÷ 10⁶, dm³ ÷ 1000, °C + 273.
Assumptions of the kinetic theory for an ideal gas: Particles have negligible volume; there are no intermolecular forces; collisions are perfectly elastic; particles are in constant random motion.
When do real gases deviate most from ideal behaviour, and why?: At high pressure (particles close together, so their own volume is no longer negligible) and low temperature (particles move slowly, so intermolecular attractions become significant).
Conditions under which a gas behaves most ideally: Low pressure and high temperature. Small non-polar molecules (He, H₂) behave more ideally than molecules with stronger intermolecular forces (NH₃, H₂O).
How do you find Mr from gas data?: M = mRT ÷ (pV), using SI units. e.g. 4.40 g in 2.24 × 10⁻³ m³ at 101 000 Pa and 273 K: n ≈ 0.0997 mol, so Mr ≈ 44.

Giant ionic structure: properties: High melting point (strong electrostatic attraction between ions). Conducts only when molten or aqueous (ions free to move). Often soluble in water.
Simple molecular structure: properties: Low melting point: only weak intermolecular forces are overcome. Does not conduct. Solubility depends on polarity (like dissolves like).
Giant covalent structure: properties: Very high melting point: many strong covalent bonds must be broken. Does not conduct (except graphite). Insoluble.
Giant metallic structure: properties: High melting point (attraction of ions to the electron sea). Conducts as a solid and when molten. Insoluble.
Diamond and graphite compared: Diamond: 4 bonds per C, tetrahedral 3D network, very hard, does not conduct. Graphite: 3 bonds per C, hexagonal layers held by weak forces (soft, layers slide), one delocalised electron per atom so it conducts.
Why does iodine melt at 114 °C but diamond needs over 3500 °C?: Iodine is simple molecular: melting overcomes only weak intermolecular forces. Diamond is giant covalent: many strong covalent bonds must break.