Topic 1 · 5.1–5.2 · Free
Topic Notes · Easy summaries with diagrams
Chapter 5 — chapter 5
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Topic 1 of 7
📘Easy summary
Gases have no fixed shape or volume, are highly compressible, diffuse rapidly and exert pressure due to collisions of molecules with the walls. Their behaviour is described by Boyle's law (V ∝ 1/P), Charles's law (V ∝ T) and Avogadro's law (V ∝ n). Combining them gives the ideal gas equation PV = nRT, where R = 8.314 J K⁻¹ mol⁻¹ (0.0821 dm³ atm K⁻¹ mol⁻¹). Since n = m/M, PV = (m/M)RT, so molar mass M = mRT/PV, and density d = PM/RT. Use SI units: P in Pa, V in m³, T in K.
⭐Key points
- PV = nRT.
- M = mRT/PV.
- SI: Pa, m³, K.
🔬Diagram
🌿Real-life example
0.560 g gas in 2.87 × 10⁻⁴ m³ at 300 K and 1.01 × 10⁵ Pa → M ≈ 48 g mol⁻¹.
💡Exam tip
- Convert cm³ to m³ (× 10⁻⁶) and °C to K (+ 273).
✅Quick check
1. R in SI units:
2. M from gas data:
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