MHT-CET Chemistry · Teaching notes
States of Matter — MHT-CET Chemistry
The gas-phase chapter of MHT-CET Chemistry — a compact, calculation-friendly topic (31 PYQs) built on the gas laws and one master equation, PV = nRT. It teaches in two movements: (1) the gas laws and the ideal gas equation — Boyle's, Charles', Gay-Lussac's and the combined gas law, then PV = nRT with its unit-matched R values; (2) real gases, Dalton's law of partial pressures and the kinetic theory of gases — partial pressure from mole fraction, root-mean-square speed, the KTG postulates and van der Waals deviation. Almost every question is a one- or two-step plug-in; the recurring traps are units (kelvin, matching R) and remembering that partial pressure tracks moles, not mass. Every PYQ tagged.
Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.
Subtopic notes
Gas Laws and the Ideal Gas Equation
18 PYQsFour simple gas laws (Boyle, Charles, Gay-Lussac, combined) each fix one variable and relate the rest; the ideal gas equation PV = nRT ties pressure, volume, moles and temperature together in a single formula.
Real Gases, Dalton's Law and the Kinetic Theory of Gases
13 PYQsIn a gas mixture each component pushes independently, so its partial pressure is just its share of the moles times the total pressure; the kinetic theory explains this, gives the speed of the molecules, and shows why real gases stray from ideal behaviour.
Formula & revision sheet
9 formulas · 1 reference tables · 19 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
9 formulas · 1 reference tables · 19 gotchas across all subtopics — the exam-eve cheat-sheet
Formulas (6)
- Boyle's law — pressure and volume · Boyle's law
- Charles' law — volume and temperature · Charles' law
- Gay-Lussac's law — pressure and temperature · Gay-Lussac's law
- Combined gas law · Combined gas law
- Ideal gas equation, PV = nRT · Ideal gas equation
- Equal masses in equal volumes — lightest gas, highest pressure · Pressure vs molar mass (equal mass, V, T)
Watch out for (11)
- No unit conversion inside Boyle's law→ Boyle's law — pressure and volume
- Boyle's law is P vs V — not PV vs P→ Boyle's law — pressure and volume
- Kelvin, always — never Celsius in the ratio→ Charles' law — volume and temperature
- Absolute zero is negative→ Charles' law — volume and temperature
- Do not mix up the three simple laws→ Gay-Lussac's law — pressure and temperature
- Absolute temperature here too→ Gay-Lussac's law — pressure and temperature
- T on the DENOMINATOR, in kelvin→ Combined gas law
- Match R's units to the pressure and volume→ Ideal gas equation, PV = nRT
- Watch a printed exponent typo→ Ideal gas equation, PV = nRT
- Equal MASS, not equal moles→ Equal masses in equal volumes — lightest gas, highest pressure
- Lightest gas = highest pressure→ Equal masses in equal volumes — lightest gas, highest pressure
Formulas (3)
Reference tables (1)
Postulates of the kinetic theory of gases5 rows
| Postulate | Statement |
|---|---|
| Negligible molecular volume | The actual volume of the gas molecules is negligibly small compared with the total volume of the container; the gas is mostly empty space. This assumption fails at high pressure, when molecules are squeezed close together and their own volume is no longer negligible. |
| No intermolecular forces | There are no forces of attraction or repulsion between the molecules of an ideal gas; they move completely independently. This assumption fails at low temperature / high pressure, when attractions pull molecules together — the reason gases can be liquefied. |
| Elastic collisions | Collisions between molecules, and with the walls, are perfectly elastic — the total kinetic energy is conserved during every collision. |
| Kinetic energy proportional to temperature | The average kinetic energy of the molecules is directly proportional to the absolute temperature; it depends only on T, not on the gas's identity. |
| Continuous random motion | Molecules are in constant, rapid, random straight-line motion in all directions, colliding with one another and the container walls. |
Watch out for (8)
- Partial pressure follows moles, not mass→ Dalton's law of partial pressures
- Use the total moles in the denominator→ Dalton's law of partial pressures
- Take the square root at the end→ Root-mean-square velocity
- Use absolute temperature in kelvin→ Root-mean-square velocity
- Kinetic energy depends on temperature, not on the gas→ Postulates of the kinetic theory of gases
- Ideal gas = zero volume AND zero force→ Postulates of the kinetic theory of gases
- Z = 1 means ideal, in either direction→ Real gases and the compressibility factor
- Multiply, do not add, the ideal molar volume→ Real gases and the compressibility factor
PYQ weightage by concept
10 concepts · 31 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
10 concepts · 31 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Boyle's law — pressure and volume | 5 | 16% |
| Charles' law — volume and temperature | 4 | 13% |
| Ideal gas equation, PV = nRT | 4 | 13% |
| Equal masses in equal volumes — lightest gas, highest pressure | 3 | 10% |
| Gay-Lussac's law — pressure and temperature | 1 | 3% |
| Combined gas law | 1 | 3% |
| Concept | PYQs | Share |
|---|---|---|
| Dalton's law of partial pressures | 7 | 23% |
| Real gases and the compressibility factor | 4 | 13% |
| Root-mean-square velocity | 1 | 3% |
| Postulates of the kinetic theory of gases | 1 | 3% |
Test yourself on States of Matter
15 past MHT-CET questions from this chapter, timed at 14 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.