Why must temperature be in Kelvin in gas law calculations?

Gas laws involve direct proportionality with temperature (V ∝ T, P ∝ T). If we used Celsius, 0°C would imply zero volume/pressure, which is physically wrong. Kelvin scale (absolute temperature) starts at absolute zero (−273°C) where molecular motion theoretically stops. T(K) = T(°C) + 273.

What are the conditions under which real gases behave like ideal gases?

Real gases approach ideal behavior at: (1) High temperature — thermal energy dominates over intermolecular attractions; (2) Low pressure — molecules are far apart, so volume of molecules and intermolecular forces become negligible. Noble gases (He, Ne) behave most like ideal gases.

State Dalton's Law of Partial Pressures with an example.

Dalton's Law: Total pressure of a gas mixture = sum of partial pressures. P_total = P₁ + P₂ + ... Example: Air contains N₂ (78%) and O₂ (21%). At 1 atm, P(N₂) = 0.78 atm, P(O₂) = 0.21 atm. Application: collecting gases over water — correct for water vapour pressure.

Ideal Gas Law and Gas Laws

States of Matter • Class 11 Chemistry • NCERT • CBSE

The Ideal Gas Law: PV = nRT where P = pressure, V = volume, n = moles, R = 8.314 J/mol·K, T = temperature in Kelvin. Boyle's Law: PV = constant at fixed T. Charles' Law: V/T = constant at fixed P. Avogadro's Law: V ∝ n at fixed T and P.

Key Formulas

PV = nRT
P₁V₁ = P₂V₂ (Boyle's Law)
V₁/T₁ = V₂/T₂ (Charles' Law)
P₁V₁/T₁ = P₂V₂/T₂
v_rms = √(3RT/M)

Frequently Asked Questions

Why must temperature be in Kelvin in gas law calculations?: Gas laws involve direct proportionality with temperature (V ∝ T, P ∝ T). If we used Celsius, 0°C would imply zero volume/pressure, which is physically wrong. Kelvin scale (absolute temperature) starts at absolute zero (−273°C) where molecular motion theoretically stops. T(K) = T(°C) + 273.
What are the conditions under which real gases behave like ideal gases?: Real gases approach ideal behavior at: (1) High temperature — thermal energy dominates over intermolecular attractions; (2) Low pressure — molecules are far apart, so volume of molecules and intermolecular forces become negligible. Noble gases (He, Ne) behave most like ideal gases.
State Dalton's Law of Partial Pressures with an example.: Dalton's Law: Total pressure of a gas mixture = sum of partial pressures. P_total = P₁ + P₂ + ... Example: Air contains N₂ (78%) and O₂ (21%). At 1 atm, P(N₂) = 0.78 atm, P(O₂) = 0.21 atm. Application: collecting gases over water — correct for water vapour pressure.

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