Explicit science instruction
At constant pressure and amount, ideal-gas volume is proportional to absolute temperature: V/T is constant. Temperature must be in kelvin.
At constant pressure and temperature, gas volume is proportional to amount n. These relationships combine with Boyle’s law in PV=nRT.
The gas constant R carries units that must match pressure and volume units. Dimensional consistency is part of the calculation, not an afterthought.
Vocabulary: Charles’s law; Avogadro’s law; ideal gas law; kelvin; gas constant.
Worked example with reasoning
At constant pressure, a gas at 300 K occupies 2.0 L. Heating to 450 K predicts V₂=2.0×450/300=3.0 L.
Guided question
Why is using 30°C directly in V₁/T₁=V₂/T₂ incorrect? Convert it and explain the physical reason for an absolute scale.
Independent work
- Solve two temperature–volume problems using kelvin.
- Solve one PV=nRT problem with supplied R and compatible units.
- Perform a unit audit for each calculation.
Misconception check
Celsius is useful for everyday temperature differences but cannot replace kelvin in direct gas-law proportionality.
Formative understanding check
Why must absolute temperature be used in gas-law ratios?
Reveal response
The proportional model is referenced to an absolute zero of thermal motion; Celsius has an arbitrary zero offset.
Mentor evidence conference
Ask Archaemenes to check the model assumptions, unit logic, and physical direction of the result.
Teacher guidance
Foundation: Practice kelvin conversion and proportional setup.
Core: Solve combined gas relationships with units.
Extended: Compare calculated ideal behavior with a supplied real-gas deviation.