Concept · Thermodynamics

Ideal gas

equation of state PV/T=const (PV=nRT), isothermal (P~1/V hyperbola)/isobaric (V~T)/isochoric (P~T) processes and their P-V, P-T, V-T graphs, Kelvin-vs-Celsius conversion in ratios

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Named traps

10 ways this goes wrong.

Each is a named misconception the questions are built to catch. Open one for the move that tempts, and the fix.

Boyle/Charles relation invertedTreats pressure as proportional to volume (Boyle) or volume as inversely proportional to T (Charles), inverting the dependence.→
Charles extrapolation to 0 ignoredIgnores that an ideal-gas volume extrapolates to zero only at absolute zero (not 0 Celsius), mishandling the proportional reasoning.→
Combined law with changing amountApplies p1V1/T1=p2V2/T2 while gas is added, leaked, or removed, violating the fixed-n requirement.→
Gas law uses CelsiusSubstitutes Celsius temperature into a gas-law ratio where absolute (Kelvin) temperature is required, so a ratio like T2/T1 is wrong.→
Iso-process conditions confusedConfuses isothermal, isobaric, and isochoric processes, e.g. holds pressure constant in an isothermal change.→
Isotherm drawn as straight lineDraws an isothermal P-V process as a straight line instead of a P~1/V hyperbola.→
P-V/P-T process path misreadMisidentifies which curve or line on a P-V, P-T, or V-T diagram is isothermal vs isobaric vs isochoric.→
PV=nRT rearranged wrongSolves the equation of state incorrectly for the target variable, e.g. P=nRTV or T=PV/(nR) mis-placed.→
V-T line origin set at Celsius zeroReads the isobaric V-T (or isochoric P-T) straight line as passing through 0 Celsius instead of extrapolating to absolute zero.→
pV constant regardless of THolds pV constant during heating at fixed amount, ignoring that pV is proportional to absolute temperature.→

Key formulas

No formula sheet is matched to this concept yet. Work it from first principles, and watch the traps.

Shaky underneath?

If the concept underneath still feels loose, patch it here before coming back to CSCA questions.

FoundationsPhysics 2 breadth