Which expression represents Charles' Law in two-point form?

Which expression represents Charles' Law in two-point form?

• A. P1V1 = P2V2
• B. P1/T1 = P2/T2
• C. V1/T1 = V2/T2
• D. V1 = T1

Answer: (C)

Charles' Law states that, at constant pressure, volume changes directly with absolute temperature. When you compare two states, the ratio of volume to temperature stays the same, so the two-point form is V1/T1 = V2/T2, with temperatures in Kelvin. This expresses the direct proportionality: increasing temperature (in Kelvin) while holding pressure fixed leads to a proportional increase in volume. The other expressions don’t capture this direct V–T relationship at constant pressure: P1V1 = P2V2 is Boyle’s law (P–V at constant T), P1/T1 = P2/T2 would describe a P–T relation at constant volume (Gay-Lussac’s style), and V1 = T1 is not a meaningful gas-law form without units.

Charles' Law states that, at constant pressure, volume changes directly with absolute temperature. When you compare two states, the ratio of volume to temperature stays the same, so the two-point form is V1/T1 = V2/T2, with temperatures in Kelvin. This expresses the direct proportionality: increasing temperature (in Kelvin) while holding pressure fixed leads to a proportional increase in volume. The other expressions don’t capture this direct V–T relationship at constant pressure: P1V1 = P2V2 is Boyle’s law (P–V at constant T), P1/T1 = P2/T2 would describe a P–T relation at constant volume (Gay-Lussac’s style), and V1 = T1 is not a meaningful gas-law form without units.