Gas laws and isobaric heating When a gas is heated while the pressure is held constant (isobaric process), the governing ideal-gas relationship is known as:

Introduction / Context:
In introductory thermodynamics and physical chemistry, several “gas laws” describe how an ideal gas behaves when one state variable is held constant. This question targets the scenario of heating at constant pressure (an isobaric process), asking which named relationship correctly governs the volume–temperature change.

Given Data / Assumptions:

• Ideal-gas behavior is assumed so that p * V = n * R * T applies.
• Process condition: pressure p is held constant (isobaric heating).
• Amount of gas n is fixed (closed mass).

Concept / Approach:
For a fixed amount of an ideal gas at constant pressure, the volume is directly proportional to absolute temperature: V ∝ T. This proportionality is historically called Charles' law. By contrast, Boyle's law refers to isothermal changes (p * V = constant), Gay-Lussac's law often denotes the p–T relation at constant volume, and Avogadro's law relates volume to moles at fixed p and T.

Step-by-Step Solution:
Start with p * V = n * R * T.At constant p and fixed n, rearrange to V = (n * R / p) * T.Hence V / T = constant, which is exactly Charles' law.Therefore, the governing law for isobaric heating is Charles' law.

Verification / Alternative check:
Graphing V versus T (in kelvin) at constant pressure gives a straight line through the origin. Laboratory piston–cylinder demonstrations show that as the gas is heated at fixed external pressure, the piston rises proportionally with T, consistent with Charles' law.

Why Other Options Are Wrong:

• Boyle's law: p * V = constant holds when T is constant, not when p is constant.
• Gay-Lussac law: commonly states p ∝ T at constant V, which is not the present constraint.
• Avogadro's law: V ∝ n at fixed p and T; unrelated to heating at constant p with fixed n.
• Dalton's law: about partial pressures in mixtures, not single-gas isobaric heating.

Common Pitfalls:
Using Celsius instead of kelvin breaks the direct proportionality V ∝ T. Always work with absolute temperature for gas laws.

Final Answer:
Charles' law