Charles’s Law (Vol-Temp Law)

Charles’s Law is a fundamental principle describing the thermal expansion of gases. The initial work was conducted by Jacques Charles around 1787. He investigated how the volume of a fixed amount of gas changed with temperature while keeping the 压力 constant, finding a consistent linear relationship. However, Charles never published his findings. The law became widely known after Joseph Louis Gay-Lussac, who had been independently investigating the same phenomenon, published his own results in 1802. In his paper, Gay-Lussac generously credited Charles for the original, unpublished work, which is why the law is most commonly named after Charles.

The law’s profound significance lies in its extrapolation. By plotting volume versus temperature for various gases, scientists noted that all the lines, when extended backwards, converged to a single point of zero volume. This theoretical temperature was determined to be -273.15 °C. This point was recognized as absolute zero, the lowest possible temperature, which became the foundation for the Kelvin absolute temperature scale. On the Kelvin scale, where 0 K is absolute zero, the law takes its simple proportional form [latex]V = kT[/latex]. Microscopically, heating a gas at constant pressure increases the kinetic energy of its molecules, making them move faster. To maintain constant pressure (i.e., a constant rate of collisions with the container walls), the volume must expand, giving the faster-moving molecules more space to travel between collisions.