Combined Gas Law
The three gas laws that laid the foundation for the ideal gas law are as follows:
Boyle's law: At constant temperature, the volume of a gas is inversely proportional to its pressure.
Charles's law: At constant pressure, the volume of a gas is proportional to the absolute temperature.
Gay-Lussac's law: At constant volume, the pressure of a gas is proportional to its temperature.
The combined gas law combines these laws and summarizes the relationship between thermodynamic variables (volume V, pressure p, and absolute temperature T):
Note that the temperature is absolute, so it must be expressed in Kelvin (K) as opposed to Celsius (°C) or Fahrenheit (°F) for the equation to hold numerically. Typically, experiments are conducted at standard pressure and temperature, 101.3 kPa and 25°C. It is important to note that sometimes volume, pressure and temperature are expressed in terms of non-standard units. The following table contains conversions to SI units:
Use the sliders to set the volume, temperature, and pressure of the gas in the left panel below. The same gas is moved to the right panel, where the temperature and pressure are set to standard conditions ( 25°C , 101.3 kPa ). Can you calculate what the volume will be?
Pressure: 101.3 kPa
Temperature: 25°C (298 K)
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