Science, Tech, Math › Science Gay-Lussac's Law Definition Share Flipboard Email Print Gay-Lussac's Law is an ideal gas law. Tetra Images/Jessica Peterson,/Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 12, 2019 Gay-Lussac's law is an ideal gas law which states that at constant volume, the pressure of an ideal gas is directly proportional to its absolute temperature (in Kelvin). The formula for the law may be stated as: Pwhere PGay-Lussac's law is also known as the pressure law. French chemist Joseph Louis Gay-Lussac formulated it around 1808. Other ways of writing Gay-Lussac's law make it easy to solve for the pressure or temperature of a gas: PPTWhat Gay-Lussac's Law Means The importance of this gas law is that it shows that increasing the temperature of a gas causes its pressure to rise proportionally (assuming the volume doesn't change). Similarly, decreasing the temperature causes the pressure to fall proportionally. Gay-Lussac's Law Example If 10.0 L of oxygen exerts 97.0 kPa at 25 degrees Celsius, what temperature (in Celsius) is needed to change its pressure to standard pressure? To solve this, you first need to know (or look up) standard pressure. It's 101.325 kPa. Next, remember that gas laws apply to absolute temperature, which means Celsius (or Fahrenheit) must be converted to Kelvin. The formula to convert Celsius to Kelvin is: K = degrees Celsius + 273.15 K = 25.0 + 273.15 K = 298.15 Now you can plug the values into the formula to solve for the temperature: TTTAll that's left is to convert the temperature back to Celsius: C = K - 273.15 C = 311.44 - 273.15 C = 38.29 degrees Celsius Using the correct number of significant figures, the temperature is 38.3 degrees Celsius. Gay-Lussac's Other Gas Laws Many scholars consider Gay-Lussac to be the first to formulate Amonton's law of pressure-temperature. Amonton's law states that the pressure of a certain mass and volume of a gas is directly proportional to its absolute temperature. In other words, if the temperature of a gas increases, so does the gas's pressure, providing its mass and volume remain constant. Gay-Lussac is also credited for other gas laws, which are sometimes called "Gay-Lussac's law." For instance, Gay-Lussac stated that all gases have the same mean thermal expansivity at constant pressure and temperature. Basically, this law states that many gases behave predictably when heated. Gay-Lussac is sometimes credited as being the first to state Dalton's law, which says that the total pressure of a gas is the sum of the partial pressures of individual gases.