5-4 Boyle, Gay-Lussac + Combined Gas Law

5-4 BOYLE’S LAW, GAY-LUSSAC’S LAW AND COMBINED GAS LAW BOYLE’S LAW Describes the relationship between volume and pressure (temperature and amount of gas are held constant). The volume of a gas is inversely proportional to its pressure. • As the volume of a gas increases, the pressure decreases. • As the volume of a gas decreases, the pressure increases. Smaller volume → less space for particles to move → particles hit container more often → pressure increases. APPLICATIONS OF BOYLE’S LAW BREATHING • Inhalation – volume increases, pressure decreases → draws air into lungs • Exhalation – volume decreases, pressure increases → forces air out of lungs SYRINGES – DRAWING BLOOD • Pulling back on the syringe increases the volume of the cylinder → pressure inside the syringe drops • Blood pressure in the body is now higher → pushes blood into syringe CALCULATING BOYLE’S LAW We can express Boyle’s law by initial (1) conditions and final (2) conditions. *Pressure is always in kPa, Volume in L P1V1 = P2V2 PRACTICE! Helium gas has a volume of 8.25 L at 446 kPa. What pressure must be applied to the gas when it occupies 12 L? GAY-LUSSAC’S LAW Describes the relationship between temperature and pressure (volume and amount of gas must be held constant). The temperature is directly proportional to the pressure: • As the temperature increases, the pressure increases. • As the temperature decreases, the pressure decreases. Higher temperature → higher kinetic energy → particles move faster → particles collide with the container and each other more → pressure increases. APPLICATIONS OF GAY-LUSSAC’S LAW PRESSURE COOKER • Heat is applied to the pressure cooker → temperature rises • Higher temperature boils the water inside → creates steam, increasing pressure • Higher pressure raises the boiling point of water → food cooks faster TIRE PRESSURE • Heat from friction increases tire pressure after driving → tire pressure rises • Inflating tires in cold weather can cause them to burst when it is hot → pressure increases with temperature CALCULATING GAY-LUSSAC’S LAW We can express Gay-Lussac’s law by initial (1) conditions and final (2) conditions. *Pressure is always in kPa, Temperature is always in K! 𝐏𝟏 𝐏𝟐 = 𝐓𝟏 𝐓𝟐 PRACTICE! A soccer ball is inflated indoors with a pressure of 85 kPa at 25°C. If it is taken outside, where the temperature on the playing field is -11.4°C, what is the pressure of the gas inside the soccer ball? COMBINED GAS LAW • Describes the relationship between volume, temperature, and pressure. • Number of moles of gas is held constant. • Combines the three laws together: Charles, Boyle, Gay-Lussac. 𝐏𝟏 𝑽𝟏 𝐏𝟐 𝑽𝟐 = 𝐓𝟏 𝐓𝟐 PRACTICE! A balloon at the top of Mount Logan occupies a volume of 775 mL at a temperature of −28°C and a pressure of 92.5 kPa. What is the pressure at the bottom of the mountain if the same balloon has a volume of 825 mL at a temperature of 15°C?