Ideal Gas Laws AKS 27b I can relate pressure and volume in Boyle’s law. AKS 27b I can relate temperature and volume in Charles’ law. AKS 27b I can relate temperature and pressure in Gay Lussac’s law.

Why does a gas behave differently than solids or liquids? Gas particles (molecules or atoms) are far apart from each other, and they move independently. Therefore, there is extra space between particles for them to be compressed or expanded.

What do the Ideal Gas Laws tell us? The Ideal Gas Laws tell us how changes in volume, temperature, or pressure affect the other conditions. Remember, these laws all work with a set mass of a gas – the same number of particles as conditions change. No gas behaves perfectly, but they do come fairly close to “ideal.”

Definitions you need to know Temperature: the average kinetic energy of gas particles. (i.e. how fast the particles move) ºF ºC K -459 32 212 -273 100 273 373

Definitions you need to know Volume: how much space the gas occupies (Remember, a gas fills the volume of its container.)

Definitions you need to know Pressure: the force of gas particles hitting against the walls of the container Mercury Barometer

Boyle’s Law For a fixed amount of gas at a constant temperature, the volume of the gas increases as the pressure decreases. V↑ P↓

Boyle’s Law What is constant? Temperature What changes? Volume and Pressure Volume increases, pressure decreases; Volume decreases, pressure increases. Inverse relationship The same number of particles are in a smaller space (less volume), so they strike the sides of the container more often (more pressure), even though each one has not changed speed (temperature). Short video changing Pressure Video of Respiratory System changing Volume Image from http://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&docid=MRK6-_AK0IuqaM&tbnid=buV6PjYz3Dv_0M&ved=0CAcQjB0&url=http%3A%2F%2Fwww.cyberphysics.co.uk%2Ftopics%2Fkinetic_theory%2Fboyle.htm&ei=-YIdVMOlDIjzgwSUloDQDw&psig=AFQjCNGZQYjAnjH5vIqhuHyVx4aW-fdlaQ&ust=1411306617299905

Boyle’s Law What is constant? Temperature What changes? Volume and Pressure Graphing relationship: Inverse (negative slope) Image from http://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&docid=MRK6-_AK0IuqaM&tbnid=buV6PjYz3Dv_0M&ved=0CAcQjB0&url=http%3A%2F%2Fwww.cyberphysics.co.uk%2Ftopics%2Fkinetic_theory%2Fboyle.htm&ei=-YIdVMOlDIjzgwSUloDQDw&psig=AFQjCNGZQYjAnjH5vIqhuHyVx4aW-fdlaQ&ust=1411306617299905

Temperature is constant Boyle’s Law Memory Aid Boyle As volume goes up and down, pressure does the opposite. “P” up/down makes “B” for Boyle. Temperature is constant P b This makes a tire pump work. Image from http://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&docid=MRK6-_AK0IuqaM&tbnid=buV6PjYz3Dv_0M&ved=0CAcQjB0&url=http%3A%2F%2Fwww.cyberphysics.co.uk%2Ftopics%2Fkinetic_theory%2Fboyle.htm&ei=-YIdVMOlDIjzgwSUloDQDw&psig=AFQjCNGZQYjAnjH5vIqhuHyVx4aW-fdlaQ&ust=1411306617299905

Charles’ Law For a fixed amount of gas at a constant pressure, the volume of the gas increases as the temperature increases. Note: because volume is increasing, density is reducing, too. This is what causes convection currents (wind) in our atmosphere. V↑ T ↑

Charles’ Law What is constant? Pressure What changes? Volume and Temperature Temperature increases, volume increases; Temperature decreases, volume decreases. Direct relationship The same number of particles are moving faster (higher temperature), so they strike the sides of the container more often (more pressure), so the balloon expands. The container (balloon volume) expands. Cooling the gas will shrink the balloon Video: heating a balloon makes it expand Video: cooling a balloon makes it shrink

Charles’ Law What is constant? Pressure What changes? Volume and Temperature Graphing relationship: Direct (positive slope)

Charles’ Law is about temperature changes – Cold / Hot Memory Aids As temperature goes up and down, volume does the same. “C” for Charles in the hot air balloon. “V” is the basket with Charles in it. Pressure is constant. As volume increases (expanding balloon), the density of the air inside the balloon is reduced, so the balloon rises. Charles’ Law is about temperature changes – Cold / Hot C H a r l e s

Gay-Lussac’s Law For a fixed amount of gas at a constant volume, the pressure of the gas increases as the temperature increases. P↑ T ↑

Gay-Lussac’s Law What is constant? Volume What changes? Pressure and Temperature Temperature increases, pressure increases; Temperature decreases, pressure decreases. Direct relationship The same number of particles are moving faster (higher temperature), so they strike the sides of the container more often (more pressure). If the container cannot expand, pressure increases. Pressure cookers work this way. Overfilled balloons pop on a hot day; they can’t expand. Video: tanker collapse (cooling steam lowers the pressure)

Gay-Lussac’s Law What is constant? Volume What changes? Pressure and Temperature Graphing relationship: Direct (positive slope)

Gay-Lussac’s Law Memory Aids The tanker got “sacked” as a result of Gay-Lussac. (low pressure as steam cooled inside) Only a loser (“Lose”-sac) would throw an aerosol can into a fire (pressure builds up dangerously in a closed can).

To remember which constants go with which law . . . Boyle’s Law – Temperature is constant Charles’ Law – Pressure is constant Gay-Lussac’s Law – Volume is constant BLT Cheese Pizza Green Veggies

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