1. Boyle’s law Volume of a gas is inversely proportional to the pressure on a gas. V  1/P Therefore VP = k (some constant for each gas) V i P i = V f P f i is initial f is final

2. Boyle’s Law If you have 145 mL of a gas at 67 kPa. What volume will it occupy at 127 kPa? VP = VP 145 mL (67kPa) = V (127 kPa) V = 76 mL

3. Boyle’s Law Fill a cup with water and while under water, turn it upside down and pick it up. This action tries to increase the volume inside the cup. Pressure drops and outside pressure will push in allowing you to pick up water against gravity. Don’t raise the cup over the water line

4. Water in a cup Water Cup (with a little bit of air in it) Gravity wants to pull the water in the cup down. However if it fell it would leave a big space of nothing (vacuum) Air pressure pushes to stop the vacuum from forming by pushing on the surface of the liquid. Not allowing the water level to rise. The water will fall once the air pressure equals the pressure (weight divided by area) of the water being lifted. Which would make the water level rise.

5. Barometer Pressure can be measured with a barometer. Which works just like the cup but with mercury.

6. Why use mercury? Mercury is dense and will fill a small tube About 760 mm Hg is needed under normal conditions. Water would fill a 10 m high tube to replace mercury Standard pressure is 760 torr or 29.9 inches Hg

7. Modern Barometers Digital Barometers use a sensor with a sealed drum. Top of the drum is flexible. Sealed inside the drum is air at a known (calibrated) pressure. Higher outside pressure pushes the drum in. Lower outside pressure bows the drum out.

8. High pressure low pressure drum

9. High pressure low pressure drum

10. High pressure low pressure drum

11. How do substances expand? Cooling makes substances contract. Especially with gases. Charles’ Law: The volume of a gas is directly proportional to the temperature of that gas. V  T; V/T = k V i /T i = V f /T f

12. Charles’ Law If you have 6.7 L of a gas at 298 K, what volume will it occupy at 0 o C? V/T = V/T 6.7 L / (298 K) = V / (273 K) *Temp must be in Kelvin because zero would make it undefined! V = 6.1 L

13. Charles’ Law Volume = 0.731 L of a gas at 318 K, What is the temperature if it occupies 1.34 L? V/T = V/T 0.731 L / (318 K) = 1.34 L / T T = 583 K

14. Gay-Lussac’s Law The pressure of a gas is directly proportional to its temperature. T/P = T/P This is why an aerosol can or a tire feels cooler when air is released. It is also how a diesel engine ignites the fuel. It compresses it until it ignites.

15. Combined Gas Law This is made by combining Charles’ and Boyle’s Law. V i P i / T i = V f P f / T f Temperature must be in Kelvin (so it can never be 0) Volume and pressure can be in any unit as long as it is the same on both sides.

16. A problem If a gas occupies 34 L at 1.2 atm and 290 K, what volume will it occupy at 1.1 atm and 280 K? V i P i / T i = V f P f / T f 34L (1.2atm) / 290 K = V (1.1atm)/280K V = 36 L

17. A problem If a gas occupies 24 mL at 115 kPa and 13 o C, what volume will it occupy at 101 kPa and 0 o C? 24 mL (115kPa)/286 K = V (101kPa)/273 K V = 26 mL (don’t forget to convert temp to K)