Chemistry Notes Unit 7: P, V and ‘n’

(1) Pressure & Volume P = Pressure; V = Volume “Boyle’s Law” Relationship: Inverse Volume increases = Pressure decreases Volume decreases = Pressure increases *Temperature and ‘n’ constant Equation: P1V1 = P2V2

(2) Pressure & Volume Graph

(3) PV Example #1 You have a gas in a closed container that occupies 50 mL and has a pressure of 2 atm. What would be the new pressure if the gas was compressed to a new volume of 30 mL? ______________________________________________ a. What are your knowns and unknowns? Circle the unknown and underline the knowns. b. What is held constant? c. What is the cause and effect (use “so”): d. Calculate. Show all units. Once finished, check answer to see if it makes sense. e. Draw pictures.

(4) PV Example #2 What would be the new volume of 150 cm3 of gas at 20oC and at a pressure of 760 mmHg were changed to a pressure of 500 mmHg? ________________________________________________ a. What are your knowns and unknowns? Circle the unknown and underline the knowns. b. What is held constant? c. What is the cause and effect (use “so”): d. Calculate. Show all units. Once finished, check answer to see if it makes sense. e. Draw pictures.

(5) PV Example #3 A closed syringe contains 3 “puffs” of air and has an initial volume of 20 cm3 and a pressure of 30 psi. Without changing the temperature, the volume is increased to 45 cm3. What is the new pressure? ________________________________________________ What are the knowns and unknowns? What’s held constant? What’s the cause and effect? Calculate the new pressure. ________________________________________________ If 1 atm = 14.7 psi = 760 mmHg = 101.3 kPa, and if 1 kPa = 1000 Pa, convert the new pressure to Pa.

(6) PV Example #4 A closed syringe has an initial volume of 40 mL and a pressure of 12 psi. Without changing the temperature, the pressure is decreased to 8 psi. What is the new volume in poop sq? ______________________________________________ Convert the final volume to Liters using factor labeling.

(7) Pressure & # of Particles P = Pressure; n = # of Particles Relationship: Linear # of Particles increases = Pressure increases # of Particles decreases = Pressure decreases *Temperature and Volume constant Equation: P1 / n1 = P2 / n2

(8) Pressure & ‘n’ Graph Pressure n

(9) P/n Example #1 5.5 puffs of air have a pressure of 900 mmHg. What is the pressure when three puffs of air are removed? ______________________________________________

(10) P/n Example #2 A bicycle tire has a pressure of 30 psi and has 5 puffs of air in it. What is the new pressure when 1 extra puff of air is added to the tire? ______________________________________________