The Gas Laws Boyle’s Law Boyle’s Law Pressure – Volume relationship The volume of a fixed mass of gas varies inversely with the pressure at constant temperature. Boyle’s law If we reduce the volume of the container by half, but still have the same number of molecules, then the number of molecules per unit volume doubles. If we have more molecules per unit volume then we will have more collisions within a given area of the walls, which will cause the pressure to increase. Boyle’s Law Boyle’s Law Mathematically expressed as V = k (1/P) or PV = k Can be used to compare changing conditions of a gas at constant temperature. P1V1 = P2V2 Example problem A sample of oxygen gas has a volume of 150. mL when its pressure is 0.947 atm. What will the volume be at a pressure of 0.987 atm if the temperature remains constant? Rearrange the Equation to solve for V2 V2 = P1V1 P2 Answer = ___________ Example problem A sample of oxygen gas has a volume of 150. mL when its pressure is 0.947 atm. What will the volume be at a pressure of 0.987 atm if the temperature remains constant? Rearrange the Equation to solve for V2 V2 = P1V1 P2 Answer = 144 mL O2 Example problem 2 A balloon filled with helium gas has a volume of 500 mL at a pressure of 1 atm. The balloon is released and reaches an altitude of 6.5 km, where the pressure is 0.5 atm. If the temperature has remained the same, what volume does the gas occupy at this height? Answer: _________________ Example problem 2 A balloon filled with helium gas has a volume of 500 mL at a pressure of 1 atm. The balloon is released and reaches an altitude of 6.5 km, where the pressure is 0.5 atm. If the temperature has remained the same, what volume does the gas occupy at this height? 1000 mL He Example problem 3 The piston of an internal combustion engine compresses 450. mL of gas. The final pressure is 15 times greater than the initial pressure. What is the final volume of the gas, assuming constant temperature? Answer: _________________ Example problem 3 The piston of an internal combustion engine compresses 450. mL of gas. The final pressure is 15 times greater than the initial pressure. What is the final volume of the gas, assuming constant temperature? 30.0 mL
