Basic Chemistry Chapter 11 Gases Chapter 11 Lecture Fourth Edition Chapter 11 Gases 11.3 Pressure and Volume (Boyle’s Law) Learning Goal Use the pressure-volume relationship (Boyle’s law) to determine the final pressure or volume when the temperature and amount of gas are constant.

Boyle’s law states that the pressure (P) of a gas is inversely related to its volume (V) when T and n are constant if the pressure (P) increases, then the volume (V) decreases Figure 11.4 Boyle’s law: As Volume decreases, gas molecules become more crowded, which causes the pressure to increase. Pressure and volume are inversely related.

Boyle’s Law Boyle’s law is an indirect relationship between pressure and volume. An indirect relationship between variables means as one variable increases the second decreases. P1V1 = P2V2 Temperature and moles are constant.

Boyle’s Law Equation The equation for Boyle’s law can be rearranged to solve for any factor. At a constant temperature and amount of gas: P1V1 = P2V2 Boyle’s law To obtain V2, divide both sides by P2.

Guide to Using the Gas Laws

Learning Check Freon-12, CCl2F2, is a gas used in refrigeration systems. What is the new volume (L) of an 8.0-L sample of Freon gas initially at 550 mmHg after its pressure is changed to 2200 mmHg at constant T?

Solution What is the new volume (L) of an 8.0-L sample at 550 mmHg after its pressure is changed to 2200 mmHg at constant T? Step 1 Organize the data in a table of initial and final conditions. We can predict that as P increases, V decreases. Conditions 1 Conditions 2 P1 = 550 mmHg P2 = 2200 mmHg V1 = 8.0 L V2 = ?

Solution What is the new volume (L) of an 8.0-L sample at 550 mmHg after its pressure is changed to 2200 mmHg at constant T? Step 2 Rearrange the gas law equation to solve for the unknown quantity. Solve Boyle’s law for V2. Increasing P decreases V when n and T are constant.

Solution What is the new volume (L) of an 8.0-L sample at 550 mmHg after its pressure is changed to 2200 mmHg at constant T? Step 3 Substitute values into the gas law equation and calculate. The pressure ratio decreases the volume.

Learning Check For a cylinder containing helium gas, indicate if cylinder A or B represents the new volume for the following changes (n and T are constant): Pressure decreases Pressure increases

Solution For a cylinder containing helium gas, indicate if cylinder A or B represents the new volume for the following changes (n and T are constant): Pressure decreases Cylinder B Pressure increases Cylinder A

Learning Check A balloon of helium gas has a volume of 6.4 L at a pressure of 0.70 atm. At 1.40 atm (T and n constant), is the new volume represented by A, B, or C?

Solution A balloon of helium gas has a volume of 6.4 L at a pressure of 0.70 atm. At 1.40 atm (T and n constant), is the new volume represented by A, B, or C? At a higher pressure (T and n constant), the new volume is represented by the smaller balloon A.

Chemistry Link to Health During inhalation, the lungs expand the pressure in the lungs decreases air flows toward the lower pressure in the lungs

Chemistry Link to Health During exhalation, lung volume decreases pressure within the lungs increases air flows from the higher pressure in the lungs to the outside