Chapter 11 Behavior of Gases

Section 11.1 Gas Pressure

Gas Pressure The deflated basketball has less particles inside of it than the inflated ball. Inflating the basketball increases the number of particles inside the ball. The increased number of particles inside the ball strike the inner wall of the ball and the pressure increases. TEXTBOOK PAGE 370

Number of Particles & Pressure Because the inflated ball has a greater number of particles (pressure) , it has a greater mass. The more particles there are, the more collisions with the walls of the container. Therefore, the pressure is directly proportional to the number of particles.

Temperature & Pressure At higher temperatures, particles in a gas have greater kinetic energy. An increase in kinetic energy means that the particles move faster and collide with the container walls more often, resulting in an increase in pressure.

Measuring Pressure Barometer Measures the pressure exerted by the atmosphere. Pressure Gauge Measures pressure in a closed system (tank, tire, etc.).

Top of the Mountain When you climb a mountain, atmospheric pressure decreases because the overall depth of the air above you is less than at the base of the mountain.

Standard Atmospheric Pressure The pressure that supports a 760-mm column of mercury. 1.00 atm = 760 mm Hg

Pressure Units Pascal (Pa) is the SI unit for measuring pressure. kPa = Kilopascal 1kPa = 1000 Pa

Pressure Conversions 1atm = 760 mmHg = 101.3 kPa Ex: The air pressure for a certain tire is 109 kPa. What is this pressure in atmospheres? Write the given amount over 1 109 kPa 1 Write the conversion factor Multiply and divide the values. Make sure to cancel units. (Answer: 1.08 atm)

Check Point The weather news gives the atmospheric pressure as 1.07 atm. What is this atmospheric pressure in mm Hg? (Answer: 813 mm Hg). What is 515 mmHg in kPa? (Answer 68.4 kPa)

Section 11.2 Gas Laws

Boyle’s Law Pressure and volume of a gas at a constant temperature are inversely proportional (opposite relationship). Pressure Volume

Boyle’s Law As the pressure is increased (more weights), the volume of the container is decreased.

Boyle’s Law

Boyle’s Law

Boyle’s Law Formula Example: P1 = 125 kPa V1 = 3.50 L P2 = ? Solve for P2

Check Point Find the new volume. A 175 mL sample of neon had its pressure changed from 75 kPa to 150 kPa.  What is its new volume?

Have your ears ever popped? Boyle’s law explains the discomfort you may feel in your ears when ascending in an airplane or driving up into the mountains. When you fly or drive to a higher altitude, the air around you and in your ears decreases, causing the volume of air in your ears to increase. When your ears “pop”, the air is released from your ears.

Charles’ Law At a constant pressure, the volume of a gas is directly proportional to its Kelvin temperature. Volume Temperature

 C + 273 = K Converting to Kelvin If the temperature is not in Kelvin it must be converted.  C + 273 = K

Charles’ Law

Volume and Temperature The straight line shows that volume is directly proportional to temperature.

Charles’ Law or Example: A sample of nitrogen occupies a volume of 250 mL at 25 oC.   What volume will it occupy at 95 oC?(don’t forget to convert to Kelvin)

Check Point or Find the new temperature. Fluorine gas at 300 K occupies a volume of 500mL.  What temperature should it be to bring the new volume to 300 mL?

Combined Gas Law The combined gas law is the combination of Boyle’s Law and Charles’ Law.

Standard Temperature & Pressure (STP) STP is defined as a temperature of 0.00 C or 273 K and a pressure of 1 atm.

Combined Gas Law Example: A cylinder of compressed oxygen gas has a volume of 30 L and 100 atm pressure at 27C. The cylinder is cooled until the pressure is 5.0 atm. What is the new temperature of the gas in the cylinder? (the volume remains the same) Answer = 15 K

Check Point Carbon dioxide occupies a 2.54 L container at STP. What will be the volume when the  pressure is 150 KPa and 26oC?      V2 =  [2.54 L][101.3 kPa][299K]                               [150 kPa ][273 K] =  1.88 L

Check Point Oxygen occupies a fixed container of 5.5L at STP. What will happen to the pressure if the temperature rises to 300K?       P2 = [5.5 L] [ 101.3 kPa][300 K]                 [5.5 L]   [ 273 K] =  111.3 KPa

Law of Combining Gas Volumes At the same temperature and pressure, volumes of gases combine or decompose in ratios of small whole numbers.

Avogadro’s Principle Equal volumes of gases at the same temperature and pressure contain equal number of particles.