Homework: Pressure Worksheet (I need labs from some of you!!!)

Under pressure, the particles in a gas are forced closer together. Compressibility Gases are easily compressed because of the space between the particles in a gas. The distance between particles in a gas is much greater than the distance between particles in a liquid or solid. Under pressure, the particles in a gas are forced closer together.

Factors Affecting Gas Pressure Aerosol Spray Paint The pressure of the gas inside a new can of spray paint is greater than the air pressure outside the can. When gas rushes though an opening in the top of the can, it propels, or forces, paint out of the can. As the can is used, the pressure of the propellant decreases. Relating Cause and Effect What happens when the pressure of the propellant equals the air pressure outside the can?

Factors Affecting Gas Pressure Three factors that affect gas pressure amount of gas volume temperature

Factors Affecting Gas Pressure Amount of Gas As the amount of gas inside a container increases, the pressure inside of the container also increases

Factors Affecting Gas Pressure If the gas pressure increases until it exceeds the strength of an enclosed, rigid container, the container will burst. When a gas is pumped into a closed rigid container, the pressure increases as more particles are added. If the number of particles is doubled, the pressure will double. Predicting What would happen to the pressure in the container if the number of particles were tripled? If the number of particles were cut in half?

Factors Affecting Gas Pressure Volume By placing the same amount of gas in a smaller volume, you raise the pressure. The more a gas is compressed, the greater is the pressure inside the container. Volume down = pressure up

Factors Affecting Gas Pressure When the volume of the container is halved, the pressure the gas exerts is doubled. A piston can be used to force a gas in a cylinder into a smaller volume. When the volume is decreased, the pressure the gas exerts is increased. Interpreting Diagrams What happens to the gas pressure when the volume is reduced from 1 L to 0.5 L?

Factors Affecting Gas Pressure Temperature Heating a gas causes the pressure to increase. Heating increases the kinetic energy, which makes the particles move with more energy Temperature up = Pressure up

Factors Affecting Gas Pressure When the Kelvin temperature of the enclosed gas doubles, the pressure of the enclosed gas doubles. An increase in temperature causes an increase in the pressure of an enclosed gas. The container can explode if there is too great an increase in the pressure.

Manometer: a device used to determine vapor pressure of a liquid 13.2 Vapor Pressure Manometer: a device used to determine vapor pressure of a liquid The vapor pressure of a contained liquid can be measured in a manometer. The vapor pressure is equal to the difference in height of the mercury in the two arms of the U-tube. Calculating What is the difference in vapor pressure between ethanol at 0°C and ethanol at 20°C?

Pressure Conversions 1 atm = 760 mm Hg = 101325 Pa = 101 Pressure Conversions 1 atm = 760 mm Hg = 101325 Pa = 101.3 kPa Use the ratio method.

How many mm Hg is 0.50 atm? 0.50 atm = 1 atm x mm Hg 760 mm HG

How many kPa is 0.50 atm?

How many atm is 60.50 mm Hg?

How many kPa is 2.3 atm?

Ideal Gases and Real Gases Under what conditions are real gases most likely to differ from ideal gases?

Ideal Gases and Real Gases There are attractions between the particles in an ideal gas. Because of these attractions, a gas can condense,or even solidify, when it is compressed or cooled. In this flask used to store liquid nitrogen, there are two walls with a vacuum in between.

Ideal Gases and Real Gases Real gases differ most from an ideal gas at low temperatures and high pressures.

Ideal Gases and Real Gases This graph shows how real gases deviate from the ideal gas law at high pressures. INTERPRETING GRAPHS a. Observing What are the values of (PV)/(nRT) for an ideal gas at 20,000 and 60,000 kPa? b. Comparing What variable is responsible for the differences between the two (CH4) curves? c. Making Generalizations How does an increase in pressure affect the (PV)/(nRT ) ratio for real gases?

14.1 Section Quiz. 1. Compared to liquids and solids, gases are easily compressed because the particles in a gas attract each other. are spaced relatively far apart. are very small. repel each other.

14.1 Section Quiz. 2. Gas pressure is affected by temperature, volume, and the amount of the gas. temperature, volume, and the molar mass of the gas. phase diagram, volume, and the size of the container. temperature, phase diagram, and the mass of the gas container.

14.1 Section Quiz. 3. For gases, the SI units for volume (V), pressure (P), and temperature (T) are, respectively, liters, kilopascals, and °C. liters, kilopascals, and kelvins. cm3, kilopascals, and kelvins. liters, atmospheres, and °C.