CLE Apply the kinetic molecular theory to describe solids, liquids, and gases. CLE Investigate characteristics associated with the gaseous state. SPI Investigate similarities and differences among solids, liquids and gases in terms of energy and particle spacing. SPI Predict how changes in volume, temperature, and pressure affect the behavior of a gas. CLE Explore the mathematics of chemical formulas and equations. SPI Convert among the following quantities of a substance: mass, number of moles, number of particles, molar volume at STP

Up, Up and Away with Gases

Kinetic Molecular Theory (KMT) used to describe behavior of gases, liquids and solids

all matter is composed of small particles (molecules) particles are in constant motion (kinetic energy – energy of motion) collisions between particles are elastic (no loss of KE)

gas liquidsolid

Gas weak attractive forces between particles, so particles spaced far apart relative to their size frequent collisions due to constant, random motion

We will use the KMT to look at the following characteristics of gases: volume temperature pressure

Volume amount of space an object occupies gas particles expand to fill volume of container because of distance between particles gases can easily be compressed

Gases are “springy”

Temperature related to the average kinetic energy of particles

Celsius scale based on freezing and boiling points of water (0 o C – 100 o C) Temperature scales

Kelvin scale based on absolute zero (0 K) temperature at which particles are at lowest possible energy no negative numbers

K = o C o C = K – 273

Temperature conversions a. 110 o C to K b. 303 K to o C c o C to K

Pressure force exerted over an area

Gas particles exert pressure when they collide with sides of container.

Barometer device used to measure atmospheric pressure Atmosphere forms an ocean of air above us.

Pressure units: millimeters of mercury (mm Hg) / torr pounds per square inch (psi) atmospheres (atm) kilopascals (kPa)

In order to compare two different gas samples, scientist define standard conditions. Compare apples to apples, not apples to oranges!

Standard Temperature and Pressure (STP) 0 o C 273 K 760 mm Hg (torr), 14.7 psi, 1.00 atm, kPa (atmospheric pressure at sea level)

In marked contrast to solids and liquids, gas volumes change noticeably with small changes in pressure and temperature.

Gas laws simple mathematical relationships between the volume, temperature, pressure, and amount of a gas

Ideal gas particles have mass but no volume; no attractive forces between particles

Most gases behave as ideal gases except under the conditions of: 1) very high pressure 2) very low temperature

Robert Boyle

Boyle’s Law (volume and pressure) The volume of a fixed amount of gas held at a constant temperature varies inversely with the pressure. P 1 V 1 = P 2 V 2

Every breath I take...

As the diaphragm contracts and flattens, chest cavity enlarges. Volume increases and pressure decreases (Boyle’s law.) This creates a vacuum, which pulls air into the lungs. Note: temperature is not kept completely constant.

Oxygen is collected in a 5.00 L glass bulb at a pressure of 740 mmHg. It is then pumped into an evacuated container having a volume of 1.50 L. What is the pressure of the gas? Answer: mmHg

An air-filled balloon has a volume of L at sea level (standard pressure.) What is the volume of the balloon at the top of a mountain where atmospheric pressure is 745 mm Hg? Answer: L

Jacques Charles French scientist early balloonist

Charles’s Law (volume and temperature) The volume of a given amount of gas is directly proportional to its kelvin temperature at constant pressure.

As air inside balloon is heated, volume increases (Charles’s law.) Keep heating and some air spills out the bottom. Less air inside makes balloon lighter and lifts off ground.

A sample of hydrogen gas occupies a volume of 125 mL at 300. K. Predict its volume at standard temperature. Answer: 114 mL

A sample of air in a piston at 25 o C occupies 35 mL. What volume will it occupy if the temperature is raised to 250 o C? Hint: Watch temperature units! Answer: 61 mL

A gas occupies a volume of 562 mL at a temperature of o C. To what temperature, in 0 C, must the gas be lowered, if it is to occupy mL? Answer: 7 o C

Joseph Louis Gay-Lussac French chemist and physicist

Gay-Lussac’s Law: (pressure and temperature) The pressure of a fixed amount of gas varies directly with the kelvin temperature when the volume remains constant.

Before a trip from New York to Boston, the pressure in an automobile tire is 1.8 atm at 20. o C. At the end of the trip, the pressure gauge reads 1.9 atm. What is the new Celsius temperature of the air inside the tire? Answer: 36 o C

At 120. o C, the pressure of a sample of nitrogen is 1.07 atm. What will the pressure be at 205 o C? Answer: 1.30 atm

Combined Gas Law states the relationship among pressure, temperature, and volume of a fixed amount of gas

The volume of a gas is 27.5 mL at 22.0 o C and atm. What will the volume be at 15.0 o C and atm? Answer: 26.3 mL

A student collects 450. mL of hydrogen chloride gas at 750. mm Hg and 17 o C. What is the volume of the gas at STP? Answer: 418 mL

A 700. mL gas sample at STP is compressed to a volume of 200. mL, and the temperature is increased to 30.0 o C. What is the new pressure of the gas in kilopascals? Answer 394 kPa

Avogadro’s principle Equal volume of gases at the same temperature and pressure contain equal numbers of particles.

Molar volume One mole of any gas at STP occupies a volume of 22.4 L 1 mol = 22.4 L

How many moles of acetylene (C 2 H 2 ) gas occupy a volume of 3.25 L at STP? Answer: mol C 2 H 2

Answer: 71.7 L O 2 What volume will 3.20 mol of oxygen gas occupy at STP?

What is the volume of 7.17 g of neon gas at STP? Answer: 7.96 L Ne What is the volume of 5.0 g of hydrogen gas at STP? Answer: 56 L H 2

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