Chemistry – Mendoza

Ch 14 GasesSection 13.1 Introduction to gases (YES, IT SAYS 13.1)

VocabularyReview

– Gas – State of matter– Kinetic energy – energy due to motion

Newkinetic-molecular theoryelastic collisiontemperaturediffusionpressurebarometerpascalAtmosphereDalton’s law of partial pressures

Main Idea- Gases expand, diffuse, exert pressure, and can be compressed because they are in a low density state consisting of tiny, constantly-moving particles.

Intro to Gases• What is a gas?

– A form of matter– Used everywhere!

• Phases & Properties:– ______________ uniform composition & properties– ______________ matter with a fixed volume & shape

ex. ice cube– ______________ matter that flows, has a fixed volume & takes the shape of

its containerex. liquid water

– ______________ Matter that has no definite volume & takes the shape & volume of its container

ex. water vaporex. He, O2, CO2, H2, Cl2

• ______________________________:– In solids, molecules close & can hardly move – In liquids, more spread out & move a bit more– In gas, FAR apart & can move freely

• Pressure:– A ______________applied over a unit of area. – For a gas, press results from gas molecule ___________________with the wall of its

container – Can be measured in units called _________________ or ________________________

Changes to GasesAdding a gas:

– Adds more gas molecules– More collisions– _____________________________– Ex. Double # of molec = ________________________

Removed a Gas:– Removes gas molecules– Less collisions– ____________________________

Change Size of Container:– Decrease container size– Decreases space for molecules to move– Increases collisions– ____________________________

Change Size of Container:– Increase container size– Increases space for molecules to move– Decreases collisions– ____________________________

Heating a Gas:– Gas molecules absorb heat– Molecules move more rapidly– Increase collisions– _____________________________

Cooling a Gas:– Gas molecules release heat– Molecules move more slowly– Decrease collisions– _____________________________

Summary:• Add more gas Pressure• Remove gas Pressure• Reduce Size Pressure• Increase Size Pressure• Increase Temp Pressure• Decrease Temp Pressure

All of these beliefs are based on the _______________________________________:– A gas is composed of particles– Gas particles move rapidly & are in constant random motion– All collisions are perfectly elastic– Kinetic energy proportional to temperature

The Kinetic-Molecular Theory

Kinetic-molecular theory explains the different properties of solids, liquids, and gases. Atomic composition affects chemical properties. Atomic composition also affects physical properties. The kinetic-molecular theory describes the behavior of matter in terms of ______________________. Kinetic-molecular theory explains the different properties of solids, liquids, and gases. Gases consist of small particles separated by empty space. Gas particles are too far apart to experience significant attractive or repulsive forces. Gas particles are in ____________________________________.

Kinetic energy of a particle depends on ____________________________________. Temperature is a measure of the average kinetic energy of the particles in a sample of matter.

Explaining the Behavior of Gases

Great amounts of ______________exist between gas particles. ________________________ reduces the empty spaces between particles.

• Gases __________________________ past each other because there are no significant forces of attraction.

• _____________________ is the movement of one material through another.

• ______________________is a gas escaping through a tiny opening.• __________________________________________________ states that the rate of effusion for a gas

is inversely proportional to the square root of its molar mass.• Graham’s law also applies to _________________.

Gas Pressure• Pressure is defined as ___________________________________.• Gas particles exert pressure when they collide with the walls of their container.• The particles in the earth’s atmosphere exert pressure in all directions called ___________________.• There is ___________air pressure at _____________________________ because there are fewer

particles present, since the force of gravity is less.• Torricelli invented the ________________________.

– Barometers are instruments used to measure atmospheric air pressure.• The SI unit of force is the __________________________.

– One pascal(Pa) is equal to a force of one Newton per square meter or N/m2.– One atmosphere is equal to 760 mm Hg or 101.3 kilopascals.

• Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases of the mixture.

– The partial pressure of a gas depends on the number of moles, size of the container, and temperature and is independent of the type of gas.

– Ptotal = P1 + P2 + P3 +...Pn– Partial pressure can be used to calculate the amount of gas produced in a chemical reaction.

13.1 Check

One mole of oxygen in a 5.0 liter container has the same partial pressure as one mol of hydrogen in the same container. This is a demonstration of what law? A. law of conservation of mass B. law of definite proportions C. law of conservation of energy D. Dalton’s law of partial pressures

One mole of oxygen in a 5.0 liter container has the same partial pressure as one mol of hydrogen in the same container. This is a demonstration of what law? A. law of conservation of mass B. law of definite proportions C. law of conservation of energy D. Dalton’s law of partial pressures

14.1 The Simple Gas Laws

VocabularyReview

Gas – State of matterKinetic energy – energy due to motion

NewBoyle’s lawabsolute zeroCharles’s lawGay-Lussac’s law

Main Idea- For a fixed amount of gas, a change in one variable—pressure, temperature, or volume—affects the other two.

Before starting….• Gases behave in different ways & obey “laws”• But when we are discussing gases we assume that we are dealing with an ideal gas. • An _______________________ follows the gas laws at all conditions of temperature & pressure• There are, however, exceptions!

Boyle's Law• Boyle’s law states that the volume of a fixed amount of gas held at a constant temperature varies

inversely with the pressure.

P1V1 = P2V2 where P = pressure and V = volume

So… ____________________________________________________

____________________________________________________

Boyle’s Law ExampleA balloon is filled with 30L of He gas at 100kPa. What is the volume when the balloon rises to an altitude where the pressure is 25kPa?

Boyle’s Law ExampleThe pressure on 2.50L of anesthetic gas is changed from 100kPa to 40kPa. What will be the new volume if the temperature remains constant?

Charles's Law• As temperature increases, so does the volume of gas when the amount of gas and pressure do not

change. • Kinetic-molecular theory explains this property.

• _____________________________ is zero on the Kelvin scale.

• Charles’s law states that the volume of a given amount of gas is ____________________________ to its kelvin temperature at constant pressure.

Charles’ Law ExampleA balloon inflated in a room at 20oC has a volume of 10L. The room is then heated to 40oC. What is the new volume of the balloon if the pressure is unchanged?

• This makes sense – volume should ___________________when temperature increases!

Gay-Lussac's Law• Gay-Lussac’s law states that the pressure of a fixed amount of gas varies directly with the kelvin

temperature when the volume remains constant.

Gay-Lussac’s Law ExampleGas that was left in a hairspray can is at a pressure of 200kPa and a temp of 21oC. Someone throws the can in a hot fire and its temperature rises to 900oC. What is the internal pressure on the can?

14.1 Check

Boyle’s Law explains which relationship of properties in gases?

A. pressure and volume B. amount and pressure C. temperature and volume D. volume and temperature

Atoms are in their lowest energy state at what temperature?

A. 0° Celsius B. 0° Fahrenheit C. –100° Celsius D. 0 kelvin

T

P

14.1 Check (cont.)

What would happen to the volume if the temperature of a gas were doubled? Pressure?V1 = V2

T1 T2

For spring break a family drives from Colorado to Florida. When they arrive in Florida, your car tire bursts. Explain.

Colorado – _______________________________________

Florida – _______________________________________

Tire can’t hold & bursts

You are filling up helium balloons. Under which conditions will you be able to fill the most balloons?a. Low press b. High pressc. High temp d. Low temp

14.2 The Combined Gas Law and Avogadro’s Principle VocabularyReview

mole: an SI base unit used to measure the amount of a substance; the amount of a pure substance that contains 6.02 × 1023 representative particles

Newcombined gas lawAvogadro’s principlemolar volume

Main Idea – Boyle’s, Charles’s, and Gay-Lussac’s laws can be combined into a single equation in which all 3 variables, temp, pressure, and volume, change.

The Combined Gas Law• The combined gas law states the relationship among __________________, __________________,

and _________________of a __________________________of gas.

Avogadro's Principle• Avogadro’s principle states that _________________________ of gases at the same temperature and

pressure contain _______________________________________.

• The molar volume of a gas is the volume __________ occupies at _____________ and ___________________ of pressure.

• 0.00°C and 1.00 atm are called ___________________________________________(STP).• At STP, ___________ of gas occupies _______________.

Example – Combined Gas LawA cylinder of compressed oxygen gas has a volume of 30L & 100 kPa pressure at 27oC. The cylinder is cooled until the pressure is 5.0 kPa. What is the new temp of the gas in the cylinder?

14.2 Check

3.00 mol of O2 at STP occupies how much volume?

A. 30.0 L B. 22.4 L C. 25.4 L D. 67.2 L

14.3 The Ideal Gas LawVocabularyReview

moleNew

ideal gas constant (R)ideal gas law

Main Idea - The ideal gas law relates the number of particles to pressure, temperature, and volume.

• Ideal gas particles occupy a negligible volume and are far enough apart to exert minimal attractive or repulsive forces on each other.

• Combined gas law to ideal gas law

• The ideal gas constant is represented by R and is 0.0821 L•atm/mol•K when pressure is in atmospheres.

• The ideal gas law describes the physical behavior of an ideal gas in terms of pressure, volume,

temperature, and amount. R

The Ideal Gas Law—Molar Mass and Density • Molar mass and the ideal gas law

• Density and the ideal gas law

Example – Ideal Gas LawA steel cylinder with a volume of 20.0L is filled with nitrogen gas to a pressure of 20,000 kPa at 27oC. a) How many moles of N2 gas does the cylinder contain?

b) How many grams of nitrogen gas?

Example – Ideal Gas Law2.24 x 106L CH4 is at a pressure of 1500kPa & a temp of 42oC. What is the mass of the gas?

Real Versus Ideal Gases• Ideal gases follow the assumptions of the kinetic-molecular theory.• Ideal gases experience:

– There are no intermolecular attractive or repulsive forces between particles or with their containers.

– The particles are in constant random motion.– Collisions are perfectly elastic.– No gas is truly ideal, but most behave as ideal gases at a wide range of temperatures and

pressures.• Real gases deviate most from ideal gases at high pressures and low temperatures.• Polar molecules have larger attractive forces between particles.• Polar gases do not behave as ideal gases.• Large nonpolar gas particles occupy more space and deviate more from ideal gases.

14.3 Check

Which of the following is NOT one of the related physical properties described in the ideal gas law? A. pressure B. volume C. density D. temperature

Which of the following is NOT one of the related physical properties described in the ideal gas law? A. pressure B. volume C. density D. temperature

14.4 Gas law stoichiometryVocabularyReview

CoefficientMole ratio

Main Idea - When gases react, the coefficients in the balanced chemical equation represent both molar amounts and relative volumes.

Stoichiometry of Reactions Involving Gases• The gas laws can be applied to calculate the stoichiometry of reactions in which gases are reactants

or products.2H2(g) + O2(g) → 2H2O(g)

2 mol H2 reacts with 1 mol O2 to produce 2 mol water vapor.

Stoichiometry and Volume-Volume Problems• Coefficients in a balanced equation represent volume ratios for gases.

Example Volume-VolumeWhat volume of oxygen gas is needed for the complete combustion of 4.00 L of propane gas (C3H8)? Assume constant pressure and temperature.

Stoichiometry and Volume-Mass Problems• Mass must be found by converting to moles or volumes.

Example Volume-MassAmmonia is synthesized from hydrogen and nitrogen gases.

N2(g) + 3H2(g) → 2NH3(g)

If 5.00 L of nitrogen reacts completely by this reaction at a constant pressure and temperature of 3.00 atm and 298 K, how many grams of ammonia are produced?

14.4 CheckHow many mol of hydrogen gas are required to react with 1.50 mol oxygen gas in the following reaction?

2H2(g) + O2(g) → 2H2O(g) A. 1.00 B. 2.00C. 3.00D. 4.00

How many liters of hydrogen gas are required to react with 3.25 liters of oxygen gas in the following reaction?A. 2.00 B. 3.25C. 4.00D. 6.50