Gases

Gases(7) Science concepts. The student

knows the variables that influence the behavior of gases. The student is expected to:

(A) describe interrelationships among

temperature, particle number, pressure, and volume of contained within a closed system; and

(B) illustrate the data obtained from

investigations with gases in a closed system and determine if the data are consistent with the Universal Gas Law.

(4) (C) compare solids, liquids, and gases in terms of compressibility, structure, shape, and volume Supporting

(9) Science concepts. The student

understands the principles of ideal gas behavior, kinetic molecular theory, and the conditions that influence the behavior of gases. The student is expected to:

(A) describe and calculate the

relations between volume, pressure, number of moles, and temperature for an ideal gas as described by Boyle's law, Charles' law, Avogadro's law, Dalton's law of partial pressure, and the ideal gas law Readiness

Gases(7) Science concepts. The student

knows the variables that influence the behavior of gases. The student is expected to:

(A) describe interrelationships

among temperature, particle number, pressure, and volume of contained within a closed system; and

(B) illustrate the data obtained from

investigations with gases in a closed system and determine if the data are consistent with the Universal Gas Law.

(B) perform stoichiometric calculations, including determination of mass and volume relationships between reactants and products for reactions involving gases Supporting

(C) describe the postulates of

kinetic molecular theory. Supporting

Gases - CCRS Properties and behavior of gases, liquids, and

solids

1. Understand the behavior of matter in its various states: solid, liquid, and gas.

a. Describe how gas pressure is affected by volume, temperature, and the addition of gas.

b. Describe the behavior of solids, liquids, and gases under changes in pressure.

Gases - CCRS3. Understand principles of ideal gas behavior and

kinetic molecular theory. a. Use the kinetic molecular theory to explain how

gas pressure is affected by volume, temperature, and the addition of gas.

b. Distinguish between real and ideal gas behavior, and identify the criteria in the kinetic molecular theory that conflict with the properties of real gases.

4. Apply the concept of partial pressures in a mixture

of gases. a. Use Dalton’s Law to determine the partial

pressure of a gas in a mixture of gases.

Prior Knowledge

• Dimensional analysis

• Characteristics of the 3 phases of matter

• Direct and inverse relationships

Engage

Simulate a gas with particles in a box

KMT – thinking about gas particles• If you pour a sample from a small box into a large

box, what changes? What stays constant?

• If you pour a sample from a large box into a small box, what changes? What stays constant?

• What if the boxes are connected and a valve is opened?

• If you heat up the sample, what happens?

• What does adding particles do?

Gas Law ProblemsRather than learning all of the laws separately, use:

nT

PV

nT

PV

Variable Initial Final

P

V

n

T

Prediction: ______________________

What conversions are necessa

ry?

Gas Formulas

(Initial Pressure)(Initial Volume)(Initial Moles)(Initial Temperature)

(Final Pressure)(Final Volume)(Final Moles)(Final Temperature)=

1 1

1 1

P Vn T

= 2 2

2 2

P Vn T

Pressure)(Volume) = (moles)(Ideal Gas Constant)(Temperature)

PV = nRT

Total pressure of a gas = sum of the partial pressures of the component gas

Pt = P1 + P2 + P3 +…

A sample of gas occupies a volume of 1.60 L at a pressure of 720. torr. What would be the pressure of this gas if it were compressed to 1.20 L at the same temperature?

A. 540. torr

B. 960. torr

C. 360. torr

D. 1440 torr

Two flasks are connected by a stopcock as shown below. The 5.0 L flask contains CH4 at a pressure of 3.0 atm, and the 1.0 L flask contains C2H6 at a pressure of 0.55 atm. Calculate the pressure of CH4 after the stopcock is opened. Assume that the temperature remains constant.

Gas Law Problems

nRTPV

Variable Quantity Conversions

P

V

n

T

What conversions are necessa

ry?

nRTPV

What would be the mass of 400. mL of hydrogen collected at 20°C and 740 torr?

Pt = P1 + P2 + P3 +…

A gaseous mixture containing 1.5 moles argon and 3.5 moles of carbon dioxide has a total pressure of 7.0 atm. What is the partial pressure of carbon dioxide?

P atm = P gas + P water vapor

Gas Stoichiometry

At STP, 22.4 L = 1 mole

At other conditions, use PV = nRT to solve for moles

2 K + 2 H2O 2 KOH + H2

Calculate the volume of hydrogen gas produced at standard temperature and pressure when 18.0 grams of potassium is reacted with an excess of water.

If 400. mL of hydrogen was prepared by reacting magnesium with hydrochloric acid 20oC and 740 torr, what mass of magnesium was required?

Each of the following examples gives a change in volume, temperature, amount, or pressure of a gas sample. Indicate whether the other variable mentioned would increase or decrease. If a variable is not mentioned, assume it is constant.

• Additional gas is added to a soccer ball. The pressure -

• An inflated balloon is placed in a refrigerator. The volume -

• A piston in an engine compresses the gas. The volume -

• The volume of an inflated balloon increases when the amount

of gas in the balloon -

• A person sits on an air mattress. The pressure inside of the

mattress -

Focus on conceptual

understanding as well

as the quantitative

problems

• Claudia Wallace wallacec@cfbisd.edu

• Jane Smith smithja@friscoisd.org

• Karen Comptonkaren.compton@pisd.edu