The Other Gas Law n - PBworkschemistry121.pbworks.com/w/file/fetch/66414805/Chapter 7 Gases 2.pdf · Step 1 State the given and needed quantities. ... Karen Timberlake Chapter 7

1

© 2013 Pearson Education, Inc. Chapter 7, Section 7

General, Organic, and Biological Chemistry

Fourth Edition

Karen Timberlake

Volume and Moles Relationship

(Avogadro’s Law)

The Other Gas Law

© 2013 Pearson Education, Inc.


Avogadro’s Law: Volume and

Moles

Avogadro’s law states that

� the volume of a gas is directly related to the number of moles (n) of gas.

� T and P are constant.

2


Learning Check

If 0.75 mole of helium gas occupies a volume of 1.5 L, what volume will 1.2 moles of helium occupy at the same temperature and pressure?

A. 0.94 L

B. 1.8 L

C. 2.4 L

3 © 2013 Pearson Education, Inc. Chapter 7, Section 7

Solution

If 0.75 mole of helium gas occupies a volume of 1.5 L, what volume will 1.2 moles of helium occupy at the same temperature and pressure?Step 1 Organize the data in a table of initial and final

conditions.

Analyze the Problem.

Conditions 1 Conditions 2 Know Predict

V1 = 1.5 L V2 = ? V increases

n1 = 0.75 mole n2 = 1.2 moles n increases

4


Solution

If 0.75 mole of helium gas occupies a volume of 1.5 L, what volume will 1.2 moles of helium occupy at the same temperature and pressure?

Step 2 Rearrange the gas law equation to solve forthe unknown quantity.

Step 3 Substitute values into the gas law equation

and calculate.

Answer is C.


To make comparisons between different gases, we use arbitrary conditions called standard temperature (273 K) and standard pressure (1 atm). Standard temperature and pressure is abbreviated as STP.

Standard temperature (T) = 0 °C or 273 K

Standard pressure (P) = 1 atm (760 mmHg)

STP

6

2


Molar Volume

The molar volume of a gas measured at STP (standard temperature and pressure) is 22.4 L for 1 mole of any gas.

Avogadro’s law indicates that 1 mole of any gas at STP has a volume of 22.4 L.


Molar Volume as a Conversion

Factor

The molar volume at STP

� has about the same volume as 3 basketballs.

� can be used to form 2 conversion factors.

8

and


Guide to Using Molar Volume


Using Molar Volume

What is the volume occupied by 2.75 moles of N2 gas at STP?

Step 1 State the given and needed quantities.


Step 2 Write a plan to calculate the neededquantity.

moles N2 liters N2

Given Need

2.75 moles of N2 at STP Liters of N2

molar volume

10


What is the volume occupied by 2.75 moles of N2 gas at STP?

Step 3 Write the equalities and conversion factorsincluding 22.4 L/mole at STP.

Step 4 Set up the problem with factors to cancelunits.

Using Molar Volume


Gases in Chemical Reactions

The volume or amount of a gas at STP in a chemicalreaction can be calculated from

� STP conditions.

� mole−mole factors from the balanced equation.

12

3


Guide to Reactions Involving Gases


Gases in Equations at STP

What volume (L) of O2 gas is needed to completelyreact with 15.0 g of aluminum at STP?

Step 1 State the given and needed quantities.Analyze the Problem.

14




Step 2 Write a plan to calculate the needed quantity.

grams molar moles mole−mole moles molar litersof Al mass of Al factor of O2 volume of O2

molar mass

mole-molefactor

molarvolume



Step 3 Write the equalities and conversion factorsincluding the molar volume.


16




Step 4 Set up the problem and calculate



Fourth Edition

Karen Timberlake

Chapter 7The Ideal Gas Law


4


The four properties used in the measurement of a gas,

� pressure (P),

� volume (V),

� temperature (T), and

� amount (n),

can be combined to give a single expression called theideal gas law. PV = nRT

Ideal Gas Law


Rearranging the ideal gas law equation shows that thefour gas properties equal a constant, R.

To calculate the value of R, we substitute the STPconditions for molar volume into the expression:

R, Ideal Gas Constant

20


Another value for the universal gas constant, R, is obtained using mmHg for the STP pressure. What is the value of R when a pressure of 760 mmHg rather than 1.00 atm is used?

Learning Check


Another value for the universal gas constant, R, isobtained using mmHg for the STP pressure. Whatis the value of R when a pressure of 760 mmHgrather than 1.00 atm is used?

Solution

22


Unit Summary for R, the Ideal

Gas Constant


Guide to Using the Ideal Gas Law

24

5


Dinitrogen oxide (N2O), laughing gas, is used by dentists as an anesthetic. If a 20.0 L tank of laughing gas contains 2.86 moles of N2O at 23 °C, what is the pressure (mmHg) in the tank?

Learning Check


If a 20.0 L tank of laughing gas contains 2.86 moles ofN2O at 23 ˚C, what is the pressure (mmHg) in the tank?

Step 1 State the given and needed quantities.


Solution

26



Step 2 Rearrange the ideal gas law equation to solvefor the needed quantity.

Solution



Step 3 Substitute the gas data into the equation andcalculate the needed quantity.

Solution

28


Ideal Gas Law and Molar Mass


Learning Check

A cylinder contains 5.0 L of an unknown gas at 20.0 ˚C and 0.85 atm. If the mass of the gas in the cylinder is 5.8 g, what is the molar mass of the gas?

30

6


A cylinder contains 5.0 L of an unknown gas at 20.0 ˚Cand 0.85 atm. If the mass of the gas in the cylinder is5.8 g, what is the molar mass of the gas?

Step 1 State the given and needed quantities.Analyze the Problem

Solution


A cylinder contains 5.0 L of an unknown gas at 20.0 ˚Cand 0.85 atm. If the mass of the gas in the cylinder is5.8 g, what is the molar mass of the gas?Step 2 Rearrange the ideal gas law equation to solve

for the number of moles.

Step 3 Obtain the molar mass by dividing the givennumber of grams by the number of moles.

Solution

32


Chemical Reactions and the Ideal

Gas Law


Learning Check

Nitrogen gas reacts with hydrogen gas to produce ammonia (NH3) gas. How many liters of NH3 can be produced at 0.93 atm and 24 ˚C from a 16.0-g sample of nitrogen gas and an excess of hydrogen gas?

34


Solution

How many liters of NH3 can be produced at 0.93 atm and24 ˚C from a 16.0-g sample of nitrogen gas and anexcess of hydrogen gas?

Step 1 State the given and needed quantities.Analyze the Problem.


Solution


Step 2 Write a plan to convert the given quantity tothe needed moles.

grams molar moles mole−mole molesof N2 mass of N2 factor of NH3

36

7



Step 3 Write the equalities for molar mass and mole–mole factors.

Solution


Solution


Step 4 Set up the problem to calculate moles ofneeded quantity.

38


Solution


Step 5 Convert the moles of needed to volume using the ideal gas law equation.



Fourth Edition

Karen Timberlake

Dalton’s Law of Partial

Pressures



In a gas mixture, each gas exerts its partial pressure, which is the pressure it would exert if it were the only gas in the container.

Dalton’s law states that the total pressure of a gas mixture is the sum of the partial pressures of the gases in the mixture.

Partial Pressure, Dalton’s Law


Dalton’s Law of Partial Pressures indicates that pressure depends on the total number of gas particles.

Dalton’s Law of Partial Pressures

42

8


For example, at STP, one mole of a pure gas willexert the same pressure as one mole of a gasmixture in a 22.4 L container.

V = 22.4 L

Gas mixtures

Total Pressure

0.5 mole O2

0.3 mole He

0.2 mole Ar

1.0 mole

1.0 mole N2

0.4 mole O2

0.6 mole He

1.0 mole

1.0 atm 1.0 atm 1.0 atm


Composition of Air

Air is a mixture of gases, including nitrogen, oxygen, carbon dioxide, argon, and water gases.

44


Guide to Solving for Partial

Pressure


Learning Check

A scuba tank contains a mixture of He and O2 gases at 7.00 atm. If the pressure of O2 gas is 1140 mmHg, what is the partial pressure of He gas in the tank?

46


A scuba tank contains a mixture of He and O2 gases at7.00 atm. If the pressure of O2 gas is 1140 mmHg, whatis the partial pressure of He gas in the tank?

Step 1 Write the equation for partial pressures.

Step 2 Rearrange the equation to solve for theunknown pressure.

Solution


A scuba tank contains a mixture of He and O2 gases at7.00 atm. If the pressure of O2 gas is 1140 mmHg, whatis the partial pressure of He gas in the tank?

Step 3 Substitute known pressures into theequation and calculate the unknown partialpressure.

Solution

48

9


Blood Gases

� In the lungs, O2 enters the blood, at the same time that CO2 is released.

� In the tissues, O2 enters the cells, which release CO2

into the blood.


Blood Gases

In the body,

� O2 flows into the tissues because the partial pressure of O2 is higher in blood and lower in the tissues.

� CO2 flows out of the tissues because the partial pressure of CO2 is higher in the tissues and lower in the blood.

Partial Pressures (mmHg) in Blood and Tissue

Gas Oxygenated Deoxygenated Tissues

Blood Blood

O2 100 mmHg 40 mmHg 30 mmHg or less

CO2 40 mmHg 46 mmHg 50 mmHg or greater

50


Changes in Partial Pressures of

Blood Gases During Breathing

51

Documents

The Other Gas Law n - PBworkschemistry121.pbworks.com/w/file/fetch/66414805/Chapter 7 Gases 2.pdf · Step 1 State the given and needed quantities. ... Karen Timberlake Chapter 7