Common Gases

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© 2013 Pearson Education, Inc. Chapter 7, Section 1

General, Organic, and Biological Chemistry

Fourth Edition

Karen Timberlake

7.1Properties of Gases

Chapter 7Gases

© 2013 Pearson Education, Inc.Lectures


Common Gases

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Of the elements on the periodic table, some exist as agas at room temperature, these include

� the Noble Gases, Group 8A (18),

� H2, N2, O2, F2, Cl2, and

� many oxides of nonmetals such as CO, CO2, NO, NO2, SO2, and SO3.


Gases and Environmental

Concerns

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Some gases are responsible for environmental andhealth concerns including

� methane, CH4,and carbon dioxide, CO2 � both greenhouse gases involved in climate change

� chlorofluorocarbons (CFCs) � involved in depleting the ozone layer, which filters out UV light reaching Earth,

� nitrogen oxides found in smog (respiratory irtitants), and

� volatile organic compounds (VOCs), such as compounds found in paint thinners, plastics, industrial solvents, pesticides


Kinetic Theory of Gases

A gas consists of small particles that

� move randomly with high velocities.

� have essentially no attractive (or repulsive) forces toward each other.

� have a very small volume compared to the volume of the containers they occupy.

� are in constant motion.

� have kinetic energies that increase with an increase in temperature.

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Properties of Gases

Gases are described in terms of four properties:

1. pressure (P),

2. volume (V),

3. temperature (T), and

4. amount (n).

5 © 2013 Pearson Education, Inc. Chapter 7, Section 2

Gas pressure

� is the force acting on a specific area.

� has units of atm, mmHg, torr, lb/in.2, and kilopascals(kPa).

1 atm = 760 mmHg (exact)

1 atm = 760 torr (exact)

1 atm = 14.7 lb/in.2

1 atm = 101.325 kPa

Gas Pressure

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Fourth Edition

Karen Timberlake

1. Pressure and Volume Relationship

(Boyle’s Law)

The Original Gas Laws

© 2013 Pearson Education, Inc.


Boyle’s Law –oldest gas law

Boyle’s law states that

� the pressure of a gas is inversely related to its volume when temperature (T) and amount of gas (n) are constant.

� if the pressure (P) increases, then the volume (V) decreases.

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In Boyle’s law,

� the product P × V is constant as long as T and n do not change.

� it can be stated that since P × V is a constant.P1V1 = P2V2 (T, n constant)

PV Constant in Boyle’s Law


Guide to Using Gas Laws

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Solving for a Gas Law Factor

A sample of nitrogen gas (N2) has a volume of 4.2 L at 1.0 atm. If the pressure is decreased to 0.75 atm with no change in the temperature or amount of gas, what will be the new volume?Step 1 Organize the data in a table of initial and

final conditions.Analyze the Problem.

Factors T and n remain constant.

Conditions 1 Conditions 2 Know Predict

V1 = 4.2 L V2 = ? V increases

P1 = 1.0 atm P2 = 0.75 atm P decreases



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A sample of nitrogen gas (N2) has a volume of 4.2 Lat 1.0 atm. If the pressure is decreased to 0.75 atmwith no change in the temperature or amount ofgas, what will be the new volume?Step 2 Rearrange the gas law equation to solve

for the unknown quantity.P1V1 = P2V2 Boyle’s Law

To solve for V2 , divide both sides by P2.

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A sample of nitrogen gas (N2) has a volume of 4.2 Lat 1.0 atm. If the pressure is decreased to 0.75 atmwith no change in the temperature or amount ofgas, what will be the new volume?

Step 3 Substitute values into the gas law equation and calculate.


Boyle’s Law and Breathing:

Inhalation

During inhalation,

� the lungs expand,

� the pressure in the lungs decreases, and

� air flows towards the lower pressure in the lungs.

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Boyle’s Law and Breathing:

Exhalation

During exhalation,

� lung volume decreases,

� pressure within the lungs increases, and

� air flows from the higher pressure in the lungs to the outside.



Fourth Edition

Karen Timberlake

The Gas Laws


2. Temperature and Volume Relationship

(Charles’ Law)


Charles’s Law

Charles’s law states that,

� the Kelvin temperature of a gas is directly related to the volume of the gas,

� P and n are constant, and

� as the temperature of a gas increases, the molecules move faster and its volume increases to maintain constant P.


Charles’s law states that when the temperature of a gas increases, making the molecules move faster, the volume of the gas must increase to maintain constant pressure.

Charles’s Law: V and T

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A sample of neon gas has a volume of 3.1 L and a temperature of 12 ˚C. Find the new volume (L) of the gas if the temperature rises to 32 ˚C. Assume the pressure and amount of gas remain constant.

Step 1 Organize the data in a table of initial andfinal conditions.

Analyze the Problem.



T1 = 12 °C + 273

= 285

T1 = 32 °C+ 273

= 305 KT increases

V1 = 3.1 L V1 = ? V increases



Step 2 Rearrange the gas law equation to solvefor the unknown quantity.


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Step 3 Substitute values into the gas law equationand the table.




Fourth Edition

Karen Timberlake

3. Temperature and Pressure Relationship

(Gay-Lussac’s Law)

The Gas Laws



Gay-Lussac’s Law: P and T

Gay-Lussac’s law states that

� the pressure exerted by a gas is directly related to the Kelvin temperature.

� V and n are constant.

� an increase in temperature increases the pressure of a gas.


Calculation with Gay-Lussac’s

Law

A gas has a pressure at 2.0 atm at 18 ˚C. What is the new pressure when the temperature is increased to 62 ˚C? (V and n constant)

Step 1 Organize the data in a table of initial and final conditions.



P1 = 2.0 atm P2 = ? P increase

T1 = 18 °C + 273

= 291 K

T2 = 62 °C + 273

= 335 KT increase

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Law


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



Law


Step 3 Substitute values into the gas law equation and calculate.

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Fourth Edition

Karen Timberlake

The Combined Gas Law



Combined Gas Law

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The combined gas law uses Boyle’s Law, Charles’sLaw, and Gay-Lussac’s Law (n is constant).


Combined Gas Law

By using the combined gas law, we can derive any of the gas laws by omitting those properties that do not change.


A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm (n constant)?

Step 1 Organize the data in a table of initial and final

conditions.


Using the Combined Gas Law

Conditions 1 Conditions 2

P1 = 0.800 atm P2 = 3.20 atm

V1 = 0.180 L V2 = 90.0 mL= 0.0900 L

T1 = 29 °C + 273 = 302 K T2 = ?

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A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm (n constant)?

Step 2 Rearrange the gas law equation to solve for

the unknown quantity.



A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm

(n constant)?

Step 3 Substitute values to solve for unknown.



A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)?

Learning Check



Step 1 Organize the data in a table of initial and finalconditions.


Solution

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

Solution



Step 3 Substitute values into the gas law equationand calculate.

Solution

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Common Gases

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