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Chapter 13 Gases

- 13.1 Pressure
- Objectives
- To learn about atmospheric pressure and the way

in which barometers work - To learn the various units of pressure.

13.1 Pressure

- Automobile tires, basketballs, balloons, and soda

bottles. - What happens to a balloon when you place it in a

freezer? - Why?

13.1 Pressure

- Evangelista Torricelli invented the
- BAROMETER device to measure pressure
- At sea level the height of the column of mercury

is 760 mm.

Pressure exerted by the atmospheric gases on the

surface of the mercury in the dish keeps the

mercury in the tube.

13.1 Pressure

- Weather
- -low pressure STORMS
- -high pressure nice weather

13.1 Pressure

- Units of Pressure
- -mm Hg torr
- Standard atmosphere (atm)
- 1 std. atm.1,000 atm760.0mm Hg760.0 torr

1 std. atm101, 325 Pascal 1.000 std. atm14.69

psi

Measuring pressure

Atmospheric pressure-h

Manometer

Atmospheric pressure h

13.1 Pressure

- The height of mercury in a mercury barometer is

measured to be 732 mm. Represent this pressure

in atm, torr, and pascals. - The pressure of a gas is measured to be 2.79 x

105 Pa. Represent this pressure in atm, torr,

and psi.

0.963 atm 732 torr 9.76 x 104 Pa

2.75 atm 2.10 x 103 torr 40.4 psi

Homework, Self-Check exercise 13.1

13.2 Pressure and Volume Boyles Law

- Objectives
- To understand the law that relates the pressure

and volume of a gas. - To do calculations involving this law.

Robert Boyle Irish scientist -studied the

relationship between the pressure of the trapped

gas and its volume

P x Vconst. PVk Boyles Law Inversely proport

ional

Figure 13.6 Illustration of Boyles law.

P1V1P2V2

13.2 Pressure and Volume Boyles Law

- A sample of neon gas has a pressure of
- 7.43 atm in a container with a volume of

45.1 L. This sample is transferred to a container

with a volume of 18.4 L. What is the new

pressure of the neon gas? - Assume constant temperature.

18.2 atm

13.2 Pressure and Volume Boyles Law

- A steel tank of oxygen gas has a volume of 2.00L.

If all of the oxygen is transferred to a new

tank with a volume of 5.50 L, the pressure is

measured to be 6.75 atm. What was the original

pressure of the oxygen gas? - Assume constant temperature.

18.6 atm

Homework 7-10 p. 435

13.3 Volume and Temperature Charless Law

- Objectives
- To learn about absolute zero.
- To learn about the law relating the volume and

temperature of a sample of gas at constant moles

and pressure, and to do calculations involving

that law.

13.3 Volume and Temperature Charless Law

- Objectives
- To learn about absolute zero.
- To learn about the law relating the volume and

temperature of a sample of gas at constant moles

and pressure, and to do calculations involving

that law.

Jacques Charles (first solo H balloon flight) -sho

wed that the volume of a gas (at constant

pressure) increases with the temperature.

Absolute zero point where you get 0 volume -273oC

13.3 Volume and Temperature Charless Law

- Charless Law
- V/T constant
- V1 V2
- T1 T2

13.3 Volume and Temperature Charless Law

- A 2.45 L sample of nitrogen gas is collected at

273 K and heated to 325K. Calculate the volume of

the nitrogen gas at 325 K. - Assume constant pressure.

2.92 L

13.3 Volume and Temperature Charless Law

- A sample of methane gas is collected at 285 K and

cooled to 245K. At 245 K the volume of the gas

is 75.0 L. Calculate the volume of the methane

gas at 285K. - Assume constant pressure.

87.2 L

13.3 Volume and Temperature Charless Law

- Consider a gas with a volume of 5.65 L at 27 C

and 1 atm pressure. At what temperature will

this gas have a volume of 6.69 L and 1 atm

pressure.

82oC (355K)

13.3 Volume and Temperature Charless Law

- Consider a gas with a volume of 9.25L at 47oC and

1 atm pressure. At what temperature does this

gas have a volume of 3.50 L and 1 atm pressure.

-152oC (121K)

13.4 Volume and Moles Avogadros Law

- Objective
- 1) To understand the law relating the volume and

the number of moles of a sample of gas at

constant temperature and pressure, and to do

calculations involving this law.

Avogadros Law

V1 V2 n1 n2

13.4 Volume and Moles Avogadros Law

- If 2.55 mol of helium gas occupies a volume
- of 59.5 L at a particular temperature and
- pressure, what volume does 7.83 mol of helium

occupy under the same conditions?

183 L

13.4 Volume and Moles Avogadros Law

- If 4.35 g of neon gas occupies a volume of
- 15.0 L at a particular temperature and pressure,

what volume does 2.00 g of neon gas occupy under

the same conditions?

6.90 L

13.5 The Ideal Gas Law

- Ideal Gas Law
- PVnRT
- RUniversal gas constant (proportionality

constant) - R 0.08206 L atm/ oK
- Based on experimental measurements.
- Most gases obey this equation at 1 atm or lower

and 0oC or higher

13.5 The Ideal Gas Law

- Ideal Gas Law
- When the number of moles and type of gas are a

constant.

P1V1 P2V2 T1 T2

13.5 The Ideal Gas Law

- A sample of neon gas has a volume of 3.45 L at

25oC and a pressure of 565 torr. Calculate the

number of moles of neon present in the gas sample.

0.105 mol

13.5 The Ideal Gas Law

- A 0.250 mol sample of argon gas has a volume of

9.00 L at a pressure of 875 mm Hg. What is the

temperature (in oC) of the gas?

232oC

13.5 The Ideal Gas Law

- Consider a sample of helium gas at 23oC with a

volume of 5.60 L at a pressure of 2.45 atm. The

pressure is changed to 8.75 atm and the gas is

cooled to 15oC. Calculate the new volume of the

gas using the ideal gas law equation.

1.53 L

13.5 The Ideal Gas Law

- Consider a sample of helium gas at 28oC with a

volume of 3.80 L at a pressure of 3.15 atm. The

gas expands to a volume of 9.50 L and the gas is

heated to 43oC. Calculate the new pressure of

the gas using the ideal gas law equation.

1.32 atm

13.6 Daltons Law of Partial Pressures

- Objectives To understand the relationship

between the partial and total pressures of a gas

mixture, and to use this relationship in

calculations. - Scuba divers use helium and oxygen instead of

air. Air contains nitrogen that dissolves in the

blood as a result of high pressure. Nitrogen

bubbles out and the diver gets the bends.

13.6 Daltons Law of Partial Pressures

- John Dalton For a mixture of gases in a

container, the total pressure exerted is the sum

of the partial pressures of the gases present. - Partial pressure pressure that the gas would

exert if it were alone in the container. - Daltons law of partial pressures
- PtotalP1 P2 P3

Ptotalntotal (RT/V)

The pressure doesnt depend on the forces

amongst the particles. The volume of the

individual gas particles is not important.

Figure 13.12 The production of oxygen by

thermal decomposition.

13.6 Daltons Law of Partial Pressures

- A sample of solid potassium chlorate KClO3, was

heated in a test tube and decomposed according to

the reaction - 2KClO3(s) 2KCl(s) 3O2
- The oxygen produced was collected by displacement

of water at 22oC. The resulting mixture of O2

and H2O vapor had a total pressure of 754 torr

and a volume of 0.650L. Calculate the partial

pressure of O2 in the gas collected and the

number of moles of O2 present. The vapor

pressure of water at 22oC is 21 torr.

13.6 Daltons Law of Partial Pressures

- PtotalPO2 PH2O
- 754PO2 21
- PO2 733 torr
- nO2 PO2V 733/7600.964 atm
- RT
- nO2 (0.964 atm)(0.650L)
- (0.08206) (295)

13.6 Daltons Law of Partial Pressures

- A 5.00 g sample of helium gas is added to a 5.00

g sample of neon in a 2.50 L container at 27oC.

Calculate the partial pressure of each gas and

the total pressure.

12.3 atm He 2.44 atm Ne 14.7 atm total

13.6 Daltons Law of Partial Pressures

- A sample of oxygen gas is saturated with water

vapor at 30.0oC. The total pressure is 753 torr

and the vapor pressure of water at 30.0 C is

31.824 torr. What is the partial pressure of the

oxygen gas in atm?

0.949 atm

Homework 23-30 and 33-36

13.6 Daltons Law of Partial Pressures

- A sample of oxygen gas is saturated with water

vapor at 27oC. The total pressure is 785 torr

and the partial pressure of oxygen is 758.3 torr.

What is the vapor pressure of water at 27oC?

26.7 torr

13.8 The Kinetic Molecular Theory of Gases

- Objectives To understand the basic postulates of

the kinetic molecular theory

Postulates of KMT.

13.9 The Implications of the Kinetic Molecular

Theory

- Objectives To understand the term temperature.
- To learn how the kinetic molecular theory

explains the gas laws.

13.9 The Implications of the Kinetic Molecular

Theory

- The temperature of a gas how rapidly, its

individual particles are moving. - High temperatures move very fast.
- Low temperatures move slower.

As the gas is heated to a higher temperature, the

particles move faster, hitting the walls more

often. Pressure increases with increasing

temperature

13.10 Real Gases

- Objectives To describe the properties of real

gases.

As real gases are compressed into smaller and

smaller volumes, the particles of the gas begin

to occupy a significant fraction of the available

volume..

Start to attract to each other here PVnRT not

true

13.11Gas Stoichiometry

- Objectives
- To understand the molar volume of an ideal gas.
- To learn the definition of STP
- To use these concepts and the ideal gas equation.

13.11Gas Stoichiometry

- For 1 mol of an ideal gas at 0oC (273K) and 1

atm, the volume will be. - VnRT/P (1.00mol)(0.08206)(273) 22.4L
- 1 atm.
- 22.4 L is called the molar volume
- Standard temperature and pressure (abbreviated

STP). Contains 1 mol of an ideal gas at STP.

13.11Gas Stoichiometry

- A sample of argon gas has a volume of 3.45 L at

STP. What is the mass of the argon?

6.15 g

13.11Gas Stoichiometry

- A sample of hydrogen gas occupies a volume of

15.0L at STP. What volume will this sample

occupy at 22oC and 2.50 atm?

6.48 L

13.11Gas Stoichiometry

- When magnesium reacts with hydrochloric acid,

hydrogen gas is produced - Mg(s) 2HCl MgCl2(aq) H2(g)
- Calculate the volume of hydrogen gas produced at

STP by reacting 5.00 g Mg and an excess of HCl

(aq)

4.61 L

13.11Gas Stoichiometry

- When subjected to an electric current, water

decomposes to hydrogen and oxygen gas 2H2O(l)

2H2(g) O2(g) - If 25.0g of water is decomposed, what volume of

oxygen gas is produced at STP?

15.5 L