HOMEWORK for Chapter 11: Gases

Key

HOMEWORK for Chapter 11: Gases

11.1 Properties of Gases (Read pgs. 327 - 330 in the chemistry textbook)

11.2 Gas Pressure (Read pgs. 330 - 332 in the chemistry textbook)

1. What is the Kinetic Molecular Theory (KMT) of Gases?

A theory that about the behavior of gas particles:

5 tenets (principles)

I. Small, random movement, high velocity

II. VERY small IMFs (often considered nonexistent)

III. Average EK is proportional to Kelvin temperature

IV. Volume occupied by the individual gas particles is VERY small (considered negligible)

V. Constant motion, straight-line paths

2. What are the 4 gas properties and their units?

PROPERTIES UNITS

I. Pressure (P) atmospheres (atm)

Torricelli (torr)

millimeters of mercury (mmHg)

Pascals (Pa)

kilopascals (kPa)

II. Volume (V) Liters (L), milliliters (mL)

III. Temperature (T) Kelvin (K)

IV. Amount in moles(n) moles (n)

3. Explain each of the 4 gas properties.

PROPERTIES Explanation

Gas Pressure the force of the collisions of gas

molecules with the walls of the

container

Atmospheric pressure the force of the collisions of the

gas molecules making up the

atmosphere with whatever they

touch

more collisions = more pressure

less collisions = less pressure

Volume the space occupied by the gas –

if the gas is in a container the

volume of the gas is equal to the

volume of the container

Temperature determines the average EK and

therefore the number of

collisions of the particles

Amount the quantity of gas present in

the container

4. Use the KMT to explain why a gas completely fills a container of any size and shape.

Gas particles are constantly moving at high speeds in random, but

straight-line directions. They would travel indefinitely if nothing

stopped them. Eventually they encounter the walls of the container

– at which point the volume being occupied by all the gas particles

is equal to the volume of the container

5. Identify the property of a gas that is described by each of the following:

Temperature a) increases the EK of gas particles

Pressure b) the force of the gas particles hitting the walls of the container

Volume c) the space that is occupied by a gas

6. Use the KMT to explain each of the following:

(a) Gases move faster at higher temperatures.

the average EK of a gas is proportional to the Kelvin temperature – as T↑ so does the average EK of the gas particles

(b) Gases can be compressed more easily than liquids or solids.

individual gas particles are considered to occupy NO space, and to be very far apart

the IMFs between individual gas particles is considered negligible – so the particles are free to move away from one another – less mass per unit of space = lower density

(d) A container of nonstick cooking spray explodes when thrown into a fire.

at higher temperatures the gas particles collide more often with the walls of the container – eventually the number of collisions creates a pressure greater than can be borne by the walls of the container – so it “explodes”

6. Continued:

(e) The air in a hot-air balloon is heated to make the balloon rise.

the higher temperature inside the balloon makes the gas particles move away from each other so that the gas inside the balloon is less dense than the gas of the surrounding atmosphere

(f) You can smell the odor of cooking onions from far away.

gas molecules move at very high velocities in random, straight-line directions – eventually they will fill the entire house (or even the entire outside area surrounding a bakery)

7. Identify the property of a gas that is measured in each of the following.

Temperature a) 350 K

Volume b) the space occupied by a gas

Amount c) 2.00 mole of O2

Pressure d) the force of gas particles colliding with the walls of the container

Temperature a) 425 K

Pressure b) 1.0 atm

Volume c) 10.0 L

Amount d) 0.50 mol of He

8. What is the definition of pressure?

the force acting on a certain area

Pressure (P) = ForceArea

9. What is a barometer?

a device used for measuring atmospheric pressure

10. How does a barometer work?

The pressure of the earth’s atmosphere pushing down on the surface of the mercury in the open dish will “push” the mercury a certain height up the

evacuated tube. The greater the

pressure of the atmosphere the

higher up the tube the mercury

will be pushed – and vice versa.

The units used to measure the

height of the column can vary

with the type of liquid in the

barometer and the measurement

system being used.

At STP the earth’s atmosphere will push a column of mercury up 760 millimeters – o r – 760 mmHg

11. What is STP?

Standard Temperature and Pressure at sea level

· Standard Temperature = 0oC, or 273 Kelvin

· Standard Pressure = 1 atm

this means that at sea level, when the temperature is 0oC the pressure of the earth’s atmosphere is defined as 1 atmosphere

12. Why isn’t standard pressure 760 mmHg?

IT IS!!!!

Standard pressure is measured in many different units, but it is customary (and simpler) to use “atmospheres” because it equals 1

13. What are some other “units” of standard pressure?

Units Abbreviation

1 atmosphere 1 atm

760 millimeters of mercury 760 mmHg

29.9 inches of mercury 29.9 in. Hg

760 torricelli 760 torr

101,325 Pascal 101,325 Pa*

101.325 kilopascal 101.325 kPa

14.70 pounds per square inch 14.70 lb/ in2

* The official SI unit of pressure

14. Is atmospheric pressure the same at all location on Earth? Explain.

The pressure is greatest at the lowest spots on Earth and least at the highest spots.

Example:

top of Mt. Everest ≈ 20,500 ft above sea level ≈ 33 kPa

bottom of Death Valley = 282 ft below sea level ≈ 105 kPa

15. Why does the height of a column of mercury in a barometer change from day to day?

b/c the atmospheric pressure changes day to day

on days with higher atmospheric pressure the column is higher, and vice-versa

16. Water is cheaper and safer to use than mercury, and, it will rise and fall with daily changes in atmospheric

pressure. Why aren't barometers commonly made out of water? HINT: Mercury is approximately 13.5

times more dense than water.

29.9 inches × 13.5 = 403.65 inches ÷ 1 ft12 inches = 33.6 ft

a water barometer would have to be over 30 foot tall!!

17. An oxygen tank contains oxygen (O2) at a presure of 2.00 atm. What is the pressure in the tank in terms of

the following units?

(a) torr

2.00 atm ( 760 torr1 atm ) = 1520 torr

(b) kPa

2.00 atm ( 101.325 kPa1 atm ) = 203 kPa

2.00 atm ( 760 mmHg1 atm ) = 1520 mmHg

(d) lb/in2

2.00 atm ( 14.70lbin21 atm ) = 29.4 lbin2

17. On a climb up Mt. Whtney, the atmospheric pressure drops to 467 mmHg. What is the pressure in terms of

the following units?

(a) atm

467 mmHg ( 1 atm760 mmHg ) = 0.614 atm

(b) torr

467 mmHg ( 760 torr760 mmHg ) = 467 torr

467 mmHg ( 101,325 Pa760 mmHg ) = 62, 300 Pa

(d) in. Hg

467 mmHg ( 29.9 in.Hg760 mmHg ) = 18.4 lbin2