CHAPTER SIX- GASES

Question 1

The most important gas in the atmosphere (to us) is _______, which constitutes about ______% of the atmosphere.

Answer 1

Oxygen; 21%

Question 2

Of the elements on the periodic table, only a handful of exist as gases at room temperature. What are they?

Answer 2

H2, N2, O2, F2, Cl2 and the noble gases.

Question 3

Another group of gases includes the oxides of the nonmetals on the upper right coercer of the periodic table, such as _________

Answer 3

CO, CO2, NO, NO2, SO2 and SO3.

Question 4

Generally molecules that are gases at room temperature have fewer than ____ atoms from the first or second period.

Answer 4

5

Question 5

What are the characteristics of gases?

• Gas particles are (close or far apart?).
• A gas has no definite ______ or ______ and will _________ fill any container.
• The attractive forces between gas particles are _________

Answer 5

Gas particles are far apart.

A gas has no definite shape or volume and will completely fill any container.

The attractive forces between gas particles are minimal

Question 6

What is the KINETIC MOLECULAR THEORY OF GASES?

Answer 6

It is a model for the behavior of a gas; helps us understand gas behavior.

Question 7

The KINETIC MOLECULAR THEORY OF GASES:

1. A gas consists of small particles (______ or ________) that move ________ with ______ velocities.

This causes a gas to fill the _______ ______ of a container.

Answer 7

atoms or molecules that move randomly with high velocities.

entire volume

Question 8

The KINETIC MOLECULAR THEORY OF GASES:

2. The attractive forces between the particles of a gas are usually very _________.

Gas particles are _______ ______ and fill a container of _________ size or shape.

Answer 8

small

far apart; fill a container of any size or shape

Question 9

The KINETIC MOLECULAR THEORY OF GASES:

3. The actual volume occupied by gas molecules is considered _______ ________ compared with the volume that the gas occupies.

The volume of the gas is considered ______ the volume of the container.

Most of the volume of a gas is _____ ______, which allows gases to be easily ________.

Answer 9

extremely small

equal to

empty space, compressed

Question 10

The KINETIC MOLECULAR THEORY OF GASES:

4. Gas particles are in constant motion, moving _______ in ________ paths.

When gas particles collide, they ______ and travel in _______ __________. Every time they hit the walls of the container, they ____ ____.

An increase in the number of collisions against the walls of the container causes an increase in the ___________.

Answer 10

rapidly, straight

rebound, new directions, exert pressure

pressure of the gas

Question 11

The KINETIC MOLECULAR THEORY OF GASES:

The average kinetic energy of gas molecules is proportional to the _____ temperature.

Gas particles move ______ as the temperature increases. At higher temperatures, gas particles hit the walls of the container _______ often, with _______ force, producing _______ pressures.

Answer 11

Kelvin

faster

more, more, higher

Question 12

When we talk about a gas, we describe it in terms of 4 properties, which are….

Answer 12

pressure, volume, temperature and the amount of gas

See the chart on page 217 for a summary of the four properties of a gas (Table 6.1)

Question 13

What is atmospheric pressure?

Answer 13

The gas particles in the air, mostly oxygen and nitrogen, exert a pressure on us called ATMOSPHERIC PRESSURE.

As you go to higher altitudes, the atmospheric pressure is less because there are fewer particles in the air.

Question 14

PRESSURE (P):

The most common units used for gas pressure measurement in the US are _______ and ________.

…or __________ in other countries.

Answer 14

• the atmosphere (atm)
• millimeters of mercury (mmHg)

… kilopascals

Question 15

VOLUME (V):

The volume of gas equals ___________

When you inflate a tire or a basketball, you are ____________. The _______ in the number of particles hitting the walls of the object _______ its volume.

The most common units for volume measurements are _____ and ______

Answer 15

the size of the container in which the gas is placed.

…adding more gas particles; increase, increases

liters (L) and milliliters (mL)

Question 16

TEMPERATURE (T):

The temperature of a gas is related to the _____ ______ of its particles.

Although you measure gas temperature using a ________ thermometer, all comparisons of gas behavior and all calculations related to temperature must use the ______ temperature scale.

Answer 16

kinetic energy

Ex: if we have a gas at 200 K in a rigid container and heat it to a temperature of
400 K, the gas particles will have twice the kinetic energy that they did at 200 K.This also means that the gas at 400 K exerts twice the pressure of the gas at 200 K.

Celsius; Kelvin

Question 17

AMOUNT OF GAS (n):

Usually we measure the amount of gas by its mass in ___________. In gas law calculations, we need to change the ____ of gas to ________.

Answer 17

grams

grams; moles

Question 18

When billions and billions of gas particles hit against the walls of a container, they exert __________, which is defined as _______________ (also give the formula)

Answer 18

pressure

a force acting on a certain area

Pressure (P)= force/area

Question 19

The atmospheric pressure can be measured using a ____________.

One ATMOSPHERE (atm) is defined as EXACTLY __________ mmHg

One atmosphere is also ______ torr, a pressure until named to honor the inventor of the barometer.

Answer 19

barometer

760 millimeters of mercury

760 torr. Because they are equal, until of torr and mmHg are used interchangeably.

1 atm= 760 mmHg = 760 torr (exact)
1 mmHg = 1 torr (exact)

Question 20

In SI units, pressure is measured in _______.

1 atm is equal to ____________ of these.

Answer 20

pascals (Pa)

1 atm= 101.325 Pa

Because pascal is a very small unit, it is likely that pressures would be reported in kilopascals.

1 atm= 1.01325 x 10^5 Pa = 101.325 kPa

Question 21

The US equivalent of 1 atm is ___________.

Answer 21

14.7 lb/in.^2 (psi)

1 atm= 14.7 lb/in.^2

Question 22

Atmospheric pressure changes with variations in ________ and ________.

Answer 22

weather and altitude

hot day- a column of air has more molecules, which increase the pressure on the mercury surface. The mercury column rises, indicating a higher atmospheric pressure.

rainy day- atmosphere exerts less pressure, which causes the mercury column to fall. (Low pressure system)

above sea level- the density of the gases in the air decreases, which causes lower atmospheric pressures.

below sea level- at the Dead Sea, the atmospheric pressure is greater than 760 mmHg. Divers must be concerned about increasing pressures on their ears and lungs.

Question 23

BOYLE’S LAW- Pressure and Volume

Answer 23

When a change in one property causes a change in another property, the properties are related. If the changes occur in opposite directions, the properties have an INVERSE RELATIONSHIP.

The inverse relationship between PRESSURE and VOLUME of a gas is known as BOYLE’S LAW.

The law states that the volume (V) of a sample of gas changes inversely with the pressure (P) of the gas as long as there is no change in the temperature (T) or amount of gas (n).

P1V1= P2V2

Question 24

In BOYLE’S LAW, if the volume or pressure of a gas sample changes without any change in the temperature or in the amount of the gas, the new pressure and volume will give ______.

Answer 24

…the same PV product as the initial pressure and volume. Then we can set the initial and final PV products equal to each other.

Question 25

CHARLES’S LAW: Volume and Temperature

Answer 25

The volume (V) of a gas is directly related to the temperature (T) when there is no change in the pressure (P) or amount (n) of gas.

A direct relationship is one in which the related properties increase or decrease together.

For 2 conditions, we can write Charles’s law as follows:

V1/T1 = V2/T2

Question 26

All temperatures used in gas law calculations must be converted to their corresponding ______ temperatures.

Answer 26

Kelvin (K)

Question 27

To determine the effect of changing temperature on the volume of a gas, the pressure and the amount of gas are kept constant. If we increase the temperature of a gas sample, we know from the kinetic molecular theory that the motion (kinetic energy) of the gas particles will ________.

To keep the pressure constant, the volume of the container must _______.

If the temperature of the gas decreases, the volume of the container must _______ to maintain the same pressure when the amount of gas is constant.

Answer 27

increase

increase

decrease

Question 28

GAY-LUSSAC’s LAW:

Temperature and Pressure

Answer 28

The pressure of a gas is directly related to its Kelvin temperature.

An increase in temperature increases the pressure of a gas and a decrease in temperature decreases the pressure of the gas, as long as the volume and amount of gas do not change.

P1/T1 = P2/T2

Question 29

What is VAPOR PRESSURE?

Each liquid exerts its own vapor pressure at a given ______________.

Answer 29

Liquid molecules with sufficient kinetic energy can break away from the surface of the liquid as they become gas particles or vapor.

In an open container, all the liquid will eventually evaporate.

in a closed container, the vapor accumulates and creates pressure called VAPOR PRESSURE.

Each liquid exerts its own vapor pressure at a GIVEN TEMPERATURE.

Question 30

A liquid reaches its boiling point when its vapor pressure _________________.

Answer 30

…becomes equal to the external pressure.

As boiling occurs, bubbles of the gas form within the liquid and quickly rise to the surface.

EX: at an atmospheric pressure of 760 mmHg, water will boil at 110 degreesC, the temperature at which its vapor pressure reaches 760 mmHg

Question 31

At higher altitudes, atmospheric pressures are _______ and the boiling point of water is _____ than 100 degrees C.

Answer 31

lower, lower

The boiling point differs, depending on the atmospheric pressure of a particular location.

A boiling temperature below 100 degrees C means that it takes longer to cook food. Some people will use a pressure cooker to obtain high temperatures (water is heated in a closed container so that pressures above 1 atm are obtained, which raises the boiling temperature of water above 100 degrees C).

Hospitals use an autoclave to sterilize lab and surgical equipment.

Question 32

What is the COMBINED GAS LAW?

Answer 32

All of the pressure-solums-temperature relationships for gases that we have studied may be combined into a single relationship called the COMBINED GAS LAW.

This is useful for studying the effect of changes in TWO of these variables on the third as long as the amount of gas (number of moles) remains constant.

P1V1/T1 = P2V2/T2

Question 33

What is AVOGADRO’S LAW?

Answer 33

The volume of a gas is directly related to the number of moles of a gas when temperature and pressure do not change.

Ex: if the number of moles of a gas is doubled, then the volume will also double as long as we do not change the pressure or the temperature.

V1/n1 = V2/n2

Question 34

Using Avogadro’s law, we can say that any two gases will have _______ volumes if they contain the same number of moles of gas at the same __________ and ________.

Answer 34

equal, temperature and pressure

Question 35

What are STANDARD TEMPERATURE and STANDARD PRESSURE?

Answer 35

To help us make comparisons between different gases, arbitrary conditions called STANDARD TEMPERATURE (273 K) and STANDARD PRESSURE (1 atm) together abbreviated STP, were selected by scientists.

Standard temperature is exactly 0 degrees C (273 K)

Standard pressure is exactly 1 atm (760 mmHg)

Question 36

What is MOLAR VOLUME?

Answer 36

At STP, one mole of any gas occupies a volume of 22.4 L, which is about the same as the volume of 3 basketballs.

This volume, 22.4 L, of any gas at STP is called its MOLAR VOLUME.

Question 37

When a gas is at STP conditions (_____ degrees C and _____ atm), its molar volumed can be used to write conversion factors between the number of moles of gas and its volume, in liters.

The molar volume conversation factors are used to convert between the number of moles of gas and its ________.

Answer 37

0 degrees C and 1 atm

MOLAR VOLUME CONVERSION FACTORS:

1 mole of gas at STP= 22.4 L of gas

1 mole gas (STP)/22.4 L gas and
22.4 L gas/ 1 mole gas (STP)

The molar volume conversation factors are used to convert between the number of moles of gas and its VOLUME.

Question 38

What is DALTON’s LAW? (Partial Pressure)

Answer 38

Many gas samples are a mixture of gases. In gas mixtures, scientists observed that all gas particles behave in the same way. Therefore, the total pressure of the gases in a mixture is a result of the collisions of the gas particles regardless of what type of gas they are.

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.

Ptotal = P1 + P2 + P3 + …

Question 39

The ______ of gas molecules, not the _____, determines the pressure in a container.

Answer 39

The NUMBER of gas molecules, not the TYPE OF GAS, determines the pressure in a container.

Question 40

The air you breathe is a mixture of gases. What we call the atmospheric pressure is actually the sum of _______________.

Answer 40

the partial pressures of the gases in the air.