Chem 1010- Exam 2 Study Guide

A gas consists of small particles that

• move rapidly in straight lines

• have essentially no attractive (or
  repulsive) forces 

• are very far apart

• have very small volumes
  compared to the volume of the container they occupy 

• have kinetic energies that
  increase with an increase in temperature

The volume of a gas…

• is the same as the volume of the container it occupies

• is usually measured in liters or milliliters

• increases with an increase in temperature at a constant pressure 

The temperature of a gas relates to the

average kinetic energy of the molecules and is measured in the Kelvin (K) temperature scale

Pressure is a measure of the gas particle collisions with sides of a container and is measured in units of 

• millimeters of mercury (mmHg) or Torr

• atmospheres (atm)

• pascals (Pa) or kilopascals (kPa)

• pounds per square inch (psi)

Gas particles in the air exert
pressure on us. It is called

atmospheric pressure

A barometer…

• measures the pressure exerted by the gases in the atmosphere

• indicates atmospheric pressure as the height in millimeters of the mercury column

• 760 mmHg = 1 atm = 760 Torr

Atmospheric pressure

• is the pressure exerted by a column of air from the top of the atmosphere to the surface of Earth

• decreases as altitude increases

• is 1 atm at sea level

Atmospheric pressure changes with variations in weather
and altitude. 

• On a hot, sunny day, the mercury column _____, indicating a higher atmospheric pressure.

• On a rainy day, the atmosphere exerts less pressure, which causes the mercury column to ____.

rises; fall

  What is 475 mmHg expressed in atmospheres?

0.625 atm

The pressure in a tire is 2.00 atm. What is this pressure
in millimeters of mercury?

1520 mmHg

The downward pressure on the Hg in a barometer is _____ the pressure of the atmosphere.

the same as

A water barometer is 13.6 times taller than a Hg barometer (d_Hg = 13.6 g/mL) because

H₂O is less dense than mercury

According to the Kinetic Molecular Theory, what happens to the kinetic energy of gas particles when the temperature of the gas increases?

The inverse relationship between the pressure and volume of a gas is known as

Boyle’s Law

Boyle’s Law

Changes occur in opposite directions. When volume increases, the pressure decreases provided the temperature and moles of the gas remain constant.

Boyle’s law states that

• the pressure of a gas is inversely related to its
  volume when T is constant

• the product P × V is
  constant when temperature and amount of a gas are
  held constant

• if volume decreases,
  the pressure increases

    P₁V₁ = P₂V₂

In Boyle’s Law, what is constant?

temperature

During an inhalation,

• the lungs expand

• the pressure in the
  lungs decreases

• air flows toward the lower pressure in the lungs

During an exhalation,

• lung volume decreases

• pressure within the lungs increases

• air flows from the higher pressure in the lungs to
  the outside

Freon-12, CCl₂F₂, was used in refrigeration systems. What is
the new volume of an 8.0-L sample of Freon gas initially at 

550 mmHg after its pressure is changed to 2200 mmHg at
constant temperature and moles?

2.0 L

A sample of oxygen gas has a volume of 12.0 L at 600 mmHg. What is the new pressure when the volume changes to 36.0 L at a constant T and n? 

200 mmHg

For a cylinder containing helium gas, indicate whether cylinder A or cylinder B represents the new volume for the following

changes. (n and T are constant.)

If a sample of helium gas has a volume of 120 mL and a

pressure of 850 mmHg, what is the new volume if the pressure

is changed to 425 mmHg at a constant T and n?

240 mL

A sample of helium gas in a balloon has a volume of 6.4 L at a pressure of 0.70 atm. At 1.40 atm (T and n are constant), is the new volume represented by A, B, or C?

If we increase the temperature of a gas sample, kinetic molecular theory states that the motion (kinetic energy) of the gas particles will ___________.

also increase

If the amount and pressure of the gas is held constant, the volume of the container will _______.

increase

In Charles’s law,

• the Kelvin temperature of a gas is directly related to the volume 

• pressure and moles of gas are constant

• when the temperature of a sample of gas increases, its volume increases at a constant pressure

What is constant in Charle’s Law?

P and n

A balloon has a volume of 785 mL at 21 °C. If the temperature drops to 0 °C, what is the new volume of the balloon at constant pressure and moles?

729 mL

A sample of oxygen gas has a volume of 420 mL at a temperature of 18 °C. At what temperature (in degrees Celsius) will the volume of the oxygen be 640 mL? (P and n are constant.)

  170 °C

Use the gas laws to complete each sentence with increases
or decreases.       

A. Pressure _______ when V decreases at a constant temperature and moles. 

B. When T decreases, V _______ at constant pressure and moles.

C. Pressure _______ when V changes from 12 L to 24 L at constant temperature and moles.

D. Volume _______when T changes from 15 °C to 45 °C at constant pressure and moles.

According to Charles’s Law, if the temperature of a gas is doubled (while keeping pressure and the amount of gas constant), what happens to the volume?

Gay-Lussac’s law

when the Kelvin temperature of a gas is doubled and the volume and amount of gas do not change, the pressure also doubles.

In Gay-Lussac’s law,

• the pressure exerted by a gas is directly related to the Kelvin temperature of the gas

What is constant in Gay-Lussac’s law?

volume and amount of gas

A gas has a pressure at 2.0 atm at 18 °C. What is the new pressure when the temperature is 62 °C? (Volume and moles remain constant.)

2.3 atm

A gas has a pressure of 645 Torr at 128 °C. What is the temperature in degrees Celsius if the pressure increases to 824 Torr? (V and n remain constant.)

239°C

Explain why water boils at a lower temperature in the mountains than at sea level.

Atmospheric pressure in the mountains is less than at sea level. The vapor pressure of the water reaches the atmospheric pressure at a lower temperature.

The combined gas law uses the pressure–volume–temperature relationships from Boyle’s law, Charles’s law, and Gay-Lussac’s law where n is constant.

A gas has a volume of 675 mL at 35 °C and 646 mmHg pressure. What is the volume (in milliliters) of the gas at −95 °C and a pressure of 802 mmHg? (n is constant.)

314 mL

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

604 K

In Avogadro’s law,

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

What is constant in Avogadro’s law?

T and P

If 0.75 mole of helium gas occupies a volume of 1.5 L, what volume (in liters) will 1.2 moles of helium occupy at the

same temperature and pressure?

2.4 L

The volumes of gases can be compared at STP, Standard Temperature and Pressure, when they have

• the same temperature

standard temperature (T )     

0 °C  or 273 K

• the same pressure

standard pressure (P )   

1 atm (760 mmHg)

At standard temperature and pressure (STP), 1 mole of a gas occupies a volume of 22.4 L, which is called its ____________.

molar volume

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

61.6 L N2

What is the volume at STP of 4.00 g of CH₄?

5.60 L

How many grams of He are present in 8.00 L of gas at STP?

1.43 g

The ____________ of a
gas is the pressure that each
gas in a mixture would exert if it were by itself in the container.

partial pressure

Dalton’s law of partial pressures indicates that

• pressure depends on the total number of gas particles, not on the types of particles

• the total pressure exerted by gases in a mixture is the sum of the partial pressures of those gases

   

The air we breathe

• is a mixture of
  different gases

• contains mostly N₂ and
  O₂, and small amounts
  of other gases

A scuba tank contains O₂ with a pressure of 0.450 atm and He at 855 mmHg. What is the total pressure, in millimeters of mercury, in the tank? (Volume and temperature are constant.)

1.20 × 10³ mmHg

For a deep dive, a scuba diver uses a mixture of helium and oxygen with a pressure of 8.00 atm. If the oxygen has a partial pressure of 1280 mmHg, what is the partial pressure of the helium? (Volume and temperature are constant.)

4800 mm Hg

A gas mixture contains Nitrogen at a partial pressure of 400 mmHg and Oxygen at a partial pressure of 300 mmHg. What is the total pressure of the mixture?