Chapter 14 - Properties of Gases

A gas at 155 kPa and 25⁰C has an initial volume of 1.00 L. The pressure of the gas increases to 605 kPa as the temperature is raised to 125⁰C. What is the new volume?

0.342 L

A sealed cylinder of gas contains nitrogen gas at 1.00 x 10³ kPa pressure and a temperature of 20⁰C. When the cylinder is left in the sun, the temperature of the gas increases to 50⁰C. What is the new pressure in the cylinder?

1.10 x 10³ kPa

A 5.00-L air sample has a pressure of 107 kPa at a temperature of -50.0⁰C. If the temperature is raised to 102⁰C and the volume expands to 7.00 L, what will the new pressure be?

1.29 x 10² kPa

A sample of nitrogen gas has a pressure of 6.58 kPa at 539 K. If the volume does not change, what will the pressure be at 211 K?

2.58 kPa

Calculate the ratio of the velocity of helium atoms to the velocity of fluorine molecules at the same temperature.

3.08:1

A gas mixture containing oxygen, nitrogen, and carbon dioxide has a total pressure of 32.9 kPa. If PO₂ = 6.6 kPa and PN₂ = 23.0 kPa, what is PCO₂?

3.3 kPa

Nitrous oxide (N₂O) is used as an anesthetic. The pressure on 2.50 L of N₂O changes from 105 kPa to 40.5 kPa. If the temperature does not change, what will the new volume be?

6.48 L

Calculate the percent composition of 2-propanolol (C₃H₇OH) - Chapter 12

60.0% C, 13.3% H, 26.7% O

A gas with a volume of 4.00 L at a pressure of 205 kPa is allowed to expand to a volume of 12.0 L. What is the pressure in the container if the temperature remains constant?

68.3 kPa

The ideal gas constant (R) has the value ________ (L∙kPa)/(K∙mol).

8.31

How does the vacuum in the flask used to store liquid nitrogen prevent heat transfer?

A vacuum contains no matter to allow the transfer of kinetic energy between molecules.

What is dissolved nitrogen?

As a diver descends, the water exerts greater pressure. More gas pressure is required to keep the lungs expanded. This increased gas pressure causes more nitrogen to dissolve in the diver's blood.

What is decompression sickness?

As the diver returns to the surface, pressure decreases and dissolved nitrogen is released from the blood. Bubbles of nitrogen can block small blood vessels and reduce the supply of oxygen to cells, causing severe pain in the joints, dizziness, and vomiting.

What is nitrogen narcosis?

Below a depth of about 30 meters, dissolved nitrogen interferes with the transmission of nerve impulses. The effects are similar to those of alcohol and include dizziness, slowed reaction time, and an inability to think clearly.

Use kinetic theory to explain why the can collapsed inward.

Boiling the water fills the can with steam. When the can is plunged upside down in the ice water, the steam is trapped and rapidly condenses, reducing gas pressure inside the can. The walls of the can are not strong enough to resist the comparatively high atmospheric pressure, which crushes the can.

Balloons used in parades are filled with helium so they will float above the crowd along the parade route. There is a drawback to using helium in a balloon. What is it?

Both helium atoms and the molecules in air can pass freely through the tiny pores in a balloon. But a helium-filled balloon will deflate sooner than an air-filled balloon. Kinetic theory can explain this difference. If the balloons are at the same temperature, the particles in each balloon have the same average kinetic energy. But helium atoms are less massive than oxygen or nitrogen molecules. So the molecules in air move more slowly than helium atoms with the same kinetic energy. Because the rate of effusion is related only to a particle's speed, Graham's law can be written as follows for two gases, A and B. See picture for remaining info.

What type of air do scuba divers use?

Compressed air. The diver chooses the compressed gas mixture that best suits the depth and length of the planned dive. For deep dives, some or all of the nitrogen may be replaced with helium.

This is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout.

Diffusion. In Figure 14.18A, bromine vapor is diffusing through the air in a graduated cylinder. The bromine vapor in the bottom of the cylinder has started to move upward toward the area where there is a lower concentration of bromine. In Figure 14.18B, the bromine has diffused almost to the top of the cylinder. If the process is allowed to continue, the bromine vapor will spill out of the cylinder.

Gas pressure results from collisions of _____________ in a gas with an object.

Particles. If the number of particles increases in a given volume, more collisions occur. If the average kinetic energy of the particles increases, more collisions occur. In both cases, the pressure increases. Gas pressure depends only on the number of particles in a given volume and on their average kinetic energy. Particles in a mixture of gases at the same temperature have the same average kinetic energy. So the kind of particle is not important.

You can raise the pressure exerted by a contained gas by _____________ its volume.

Reducing. The more the gas is compressed, the greater is the pressure that the gas exerts inside the container. When gas is in a cylinder, as in an automobile engine, a piston can be used to reduce its volume. The snug-fitting piston keeps gas from escaping as the cylinder moves down and up. Figure 14.6 shows a cylinder of gas under two different conditions. When the cylinder has a volume of 1 L, the gas exerts a pressure of 100 kPa. When the volume is halved to 0.5 L, the pressure is doubled to 200 kPa. Increasing the volume of the contained gas has the opposite effect. If the volume is doubled, the particles can expand into a volume that is twice the original volume. With the same number of particles in twice the volume, the pressure of the gas is cut in half.

Why must Kelvin temperatures be used in calculations that involve gases?

Temperatures measured on the Kelvin scale are directly proportional to the average kinetic energy of the particles. Celsius temperatures are not.

What is Surface interval time to a diver?

The longer a diver spends at the surface, the more nitrogen is excreted through the lungs. A diver can move from Group H to Group A after 8 hours at the surface.

Explain the reasons why real gases deviate from ideal behavior.

The particles in a real gas have a finite volume and are attracted to one another.

If a gas is compressed from 4 L to 1 L and the temperature remains constant, what happens to the pressure?

The pressure quadruples.

What happens to the particles in a gas when the gas is compressed?

The space between the particles is reduced.

In your own words, state Dalton's law of partial pressure.

The total pressure of a gaseous mixture is equal to the sum of the individual pressures of each gas.

What do dive tables do?

They help a diver avoid decompression sickness. Divers use the data to control the length and frequency of their dives, and at the rate at which the return to the surface.

True or False. Gases are easily compressed because of the space between the particles in a gas.

True. Remember that the volume of the particles in a gas is small compared to the overall volume of the gas. So the distance between particles in a gas is much greater than the distance between particles in a liquid or solid. Under pressure, the particles in a gas are forced closer together, or compressed.

Write the mathematical equation for Charles's law and explain the symbols.

V₁/T₁ = V₂/T₂ V₁ and V₂ are the initial final volumes; T₁ and T₂ are the initial and final temperatures.

Which compound contains at least one double bond? Chapter 8

b, SO²

There is another process that involves the movement of molecules in a gas. This process is called ______.

effusion. During effusion, a gas escapes through a tiny hole in its container. With effusion and diffusion, the type of particle is important. Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.

Which gas effuses faster at the same temperature: molecular oxygen or atomic argon?

molecular oxygen

Calculate the volume of a gas (in L) at a pressure of 1.00 x 10² kPa if its volume at 1.20 x 10² kPa is 1.50 x 10³ mL.

1.80 L

Oxygen is produced in the laboratory by heating potassium nitrate (KNO₃). The data table below gives the volume of oxygen produced at STP from different quantities of KNO₃. Use the data to determine the mole ratio by which KNO₃ and O₂ react. Mass of KNO₃ (g) Volume of O₂ (cL) 0.84 9.3 1.36 15.1 2.77 30.7 4.82 53.5 6.96 77.3

2 mol KNO₃ for each 1 mol O₂

During an effusion experiment, a certain number of moles of an unknown gas passed through a tiny hole in 75 seconds. Under the same conditions, the same number of moles of oxygen gas passed through the hole in 30 seconds. What is the molar mass of the unknown gas?

2.0 x 10² g

A child's lungs can hold 2.20 L. How many grams of air do her lungs hold at a pressure of 102 kPa and a body temperature of 37⁰C? Use a molar mass of 29g for air, which is about 20% O₂ (32g/mol) and 80% N₂ (28g/mol).

2.5 g air

When the temperature of a rigid hollow sphere containing 685 L of helium gas is held at 621 K, the pressure of the gas is 1.89 x 10³ kPa. How many moles of helium does the sphere contain?

2.5 x 10² mol He(g)

An atom of lead has a mass 17.16 times greater than the mass of an atom of carbon -12. What is the molar mass of this isotope of lead? Chapter 10

206 g

At what altitude does a weather balloon burst?

27,000 meters. The combined gas law can help to explain this situation. Both outside temperature and pressure drop as the balloon rises. These changes have opposite effects on the volume of the weather balloon. A drop in temperature causes the volume of an enclosed gas to decrease. A drop in outside pressure causes the volume to increase. Given that the balloon bursts, the drop in pressure must affect the volume more than the drop in temperature does. The combined gas law can also help you solve gas problems when only two variables are changing. It may seem challenging to remember four different expressions for the gas laws. But you actually only need to remember one expression - the combined gas law. You can derive the other laws from the combined gas law by holding one variable constant.

If a sample of gas occupies 6.90 L at 325⁰C, what will its volume be at 25⁰C if the pressure does not change?

3.39 L

If 4.50 g of methane gas (CH₄) us ub a 2.00-L container at 35⁰C, what is the pressure in the container?

3.60 x 10² kPa

What is the volume occupied by 1.24 mol of a gas at 35⁰C if the pressure is 96.2 kPa?

33.0 L

The pressure in a car tire is 198 kPa at 27⁰C. After a long drive, the pressure is 225 kPa. What is the temperature of the air in the tire? Assume that the volume is constant.

341 K (68⁰C)

Exactly 5.00 L of air at -50.0⁰C is warmed to 100.0⁰C. What is the new volume if the pressure remains constant?

8.36 L

How many electrons, protons, and neutrons are there in an atom of lead-206? Chapter 4

82 protons, 82 electrons, 124 neutrons

A gas with a volume of 3.00 x 10² mL at 150⁰C is heated until its volume is 6.00 x 10² mL. What is the new temperature of the gas if the pressure remains constant during the heating process?

846 K (573⁰C)

Determine the total pressure of a gas mixture that contains oxygen, nitrogen, and helium. The partial pressures are: PO₂ = 20.0 kPa, Pₙ2 = 46.7 kPa, and PHe = 26.7 kPa.

93.4 x kPa

What is the End-of-dive lettergroup to a diver?

At the end of a dive, the diver matches the time and depth of the dive to a letter group. Letter A represents the least amount of nitrogen left in the blood after the dive. The circled numbers show the maximum time a diver can spend at a given depth without having to make a decompression stop during the ascent.

What is the name of the law that combines Boyle's, Charles's, and Gay-Lussac's laws?

Combined gas law (original name huh? :D) This law describes the relationship among the pressure, temperature, and volume of an enclosed gas. The combined gas law allows you to do calculations for situations in which only the amount of gas is constant. P₁ x V1/T₁ = P₂ x V₂/T₂

What does a repetitive dive timetable do for a diver?

Divers this table to determine an adjusted maximum dive time before doing a second dive. They also use the table to determine a letter group at the end of the second dive.

True or false. The amount of gas, volume and moles are factors that affect gas pressure.

False. The amount of gas, volume, and TEMPERATURE are factors that affect gas pressure.

True or false. You CAN use the combined gas law to calculate the number of moles of a gas in a fixed volume at a known temperature and pressure.

False. You CANNOT use the combined gas law to calculate the number of moles of a gas in a fixed volume at a known temperature and pressure.

FYI Aerosol cans depend on the movement of a gas from a region of high pressure to a region of lower pressure.

Figure 14.5 shows how a can of spray paint works. The can contains a gas stored at high pressure. The air outside the can is at a lower pressure. Pushing the spray button creates an opening between the inside of the can and the air outside. The movement of the gas propels, or forces, the paint of the can. As the gas is depleted, the pressure inside the can decreases until the gas can no longer propel paint from the can.

How do real gases differ from ideal gases?

Figure 14.5 shows how the value of the ratio (PV/nRT) changes as pressure increases. For an ideal gas, the result is a horizontal line because the ratio is always equal to 1. For real gases at high pressure, the ratio may deviate, or depart, from the ideal. When the ratio is greater than 1, the curve rises above the ideal gas line. When the ratio is less than 1, the curve drops below the line. The deviations can be explained by two factors. As attractive forces reduce the distance between particles, a gas occupies less volume than expected, causing the ratio to be less than 1. But the actual volume of the molecules causes the ratio to be greater than 1. In portions of the curves above the line, intermolecular attractions dominate. In portions of the curves above the line, molecular volume dominates. Look at the curves for methane (CH₄) at 0⁰C and at 200⁰C. At 200⁰C, the molecules have more kinetic energy to overcome intermolecular attractions. So the curve for CH₄ at 200⁰ never drops below the line.

What law states that the pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant?

Gay-Lussac's law. Joseph Gay-Lussac (1778-1850), a French chemist, discovered the relationship between the pressure and temperature of a gas in 1802. His name is on the gas law that describes the relationship. Look at Figure 14.11. When the temperature is 300 K, the pressure is 100 kPa. When the temperature is doubled to 600 K, the pressure doubles to 200 kPa. Because Gay-Lussac's law involves direct proportions, the ratios P₁/T₁ and P₂/T₂ are equal at constant volume. You can write Gay-Lussac's law as follows. P₁/T₁ = P₂/T₂ Gay-Lussac's law can be applied to reduce the time it takes to cook food. One cooking method involves placing food above a layer of water and heating the water. The water vapor, or steam, that is produced cooks the food. Steam that escapes from the pot is at a temperature of about 100⁰C when the pressure is near one atmosphere. In a pressure cooker, steam is trapped inside the cooker. The temperature of the steam reaches about 120⁰C. The food cooks faster at this higher temperature, but the pressure rises, which increases the risk of an explosion. A pressure cooker has a valve that allows some vapor to escape when the pressure exceeds the set value.

The Scottish chemist Thomas Graham studied rates of effusion during the 1840s. From his observations, he proposed a law. What was it's name?

Graham's law of effusion. It states that the rate of effusion of a gas is inversely proportional to the square root of the gas's molar mass. This law can also be applied to the diffusion of gases. Graham's law makes sense if you know how the mass, velocity, and kinetic energy of a moving object are related. The expression that relates the mass (m) and the velocity (v) of an object to its kinetic energy (KE) is KE = 1/2mv². For the kinetic energy to be constant, any increase in mass must be balanced by a decrease in velocity. For example, a ball with a mass of 2 g must travel at 5 m/s to have the same kinetic energy as a ball with a mass of 1 g traveling at m/s. There is an important principle here. If two objects with different masses have the same kinetic energy, the lighter object must move faster.

Why does a balloon filled with helium deflate more quickly than a balloon filled with air?

Helium atoms have a smaller molar mass than oxygen and nitrogen molecules and effuse faster through pores in the balloon.

What real gas comes closet to having the characteristics of an idea gas? Explain your answer.

Helium gas is composed of small atoms with little attraction for each other.

Why do aerosol containers display the warning, "Do not incinerate"?

High temperatures increase the pressure of the contents of the container and may cause it to explode.

The gas law that includes all four variables - P, V, T, and n is called the ______ _______ _______.

Ideal gas law. It is usually written as follows: P x V = n x R X T or PV = nRT

How are the pressure, volume, and temperature of a gas related?

If the temperature is constant, as the pressure of a gas increases, the volume decreases. In turn, as the pressure decreases, the volume increases.

A sealed bag of potato chips bulges at the seams when placed in a sunny location. The bag bulges because an ___________ in the temperature of an enclosed gas causes an increase in its pressure. You can use kinetic theory to explain what happens.

Increases. As a gas is heated, the temperature increases and the average kinetic energy of the particles in the gas increase. Faster-moving particles impact the walls of their container with more energy. Look at Figure 14.7. The volume of the container and the amount of gas is constant. When the Kelvin temperature of the enclosed gas doubles from 300 K to 600 K, the pressure of the enclosed gas doubles from 100 kPa to 200 kPa. A gas in a sealed container may generate enormous pressure when heated. For that reason, an aerosol can, even an "empty" one, may explode if thrown onto a fire. By contrast, as the temperature of an enclosed gas decreases, the pressure decreases. The particles, on average, move more slowly and have less kinetic energy. They strike the container walls with less force. Halving the Kelvin temperature of a gas in a rigid container decreases the gas pressure by half.

As the temperature of an enclosed gas increases, the volume __________, if the pressure is constant?

Increases. Figure 14.9 compares the volume of a balloon in a mixture of ice,s alt, and water t the volume of the same balloon in hot water. The amount of gas and the pressure are constant. In 1787, the French physicist Jacques Charles studied the effect of temperature on the volume of a gas at constant pressure. When he graphed his data, Charles observed that a graph of gas volume versus temperature (in ⁰C) is a straight line for any gas. When he extrapolated, or extended, the line to zero volume (V=0), the line always intersected the temperature axis at -273.15⁰C. This value is equal to 0 on the Kelvin temperature scale. The observations that Charles made are summarized in Charle's Law.

As the temperature of an enclosed gas _________, the pressure increases, if the volume is constant.

Increases. When tires are not inflated to the recommended pressure, fuel efficiency and traction decrease. Treads can wear down faster. Most importantly, improper inflation can lead to tire failure. A driver should not check tire pressure after driving a long distance because the air in a tire heats up during a drive.

The contribution each gas in a mixture makes to the total pressure is called .... ?

It is called the "partial pressure" exerted by that gas. Table 14.1 shows the composition of dry air, air that does not contain any water vapor. In dry air, the partial pressure of nitrogen is 79.11 kPa. In a mixture of gases, the total pressure is the sum of the partial pressures of the gases. P total = P₁ + P₂ + P₃ + ... This equation is a mathematical expression of a law proposed by Dalton.

Define compressibility.

It is the measure of how much the volume of matter decreases under pressure.

What is the significance of the volume 22.4 L? Chapter 10

It is the volume occupied by 1 mol of a gas at STP.

What is Boyle's Law?

It states that for a given mass of gas at constant temperature, the volume of that gas varies inversely with pressure. Robert Boyle was the first person to study this pressure-volume relationship in a systematic way. In 1662, Boyle proposed a law to describe the relationship known now as Boyle's Law. Look at Figure 14.8. A gas with a volume of 1.0 L (V₁) is at a pressure of 100 kPa (P₁). As the volume increases to 2.0 L (V₂), the pressure decreases to 50 kPa (P₂). The product P₁ X V₁ (100 kPa X 1.0 L = 100 kPa∙L) is the same as the product P₂ x V₂ (50 kPa x 2.0 L = 1-- kPa∙L). As the volume decreases to 0.5 L (V₃), the pressure increases to 200 kPa (P₃). Again, the product of the pressure and the volume equals 100 kPa∙L. In an inverse relationship, the product of the two variable quantities is constant. So the product of pressure and volume at any two sets of pressure and volume conditions is always constant at a given temperature. The mathematical expression of Boyle's law is as follows. P₁ x V₁ = P₂ X V₂ The graph of an inverse relationship is always a curve, as in Figure 14.8.

What is Charles Law?

It states that the volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant. Look at the graph in Figure 14.10. When the temperature is 300 K, the volume is 1.0 L. When the temperature is 900 K, the volume is 3.0 L. In both cases, the ratio of V to T is 0.0033. The ratio V₁/T₁ is equal to the ratio V₂/T₂. Because this ratio is constant at all conditions of temperature and volume, when the pressure is constant, you can write Charles's law as follows. V₁/T₁ = V₂/T₂ The ratio of the variables is always a constant in a direct relationship, and the graph is always a straight line. It is not a direct relationship if the temperatures are expressed in degrees Celsius. So when you solve gas law problems, the temperature mus always be expressed in kelvins.

What does Dalton's law of partial pressure state?

It states that, at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases.

What is an ideal gas?

It's one that follows the gas laws at all conditions of pressure and temperature. Such a gas would have to confirm precisely to the assumptions of kinetic theory. Its particles could have no volume, and there could be no attraction between particles in the gases. As you probably suspect, there is no gas for which these assumptions are true. So an ideal gas does NOT exist. Nevertheless, at many conditions of temperature and pressure, real gases behave very much like an ideal gas.

What is real gas?

It's where the particles do have volume, and there are attractions between the particles. Based on these attractions, a gas can condense or even solidify, when it is compressed or cooled. For example, if water vapor is cooled below 100⁰C at standard atmospheric pressure, it condenses to a liquid. The behavior of other real gases is similar, although lower temperatures and greater pressures may be required. Such conditions are required to produce liquid nitrogen. Real gases differ most from an ideal gas at low temperatures and high pressures.

Describe an ideal gas?

Its particles have no volume, there are no attractions between them, and collisions are elastic. An ideal gas follows the gas laws at all temperatures and pressures.

What is the mathematical relationship between the Kelvin and Celsius temperature scales? Chapter 3

K = ⁰C + 273

What theory can help explain other properties of gases, such as their ability to expand and take the shape and volume of their containers?

Kinetic theory. The particles move along straight-line paths until they collide with other particles or the walls of their container. The motion of the particles is constant and random. Because there are no significant forces of attraction or repulsion among the particles in a gas, particles in a gas can move freely.

Explain why a gas expands until it takes the shape and volume of its container. - Chapter 13

The motion of particles in a gas is constant, random, and rapid.

What are the four variables generally used to describe a gas?

The variables and their common units are pressure (P) in kilopascals, volume (V) in liters, temperature (T) in kelvins, and the number of moles (n).

The ratio of two variables is always a constant. WHat can you conclude about the relationship between the two variables?

The variables are directly proportional.

Describe what happens to the volume of a balloon when it is taken outside on a cold winter day. Explain why the observed change happens.

The volume decreases. The molecules have less kinetic energy and cause less pressure on the inside of the balloon.

Why does a collision with an inflated air bag cause much less damage than a collision with a steering wheel or dashboard?

When a person collides with an inflated air bag, the impact forces the molecules of gas in the bag closer together. The compression of the gas absorbs the energy of the impact.

Which of these elements are metals? Chapter 6 a. arsenic b. tungsten c. xenon

a, tungsten

The following reaction takes place in a sealed 40.0-L container at a temperature of 120⁰C. 4NH₃(g) ₃+ 5O₂(g) → 4NO(g) + 6H₂O(g) a. When 34.0 g of NH₃ reacts with 96.0 g of O₂, what is the partial pressure of NO in the sealed container? b. What is the total pressure in the container?

a. 1.63 x 10² kPa b. 4.48 x 10² kPa

A 0.10-L container holds 3.0 x 10²⁰ molecules of H₂ at 100 kPa and 0⁰C. a. If the volume of a hydrogen molecule is 6.7 x 10⁻²⁴ mL, what percentage of the volume of the gas is occupied by its molecules? b. If the pressure is increased to 100,000 kPa, the volume of the gas is 1 x 10⁻⁴ L. What fraction of the total volume do the hydrogen molecules now occupy?

a. 2.0 x 10⁻³% b. 2.0%

What type of reaction are each of the following? Chapter 11 a. Calcium reacts with water to form calcium hydroxide and hydrogen gas. b. Mercury and oxygen are prepared by heating mercury (II) oxide.

a. single-replacement b. decomposition

If the pressure of the gas in a sealed container is ____________ than the outside air pressure, air will rush into the container when the container is opened.

lower. This movement causes the whoosh you hear when you open a vacuum-packed container. When the pressure of a gas in a sealed container is higher than the outside air pressure, the gas will flow out of the container when the container is unsealed.

To calculate the number of moles of a contained gas requires an expression that contains the variable _________.

n. The combined gas law can be modified to include the number of moles. The number of moles of gas is directly proportional to the number of particles. The volume occupied by a gas at a specified temperature and pressure also must depend on the number of particles. So moles must be directly proportional to volume as well. You can introduce moles into the combined gas law by dividing each side of the equation by n. P₁ x V₁ / T₁ x n₁ = P₂ x V₂ / T₂ x n₂ This equation shows that (PxV)/(Txn) is a constant. This constant holds for ideal gases - gases that conform to the gas laws. If you know the values for P, V, T, and n for one set of conditions, you can calculate a value for the constant. Recall that 1 mol of every gas occupies 22.4 L at STP (101.3 kPa and 273 K). You can use these values to find the value of the constant, which has the symbol R and is called the ideal gas constant. Insert the values of P, V, T and n into (PxV) / (T/n). R=PxV/Txn = 101.3 kPa x 22.4 L/273 K x 1 mol = 8.31 (L∙kPa)/(k∙mol)

Diffusion and effusion come from the Latin fundere meaning to ____ ______.

to pour. They differ only in their prefixes. The prefix dis- means "apart". The prefix ex- means "out".