Chapter 13 - The Nature of Gases
Change 1656 kPa to atm.
16.35 atm
The pressure at the top of Mount Everest is 33.7 kPa. Is that pressure greater or less than 0.25 atm?
33.7 kPa is greater than 0.25 atm
Iron (II) sulfide is produced when iron is heated with sulfur. (Chapter 12) Fe(s) + S(s) →∆→ FeS(s) What is the theoretical yield of FESif 25.0 g Fe is heated with 32.0 g S?
39.4 g FeS (0.448 mol)
What pressure, in kilopascals and in atmospheres, does a gas exert at 385 mm Hg?
51.3kPa, 0.507 atm
What is the key difference between gases and liquids?
According to the kinetic theory, there are no attractions between the particles in a gas. But the particles in a liquid are attracted to each other. These intermolecular attractions keep the particles in a liquid close together, which is why liquids have a definite volume.
Why is the equilibrium that exists between a liquid and its vapor in a closed container called a dynamic equilibrium?
Although some molecules are evaporating and an equal number of particles are condensing, the net amounts of vapor and liquid remain constant.
Key Concept Review
At a temperature at which particles throughout a liquid have enough kinetic energy to vaporize, the liquid begins to boil.
What results from the collisions of atoms and molecules in air with objects?
Atmospheric pressure. Atmospheric pressure decreases as you climb a mountain because the density of Earth's atmosphere decreases as the elevation increases. Air exerts pressure on Earth because gravity holds the particles in air in Earth's atmosphere.
What is a normal boiling point?
Because a liquid can have various boiling points depending on pressure, the normal boiling point is defined as the boiling point of a liquid at a pressure of 101.3 kPa.
How does perspiration help cool your body on a hot day?
Because perspiration absorbs heat as it evaporates, the remaining perspiration and the skin are cooled.
When a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to ________?
Boil. Bubbles of vapor form throughout the liquid, rise to the surface, and escape into the air.
The temperature at which the vapor pressure of the liquid is just equal to the external pressure on the liquid is called the ________ ____________?
Boiling point (bp)
What is another name for buckminsterfullerene?
Buckyball. It was the third form of carbon discovered and it was found in ordinary soot. The 60 carbon atoms in molecules of buckyball are bonded together to form a hollow sphere, or cage. The atoms are arranged in a pattern of hexagons and pentagons on the surface of the cage, similar to the pattern on the surface of a soccer ball. Since this was discovered in 1985, other molecules of carbon with hollow cages have been discovered. The one with 70 carbon atoms is shaped like a football. As a group, these forms of carbon are called fullerenes.
Key Concept Review
Conditions of pressure and temperature at which two phases exist in equilibrium are indicated on a phase diagram by a line separating the two regions representing the phases.
In a crystal, the particles are arranged in an orderly, repeating, three-dimensional pattern called a ____________ __________?
Crystal lattice
What are the 7 groups or crystal systems?
Cubic, Tetragonal, Orthorhombic, Monoclinic, Triclinic, Hexagonal, and Rombohedral A crystal has sides, or faces. The angles at which the faces of a crystal intersect are always the same for a given substance and are characteristic of that substance.
Fun Fact Boiling is a cooling process similar to evaporation.
During boiling, the particles with the highest kinetic energy escape first when the liquid is at the boiling point. Turning off the source of external heat drops the liquid's temperature below its boiling point. Supplying more heat allows more particles to acquire enough kinetic energy to escape. However, the temperature of the boiling liquid never rises above its boiling point. If heat is supplied at a greater rate, the liquid only boils faster. The vapor produced is at the same temperature as that of the boiling liquid. Although the vapor has the same average kinetic energy as the liquid, its potential (or stored energy) is much higher. Thus, a burn from steam is more severe than one from an equal mass of boiling water at the same temperature.
Key Concept Review
During evaporation, only those molecules with a certain minimum kinetic energy can escape from the surface.
In a system at constant vapor pressure, a ___________ _____________ exists between the vapor and the liquid. The system is in equilibrium because the rate of evaporation of liquid equals the rate of condensation of vapor.
Dynamic Equilibrium. At equilibrium, the particles int he system continue to evaporate and condense, but there is no net change in the number of particles in the liquid or vapor.
When vaporization (the conversion of a liquid to a gas or vapor) occurs at the surface of a liquid that is not boiling, this process is called?
Evaporation.
During ________, only those molecules with a certain minimum kinetic energy can escape fromt he surface of the liquid.
Evaporation. Most of the molecules in a liquid don't have enough kinetic energy to overcome the attractive forces and escape into the gaseous state. Even some of the particles that do escape collide with molecules in the air and rebound into the liquid.
True or false. A decrease in pressure raises the boiling point.
False. A decrease in pressure lowers the boiling point. An increase in pressure will raise the boiling point.
True or False? The motion of the particles in a gas is slow, irregular and random?
False. The motion of the particles in a gas is rapid, constant, and random. As a result, gases fill their containers regardless of the shape and volume of the containers. An uncontained gas can spread out into space without limit. The particles travel in straight-line paths until they collide with another particle, or another object, such as the wall of their container. The particles change direction only when they rebound from collisions with one another or with other objects.
The general properties of solids reflect the orderly arrangement of their particles and the ___________ ___________ of their particles.
Fixed locations. In most solids, the atoms, ions, or molecules are packed tightly together. These solids are dense and not easy to compress. Because, the particles in solids tend to vibrate around fixed points, solids do not flow.
Key Concept Review
Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.
What results from the force exerted by a gas per unit surface area of an object?
Gas pressure.
A helium-filled balloon maintains its shape because of the pressure of the _________ within it?
Gas.
What is a transparent fusion product of inorganic substances that have cooled to a rigid state without crystallizing?
Glass. Glasses are sometimes called supercooled liquids. The irregular internal structures of glasses are intermediate between those of a crystalline solid and those of a free-flowing liquid. Glasses do not melt at a definite temperature. Instead, they gradually soften when heated. This softening with temperature is critical to the glassblower's art. When a crystalline is shattered, the fragments tend to have the same surface angles as the original solid. By contrast, when an amphorous solid, such as glass, is shattered, the fragments have irregular angles and jagged edges.
Fun Fact The rate of evaporation of a liquid from an open container increases as the liquid is heated.
Heating allows a greater number of particles at the liquid's surface to overcome the attractive forces that keep them in the liquid state. The remaining particles in the liquid move faster and faster as the absorb the added energy. Thus, the average kinetic energy of the particles in the liquid increases and the temperature of the liquid increases.
When hydrogen sulfide gas is bubbled into a solution of cadmium nitrate in water, the products are nitric acid and a preciptate of cadmium sufide. Write a balanced equation for the reaction. Include physical states for all reactants and products. (Hydrogen sulfide gas is soluble in water) (Chapter 11)
H₂S(aq) + Cd(NO₃)₂(aq) → 2HNO₃ (aq) + CdS(s)
Key Concept Review
In a system at constant vapor pressure, a dynamic equilibrium exists between the vapor and the liquid. The rates of evaporation and condensation are equal.
Compare the evaporation of a liquid in a closed container with that of liquid in an open container.
In both cases, particles with sufficient kinetic energy move from the liquid to the vapor phase. In a closed container, a dynamic equilibrium is set up between the contained liquid and its vapor.
Fun Fact The phase diagram of water.
In each of the colored regions on the phase diagram, water is in a single phase. The curving line that separates water's vapor phase from its liquid phase are the equilibrium conditions for liquid and vapor. The line also illustrates how the vapor pressure of water varies with temperature. The other two curving lines give the conditions for equilibrium between liquid water and ice and between water vapor and ice. The point on the diagram at which all three curves meet is called the triple point.
Name at least one physical property that would permit you to distinguish a molecular solid from an ionic solid.
Ionic compounds generally have higher melting points than do molecular solids.
What happens to the rate of evaporation when a liquid is heated?
It evaporates faster. This occurs because heating the liquid increases the average kinetic energy of its particles. The added energy enables more particles to overcome the attractive forces keeping them in the liquid state. As evaporation occurs, the particles with the highest kinetic energy tend to escape first. The particles left in the liquid have a lower average kinetic energy than the particles that have escaped. The remaining runners have a lower average speed. As evaporation takes place, the liquid's temperature decreases. Therefore, evaporation is a cooling process.
Fun Fact The Kilauea volcano in Hawaii is the most active volcano in the world.
It has been erupting for centuries. The hot lava oozes and flows, scorching everything in its path, occasionally overrunning nearby houses. When the lava cools, it solidifies into rock. The properties of liquids are related to intermolecular interactions.
What is a barometer?
It is a device that is used to measure atmospheric pressure. The height of the mercury column in the tube depends on the pressure exerted by particles in air colliding with the surface of the mercury in the dish. Atmospheric pressure depends on weather and on altitude. In fair weather at sea level, the atmospheric pressure is sufficient to support a mercury column about 760 mm high.
What is vapor pressure?
It is a measure of the force exerted by a gas above a liquid. Over time, the number of particles entering the vapor increases and some of the particles condense and return to the liquid state. This picture shows the equation that summarizes the process. Eventually, the number of particles condensing with equal the number of particles vaporizing. The vapor pressure will then remain constant.
The _________ temperature scale reflects the relationship between temperature and average kinetic energy.
Kelvin temperature scale. The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance.
Fun Fact Kinetic comes from the Greek word kinetos, meaning "to move".
Kinetic energy is the energy an object has because of its motion.
What is the energy an object has because of its motion called?
Kinetic energy. Kinetic refers to motion.
The vapor pressure of a liquid can be determined with a device called a _____________?
Manometer. One end of a U-shaped glass tube containing mercury is attached to a container. The other end of the tube is open to the surrounding atmosphere. When there is only air in the container, the pressure is the same on both sides of the tube and the mercury level is the same in each arm of the tube. When a liquid is added to the container, the pressure int he container increases due to the vapor pressure of the liquid. The vapor pressure of the liquid pushes the mercury on the container side of the U-tube. The levels of mercury int he U-tube are no longer the same. You can determine the vapor pressure in the mm of Hg by measuring the difference between the two levels of mercury. As the vapor pressure increases, so does the difference between the two levels.
When you heat a solid, its particles vibrate more rapidly as their kinetic energy increases. The organization of particles within the solid breaks down, and eventually the solid melts. The _______ ________ is the temperature at which a solid changes into a liquid.
Melting point (mp) At this temperature, the disruptive vibrations of the particles are strong enough to overcome the attractions that hold them in fixed positions. The melting and freezing points of a substance are at the same temperature. At that temperature, the liquid and solid phases are in equilibrium.
Explain why increasing the temperature of a liquid increases its rate of evaporation.
More molecules have enough energy to escape the attractions within the liquid.
What causes the gas pressure force?
Moving bodies exert a force when they collide with other bodies. Although a single particle in a gas is a moving body, the force it exerts is extremely small. Yet it is not hard to imagine that simultaneous collisions involving many particles would produce a measurable force on an object.
Does a liquid always boil at the same temperature?
No. A liquid boils when its vapor pressure is equal to the external pressure. A change in altitude can affect the boiling point of water. In a pressure cooker, the vapor cannot escape and the vapor pressure increases. At a lower external pressure, the boiling point decreases. The particles in the liquid need less kinetic energy to escape from the liquid. At a higher external pressure, the boiling point increases. The particles in the liquid need more kinetic energy to escape from the liquid.
Key Concept Review
Particles in a gas are considered to be small, hard spheres with an insignificant volume. The motion of the particles in a gas is rapid, constant, and random. All collisions between particles in a gas are perfectly elastic.
What is the SI unit of pressure?
Pascal (Pa) It represents a very small amount of pressure.
The relationships among the solid, liquid, and vapor states (or phases) of a substance in a sealed container can be represented in a single graph. The graph is called a ___________ ___________?
Phase diagram. A phase diagram gives the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas (vapor). The conditions of pressure and temperature at which two phases exist in equilibrium are indicated on a phase diagram by a line separating the phases.
Your lab partner measures the boiling point of water in an open beaker as 108.2°C. Even though you know that water can be made to boil at this temperature, you ask your partner to repeat the measurement. Explain.
Possible answer. Since the beaker is an open container, the water should boil at 100°C at or close to sea level. Your partner probably misread the thermometer and should recheck the value.
Fun Fact Did you know that chemical reactions can also take place in solids, without a liquid or gas?
Reactions that take place in the solid state are extremely useful. These reactions occur during the manufacture of semiconductors for the electronics industry. The device that ignites the gas in a gas grill is made up of a type of ceramic called a piezoelectric. This type of ceramic produces a voltage when subjected to mechanical pressure. There is a class of light-sensitive solids called photopolymers. These solids are used to make plates for printing presses that use dry inks instead of water-basked inks. A solid-state reaction takes place in lenses that are designed to darken when exposed to light.
What does the abbreviation STP represent?
STP stands for standard temperature (0°C) and standard pressure (101.3 kPa or 1 atm).
What is the pressure required to support 760 mm of mercury in a mercury barometer at 25°C called?
Standard atmosphere (atm) The numerical relationship among the three units is given below. 1 atm = 760 mm Hg = 101.3 kPa In the case of gases, it is important to be able to relate measured values to standards. Recall that the standard temperature and pressure (STP) are defined as a temperature of 0°C and a pressure of 101.3 kPa, or 1 atm.
Key Concept Review
Sublimation occurs in solids that have vapor pressures that exceed atmospheric pressure at or near room temperature.
What is the change of a substance from a solid to a vapor without passing through the liquid state?
Sublimation. Sublimation can occur because solids, like liquids, have a vapor pressure. Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature. Iodine is another example of a substance that undergoes sublimation. This violet-black solid ordinarily changes into a purple vapor without passing through a liquid state. Dark crystals of iodine deposit on the underside of a watch glass placed on top of a beaker containing solid iodine that is being heated. The iodine vapor sublimes from iodine crystals in the bottom of the beaker and condenses to form crystals on the watch glass. Sublimation has other useful applications. If freshly brewed coffee is frozen and water vapor is removed with a vacuum pump, the result is freeze-dried coffee. Solid carbon dioxide (dry ice) is often used as a coolant for goods, such as ice cream, that must remain frozen during shipment. Dry ice has a low temperature of -78°C. Because it sublimes, it does not produce a liquid as ordinary ice does when it melts. Solid air freshners contain a variety of substances that sublime at room temperature. Sublimation is also useful for separating substances. Organic chemists use sublimation to separate mixtures and to purify compounds.
Explain the relationship between the Kelvin temperature of a substance and the kinetic energy of its particles.
The Kelvin temperature is directly proportional to the average kinetic energy.
Key Concept Review
The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance.
Describe the effect that increasing temperature has on the vapor pressure of a liquid.
The average kinetic energy increases, which allows more vapor to form above the liquid, which increases the vapor pressure.
Is the average kinetic energy of the particles in a block of ice at 0°C the same as or different from the average kinetic energy of the particles in a gas-filled weather balloon at 0°C? Explain.
The average kinetic energy is the same because the temperature is the same.
By what factor does the average kinetic energy of the molecules of gas in an aerosol container increase when the temperature is raised from 27°C (300 K) to 627°C (900 K)?
The average kinetic energy triples.
Key Concept Review
The general properties of solids and the shapes of crystals reflect the orderly arrangement and the fixed locations of particles within the solids.
Key Concept Review
The interplay between the disruptive motions of particles in a liquid and the attractions among the particles determines the physical properties of liquids.
Fun Fact In 1985, scientists discovered a new form of carbon. They called this form of carbon buckminsterfullerene, or buckyball for short.
The molecules in buckyball are hollow spheres. The carbon atoms are arranged so that the pattern on the surface of the sphere resembles the surface of a soccer ball.
What is the triple point?
The point on the diagram at which all three curves meet. It describes the only set of conditions at which all three phases can exist in equilibrium with one another.
Fun Fact As a subtance is heated, its particles absorb energy, some of which is stored within the particles.
The stored portion of the energy, or potential energy, does not raise the temperature of the substance. The remaining absorbed energy speeds up the particles - that is, increases their kinetic energy. This increase in kinetic energy results in an increase in temperature.
Explain why a liquid stays at a constant temperature while it is boiling?
The temperature remains constant while the liquid boils because the energy that is added is used to vaporize the molecules.
Fun Fact The shape of a crystal reflects the arrangement of the particles within the solid.
The type of bonding that exists between particles in crystals determines their melting points. In general, ionic solids have high melting points because relatively strong forces hold them together. By contrast, molecular solids have relatively low melting points. Not all solids melt, however. Wood and cane sugar, for example, decompose when heated.
There is a liquid-vapor equilibrium in a container. Explain why the vapor pressure in the container is not affected when the volume of the container is changed.
The vapor pressure depends only on the kinetic energy of the escaping molecules, which depends on the temperature.
What is an allotrope?
These are two ore more different molecular forms of the same element in the same physical state. Although allotropes are composed of atoms of the same element, they have different properties because their structures are different. Only a few elements have allotropes. In addition to carbon, these include the nonmetals phosphorus, sulfur, and oxygen (O₂₂ and O₃) and the matalloids boron and antimony. Diamond, graphite, and buckyballs are allotropes of carbon. Diamond has a high density and is very hard. Graphite has a relatively low density and is soft and slippery. The hollow cages in fullerenes give them great strength and rigidity.
What is an amorphous solid?
This solid lacks an ordered internal structure. Not all solids are crystalline in form; some solids are amphorous. Rubber, plastic, and asphalt are amphorous solids. Their atoms are randomly arranged.
True or false. Most solid substances are crystalline?
True.
True or False. The interplay between the disruptive motions of particles in a liquid and the attractions among the particles determines the physical properties of liquids.
True. Intermolecular attractions also reduce the amount of space between the particles in a liquid. Thus liquids are much more dense than gases. Increasing the pressure on a liquid has hardly any effect on its volume. The same is true of solids. For that reason, liquids and solids are known as condensed states of matter.
True or False. The particles in any collection of atoms or molecules at a given temperature have a wide range of kinetic energies.
True. Most of the particles have kinetic energies somewhere in the middle of this range. Therefore, average kinetic energy is used when discussing the kinetic energy of a collection of particles in a substance. At any given temperature the particles of all substances, regardless of physical state, have the same average kinetic energy.
True or False? All matter consists of tiny particles that are in constant motion.
True. The particles in a gas are usually molecules or atoms. The kinetic theory as it applies to gases includes the following fundamental assumption about gases.
The shape of a crystal depends on the arrangement of the particles within it. The smallest group of particles within a crystal that retains the geometric shape of the crystal is known as a _______ __________.
Unit cell. A crystal lattice is a repeating array of any one of fourteen kinds of unit cells. There are from one to four types of unit cells that can be associated with each crystal system. See picture for the three kinds of unit cells that can make up a cubic crystal system.
The conversion of a liquid to a gas or vapor is called?
Vaporization.
Is there a relationship between the average kinetic energy of the particles in a substance and the substance's temperature?
Yes. An increase in the average kinetic energy of the particles causes the temperature of a substance to rise. As a substance cools, the particles tend to move more slowly, and their average kinetic energy declines.
Does evaporation of a liquid in a closed container differ from evaporation in an open container?
Yes. No particles can escape into the outside air from the closed container. When a partially filled container of liquid is sealed, some of the particles at the surface of the liquid vaporize. These particles collide with the walls of the sealed container and produce a vapor pressure.
Do both the particles in gases and the particles in liquids have kinetic energy?
Yes. This energy allows the particles in gases and liquids to flow past one another. Substances that can flow are referred to as fluids. The ability of gases and liquids to flow allows them to conform to the shape of their containers.
Does an increase in the temperature of a contained liquid increase the vapor pressure?
Yes. This happens because the particles int he warmed liquid have increased kinetic energy. As a result, more of the particles will have the minimum kinetic energy necessary to escape the surface of the liquid. The particles escape the liquid and collide with the walls of the container at a greater frequency.
Which of these statements are characteristic of matter in the gaseous state? a. Gases fill their containers completely. b. Gases exert pressure. c. Gases have mass. d. The pressure of a gas is independent of its temperature. e. Gases are compressible. f. The distances between particles in a gas are relatively large.
a, b, c, e, and f.
List the intermolecular attractions between molecules in order of increasing strength. (Chapter 8) a. dispersion forces b. hydrogen bonds c. dipole interactions
a, c, b
Refer to Figure 13.9 (Page 394) to answer these questions about chloroform, ethanoic acid, water, and ethanol. a. What is the normal boiling point of ethanoic acid? b. Which liquid has the highest vapor pressure at 40°C? c. At standard atmospheric pressure, which of the substances are int he gaseous state at 70°C? d. Water boils at 100°C at standard pressure. How would the pressure on ethanol and on ethanoic acid have to change for these liquids to boil at 100°C?
a. 121°C b. chloroform c. chloroform d. The external pressure on ethanol would have to increase; the external pressure on ethanoic acid would have to the decrease.
The complete decomposition of sucrose (table sugar) caused by strong heating may be represented by this equation. (Chapter 12) C₁₂H₂₂O₁₁(s) → 11H₂O(l) + 12C(s) For the decomposition of 1.00 mol of sucrose: a. How many grams of H₂O are produced? b. What is the total number of moles or products produced? c. How many grams of C are produced?
a. 198 g H₂O b. 23 mol c. 144 g C
Write the complete electron configuration of each ion. (Chapter 7) a. Ca²⁺ b. S²⁻ c. Li⁺
a. 1s²2s²2p⁶3s²3p⁶ b. 1s²2s²2p⁶3s²3p⁶ c. 1s²
Perchloric acid forms by the reaction of water with dichlorine heptoxide. (Chapter 10) Cl₂O₇ + H₂O → 2HC1O₄ a. How many grams of C1₂O₇ react with an excess of H₂O₂ to form 56.2 g of HC1O₄? b. How many mL of water are needed to form 3.40 mol HC1O₄?
a. 51.2 g C1₂O₇ b. 30.6 mL H₂O
Identify the binary molecular compound in each pair of substances. (Chapter 9) a. Fe₂S₃ b. A1(OH)₃
a. CO b. PBr₃
List the metal that ranks higher in the activity series of metals. (Chapter 11) a. magnesium or mercury b. potassium or lithium
a. Mg b. Li
Use the graph to answer each question.
a. What is the vapor pressure of water at 40°C? b. At what temperature is the vapor pressure of water 600 mm Hg? c. What is the significance of the vapor pressure of water at 100°C? Answers: a. about 50 mm Hg b. about 94°C c. 760 mm Hg is standard pressure
Using Figure 13.11 (Page 397), identify the crystal system described by these characteristics. a. three unequal edges meet at right angles. b. three equal edges with three equal angles that are not right angles c. two equal edges and one unequal edge meet at right angles. d. three unequal edges do not meet at right angles. e. three equal edges meet at right angles.
a. orthorhombic b. rhombohedral c. tetragonal d. triclinic e. cubic
Mount McKinley in Alaska is the tallest peak in North America at 6194 m. The atmospheric pressure at its peak is 44 kPa. Use Figure 13.9 (Page 394) to find the boiling point of water at the peak of Mount McKinley.
about 77°C
Define vacuum.
an empty space with no particles and no pressure.
All ____________ between particles in a gas are perfectly elastic.
collisions During an elastic collision, kinetic energy is transferred without loss from one particle to another, and the total kinetic energy remains constant.
In a series of liquids, as the intermolecular forces of attraction strengthen, would you expect the vapor pressure to increase or decrease? Explain.
decrease; as the attractions become stronger, it is more difficult for molecules to overcome the attractions and vaporize.
How are the frequency and wavelength of light waves related? (Chapter 5)
inversely
Gas pressure is the result of ...
simultaneous collisions of billions of rapidly moving particles in a gas with an object. If there are no particles, there cannot be collisions. Consequently, there is no pressure.
Are the particles in a gas considered to be small, hard spheres with an insignificant volume OR large, soft spheres with an insignificant volume?
small, hard spheres with an insignificant volume . Within a gas, the particles are relatively far apart when compared with the distance between particles in a liquid or solid. Between the particles, there is empty space. No attractive or repulsive forces exist between the particles. The motion of one particle in a gas in independent of the motion of all the other particles.
Thin films are sometimes referred to as _________?
super crystals. A thin film consists of layers of atoms deposited on a surface at a uniform depth of 10⁻⁹ m to 10⁻⁶ m. Engineers can produce thin films with specific electrical properties by varying the element deposited and the thickness of the deposit. Interpreting.
