Gases and the Gas Laws

Combined Gas Law

(P1V1/T1)=(P2V2/T2)

various units of pressure

-1 atm -760 mm Hg -760 torr (named for Evangelista Torricelli) -101,325 pascals

Activity Chart of Metals

-In cold water: potassium, calcium, sodium -In Hot water: Magnesium -In most dilute acids: aluminum, zinc, iron, tin -Hydrogen -Not active enough: copper, mercury, silver, gold

Composition of the Earth's Crust

-Oxygen: 49.2% -Silicon: 25.7% -Aluminum: 7.4% -Iron: 4.7% -Sodium: 2.5% -Calcium: 3.4% -Potassium: 2.4% -Others

The Earth's Atmosphere

-nitrogen 78% -oxygen: 21% -argon: 0.9% -carbon dioxide: 0.03% -vary amounts of water vapor -trace amounts of hydrogen, ozone, methane, carbon monoxide, helium, neon, krypton, and xenon -Oxides and other pollutants added by factories and automobiles

Ideal Gas Constant

0.0821 (L atm)/(mol K)

Chemical Properties of Hydrogen

1.) It burns in air or in oxygen, giving off large amounts of heat. Its high heat of combustion makes it a good fuel 2.) It does not support ordinary combustion 3.) It is a good reducing agent in that it withdraws oxygen from many hot metal oxides.

Physical Properties of Hydrogen

1.) It is ordinarily a gas; colorless, odorless, tasteless when pure 2.) It weights 0.9 grams per liter at zero degrees Celsius and 1 atm. This is 1/14 as dense as air. 3.) It is slightly soluble in water 4.) It becomes a liquid at a temperature of -240 degrees celsius and a pressure of 13 atm. 5.) It diffuses (moves from place to place in gases) more rapidly than any other gas

Jacques Charles

A French chemist of the early nineteenth century, who discovered that when a gas under constant pressure is heated from 0 to 1 degrees Celsius, it expands 1/273 of it volume. It contracts this amount when the temperature is dropped 1 degree. Charles reasoned that if a gas at 0 degrees Celsius was cooled to -273 degrees Celsius, its volume would be zero. Actually, all gases are converted into liquids before this temperature is reached.

manometer

A device similar to the barometer that can be used to measure the pressure of gas in a confined container. Basically a U-tube containing mercury or some other liquid. When both ends are open to the air, the level of the liquid will be the same on both sides since the same pressure is being exerted on both ends of the tube. A vessel is then connected to one end of the U-tube. Now the height of the mercury column serves as a means of reading the pressure inside the vessel if the atmospheric pressure is known. When the pressure inside the vessel is the same as the atmospheric pressure outside, the levels of liquid are the same. When the pressure inside is greater than outside, the column of liquid will be higher on the side that is exposed to the air. Conversely, when the pressure inside the vessel is less than the outside atmospheric pressure, the additional pressure will force the liquid to a higher level on the side near the vessel.

Robert Boyle

A seventeenth century English scientist who found that the volume of a gas decreases when the pressure on it is increased, and vice versa, when the temperature is held constant

phlogiston theory

A substance called phlogiston was released when a substance burned. The theory went through several modifications before it was finally abandoned

History of Hydrogen

Although there is evidence of the preparation of hydrogen before 1766, Henry Cavendih was the first person to recognize this gas as a separate substance. He observed that, whenever it burned, it produced water. Lavoisier named it Hydrogen, which means "water former"

Ozone

Another form of oxygen and contains three atoms in its molecular structure. Since ordinary oxygen and ozone differ in energy content and form, they have slightly different properties. They are called allotropic forms of oxygen. Ozone occurs in small quantities in the upper layers of Earth's atmosphere, and can be formed in the lower atmosphere, where high-voltage electricity in lightning passes through the air. This formation of ozone also occurs around machinery using high voltage. Because of its higher energy content, oxone is more reactive chemically than oxygen. The ozone layer prevents harmful wavelengths of ultraviolet (UV) light from passing through Earth's atmosphere. UV rays have been linked to biological consequences such as skin cancer

Gases and Temperature

As the temperature of a gas is increased, its kinetic energy is increased, thereby increasing the random motion. At a particular temperature not all the particles have the same kinetic energy, but the temperature is a measure of the average kinetic energy of the particles. A graph of the various kinetic energies resembles a normal bell-shaped curve with the average found at the peak of the curve. When temperature is lowered, the gas reaches a point at which the kinetic energy can no longer overcome attractive forces between the particles (or molecules) and the gas condenses to a liquid. The temperature at which this condensation occurs is related to the type of substance the gas is composed of and the type of bonding in the molecules themselves.

Gay-Lussac's Law

At constant volume, the pressure of a given mass of gas varies directly with the absolute temperature. (P2/T1)=(P2/T2) at constant volume

temperature

Average kinetic energy

greenhouse effect

Caused by the steady increase in atmospheric carbon dioxide, attributed to fossil fuel combustion over the past century. It is resulting in a steady rise in temperatures worldwide

Standard Temperature

Defined as 273 Kelvin or absolute (0 degrees Celsius)

standard pressure

Defined as the height of mercury that can be held in an evacuated tube by 1 atmosphere of pressure (14.7 lb/in.^2). This is usually expressed as 760 mm Hg or 101.3 pascals

Preparation of Hydrogen

Electrolysis of water, which is the process of passing an electric current through water to cause it to decompose, is one method of obtaining hydrogen. This is a widely used commercial method, as well as a laboratory method. Another method of producing hydrogen is to displace it from the water molecule by using a metal. To choose the metal you must be familiar with its activity with respect to hydrogen. -very active metal + water = hydrogen + metal hydroxide -active metal + dilute acid -> hydrogen + salt of the acid -The usual laboratory method of preparing hydrogen: mossy zinc is used with dilute H2SO4, which is introduced down the thistle tube after the zinc is placed in the reacting bottle. You would not begin collecting the gas that bubbles out of the delivery tube for a few minutes so that the air in the system has a chance to be expelled and you can collect a rather pure volume of the gas generated. -In industry, hydrogen is produced by 1.) electrolysis of water, 2.) passing steam over red-hot iron or through hot coke, or 3.) by decomposing natural gas (mostly methane, CH4) with heat

Pressure

Force per unit area.

eudiometer

Glass tube closed at one end

Kinetic Molecular Theory

Has been arrived at to explain the forces between molecules and the energy the molecules possess. 3 basic assumptions: 1.) Matter in all its forms (solid, liquid and gas) is composed of extremely small particles. In many cases these are called molecules. The space occupied by the gas particles themselves is ignored in comparison with the volume of the space in which they are contained. 2.) The particles of matter are in constant motion. In solids, this motion is restricted to a small space. In liquids, the particles have a more random pattern but still are restricted to a kind of rolling over one another. In a gas, the particles are in continuous, random, straight-line motion. 3.) When these particles collide with each other or with the walls of the container, there is no loss of energy.

High Deviations

High pressures and very low temperatures. At high pressures, the molecules will be forced into closer proximity with each other as the volume decreases until the attractive force between molecules becomes a factor. This factor decreases the volume, and therefore the PV values at high pressure conditions will be less than those predicted by the Ideal Gas Law, where PV remains constant. Examining what occurs at very low temperatures creates a similar situation. Again, the molecules, because they have slowed down at low temperatures, come into closer promiximity with each other and begin to feel the attractive force between them. This tends to make the gas volume smaller, and , therefore, causes the PV to be lower than that expected in the ideal gas situation. Thus, under conditions of very high pressures and low temperatures, deviations from the expected results of the Ideal Gas Law will occur.

Charles's Law

If the pressure remains constant, the volume of a gas varies directly as the absolute temperature. Volume and temperature are in direct proportion at constant pressure. (V1/T1) = (V2/T2)

Boyle's Law

If the temperature remains constant, the volume of a gas varies inversely as the pressure changes. Then: P1V1=P2V2 at a constant temperature As the pressure increases by 2, the volume drops by 1/2

History of Oxygen

In 1774, an English scientist named Joseph Priestley discovered oxygen by heating mercuric oxide in an enclosed container with a magnifying glass. That mercuric oxide decomposes into oxygen and mercury. After his discovery, Priestley visited one of the greatest of all scientists, Antoine Lavoisier, in Paris. As early as 1773 Lavoisier had carried on experiments concerning burning, and they had caused him to doubt the phlogiston theory. By 1775, Lavoisier had demonstrated the true nature of burning and called the resulting gas "oxygen".

ozone layer

In the lower atmosphere, ozone is normally present in extremely low concentrations. The atmospheric layer 12 to 30 miles up contains more ozone that is produced by the action of ultraviolet radiation from the Sun. In this layer, however, the percentage of ozone is only 0.001 by volume. Human activity adds to the ozone concentration in the lower atmosphere where it can be a harmful pollutant. The ozone layer became a subject of concern in the early 1970s when it was found that chemicals known as fluorocarbons, or chlorofluoromethanes, were rising into the atmosphere in large quantities because of their use as refrigerants and as propellants in aerosol dispensers. The concern centered on the possibility that these compounds, through the action of sunlight, could chemically attack and destroy stratospheric ozone, which protects the Earth's surface from excessive ultraviolet radiation. As a result, US Industries and the Environmental Protection Agensy phased out the use of certain chlorocarbons and fluorocarbons as of the year 2000. There is still ongoing concern about both these environmental problems: the greenhouse effect and the deterioration of the ozone layer as it relates to possible global warming.

rate of effusion

Measures the speed at which the gas is transferred into the chamber

Ideal Gas

Molecules of the gas do not take up space in the gas volume and no intermolecular forces of attraction are serving to pull the molecules closer together.

Least Deviations

Occur at low pressures and high temperatures, therefore ideal setting. Move the molecules as far as possible from conditions that would cause condensation. Most pressures below a few atmospheres will cause most gases to exhibit sufficiently ideal properties for the application of the gas laws with a reliability of a few percent or better

normal atmospheric pressure

On average, the air pressure at sea level can support a column of mercury 760 millimeters in height. Also called standard pressure

Properties of Oxygen

Oxygen is a gas under ordinary conditions of temperature and pressure, and it is a gas that is colorless, odorless, tasteless, and slightly heavier than air; all these physical properties are characteristic of this element. Oxygen is only slight soluble in water, thus making it possible to collect the gas over water. Although oxygen will support combustion, it will not burn. This is one of its chemical properties. The usual test for oxygen is to lower a glowing splint into the gas and see if the oxidation increases in its rate to reignite the splint.

Ideal Gas Law

PV=nRT

catalyst

Speed up the rate of reaction by lowering the activation energy needed for the reaction. It is not consumed. The mechanism by which a catalyst acts is not completely understood in all cases, but it is known that in some reactions the catalyst does change its structure temporarily.

pascal

The SI system unit of pressure, named in honor of the scientist of the same name. Standard pressure is 101,325 pascals or 101.325 kilopascals. One pascal (Pa) is defined as the pressure exerted by the force of one newton acting on an area of one square meter. In many cases, as in atmospheric pressure, it is more convenient to express pressure in kilopascals.

mercury barometer

The instrument most commonly used for measuring air pressure. Atmospheric pressure is exerted on the mercury in the dish, and this in turn holds the column of mercury up in the tube. This column at standard pressure will measure 760 millimeters above the level of the mercury in the dish below. For mercury, read the top of the meniscus

diffusion

The random motion of gases in moving from one position to another. Means spreading out.

Graham's Law of Effusion (Diffusion)

The rate of effusion of a gas is inversely proportional to the square roots of its molecular mass. (rate A)/(rate B) = Square Root: (Molecular mass of B/Molecular Mass of A)

rate of diffusion

The rate of the mixing of gases. Hydrogen, with the lowest molecular mass, can diffuse more rapidly that other gases under similar conditions.

atmospheric pressure

The result of the weight of a mixture of gases. Also known as air pressure or barometric pressure. It is approximately equal to the weight of a kilogram mass on every square centimeter of surface exposed to it. This weight is about 10 newtons. It varies with altitude. At higher altitudes, the weight of the overlying atmosphere is less, so the pressure is less. Air pressure also varies somewhat with weather conditions as low and high pressure areas move with weather fronts.

Fractional Distillation

The separation of components of a mixture by making use of the difference in boiling points

effusion

The term used to describe the passage of a gas through a tiny orifice into an evacuated chamber. Means the passing of a gas through an orifice

Preparation of Oxygen

Today oxygen is usually prepared in the lab by heating an easily decomposed oxygen compound such as potassium chlorate. In this preparation manganese dioxide is often used. This compound is not used up in the reaction and can be shown to have the same composition as it had before the reaction occurred. The only effect it has is that it lowers the temperatures needed to decompose the KClO3 and therefore speeds up the reaction 2KClO3 + MnO2 -> 2KCl + 3O2(g) + MnO2

Correction of Pressure When a Gas is Collected Over Water

When a gas is collected over a volatile liquid, such as water, some of the water vapor is present in the gas and contributes to the total pressure. Assuming that the gas is saturated with water vapor at the given temperature, you can find the partial pressure due to the water vapor in a table of such water vapor values. This vapor pressure, which depends only on the temperature, must be subtracted from the total pressure to find the partial pressure of the gas being measured.

Dalton's Law of Partial Pressures

When a gas is made up of a mixture of different gases, the total pressure of the mixture is equal to the sum of the partial pressures of the components; that is, the partial pressure of the gas would be the pressure of the individual gas if it alone occupied the volume Ptotal = Pgas1 + Pgas2 + Pgas3 + ...

Correct of Difference in the Height of the Fluid

When gases are collected in eudiometers, it is not always possible to get the level of the liquid inside the tube to equal the level on the outside. This deviation of levels must be taken into account when determining the pressure of the enclosed gas. There are then two possibilities: 1.) When the level inside is higher than the level outside the tube, the pressure on the inside is less, by the height of fluid in excess, than the outside pressure. If the fluid is mercury, you simply subtract the difference from the outside pressure reading to get the corrected pressure of the gas. If the fluid is water, you must first convert the difference to an equivalent height of mercury by dividing the difference by 13.6 (since mercury is 13.6 times as heavy as water, the height expressed in terms of Hg will be 1/13.6 the height of water. Again, care must be taken that this equivalence height of mercury is in the same units as the expression for the outside pressure before it is subtracted to obtain the corrected pressure for the gas in the eudiometer. 2.) When the level inside is lower than the level outside the tube, a correction must be added to the outside pressure. If the difference in height between the inside and the outside is expressed in terms of water, you must take 1/13.6 of this quantity to correct it to millimeters of mercury. This quantity is then added to the expression of the outside pressure, which must also be in millimeters of mercury. If the tube contains mercury, then the difference between the inside and outside levels is merely added to the outside pressure to get the corrected pressure for the enclosed gas