O METANO - (74-82-8)

Introdução

Nome: methane; methyl hydride; marsh gas
* IUPAC
Registro CAS: 74-82-8
Fórmula Química: CH4
Massa Molar: 16.04246 g
Estados Físicos da Matéria: colorless gas
Percentagem de Massa: C 74.868 %; H 25.131 % 

Classificação

• o orgânico • o alcano

Usa/Função

• "Used as a fuel and in the production of many organic compounds. Major component of natural gas. Formed by anaerobic decomposition of plants (swamp gas) and by microbes in termites and certain mammals. May contribute to global warming." 1

• "Carbon dioxide and water are not the only greenhouse gases. Methane, the CFCs, N2O, O3, and CO also absorb infrared radiation. Although they are present in the atmosphere at very low concentrations, they absorb infrared radiation relatively strongly and in regions of the spectrum not absorbed by CO2 and H2O." 2

• "Constituent of illuminating and cooking gas, in the manuf[acture] of hydrogen, hydrogen cyanide, ammonia, acetylene, formaldehyde, in organic syntheses." 3

• "Basic oxides such as La2O3 and mixtures like Li2O (5% by weight) - MgO have important potential as catalysts in the oxidative coupling of methane." 4

• "When methane burns, it releases a large amount of energy, making it useful as a fuel. Humans have known about methane as a source of energy for thousands of years. Temples in the ancient world often burned "eternal flames" that may have been fueled by natural gas. In the early nineteenth century, people began using natural gas as a light source. Once oil was discovered in the 1860s, however, its use, and the electricity produced by burning oil, became much more popular, and people abandoned natural gas as a fuel except for limited use in cooking.

Natural gas has become more popular in recent years because its use results in less pollution that petroleum and other fossil fuels. Some uses include heating homes, offices, and factories; powering room heaters and air conditioners; and operating home appliances such as water heaters and stoves.

Scientists are now exploring other uses for methane and natural gas with the hope that they might eventually become the most important fuels used by humans. Methane has some advantages over petroleum and coal as a fuel. It burns more cleanly than either of these other fossil fuels, producing only carbon dioxide and water as combustion products. Some experts believe that methane could be used as a power source of fuel cells, cells that burn hydrogen to produce electricity. Adding natural gas to oil- or coal-fired burners would also help reduce the greenhouse gas emissions of these appliances.

In addition to its appliacations as a fuel, methane is used in the manufacture of a number of organic and inorganic compounds. For example, ammonia, which is then tenth most important chemical compound in the United States, based on quantity produced, is made from hydrogen and nitrogen gases. Over 90 percent of the hydrogen used to make ammonia is now obtained by reacting methane with water at high temperatures over a catalyst of iron oxide (Fe3O4). Other compounds produced from methane include methanol (methyl alcohol), acetylene (ethyne), formaldehyde (methanal), hydrogen cyanide, carbon tetrachloride, chloroform, methylene chloride, and methyl chloride.

Methane is not toxic, but it can cause suffocation by reducing or eliminating the oxygen a person needs to breathe normally. The primary hazard posed by the gas is its flammability and explosive tendency." 5

Propriedades Físicas

Ponto de Fusão:*
-182.4°C 6 = 90.75 K = -296.32°F
Ponto de Ebulição:*
-161°C 7 = 112.15 K = -257.8°F
-161.5°C 6 = 111.65 K = -258.7°F
Densidade (g/cm3):
0.4228 at -162°C 6
* - 1 atm pressure

Solubilidade

Qualitativo:
muito solúvel: benzeno 7

Ligações Químicas

: 0
: 0
Ligações σ: 4
Ligações π: 0
Completo: 4
Grupo Carboxila: 0
Hidroxila: 0
Geometry: tetrahedral
Hibridização: sp3
Ligações Químicas: polar covalent
Ionic Character: 10.61 %

Termoquímica

ΔHf° (g): -17.89 kcal/mol 8 = -74.85 kJ/mol
S° (g): 44.52 cal/(mol•K) 9 = 186.27 J/(mol•K)
ΔGf° (g): -12.15 kcal/mol 10 = -50.84 kJ/mol
The heat of combustion is the amount of heat released when one mole of a substance undergoes combustion according to the general reaction equation:
CxHyOz + 0.25(4x+y-2z) O2 (g) → x CO2 (g) + 0.5y H2O (ℓ)

ΔHcomb° (g): -212.79 kcal = -890.31824 kJ

Reações

NFPA 704 Ratings:
Health: 1 - Exposure would cause irritation with only minor residual injury.
Flammability: 4 - Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Includes pyrophoric substances. Flash point below 23°C (73°F).
Reactivity: 0 - Normally stable, even under fire exposure conditions, and is not reactive with water.

Ver Também

Wikipédia
:
Catling, David C. and Zahnle, Kevin J. The Planetary Air Leak. Scientific American, May 2009, p 36-43.
Matson, John. More Mysterious Methane. Scientific American, March 2009, p 21.
Lorenz, Ralph and Sotin, Christophe. The Moon That Would be a Planet. Scientific American, March 2010, p 36-43.
Cowen, Ron. Plumes of Martian Methane Hint at Possible Underground Microbial Life. Science News, February 14, 2009, p 10.

Fontes

(1) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill: New York, 2006; p 575.
(2) - Gillespie, Ronald J., Eaton, Donald R., Humphreys, David A., and Robinson, Edward A. Atoms, Molecules, and Reactions; Prentice-Hall: Englewood Cliffs, NJ, 1994; p 607.
(3) - The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals, 13th ed.; Budavari, S.; O'Neil, M.J.; Smith, A.; Heckelman, P. E.; Kinneary, J. F., Eds.; Merck & Co.: Whitehouse Station, NJ, 2001; entry 5979.
(4) - (a) Swaddle, T.W. Inorganic Chemistry; Academic Press: San Diego, 1997; p 123. (b) Lunsford, J.H. Angew. Chem. Int. Ed. Engl. 34, 970-980 (1995).
(5) - Schlager, Neil, Weisblatt, Jayne, Newton, David E., and Montney, Charles B. Chemical Compounds Vol. 2; Thomson-Gale: Detroit, MI, 2006; pp 445-6.
(6) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 3-205.
(7) - Estok, George K. Organic Chemistry: A Short Text; W.B. Saunders: Philadelphia, 1959; p 29.
(8) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:82.
(9) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:82.
(10) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:82.
(11) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 224.
(12) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 226.
(13) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 310.
(14) - Jolly, William L. The Chemistry of the Non-Metals; Prentice-Hall: Englewood Cliffs, New Jersey, 1966; p 4.
(15) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 214.
(16) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; pp 136, 222.
(17) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 138.
(18) - Atkins, Jones, and Laverman. Chemical Principles 6th ed.; W.H. Freeman and Company: New York, NY, 2013; p F94.