Exactly 1 mole l for an element the standard state of

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exactly 1 mole/ L § For an element The standard state of an element is the form on which the elements exists under conditions of 1 atm and 25 degrees celsius. o Enthalpies of formation are always given per mole of product in its standard state o The enthalpy change for a given reaction can be calculated by subtracting the enthalpies of formation of the reactants from the enthalpy of for- mation of the products. Remember to multiply the enthalpies of formation by integers as required by the balanced equation § Elements are not included in the calculation because elements require no change in form .
o
7.6 o Petroleum is a thick, dark liquid composed mostly of compounds called hydrocarbons that contain carbon and hydrogen. ( o Natural gas , usually associated with petroleum deposits, consists mostly of methane, but it also contains significant amounts of ethane, propane, and butane.
o Over the last several years it has become clear that there are tremendous reserves of natural gas deep in shale deposits. Estimates indicate that there may be as much as 200 trillion cubic meters of recoverable natural gas in these deposits around the globe. o A technique called hydraulic fracturing, or “fracking,” is now being used to access these gas deposits. § Fracking involves injecting a slurry of water, sand, and chemical additives under pressure through a well bore drilled into the shale. This produces frac- features in the rock that allow the gas to flow out into wells § Environmental concerns potential contamination of groundwater, risks to air quality, and possible mishandling of wastes associated with the process. o The composition of petroleum varies somewhat, but it consist consists mostly of hydrocar- bons having chains that contain from 5 to more than 25 carbons § To be used efficiently, the petroleum must be separated into fractions by boiling. The lighter molecules (hav- ing the lowest boiling points) can be boiled off, leaving the heavier ones behind. o As gasoline became more important, new ways were sought to increase the yield of gasoline obtained from each barrel of petroleum. § Burton invented a process at Standard Oil of Indiana called pyrolytic (high-temperature) cracking § Intensive research to find addi- the objectives that would promote smoother burning produced tetraethyl lead, (C2H5)4Pb, a very effective “antiknock” agent. § The addition of tetraethyl lead to gasoline became a common practice, and by 1960, gasoline contained as much as 3 grams of lead per gallon. § the use of leaded gasoline also greatly increased the amount of lead in the envi- the environment, where it can be ingested by animals and humans. § For these reasons, the use of lead in gasoline has been phased out, requiring extensive (and expensive) modifica- tions of engines and of the gasoline refining process. o Coal § Coal was formed from the remains of plants that were buried and subjected to high pressure and heat over long periods of time.

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