States of matter and the atmospheric volume?

Discussion in 'Earth Science' started by BdS, Apr 15, 2014.

  1. BdS Registered Senior Member

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    E.g. If 1 Litre of liquid fuel occupies an x volume and we burn it and mainly gas and heat is produced, have we increased the atmospheric volume by converting the liquid to a gas that occupies more space? So, do cars with an internal combustion engines inflate the atmosphere?

    E.g. When water evaporates does it also cause the atmospheric volume to increase? Assuming the answer is yes, then if the one side of the earth is being heated by the sun and evaporation is greater on the heated side. The heated side’s atmosphere volume is inflating from evaporation. Then gravity reshuffles the Earths atmosphere volume to be balanced, causing wind perhaps during the shuffling of the volume? It’s Not only evaporation or changing states causing wind, also expansion and contraction of the heating and cooling sides of the earth’s atmosphere causing pressure differences…

    If you take a small bottle of compressed gas and put it in a sealed balloon then release the compressed gas the balloon will inflate. Does the same thing (volume increases/decreases) happen to the atmosphere when states of matter change?
     
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  3. Aqueous Id flat Earth skeptic Valued Senior Member

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    The question you're asking is whether burning fuels increases the density of air. The answer comes not from comparing the expansion of a liquid into a gas, but from robbing gas molecules--mostly Oxygen--from the air, bonding them to the hydrogen and carbon atoms in the fuel, and releasing them. For that we need to know the chemical formula for the combustion of the fuel. I will pick an easy one: methane. (CH[sub]4[/sub]). The answer you are looking for comes from knowing how to balance a chemical equation:

    ?CH[sub]4[/sub] + ?O[sub]2[/sub] -> ?CO[sub]2[/sub] + ?H[sub]2[/sub]O

    Each item is the molecule known to exist. The question is: what number goes in front of each one to balance this? Answer. Let's start with 1 molecule of methane. This means there must be two molecules of water in order for the Hydrogens to balance:

    CH[sub]4[/sub] + ?O[sub]2[/sub] -> ?CO[sub]2[/sub] + 2H[sub]2[/sub]O

    If we allow 1 molecule of CO[sub]2[/sub] then the Carbons balance:

    CH[sub]4[/sub] + ?O[sub]2[/sub] -> CO[sub]2[/sub] + 2H[sub]2[/sub]O

    Now that leaves 4 atoms of Oxygen on the right which means we need two molecules on the left and we're finished:

    CH[sub]4[/sub] + 2O[sub]2[/sub] -> CO[sub]2[/sub] + 2H[sub]2[/sub]O

    This tells us that we robbed the air of 2 molecules of Oxygen and replaced them with 1 molecule of CO[sub]2[/sub] plus 2 molecules of H[sub]2[/sub]O. If that H[sub]2[/sub]O remains as water vapor, then we've increased the number of air molecules from 2 to 3. However, one or both of those water molecules will condense if conditions are right. So we can't say for sure what happens overall until we get into the question of how the atmosphere equalizes water, which is your next question.

    Whether or not the volume of a gas increases has to do with its temperature and pressure. These vary from place to place, from night to day and season to season. But on average it's safe to say that the atmosphere holds about the same amount of water vapor molecules over the long haul. This means any excess amounts must be returned through rain, fog, dew and direct chemical reactions, as well as any molecules that drift off into space from the upper atmosphere.

    While it's true that gravity is acting on the atmosphere to pressurize the lower layers, the air would fill a volume if there were no gravity, That's just from the random way molecules shoot through any space that confines them. But yes, uneven heating does produce winds, not just due to water evaporation, but from heating all the air molecules unevenly. The hotter air expands, and the cooler air contracts.

    Yes but the volume of water in the air is relatively small so the biggest factor is just the uneven heating of all air molecules.

    Overall the average density of the atmosphere must remain about the same. What happens if there are any excesses? They must be either going into chemical reactions (like forming rust, or becoming dissolved into the oceans) or else being knocked out into space. Keep in mind the biomass is highly variable, so the way living organism add or subtract certain elements from the air is another kind of system which is affecting this. Also keep in mind that the upper atmosphere is being bombarded by particles from the Sun. But the main factor that controls the amount of air the Earth holds is gravity itself.
     
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