What makes natural gas less dense than petroleum?

What about the atoms in natural gas makes it less dense than petroleum? I know that they are both a form of natural gas. This is only a theory of mine, but is petroleum more dense than natural gas because it is a hydrocarbon?

2 Responses to “What makes natural gas less dense than petroleum?”

  1. pzifisssh Says:

    "I know that they are both a form of natural gas"
    No, petroleum is not a form of natural gas.

    "is petroleum more dense than natural gas because it is a hydrocarbon?"
    No, because natural gas also is a hydrocarbon.

    The density of a gas depends on the pressure, but at the kind of pressures that we are used to talking about, solids and liquids usually are more dense than any gas. Solids are more dense because the molecules of the solid are bound to one another, whereas the molecules of gas are not bound: They’re free to bounce around and fill all of the available space.

    Liquids are a weird state—almost but not quite solid. The molecules are bound to one another, but the bonds are weak, and constantly shifting. They’re like dancers in a complicated country dance—always changing partners.

    I can’t explain the forces that bind the molecules of a liquid hydrocarbon to one another, I only know that those forces are stronger in longer hydrocarbon molecules and weaker in the smaller molecules. At any given temperature, the kinetic energy of the molecules will be great enough to break the bonds between the smaller ones, but not enough to break the bonds between the larger ones.

    Natural gas is mostly methane—the smallest possible hydrocarbon. Ethane; propane, and butane also are gasses at room temperature. Pentane is just barely a liquid at room temp: It will boil on a hot summer day. Hexane is more liquid-y, and then there’s heptane, octane, nonane,… The liquids become more viscous and less volatile as the size of the molecules increases. When you get up around twenty or so carbons in the backbone, then we’re talking about motor oil. When you get up into the thirties, then you’re talking about the soft translucent solid stuff that Americans call "paraffin wax."

    ________________________________
    Brandon C. said, "smaller molecules have more kinetic energy at a given temperature."

    Nope. Look up what "temperature" means. The temperature of a substance _is_ the average kinetic energy per molecule of substance. In a mixture of small molecules and large molecules, all of the molecules have the same kinetic energy at any given temperature.

    http://physics.about.com/od/glossary/g/temperature.htm

  2. brandon c Says:

    They are both HCs. Natural gas (methane) is a smaller molecule than the larger ones found in oil, which is composed of many different substances. The smaller molecules have more kinetic energy at a given temperature which causes them to be gases. So they are inherently in different physical states from each other, and any gas is likely to be less dense than any liquid, which in turn is likely to be less dense than any solid.