What Causes Water to Boil and What Bonds Need to Be Broken?

In summary, the differences in physical properties between methane and water, such as their different states at room temperature and pressure, can be explained by the types of bonding between atoms within the molecules and the interactions between molecules. Hydrogen bonding plays a key role in the differences, as it involves an electrostatic attraction between polar molecules. This attraction is stronger in water due to its highly polar nature compared to methane, which is non-polar. When water boils, the hydrogen bonds between molecules must be broken in order for the molecules to escape and become a gas. This requires enough kinetic energy from the molecules to overcome the bond strength. The geometry of the molecules also plays a role in determining the strength of hydrogen bonding and ultimately, the boiling point of a
  • #1
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Homework Statement



QUESTION: Methane (CH4) is a gas at room temperature and pressure while water is a liquid. In both molecules hydrogen atoms are bonded to a non-metal element. Water also has a much higher heat of vaporization than methane even though the molecular weights of these two molecules aren't that different.

I am to:
-account for these differences by describing the bonding between atoms within these two molecules, and the bonding and intermolecular interactions between molecules in each.
-indicate how electronegativity differences between the elements, and geometry of the molecules, are both important.
-explain what hydrogen bonding is.
-indicate what is happening on the molecular level when water boils, and what kind of bonds or interactions need to be broken.


The Attempt at a Solution



This question contains many little ones! I believe that hydrogen bonding involves dipole forces. I assume that in order to indicate how electronegativity differs between the elements, I would use the elements of methane (CH4). I really need a lot of help on this. Hopefully it makes sense to someone out there!
Thanks!
 
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  • #2
At standard pressure, the molecules of a liquid are much closer together than those in a gas (just look at their relative densities). For some reason, water molecules are much more comfortable with this than are methane molecules. These two have similar molecular masses so you probably want to start some place else when figuring out why methane exists as a gas at standard temperature and pressure (STP) but water is a liquid. Your instincts here are right so follow them as far as your textbook. Read up on hydrogen bonding and ask yourself how it applies to both CH4 and H2O.

It may be useful to answer the questions in an order diffent from that presented above. Try starting with the third one: "explain what hydrogen bonding is"

Once you have done this, consider the last question. Consider that water - whether it is solid, liquid, or gas - is always H2O just as methane remains CH4. This should help you determine what kinds of bonds are being broken when each transitions from one phase to another.

Now tackle the first question. H bonding plays an important role in the interactions between molecules of one species but not the other. Why is that? What is it about the shape (geometry) of each that determines if H bonding is prominent or not? What impact does H bonding have on the boiling point?

Finally, answer the question "indicate how electronegativity differences between the elements, and geometry of the molecules, are both important." You'll notice in your previous answer that geometry is important. Do you know why a molecule of water is shaped the way that it is?
 
  • #3
Thank you so much for your explanation and suggestion to rearrange the order of questions. I have found that helpful. I have been working on the first question about explaining hydrogen bonding. I have come up with a paragraph attempting to explain hydrogen bonding, but I feel like something is missing…am I really explaining hydrogen bonding or merely “stating facts.”

My paragraph...

Hydrogen bonding is when an electrostatic attraction between an atom bearing a partial positive charge in one molecule and an atom bearing a partial negative charge in a neighboring molecule interact. Compared with covalent bonds, hydrogen bonds’ have less strength; however, hydrogen bonds are considerably strong compared with other intermolecular forces. Hydrogen bonding is when extremely strong polar molecular interactions take place. Because the hydrogen atom is usually associated with strong polar groups that exhibit very strong molecular interaction, hydrogen is used in the term explaining this process. Hydrogen bonding applies to CH4 and H2O, because of how the hydrogen in the molecule exists.
 
  • #4
Your explanation of H bonding is right on the money but I think you are missing an important concept. Hydrogen bonding occures between + and - poles of polar molecules (this is analogous to the attraction between + and - poles on a magnet). Hydrogen bonding is an important force in water because water molecules are highly polar but methane molecules are highly non-polar. Do you know why this is?
 
  • #5
thanks for reading over and commenting on my paragraph on H bonding. In response to your question, does it have something to do with intermolecular forces??
 
  • #6
I have been working through the questions and applying what Blindspot wisely advised! So on to the next one (which was - indicate what is happening on the molecular level when water boils, and what kind of bonds or interactions need to be broken) --

Hydrogen bonds must be broken in order for water to boil. So the bonds that need to be broken in order for boiling to occur would be the hydrogen and oxygen bonds of water (H2O)? Water will start boiling when the kinetic energy of the water molecules is great enough to enable them to break away from each other.

I have read and googled on this and... Am I including the correct information as well as all the stages? I am scared that I won’t actually answer the question directly, so I need a *little* help?!
 

1. What is methane?

Methane is a chemical compound with the molecular formula CH4. It is a colorless and odorless gas that is the simplest hydrocarbon, consisting of one carbon atom and four hydrogen atoms.

2. How is methane formed?

Methane is formed through a process called methanogenesis, which occurs in the absence of oxygen and involves microorganisms breaking down organic matter. It can also be formed through geological processes, such as the breakdown of fossil fuels.

3. What is the bond structure of methane?

Methane has a tetrahedral molecular geometry, with each carbon-hydrogen bond being covalent. This means that the atoms share electrons in order to form the bond.

4. How does methane contribute to climate change?

Methane is a potent greenhouse gas, meaning it traps heat in the Earth's atmosphere. It is responsible for about 20% of global warming and is primarily produced through human activities such as agriculture, landfills, and fossil fuel extraction.

5. Can methane be used as a fuel?

Yes, methane is commonly used as a fuel source for heating and cooking, as well as for electricity generation. It is also the main component of natural gas, which is used to heat homes and power vehicles.

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