Melting points

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Tatiana 4B
Posts: 30
Joined: Fri Sep 28, 2018 12:28 am

Melting points

Postby Tatiana 4B » Fri Nov 09, 2018 2:28 pm

How does Hydrogen bonding explain higher melting points with H2O vs H2S?

emily gao 1C
Posts: 61
Joined: Fri Sep 28, 2018 12:29 am

Re: Melting points

Postby emily gao 1C » Fri Nov 09, 2018 3:10 pm

hydrogen bonds have a stronger attraction than other intermolecular attractions; thus, it takes more energy to change phase, so the melting/boiling points will be higher

mahika_nayak_3L
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

Re: Melting points

Postby mahika_nayak_3L » Fri Nov 09, 2018 3:17 pm

The partial positive charge of the hydrogen and the partial negative charge of the electronegative atom creates a stronger attraction. You can compare the electronegativity of S as well, which is lower than that of O. More energy is needed to break this attraction, whereas, because the attraction between various H2S molecules is not as strong, less energy is needed to break that attraction. When more energy is applied, this results in a higher melting and boiling point. Thus

Nancy Hu - 4E
Posts: 30
Joined: Fri Sep 28, 2018 12:28 am

Re: Melting points

Postby Nancy Hu - 4E » Fri Nov 09, 2018 3:20 pm

The oxygen in H2O is electronegative and can form intermolecular hydrogen bonds. On the other hand, H2S has Van Der Waals force between the molecules instead of hydrogen bonds. The h-bonds between the hydrogen and oxygen of water molecules are stronger than the Van Der Walls force so the melting points of H2O is greater than H2S because more energy would be required to break the bonds.

ran2000
Posts: 66
Joined: Fri Sep 28, 2018 12:15 am

Re: Melting points

Postby ran2000 » Sat Nov 10, 2018 8:16 pm

Hydrogen bonds by definition only form when hydrogen is directly bonded to N, F and O. The electronegativity difference in sulphur and hydrogen is much lower than that of hydrogen and oxygen. Hydrogen sulphide, thus, is less polar and the dipole formed are weaker than in water. Thus, a hydrogen bond in water is much stronger than the dipole-dipole interaction in hydrogen sulfide.

chris_tsai_4H
Posts: 52
Joined: Fri Sep 28, 2018 12:26 am

Re: Melting points

Postby chris_tsai_4H » Sat Nov 10, 2018 9:31 pm

Hydrogen bonds occur between hydrogen and elements such as oxygen, nitrogen, and fluorine. Hydrogen bonds require a lot more energy to break apart. Since H2S does not have any hydrogen bonds, and H2O does, the melting point of H2O is much higher since it requires more heat to break the bonds apart.


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