Introducing 

Prezi AI.

Your new presentation assistant.

Refine, enhance, and tailor your content, source relevant images, and edit visuals quicker than ever before.

Loading…
Transcript

Thermal Properties

About methane

CH4

Since methane molecules are nonpolar and do not form hydrogen bonds, they have different thermal properties than those of water.

  • Prokaryotic cells which exhbit anaerobic respiration in habitats where oxygen is lacking produce methane as one of their waste products.
  • Some methanogenic prokaryotes ilve in waste dumps and are delibirately encouraged to produce methane in anaerobic digesters.

H2O

They will have a lower boiling point, lower specific heat capacity and lower latent heat of vaporization because less energy is required to overcome the intermolecular forces which hold the CH4 molecules together.

  • Methane can be used as a fuel but can also contribute to the greenshouse effect when release in the atmosphere.

Structure of methane

Structure of a water molecule

A water molecule is formed by 2 covalent bonds and 2 lone pairs of electrons. The lone pairs repel bonding pairs of electrons which causes the water molecule to be bent, v-shaped.

Methane (CH4), like water, is also a held together by covalent bonds, however the sharing of electron pairs is equal- it has no lone pairs of electrons. Although there is still a difference in elctronegativity between the Carbon and Hydrogen atoms, there is no overall polarity. Thus, methane is a nonpolar molecule.

In the H2O molecule, the oxygen is more electronegative than the H and attracts the electrons in the H-O bond more strongly than does the H. The electronegativity difference between the two atoms covalently bonded together results in the electrons lying more towards the O atom. This results in the polarity of the water molecule.

  • The intermolecular forces that exist between non-polar molecules are called London, or van der Vaals forces. There is no hydrogen bonding in between methane molecules.

Hydrogen Bonding

Having seen that water is a polar molecule, because of the unequal sharing of electrons, the hydrogen atoms have a slightly positive charge and oxygen has a slightly negative charge.

Positively charged particles and negatively charged particles attract each other and form an ionic compound. However, the charges are only partial and will experience a smaller attraction. These intermolecular forces between the H2O molecules are called Hydrogen Bonds.

Hydrogen bonding occurs between molecules when a very electronegative atom (O) is joined to a hydrogen atom in the molecule. Although the hydrogen bond is a weak intermolecular force, water molecules are small so there are many of them per unit volume of water abd large numbers of hydrogen bonds- collectively, they give water its unique properties.

...Other properties

Thermal Properties of water

High Specific heat capacity:

  • Energy is required to increase the temperature of water, which also requires the hydrogen bonds to be broken. Therefore, a relatively large amount of energy is needed to raise the temperature of water. Lots of energy is also to be lost in order for water to cool down; this suggests that water is a thermally stable habitat for aquatic organisms.

High latent heat of vaporization:

  • Evaporation occurs when a molecule separates from other molecules in a liquid and becomes a vapour molecule; the heat needed for this to happen is called the latent heat of vaporization. Hydrogen bonds need to be broken, thus suggesting a lot of heat is needed. This makes it a good evaporative coolant.

High boiling point:

  • The strong attractions afforded by the hydrogen bonds suggest it takes a lot more kinetic energy in an increased temperature to break the hydrogen bonds to free the water molecules as the gas. Water is therefore a liquid over 0-100 degrees C.

Comparison of the thermal properties of water with those of methane

Learn more about creating dynamic, engaging presentations with Prezi