Why is water liquid?
Water is liquid in the temperature range between 0 ° C and 100 ° C. This is difficult to understand because water molecules are very light. This is how you can explain in chemistry why water is liquid.
Why something is liquid
If you are in chemistry If you investigate the states of aggregation, you will quickly see a connection between the molar mass, the melting point and the boiling point. The property of being liquid at room temperature can be demonstrated by the alkanes. It is immediately noticeable that water should not actually be liquid.
- The alkane methane is small and light, it consists of 4 atoms of hydrogen and one carbon atom, the molar mass is 16.043 g / mol. Methane is gaseous from -162 ° C and solidifies at -182 ° C. So it is only liquid in a temperature range of 20 °.
- Heptane changes from a liquid state to a gaseous state at a temperature comparable to that of water. The molecule has a molar mass of 100.21 g / mol and, with 7 atoms of carbon and 16 atoms of hydrogen, is almost huge compared to a water molecule. The freezing point of heptane is -91 ° C. As you can see, in the case of the alkane chain, the area in which a substance is liquid increases with the length of the chain.
- Dodecane with 12 atoms of carbon and 26 atoms of hydrogen has a molar mass of 170.34 g / mol and a freezing point of -10 ° C, which is very close to that of water.
- So water behaves very differently. The molar mass of water is 18.01528 g / mol, the molecule consists of 2 atoms of hydrogen and one atom of oxygen. So the molecule is small and light. Nevertheless, it only evaporates from 100 ° C and solidifies at 0 ° C.
To explain why molecular compounds have a lower boiling point than ...
If you want to understand why water behaves very differently, i.e. obviously independent of its size and molar mass is liquid, you need to familiarize yourself with the chemistry of the substance deal. Water has a dipole, the alkanes do not.
Explain special features of water in chemistry
- A substance is solid when its molecules swing around fixed points but do not move freely. It becomes liquid when the temperature rises, because then the particles move more violently. The molecules can move one another. The substances become gaseous when the temperature increases the kinetic energy so much that the particles lose any connection.
- It is easy to understand that the smaller and lighter the particles are, very little energy is necessary in order to convey this from the solid to the liquid state or from liquid to gaseous. This explains the relationships shown for the alkanes.
- Water has a dipole because it has two positive hydrogen nuclei in one angle of 104.45 °, the negative oxygen ion in the middle between them, i.e. at the apex of the angle. Since positive and negative charges attract each other, the water molecules arrange themselves in a fixed pattern, there is a large binding energy of the molecules.
- For this reason, water becomes liquid at temperatures at which otherwise only significantly heavier substances are liquid. It melts from 0 ° C, i.e. it becomes liquid in a temperature range like the much heavier dodecane, in this range methane has long been a gas. Even at 100 ° C it is still liquid, at this temperature the five times heavier hexane evaporates. Without a dipole, water would behave similarly to methane, i.e. from -182 ° C it would be a gas.
This is how you can explain why water is liquid.
