Properties of Water
Water melts at a very high temperature, it also boils at a very high temperature and it is stable as a liquid over a very large temperature range, see the table below. You might not think melting at 0 °C as a "high" temperature, but compared to other similar molecules it is very high!
Water is the only substance to exist in all three states, as a gas, liquid and solid under normal conditions (pressures of 1 atm and temperatures around 25 °C)
Let's make some comparisons.
- H2S melts at -85 °C, compared to water's 0 °C
- H2S is a gas at normal temperature and pressure, while water is a liquid
- H2S is only liquid for ≈24 °C, while water is liquid for 100 °C
- NH3 melts at -78 °C, compared to water's 0 °C
- NH3 is a gas at normal temperature and pressure, while water is a liquid
- NH3 is only liquid for ≈45 °C, while water is liquid for 100 °C
| molecule | mp °C | bp °C | liquid range | ambient state |
|---|---|---|---|---|
| H2O | 0 | 100 | 100 | liquid |
| H2S | -85 | -61 | 24 | gas |
| NH3 | -78 | -33 | 45 | gas |
ambient means "normal" pressure and temperature, ie 1atm and 25 °C
How does water do this?
The H-bonds in water hold the water molecules together, put another way water is "sticky" at the molecular level. This means water "likes" to be a liquid, the water molecules want to stick together, thus water has a large liquid range. H-bonding also means we have to add a lot of energy into the system to force the water molecules to seperate, that is we have to heat it to a higher temperature before we can turn liquid water into a gas (ie boil the jug!); water has a high melting point and a high boiling point (compared to other similar molecules).