1 atm refers to 1 atmosphere, the pressure of outside air at sea level on Earth. M ELTING F REEZING V APORIZATION C ONDENSATION S UBLIMATION D EPOSITION Notice the steep slope of the melting/freezing line It tells us that solid ice is less dense than liquid water, and can consequently float on top of it. This is a rare molecular property; however, it has had a huge impact on our planets hydrology. If ice did not float, but instead sank to the bottom of the worlds oceans, it would create a positive feedback loop in which the liquid water above it would be forced to the surface, where it would freeze, sink, and eventually result in a completely frozen planet highly unsuitable for life.
The triple point is the temperature and pressure at which water exists in all phases in equilibrium It is a unique feature in our solar system. Even Mars, our most similar planetary relative, does not at present have a dense enough atmosphere to allow for liquid water to exist on its surface. Instead, with average temperatures hovering around -50˚C and atmospheric pressure being 1/1000 that of Earth, water ice on Mars surface sublimates directly into vapor when temperatures are high enough. S UBLIMATION This may have been a different story in the distant past. Mars surface may indeed have been very similar to Earths. However, since liquid water is necessary for cellular stability, the surface of Mars seems comparatively inhospitable today.
Waters polarity makes it a good solvent. It is called the universal solvent because of its ability to dissolve salts and nutrients, which are key facilitators of several biological processes, including ingestion, excretion, and chemical transport within and between cells. As the universal solvent, water dissolves cations (positively charged particles) and anions (negatively charged particles) to conduct electric currents. Pure, deionized water, however, cannot conduct electricity on its own. Dissolved solutes, such as salts, are necessary to facilitate conduction. When ionized, it is the perfect medium by which cells can facilitate biochemical reactions necessary for energy exchange, metabolism, and growth. The higher the ion concentration, the higher the waters electrical conductivity. We can measure these changes using a conductivity meter. Similarly, the H + concentration of an aqueous solution can give us insight into that solutions pH. We can also measure it using a meter.pH Similarly, the H + concentration of an aqueous solution can give us insight into that solutions pH. We can also measure it using a meter.pH
pH is a numerical figure expressing the acidity or alkalinity on a logarithmic scale, on which 7 is neutral, lower values are more acidic, and higher values are more alkaline.