Estados físicos da água

Water is essential for the existence of life. The bodies of all living beings contain water, in greater or lesser quantities. In blood, for example, water is responsible for dissolving and transporting various substances throughout the body. In addition to the water necessary for bodily function, which is ingested through food, many living beings require water from the environment in which they live. Aquatic organisms, for example, inhabit lakes, rivers, or seas and only survive in these locations. The diagram on the side represents the total water on Earth. The green part corresponds to salt water, and the blue part to fresh water. It can be seen that most of the water on planet Earth is salt water. Only a small portion of Earth's fresh water is found in rivers and lakes. Most of it is frozen at the poles, making it difficult for humans to use. Another portion is stored in aquifers, which are underground reserves. Aquifers are formed by rainwater that infiltrates through pores in the soil and rocks. In nature, water can be found in three physical states: liquid, solid, and gas. Most of the water on planet Earth is in a liquid state, such as the water in rivers, lakes, and especially oceans. Ice is water in a solid state. In polar environments, ice forms a thick layer, which can be many meters thick. Icebergs are common in the polar region. These large blocks of ice generally break off from glaciers and float on the waters of the Arctic or Antarctic seas. Snow, which falls in places with very low temperatures, also forms in a solid state. Hail is composed of small ice cubes that form in rain clouds. Hailstorms occur even in warm regions. Water in a gaseous state, also called water vapor, is found in the air around us. We don't see water vapor in the air because it is invisible. The three physical states of water are present in the situation shown in the photo on the left. The water in the ice cubes is in a solid state. The water in the glass and bottle is liquid. The air surrounding the objects contains water in a gaseous state. Water's Physical State Changes Water can change its physical state, that is, pass from one state to another. This can happen when, for example, the temperature changes. The following figures show two examples of this type of change. The change of water from a solid to a liquid state is called melting. At sea level, it occurs at a temperature of 0°C. For example, ice melts outside a freezer because the air temperature around the ice is above 0°C. Conversely, liquid water turns to ice in places with temperatures below 0°C, such as inside a freezer or in cold regions of the planet. This change is called solidification. Observe the diagram below. The arrows indicate the changes that occur between the liquid and solid states of water. Liquid water can also change to a gaseous state. This change of state is called vaporization. It can occur in two main ways: Evaporation: In evaporation, water on the surface of an object, or accumulated in a puddle, absorbs some heat from the environment and slowly changes to a gaseous state. Dishes drying on a drying rack and clothes drying on a clothesline are examples of evaporation. Water vapor can return to its liquid state when subjected to temperatures lower than its initial temperature. This change of state is called condensation. Note an example of condensation in the figure of the woman shown above: the vapor rising from the pan condenses, returning to its liquid state, which can be seen by the water droplets on the pan lid. Text taken from the Science textbook, Learning Together, by Editora SM.