Substances and phase changes
All substances can exist in three phases: solid, liquid and vapour. Water is the most natural example of a substance that we use almost every day in all three phases. Water in three stages received various names - that is a bit confusing when using it as a model of substance. In solid form, we call ice, liquid form we just give water and steam form we call the pair. What is common to these three phases that water molecules remain unchanged, which means that ice, water and steam, all have the same chemical formula H2O.
When taking a substance in the solid to the liquid phase of the transition process is called trunks, and, taking them further the vapor phase of the transition process is called a boiling (evaporation). When going in the opposite direction, taking vapours of substances in the liquid phase of the transition process is called condensation and when to do next to solid phase transition process is called freezing (solidification).
At constant pressure transient display a very important characteristic.
When the ice is heated at 1 bar its temperature begins to rise until it reaches 0 C - then the ice begins to melt.
During the melting process temperature does not change - all the energy transmitted by the mixture of ice and water goes into the melting of ice, but not for heating of water. Only when the ice has melted completely further transmission of energy cause its temperature to rise. The same type of behavior can be observed when water is heated in an open pot. The temperature of water increases until it reaches 100 C-then begins evaporation. During the evaporation process temperature remains at a level of 100 C. When all the liquid water will evaporate, the temperature of steam left in the Bank will start to grow.
Temperature and pressure of the substance is subjected to determine whether there is it in solid, liquid or vapour form in two or all three forms simultaneously. In our local environment, iron appears solid, water in its liquid and gas form, and the air in the form of vapor.
Different substances have different melting and boiling points. Gold, for example, melts at 1064 C, chocolate 26 C and the majority of refrigerants melt at a temperature of about -100 C!
For a substance that is present in two phases at the same time - or undergoing a phase change of pressure and temperature become dependent. If two stages exist in a closed container and two phases are in thermal equilibrium state is called saturated. If the temperature two-phase mixture increases the pressure in the container will also increase. The relationship between pressure and temperature to saturated conditions (liquid-vapor)commonly called the vapor pressure curve. Using vapour pressure curve you can determine what pressure will be for evaporation or condensation process...
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Chillers