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Chemical changes are considered unseen because they occur at the atomic level, changing the actual structure of the thing.
Blue to red is acidic, red to blue is basic and no change is neutral.
I believe deforestation increases the biodiversity of a forest ecosystem. Trees are an essential organism for all ecosystem and forms of life. Without trees we have no oxygen, however trees so reproduce, but when you are chopping them down at the rate of deforestation(hence how it got it's name) then there is an issue
A material will change from one state or phase to another at specific combinations of temperature and surrounding pressure. Typically, the pressure is atmospheric pressure, so temperature is the determining factor to the change in state in those cases.
Names such as boiling and freezing are given to the various changes in states of matter. The temperature of a material will increase until it reaches the point where the change takes place. It will stay at that temperature until that change is completed.