When the body becomes dehydrated a chemical signal is sent that causes nephrons in the kidneys to absorb more water and excrete more salts This is an example of a?
Toasting a marshmallow is actually a chemical change. The marshmallow becomes black and crispy, it also no longer tastes the same. Thus, it is a chemical change. Roasting a marshmallow is an example of a chemical change. Generally when you heat food in the process of cooking, you will cause a chemical change.
Melting copper is an example of a physical change. The chemical change is the chemical produced when the copper is melted. e.g. when a candle melts the solid wax becomes liquid wax, that's the physical change the wick that is lit is producing C (carbon), CO2 (carbon dioxide) and H2O (water). A chemical change occurs when at least one new chemical is formed.
There are many energy changes which take place when burning a match. First, kinetic or movement energy is used to scrape the match. Then, the chemical energy stored in the match becomes heat energy of the flame. I am not familiar with your use of the term physical energy, but if by this you mean kinetic energy then yes this would be an example of physical energy into chemical energy.
Unsaturated hydrocarbons are hydrocarbons which contain one or more double carbon bonds in the chemical structure. They can become saturated hydrocarbons in the event of chemical reactions which change the structure to have only single carbon bonds - for example this occurs to an extent when unsatured cooking oil becomes saturated during cooking and becomes more solid, saturated in content.
In a chemical reaction the starting materials are treated as reactants. A chemical reaction example: N2 (nitrogen) + 3H2(hydrogen) <=> 2NH3 (ammonia), Nitrogen and hydrogen are considered as chemical reactants. In any chemical balance equation left-hand compounds are called as chemical reactants. Another example of the above is "the chemical reagent".