what do you mean by physical change and chemical change
Physical change Physical changes occur when objects or substances undergo a change that does not change their chemical composition. This contrasts with the concept of chemical change in which the composition of a substance changes or one or more substances combine or break up to form new substances. In general a physical change is reversible using physical means. For example, salt dissolved in water can be recovered by allowing the water to evaporate.
Isotope Isotopes are atoms of the same element having the same numbers of protons (atomic number), but different numbers of neutrons. They have same chemical properties due to the same electron configuration, but different physical properties.[citation needed]
Paris Peace Accords
Primary nutritional groups Phototrophs: Light is absorbed in photo receptors and transformed into chemical energy. Chemotrophs: Bond energy is released from a chemical compound.