Although physical and chemical changes can both result in a change of state, such as from liquid to gas or solid, the two processes are completely different. In a physical change, the matter simply undergoes a change in state, such as by freezing or being dissolved in water.Know More
However, the actual molecules in the substance remain chemically identical despite this change. This is the opposite of a chemical change, where the molecules undergo a chemical reaction that forms new chemical substances. This process is not reversible, as the actual chemical structure of the various atoms has been changed, unlike in a physical change, which can always be reversed. In chemical changes, the atoms in the substance always break apart or join together to form new compounds.
For instance, water can also be boiled to create steam or frozen to create ice, but each of these substances still have the same chemical makeup, H20. However, when gasoline is burned, the result is two new substances, carbon dioxide and water vapor. Similarly, when iron is exposed to oxygen, the two react to form iron oxide, or rust. Although the layers of iron underneath the rust are still pure, the chemical change at the surface is permanent, as the iron oxide cannot be changed back into pure iron.Learn More
Examples of chemical changes include burning of wood, digestion of sugar, an exploding firecracker, reactions between salts and acids and lighting a matchstick. A chemical change involves changes at the atomic and molecular level.Full Answer >
Chemical changes within matter always use energy; physical changes sometimes use energy, though they use much less energy than chemical changes. Physical changes use energy to change the physical state of a substance. Chemical changes either release or absorb energy when changing a substance into a completely new one.Full Answer >
Heat is involved in chemical change in two ways; chemical changes either result in heat being added to or removed from an object, and chemical changes require a certain amount of heat before they can take place. Both of these two mechanisms of chemical change involve the heat characteristics of the involved substance or substances and the environment in which the chemical change is taking place.Full Answer >
The term "chemical reaction" refers to any process that changes a set of chemical substances to another. That is, the substances that are put into a chemical reaction are different, on a molecular level, from those that result.Full Answer >