Chemical changes occur when energy is added or substances are mixed, causing chemical bonds to break and form a new substance with different properties. There are four types of chemical reactions: synthesis, decomposition, single and double substitution. Endothermic reactions absorb energy, while exothermic reactions produce energy. Color and smell changes can indicate a chemical change, which is irreversible unlike physical changes.
A substance undergoes a chemical change when its molecular structure is changed by adding energy to the substance or by mixing two substances together. In both cases, chemical bonds within the atomic structure break down and reattach to form another substance. The new substance usually has different physical and chemical properties than the original.
There are two types of changes in chemistry. A physical change is when the shape of the substance changes, such as normal phase changes in water due to temperature. As the temperature rises from the freezing point of water, it changes from the solid form of water to ice; to the liquid form, water; in the gaseous form, vapor.
A chemical change occurs when one substance is transformed into another substance at the atomic level, and the chemical reactions can be classified into four groups. A synthesis reaction occurs when two or more simple materials are combined to create a third, more complicated material. A decomposition reaction is the breaking down of a more complex substance into its simple parts. In single substitution reactions, one element has replaced another element in a more complex material to create a new substance. Double substitution reactions are similar to single substitution reactions, only with two elements in one material replacing two elements in another compound to create the final material.
The laws of mass and conservation of energy state that neither mass nor energy is created or destroyed, only changed to a different state. Therefore, chemical changes are also classified based on what happens to the energy as a result of the reaction. Endothermic reactions absorb energy, usually heat or electricity. Exothermic reactions produce energy, making the substance feel hot due to the energy coming from the chemical bonds of substances.
There are several ways to tell if a chemical change has occurred. A change in the color of a substance can mean that a chemical change has taken place. The color changes of leaves in autumn, the reddish brown of rust and the browning of the flesh of an apple are all examples of chemical changes shown by color changes in a substance.
A change in the smell of a substance can also be a sign that a chemical change has taken place. The sulfuric smell of rotten eggs and the smell of spoiled milk are signs that the eggs and milk have undergone chemical reactions. While the smell is, perhaps, more noticeable, there may be other visible indications of that change as well.
Unlike physical changes, chemical changes are irreversible. Breaking an aluminum can with your foot is a physical change. In theory, it is possible to remove the dents and wrinkles put into the aluminum and return it to its original state. Burning a piece of paper is a chemical change. Once burned, it cannot be unburned.
Protect your devices with Threat Protection by NordVPN
