A catalyst is defined as the substance that helps in increasing the rate of a chemical reaction by lowering the activation energy. A catalyst never gets consumed in a chemical reaction.
When a catalyst lowers the activation energy then molecules with much less energy are also able to participate in the chemical reaction. Hence, formation of products occur rapidly and thus rate of reaction increases.
Therefore, we can conclude that the catalyst is unchanged and is separate from the products after a chemical reaction has occurred.
"Normal red blood cells are rounded and disk-shaped. In sickle cell anemia, some red blood cells become deformed, so they look like sickles used to cut wheat. These unusually shaped cells give the disease its name. Sickle cell anemia is one of a group of disorders known as sickle cell disease."
Burning wood is a chemical change and not a physical change because the carbon reacts with the oxygen, and that creates ash and smoke, you cannot undo ash and smoke, so therefore, it's only a chemical change
