Answer:
1. Chemical change - Rusting is an example of a chemical change. A chemical property describes the ability of a substance to undergo a specific chemical change. A chemical property of iron is that it is capable of combining with oxygen to form iron oxide, the chemical name of rust.
2. Chemical change - burning of magnesium ribbon is a chemical change. The burning of coal, wood, or leaves is also a chemical change. In fact, the burning of any substance is a chemical change. Burning is always accompanied by the production of heat.
3. Physical & chemical change - When a molecule dissolves, it is simply surrounded by the molecules of the solvent -- its chemical composition has not changed. Therefore, when grease dissolves in soapy water, it is merely going through a physical change.
4. Chemical change - Leaves yellow as the result of a biochemical process, meaning it is a chemical reaction that occurs in a living thing. Even though some people think the change in the color of tree leaves in fall is an example of a physical change, the color change actually occurs because of chemical changes inside the leaf.
5. Chemical change - In the ripening of fruits, the chemical composition of fruit changes and it is irreversible. Hence ripening of fruits is a chemical change. Growing a tree from a plant is an irreversible change that is accompanied by a change in chemical composition. Hence, it is a chemical change.
6. Chemical change - Chemical digestion involves breaking large molecules into smaller molecules. This type of digestion is often carried out by large protein molecules called enzymes. Each enzyme breaks down a specific type of molecule. For example, pepsin is an enzyme that breaks down proteins. Amylase is an enzyme that breaks down starch. The end result of chemical digestion is a mixture of small molecules that can pass through cell membranes into cells. Once inside the cells, these molecules supply a source of chemical energy and chemical building blocks for the cell to carry out life processes.
7. Physical change - The size or shape of matter may be changed, but no chemical reaction occurs. Physical changes are usually reversible. Note that whether a process is reversible or not is not truly a criterion for being a physical change. For example, smashing a rock or shredding paper are physical changes that cannot be undone.
8. Chemical change - Baking a cake is a great way to do science without even knowing it. When you bake a cake, the ingredients go through a chemical change. A chemical change occurs when the molecules that compose two or more substances are rearranged to form a new substance! When you start baking, you have a mixture of ingredients.
9. Chemical change - During the process of digestion, the food is broken down into smaller molecules. The salivary glands present in our mouth help in the breakdown of the food. In this process, there is a formation of a new substance. Therefore, it is considered to be a chemical change.
10. Chemical change - The souring of milk is a chemical reaction. Milk that is spoiled is sour, with a foul taste and odor. It can also become lumpy and curdled.
11. Physical change - As an ice cube melts, its shape changes as it acquires the ability to flow. However, its composition does not change. Melting is an example of a physical change.
12. Physical change - Breaking glass is an example of a physical change because if you break it, it is still glass. It didn't change to another substance.
13. Physical change - Boiling water is an example of a physical change and not a chemical change because the water vapor still has the same molecular structure as liquid water (H2O). If the bubbles were caused by the decomposition of a molecule into a gas (such as H2O →H2 and O2), then boiling would be a chemical change.
14. Physical change - Evaporation of alcohol is a physical change, burning of the same is a chemical change.
15. Physical change - A physical change is a usually reversible change in the physical properties of a substance. Some examples include crumpling paper, melting an ice cube, casting silver in a mold, and breaking a glass cup.
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