Chemical & Physical Properties

When we freeze water, it undergoes a physical change. Freezing is the process in which a substance changes from a liquid state to a solid state due to the removal of heat energy. In the case of water, when it reaches its freezing point, the water molecules slow down and arrange themselves into a crystalline structure, forming ice. This change is reversible, and the chemical composition of water remains the same. Therefore, freezing water is a physical change.

Boiling water is a physical change because it involves a change in the state of matter from liquid to gas without any change in the chemical composition of water. The water molecules are heated and gain enough energy to overcome intermolecular forces, resulting in the formation of water vapor. However, the chemical properties of water remain the same before and after boiling.

Burning wood in a fireplace is a chemical change because it involves a chemical reaction. The wood undergoes combustion, combining with oxygen in the air to produce heat, light, and various byproducts such as carbon dioxide and ash. This change is irreversible and results in the formation of new substances with different properties than the original wood.

When we bake bread, it undergoes a chemical change. This is because the process of baking involves the chemical reactions between the ingredients of the bread, such as the flour, yeast, and water. These reactions cause the dough to rise and transform into a solid, cooked bread. Therefore, the change from dough to bread is a chemical change rather than a physical change.

When we dissolve sugar into water, it undergoes a physical change. This is because the sugar molecules are dispersed and evenly distributed throughout the water, forming a homogeneous mixture. The chemical composition of the sugar does not change during this process.