Physical and chemica changes.pdf

Physical change There are many cases where a substance changes the way it looks, feels or behaves, even when no chemical change has taken place. If no new substance is formed during the change, then the process is classified as a physical change. When you break a plate, you have changed the way...

Physical change There are many cases where a substance changes the way it looks, feels or behaves, even when no chemical change has taken place. If no new substance is formed during the change, then the process is classified as a physical change. When you break a plate, you have changed the way the plate looks but you have not created any new substance. This then is a physical change. It is important to be able to identify physical changes to distinguish them from chemical changes. Physical changes are happening whenever: materials or objects are broken or crushed into smaller pieces changes of state happen. A physical change is happening, for example, when a solid melts to form a liquid, or when a liquid boils to form a gas a mixture is created by mixing different materials together without them reacting something is dissolved in a liquid. For example, the characteristics of sugar change when it is dissolved in water. The characteristics of the water change too. No new substance has been formed, however, and you can still taste the sugar and can easily get it back by evaporating off the water. Dissolving one material in another creates a mixture known as a solution mixtures are separated, such as when sand is filtered from wat or fresh water is distilled from seawater. Chemical change The key difference between a physical change and a chemical change is that new substances are formed in a chemical change. When a chemical change occurs, scientists say that a chemical reaction has taken place. Chemical changes happen regularly in everyday life. For example, it’s difficult to eat a lump of raw dough. Cook it, however, and the dough changes into a new substance called bread. By heating the dough in the oven, you have caused a chemical reaction to occur. Anywhere you see a new substance being produced, you can be sure that there has been a chemical change— whether it is cooking meat, letting an apple turn brown in the sun or leaving iron to rust in the rain. Chemical reactions are happening whenever: food is cooked fruit and vegetables ripen something that was living rots and decays something is burnt something explodes a metal corrodes.