Class6 science chapter 6 question answer in oav school in english medium

What is a reversible change? A reversible change is a change that can be reversed to get back the original substance. Example: Melting of ice into water and freezing of water back into ice.

What is an irreversible change? An irreversible change is a change that cannot be reversed to get back the original substance. Example: Curdling of milk into yogurt.

Give two examples of changes that can be reversed.

• Melting of ice into water.
• Stretching a rubber band.

Give two examples of changes that cannot be reversed.

• Burning of paper.
• Rusting of iron.

What is a chemical change? A chemical change results in the formation of one or more new substances. These changes are usually irreversible. Example: Burning of wood.

What is a physical change? A physical change involves a change in the physical properties of a substance, but not its chemical composition. These changes are often reversible. Example: Boiling of water into steam.

Why is burning of wood a chemical change? When wood burns, new substances like ash and smoke are formed, which cannot be converted back into wood. Therefore, it is a chemical change.

Why is dissolving sugar in water a physical change? When sugar dissolves in water, the sugar particles disperse in the water. Upon evaporation of water, the sugar can be recovered. The chemical nature of sugar does not change, so it is a physical change.

Why is curdling of milk a chemical change? The chemical composition of milk changes due to the action of lactic acid bacteria, forming yogurt. Yogurt cannot be converted back into milk, so it is a chemical change.

Why is stretching a rubber band a physical change? Stretching a rubber band changes its shape, but its chemical composition remains the same. When the tension is released, it returns to its original shape. Therefore, it is a physical change.