Which sign indicates a chemical change rather than a physical change?

Which sign indicates a chemical change rather than a physical change?

• A. Ashes form after burning wood
• B. Water freezes
• C. Ice melts
• D. Sugar dissolves in water

Answer: (A)

The main idea is that a chemical change produces new substances with different properties, often accompanied by energy release. When wood burns, it reacts with oxygen in the air to form ashes and gases. The original wood is transformed into entirely different materials, and you can’t simply turn ashes back into wood by ordinary means. That formation of new substances and the energy change show a chemical change. The other examples are physical changes. Freezing water into ice changes only how the substance is arranged (a change of state), but it remains water. Melting ice is the reverse, still water. Sugar dissolving in water spreads the sugar particles through the water, but the chemical identity of the sugar doesn’t change, and the mixture can be separated back into sugar and water, so it’s a physical change.

The main idea is that a chemical change produces new substances with different properties, often accompanied by energy release. When wood burns, it reacts with oxygen in the air to form ashes and gases. The original wood is transformed into entirely different materials, and you can’t simply turn ashes back into wood by ordinary means. That formation of new substances and the energy change show a chemical change.

The other examples are physical changes. Freezing water into ice changes only how the substance is arranged (a change of state), but it remains water. Melting ice is the reverse, still water. Sugar dissolving in water spreads the sugar particles through the water, but the chemical identity of the sugar doesn’t change, and the mixture can be separated back into sugar and water, so it’s a physical change.