Question

understanding concepts

1. explain how a physical change differs from a chemical change
2. classify each of the following as a physical or a chemical change. explain why

(a) garbage rotting
(b) cutting up carrots
(c) a silver spoon turning black
(d) making tea from tea leaves
(e) bleaching a stain
(f) boiling an egg

1. during a power failure, blair lit four identical candles. he placed three candles very close together on a table, and one on a different table.

Explanation:

1. A physical change only alters the physical properties (such as shape, state) of a substance without changing its chemical composition. A chemical change results in the formation of a new substance with different chemical properties through a chemical reaction.

2.
(a) Garbage rotting is a chemical change as bacteria break down organic matter, forming new substances like methane and carbon - dioxide.
(b) Cutting up carrots is a physical change as it only changes the shape and size of the carrots, not their chemical composition.
(c) A silver spoon turning black is a chemical change. Silver reacts with sulfur - containing compounds in the air to form silver sulfide.
(d) Making tea from tea leaves is a physical change. The tea - making process mainly involves dissolving the soluble components of tea leaves in water without changing the chemical nature of the main substances in a fundamental way.
(e) Bleaching a stain is a chemical change. Bleach reacts with the colored substances in the stain to break them down into color - less substances.
(f) Boiling an egg is a chemical change. The heat causes the proteins in the egg to denature, changing their chemical structure.

Answer:

1. A physical change doesn't change the substance's chemical composition, while a chemical change forms a new substance.

2.
(a) Chemical change; bacteria break down organic matter to form new substances.
(b) Physical change; only changes shape and size.
(c) Chemical change; silver reacts with sulfur - containing compounds.
(d) Physical change; mainly dissolving soluble components.
(e) Chemical change; bleach reacts with colored substances.
(f) Chemical change; heat denatures egg proteins.