Using your knowledge of physical and chemical changes determine which of the following statements would indicate that a chemical change has occurred?

A. A glass is dropped onto a tile floor and shatters.
Incorrect. The glass is only changing form, so it is physical.

B. Rust forms on a metal lawn chair after a rain.
Correct! A new substance is formed (rust).

C. The boiling point of water decreases as altitude increases.
Incorrect. Boiling is a change of state, so it is physical.

D. Ice forms over a lake during a very cold winter.
Incorrect. Freezing is a change of state, so it is physical.

Sourdough bread is made by adding a small amount of starter dough which contains a lactobacillus bacterial culture to water and flour. This mixture produces gases that allow the bread to “rise” before baking. After baking, the bread has a golden brown color and a sour taste. This process of “rising” can best be classified as a chemical change because —

A. the bread tastes sour after baking
Incorrect. Taste is a physical property.

B. because the bread dough changed its shape
Incorrect. Changing shape is physical.

C. the bread has a brown color after cooking
Incorrect. Color is a physical property.

D. the gases produced by the lactobacillus allowed the bread to "rise"
Correct! Production of a gas is chemical.

Changes of state are physical changes. Using the above diagram, identify the process steps where condensation and sublimation are occurring.

A. 1 and 4
Incorrect. Changing from a solid to a liquid is melting, changing from liquid to solid is freezing.

B. 2 and 5
Incorrect. Changing from a liquid to a gas is vaporization, changing from a gas to a solid is deposition.

C. 3 and 6
Correct! Changing from a gas to a liquid is condensation, changing from a solid to a gas is sublimation.

D. 4 and 2
Incorrect. Changing from a liquid to a solid is freezing, changing from a liquid to a gas is vaporization.