Identify Chemical Reactions Practice Test

A student stirs sugar crystals into a glass of water.

Before: sugar is white crystals; water is a clear liquid.

After stirring: the sugar crystals are no longer visible, the liquid stays clear, and the water tastes sweet. If the student leaves the glass out for a long time, water can evaporate and sugar crystals can be seen again.

Which statement best describes what happened?

A student lights a dry piece of wood in a safe fire pit.

Before: the wood is a brown solid and has a woody smell.

During/after burning: bright light and heat are produced, smoke rises, and gray ash is left behind.

Which combination of observations is the strongest evidence that a chemical reaction occurred?