Your teacher asks you to follow the instructions in a lab to produce several known chemical reactions. During these procedures, you are required to record any observations that suggest chemical reactions have occurred. Which of these list of observations best describes evidence of chemical reactions?

There are five evidences that tell whether a chemical change has occurred. These are change of color, change of odor, change in temperature or energy, formation of gas and formation of a precipitate.

Explanation:

Chemical Change - This is a type of chemical reaction which occurs when the properties of one or more atoms change and results into a newly formed substance.

Let's have a further discussion of the evidences.

1. Change of Color - Color change is caused by the combination of two or more substance with different molecular structures. A popular example of this is the Statue of the Liberty, which is made of copper plates. Due to the exposure of copper to elements like water, it changed color.

2. Change of Odor - This can be best presented with rotting food. During the rotting process, the food undergoes a chemical reaction. The result is a rotten smell.

3. Change in Temperature or Energy - An example of this is the burning of wood. Its change is considered non-reversible.

4. Formation of Gas - This can be best presented with the cake batter (the one being used to make cakes or pancakes). The batter rises which means it is forming gas. This is caused by the reaction of the baking soda and the acid.

5. Formation of a Precipitate - This occurs when two soluble salts combine and their outcome is an insoluble salt (this is the precipitate).

Take note that if any of these evidences occur, then there's definitely a chemical reaction.