Chemical Reactions

Teacher Note

Use this student response to evaluate students’ prior knowledge of the concept. Ask students to be prepared to explain the reasoning for their answers.

This is a formative assessment.

Teacher Note

This formative assessment item is intended to provide the teacher with feedback on prior knowledge of this topic. Students should have learned that reactants are the substances entering a reaction, and products are created by the reaction.

As a class discussion, elicit from students other examples of substances that can be either reactants or products, depending on the reactions. For example, carbon dioxide is a product of a combustion reaction, but it is a reactant in photosynthesis. Sulfur dioxide forms when sulfur burns, but it reacts with rainwater to form sulfurous acid (acid rain).

Teacher Note

Students should understand that during a chemical reaction, types and numbers of atoms remain the same before and after the reaction. During the reaction, the atoms in the reactants are rearranged into the substances that form the products. An atom is the smallest unit of an element. Use this question as the basis for a class discussion on simple molecules, reactants, and products. Students should know that the elements carbon and oxygen make up carbon dioxide, and hydrogen and oxygen make up water. Therefore, these elements also have to be present in the reactants. Water is a compound, not an element. This formative assessment can help identify existing misconceptions students have about chemical reactions.

Teacher Note

This formative assessment activity is intended to provide the teacher with feedback on prior knowledge of this topic. Its main focus is to determine whether students are aware that a chemical reaction is a multistage process.

Divide students into pairs or small groups to answer this question. To reinforce this concept, provide each group with a model of one glucose molecule (C₆H₁₂O₆) and six oxygen molecules (O₂). Have students take the models apart and form six carbon dioxide molecules and six water molecules from the atoms in the reactants, following the sequence shown in the question.

Teacher Note

In this formative assessment have students discuss as a class why choices B, C, and D are incorrect. If either the type or number does not match, an equation does not accurately represent a chemical reaction.

Have students discuss as a class why choices B, C, and D are incorrect. For example, in choice B, one unit of contains only one Na atom, and the reactants contain two Na atoms. Similar reasoning can be used for other reactants and products.