Key Idea: Many substances react chemically in predictable ways with other substances to form new substances with different characteristic properties.

Students are expected to know that:

  1. When substances react chemically one or more new substances are formed.
  2. If a new substance does not appear, a chemical reaction did not occur.
  3. The products of a chemical reaction can be identified as new substances because each product has different characteristic properties from the original substances under the same conditions.
  4. Liquids, solids, or gases can be reactants or products in chemical reactions.
  5. It is possible for a single substance to undergo a chemical reaction, such as when the substance is heated or an electrical current flows through the substance.
  6. It is not true that all chemical reactions are irreversible.

Boundaries:

  1. Students are not expected to know that chemical reactions involve the rearrangement of atoms into new molecules. This idea is addressed in a later idea (Idea D).
  2. Students are also not expected to know that nuclear reactions are not chemical reactions nor why nuclear reactions are not chemical reactions. Nuclear reactions are addressed in later ideas (4E/H6* and 4G/H6*)
  3. By “predictable ways,” we mean that the same products will be formed when the same reactants are combined regardless of location and experimental set-up. Students are not expected to predict what the products of a reaction will be.
  4. Students are expected to know that the original substances in a chemical reaction are called reactants and the resulting substances are called products but they will not be assessed on these definitions.
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

SCM038

Chemical reactions involve two reactants (Cavallo et al., 2003; Eilks et al., 2007).

66%

58%

SCM036

A chemical change is irreversible (Cavallo et al., 2003; Calik et al., 2005).

36%

34%

SCM020

A chemical reaction occurs when a substance dissolves (Novak et al., 1991; BouJaoude, 1992; Abraham et al., 1994; Ahtee et al., 1998; Stavridou et al., 1998; Valanides, 2000; Eilks et al., 2007)

29%

21%

SCM019

A chemical reaction occurs during a change of state (Hall, 1973; Novak et al., 1991; BouJaoude, 1992; Ahtee et al., 1998; Stavridou et al., 1998).

19%

16%

SCM070

A chemical reaction always happens when two substances are combined together (AAAS Project 2061, n.d.).

18%

16%

SCM040

Chemical reactions involve only the production of gas (Cavallo et al., 2003).

11%

13%

SCM039

Chemical reactions involve liquids only (Cavallo et al., 2003).

13%

11%

SCM056

A chemical reaction always happens when two liquids are combined together (DeBoer et al., 2008).

15%

9%

SCM063

Chemical reactions occur between solids and liquids but not between solids and gases (AAAS Project 2061, n.d.).

12%

10%

SCM037

All chemical reactions are inherently dangerous (Cavallo et al., 2003).

11%

11%

SCM062

A solid substance is always formed during a chemical reaction (DeBoer et al., 2008).

9%

8%

SCM002

A chemical reaction must take place in a laboratory (Herrmann-Abell et al., 2009).

8%

7%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.