What is the type of the following reaction? 2Na solid plus Cl₂ gas, giving you 2NaCl solid. A) Double displacement, B) decomposition, C) oxidation–reduction, D) single displacement, or E, neutralization.
In this reaction, two atoms of sodium react with one molecule of chlorine gas to give two ionic formula units of sodium chloride. This is a combination reaction because two substances are chemically combining together to form one new product. However, combination reaction is not on the list of possible answers. Let’s briefly discuss the types of reactions given in answers A to E.
Let’s look at the double displacement reaction. Displacement can also be called replacement or substitution. In sports such as soccer, one player can be substituted by or replaced by another player. In this reaction, the same thing occurs. Element D can substitute or replace element B. Because it is a double displacement, element A can substitute for element C. The elements have swapped places. And we end up with CB plus AD as the products. There is no swapping or substitution in the equation given to us. So we know that A cannot be the answer.
Let’s look at B, decomposition. A decomposition reaction is usually for one reactant, in this case AB, breaking apart to form more than one product. In this case, there are two products, A and B. The equation given to us is the combination or joining together of two reactants. So B is not an answer.
Answer D, single displacement, is similar to A, a double displacement, except that here only one substance or one element is being removed from a compound. Here, element A is substituting for or replacing or displacing element B in the compound BC. And we end up with the products B plus AC. Answer D is not an answer.
Answer E, neutralization, is the reaction of an acid with a base to give salt plus water. The product in the equation given to us is a salt, in other words an ionic compound. Sodium chloride is ionic. However, we do not have water as another product. Also, the reactants, sodium and chlorine, are not acids or bases. So answer E is not the correct answer.
Let’s see if the correct answer is C, oxidation–reduction. The oxidation state of an element by itself is zero. So sodium and chlorine have an oxidation state of zero. The oxidation states of the elements in a neutral compound must add up to zero. Metals generally have positive oxidation states because if they were to form ions, they would lose electrons. Nonmetals, usually but not always, have negative oxidation states. This is because if a nonmetal were to form an ion, it usually gains electrons.
Sodium loses one electron when it reacts to form a compound. Chlorine gains one electron when it reacts to form a compound. And these two oxidation states add up to zero. Sodium has undergone oxidation. Chlorine has undergone reduction. In this reaction, both oxidation and reduction have occurred. So this type of reaction is C, an oxidation–reduction reaction.