Use the chemical equation to complete the activity.

Ha(g) + l2 (g) - 2HI(g)
A student makes the following statements:
• Hydrogen always has the same oxidation number, so it has an oxidation number of +1 in both the reactant H and product
HI.
• lodine is in Group VIA, so it has an oxidation number of -1 in both the reactant I and product HI.
• Neither hydrogen nor iodine changes oxidation states, so the reaction is not a redox reaction.
In three to five sentences, describe the mistake that the student made, and determine whether or not the reaction is a redox
reaction. Explain your answer.
(4 points)

The student's mistake is assuming that the oxidation numbers for hydrogen and iodine remain constant throughout the reaction. In reality, the oxidation number of hydrogen changes from 0 in the reactant Ha to +1 in the product HI. The oxidation number of iodine also changes from 0 in the reactant I2 to -1 in the product HI. Therefore, the reaction is indeed a redox reaction because there is a change in oxidation states for both hydrogen and iodine.