In his experiment that led to the discovery of oxygen, Priestley heated some red mercuric oxide and caused it to break apart. The chemical reaction is:

Question

HgO (s) → Hg (s) + O2 (g)

Is this chemical reaction balanced? Why or why not?

Responses

Yes, because the number of mercury atoms is the same on both sides.
Yes, because the number of mercury atoms is the same on both sides.

Yes, because the number of both mercury and oxygen atoms is the same on both sides.
Yes, because the number of both mercury and oxygen atoms is the same on both sides.

No, because the number of both mercury and oxygen atoms is different on both sides.
No, because the number of both mercury and oxygen atoms is different on both sides.

No, because the number of oxygen atoms is different on both sides.

Answer 1

The correct response is:

No, because the number of both mercury and oxygen atoms is different on both sides.

To analyze the reaction:

Reactants:

• 1 Hg (mercury)
• 1 O (from HgO)

Products:

• 1 Hg (mercury)
• 2 O (from O2)

In the reactants, there is 1 mercury atom and 1 oxygen atom (from HgO), while in the products, there is still 1 mercury atom but 2 oxygen atoms (from O2). Thus, the oxygen atoms are not balanced, and therefore the reaction is not balanced overall.