Suppose 10 atoms of carbon react with 20 atoms of oxygen to form 10 molecules of carbon dioxide. According to the law of conservation of matter, how many atoms are present in this reaction?

1. 20
2. 10
3. 15
4. 30

1 answer

The law of conservation of matter states that matter cannot be created or destroyed in a chemical reaction, only rearranged. Thus, the number of atoms present before the reaction must be equal to the number of atoms present after the reaction.

In this case, we start with 10 atoms of carbon and 20 atoms of oxygen, for a total of 30 atoms. After the reaction, we have 10 molecules of carbon dioxide, which means there are 10 atoms of carbon and 20 atoms of oxygen (since each molecule of carbon dioxide has one carbon atom and two oxygen atoms).

Therefore, the total number of atoms present in this reaction is 10 + 20 = 30.

The correct answer is 4. 30.