PHS 100 - Self Assessment

Competency #7

Learning Objective e

Write down your answer to the following question:

When iron rusts, it combines with the oxygen in the air to make rust. This process is described in the following chemical reaction:

4Fe (s) + 3O₂ (g) 2Fe₂O₃ (s)

How would you expect the mass of iron before a reaction to compare to the mass of the rust after this process is complete?

The rust would have less mass than the iron, because there is less rust than iron
The rust and the iron would have to have the same mass according the Law of Conservation of mass because oxygen is a gas and gases do not weigh anything
The rust would have a higher mass than the iron, this reaction is an exception to the Law of Conservation of Mass
The rust would have a higher mass than the iron, because it includes the mass of the iron and the mass of the oxygen
It would depend on the amount of iron you started with, a small piece of iron would weigh less than the rust, but a large piece of iron would weigh more than the rust