Paragraph: (Science-textbook/science-g5-53.txt)
Sent 1: Chemical changes produce new substances.
Sent 2: For this reason, they often cannot be undone.
Sent 3: Some chemical changes can be reversed, sort of.
Sent 4: To do so requires another chemical change to take place.
Sent 5: For example, you can undo the tarnish on copper pennies by placing them in vinegar.
Sent 6: The acid in the vinegar reacts with the tarnish.
Sent 7: This is a chemical change that makes the pennies bright and shiny again.
Sent 8: You can try this yourself at home to see how well it works.
Sent 9: Other chemical changes cannot be reversed at all or may be difficult to do.
Sent 10: Rusting is a chemical change.
Sent 11: If metal rusts, the best you can do is to sand off the rust to get down to the shiny metal.
Sent 12: Although the metal may now be shiny, the rust was removed.
Sent 13: The rust was not changed back into the original metal.
Sent 14: Some chemical reactions occur in only one direction.
Sent 15: These reactions are called irreversible reactions.
Sent 16: For example, you cannot change a fried egg back into a raw egg.
Sent 17: Can you think of some other irreversible reactions related to cooking?
Sent 18: Would you like a piece of cake?

Question: What can you do to make pennies bright and shiny again? (false/challenge)

You can use vinegar to remove the tarnishes by causing another chemical change when they react.
placing pennies in vinegar
baking them
placing them in oil
raw eggs

Question: Can chemical changes be undone? (false/challenge)

Not really, but you can create a new chemical change that will bring the substance back to its previous state.
sometimes
yes- all of the time
never

Question: What are some examples of irreversible reactions? (false/additional)

rust
baking a cake
fried egg back into a raw egg
mixing water and oil