Hints, Proof and Revolutions: teacher key

Mixing and Reactions, grade 12 edition, written for 12th grade and up. Color changes, gas and temperature changes are only hints that a reaction happened. Kitchens, rust and the Chemical Revolution show how chemists test for change.

Read the book. Print this page for the key.

Questions and answers

1. What is the only sure test that a reaction took place?
   • Checking whether the substances after the change differ from the ones before (answer)
   • Seeing bubbles of gas
   • Noticing a color change
2. What happens at equilibrium?
   • Only the forward reaction runs
   • The forward and reverse rates are equal and the amounts of each substance stay constant (answer)
   • The reaction stops forever
3. Where does the carbon dioxide in bread dough come from?
   • Baking powder
   • The Maillard reaction
   • Yeast, during fermentation (answer)
4. Why are color change, gas and temperature change called only hints?
   • Because chemists never see them
   • Because they do not prove that the substances after the change differ from those before (answer)
   • Because they only appear in kitchens
5. What did Lavoisier's accurate balance make possible?
   • Measuring the mass of the metal, the calx and the surrounding air (answer)
   • Seeing atoms directly
   • Making poisonous fumes

Words

• equilibrium: steady balance
• caramelization: sugar browning
• corrosion: metal wear
• reversible: runs both ways
• fermentation: yeast making gas