Weighing the Air: teacher key

Mixing and Reactions, grade 10 edition, written for 10th grade. Lavoisier, Priestley and Dalton changed what chemistry said about burning, water and atoms. Careful weighing showed that matter is not lost in a reaction, and catalysts and enzymes speed reactions up.

Read the book. Print this page for the key.

Questions and answers

1. What did Lavoisier find when he heated metals in closed vessels and weighed everything?
   • The air gained more mass than the metal lost
   • The metal lost as much mass as the air gained
   • The metal gained as much mass as the air lost (answer)
2. What did Priestley call the air he captured from heated mercury calx?
   • Oxygen
   • Phlogiston
   • Dephlogisticated air (answer)
3. Why does a balanced chemical equation have equal numbers of atoms on both sides?
   • It fits the law of conservation of matter (answer)
   • Because atoms change into other atoms
   • Because products always weigh more
4. What does a catalyst do to the overall reaction?
   • Changes the finish of the reaction
   • Is used up as it works
   • Speeds it up while the same start and finish stay the same (answer)
5. Why does each enzyme fit only certain reactants?
   • Its active site is where a substrate binds (answer)
   • It is used up in the reaction
   • It has a negative enthalpy sign
6. What is a calx?
   • A kind of air
   • What a burned metal became (answer)
   • A tool for weighing

Words

• phlogiston: supposed burning substance
• calx: burned metal
• catalyst: speeds up reactions
• substrate: bound reactant
• exothermic: gives off heat