ChemThink; Chemical Reations

Note: My answers are in red.


1. Starting materials in a chemical reaction are called: starting points.

2. The ending materials in a chemical reaction are called: ending points.
3. The arrow indicates a: chemical change has taken place.

4. All reactions have one thing in common: there is a: rearrangement of bonds.

5. Chemical reactions always involve breaking old bonds, forming new bonds, or both.

6. In all reactions we still have all of the same atoms at the end that we had at the start.
7. In every reaction there can never be any missing atoms or new atoms.
8. Chemical reactions only rearrange the bonds in the atoms that are already there.

9. If we use only the atoms shown, we’d have 2 atoms of H and 1 atoms of O as reactants. This would make 1 molecule of H2O, but we'd have 1 atom of O leftover. However, this reaction only makes H2O.


10. So to make H2O from oxygen gas and hydrogen gas, the balanced equation would be:

2 H2 + 1 O2 -> 2 H2O
Which is the same as: 4 H reactants with 4 atoms of them in the product. 2 O reactants with 2 of them in the product.

11. This idea is called the: Law of Conservation of Mass

12. There must be the same type and the same number of atoms before the reaction (in the reactants) and after the reaction (in the products).

13. What is the balanced equation for this reaction?
2 Cu+ 1 O2 --> 2 CuO

14. In the unbalanced equation there are:

Reactants --> Products
Cu atoms 1 Cu atoms 1
O atoms 2 O atoms 1

15. To balance this equation, we have to add 2 molecules to the products, because this reaction doesn’t make lone O atoms.

16. When we added a molecule of CuO, now the number of O atoms is balanced but the number of Cu atoms don’t match. Now we have to add more Cu atoms to the reactants.

17. The balanced equation for this reaction is

2 Cu+ 1 O2 --> 2 CuO

Reactants --> Products

# Cu atoms 2 = # Cu atoms 2

# O atoms 2 = # O atoms 2

18. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.)

1 CH4 + 1 O2 --> 1 H2O + 1 CO2

# of atoms in Reactants Element # of atoms in Products
1 C 1
4 H 2
2 O 3

19. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.)

1 N2 + 3 H2 --> 2 NH3

20. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.)

2 KCIO3 --> 2 KCI + 3 O2

21. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.)

4 AI + 3 O2 --> 2 AI2O3

SU M M A R Y

Chemical reactions always involve: breaking bonds, making bonds, or both.

The Law of Conservation of Mass says that the same atoms must be: There must be the same amount of present before and after the reaction.

coefficients; atoms