Chemical Reactions: Chem Think

C H E M I C A L R E A C T I O NS T U T O R I A L Q U EST I O NS :

1. Starting materials in a chemical reaction are called: reactants

2. The ending materials in a chemical reaction are called: products

3. The arrow indicates a: chemical change

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

5. Chemical reactions always involve: breaking bonds, forming 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 in the atoms that are already there.

9. Let’s represent a reaction on paper. For example, hydrogen gas (H2) reacts with oxygen gas (O2) to form water
(H2O): H2 + O2H2O
If we use only the atoms shown, we’d have 2 atoms of H and 2 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:

__1__ H2 + ___2__ O2 _____ H2O Which is the same as:

# of atoms in reactants	Element	# of atoms in product
4	H	4
2	O	2

11. This idea is called the__Law of Conservation of Mass________
12. There must be the same__mass_____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+___2__ 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 __CuO____ 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
+ __2__ O2 = __2_ CuO
This is the same thing as saying:

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 + _2____ O2 ___2__ H2O + __1___ CO2

# of atoms is Reactants	Element	# of atoms in product
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

# of atoms is reactants	Element	# of atoms in produc
2	N	1
2	H	3

20. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.) __2___ KClO3 __2___ KCl + __3___ O2

# of atoms in reactants	Element	# of atoms in products
1	K	1
1	Cl	1
3	O	2

21. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.) ___4__ Al + __3___ O2 = __2___ Al2O3

# of atoms in reactants	Element	# of atoms in products
1	Al	2
2	O	3

SUMMARY

1.) Chemical reactions always involve: They always involve making or breaking bonds, or bothe making and breaking bonds.
2.) The Law of Conservation of Mass says that the same atoms must be: There must be the same number of atoms before and after the reactions.
3.) To balance a chemical equation, you change the _coefficiants__ in front of each substance until there are the same number of each type of __atoms____ in both reactants and products