ChemThink

C H E M I C A L R E A C T I O NS T U T O RI 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 has taken place. Chemical Reaction
4. All reactions have one thing in common: there is a of chemical bonds. Creation or Destruction
5. Chemical reactions always involve old bonds, new bonds, or both. Breaking old bonds, forming new bonds, or both
6. In all reactions we still have all of the at the end that we had at the start. Molecules
7. In every reaction there can never be any atoms or Different
8. Chemical reactions only in the atoms that are already Use
there.
9. hydrogen gas (H2) reacts with oxygen gas (O2) to form water (H2O)
H2 + O2 = H2O
2 atoms of H and 2 atoms of O as reactants. This would
make 1 molecule H2O but we’d have 1 atom of O leftover. However, this reaction only makes H2O.

A balanced chemical reaction shows:
a) What atoms are present before (in the reactants) and after (in the products)
b) How many of each reactant and product is present before and after.
10. So to make H2O from oxygen gas and hydrogen gas, the balanced equation would be: 2 H2 + O2 = 2H2O

# of atoms in Reactant	Elements	# 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 Kind and the same number of Atom before the reaction (in the reactants) and after the reaction (in the products).
13. What is the balanced equation for this reaction? 2 Cu + O2 = CuO
14. In the unbalanced equation there are:
Reactants Products
Cu atoms 1 Cu atoms 1
O atoms 2 O atoms 2
15. To balance this equation we need to add 1 Cu molecule to the product, because this reaction doesn’t produce lone O atoms.
16. When we added a molecule of CuO, now the number of Cu atoms is balanced but the number of O atoms don’t match. Now we have to add more O atoms to the reactants.
17. The balanced equation for this reaction is
2 Cu + 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.)
CH4 + 3O2 = 2H2O + CO2

# of atoms in the reactant	Element	# of atoms in the product
1	C	1
4	H	4
6	O	6

19. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.)
2N2 + 3H2 = 2NH3

# of elements in the reactant	Element	# of atoms in the product
4	N	4
6	H	6

20. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.)
2KClO3 = 2KCl + 3O2

# of elements in the reactant	Element	# of atoms in the product
2	KCI	2
6	O	6

21. What is the balanced equation for this reaction? (Use the table to keep track of the atoms on each side.)
Al + 3O2 = Al2O3

# of elements in the reactant	Element	# of elements in the product
1	AI	1
6	O	6

SU M M A R Y
1) Chemical reactions always involve...
The forming or breaking of chemical bonds.
2) The Law of Conservation of Mass says that the same atoms must be...
The same in amount before and after a chemical reaction. This is because matter can’t be created or destroyed.
3) To balance a chemical equation, you change the number in front of each substance until there are the same number of each type of atom in both reactants and products