Unit 11: Chemical Reactions Study guide
1. Balance the following equations:
2 KClO3  2 KCl + 3 O2
____Fe2O3 + 3 H2  2 Fe + 3 H2O
3 Pb(NO3)2 + 2 AlCl3
3 AgNO3 + _____K3PO4
3 PbCl2
+ 2 Al(NO3)3
____Ag3PO4 + 3 KNO3
2. Count the total number of atoms in each molecule.
Al2(SO4)3
Zn
3NH3
17 atoms
1 atom
12 atoms
3(NH4)2SO4
45 atoms
3. How many nitrogen atoms are there in the molecule 3NH3?
3
4. How many oxygen atoms are there in the molecule CaCO3?
3
5. How many carbon atoms are there in the molecule Na2CO3?
1
6. How many hydrogen atoms are there in the molecule NaOH?
1
7. How many chlorine atoms are there in the molecule 6Cl2?
12
8. What is an exothermic reaction?
An exothermic reaction releases energy. These reactions give off heat, and the temperature
increases during the reaction. Heat energy is a product in an exothermic reaction.
9. What is an endothermic reaction?
An endothermic reaction needs energy continually added to it. These reactions absorb heat
and the temperature decreases (feels cold). Heat energy is a reactant or starting material in an
endothermic reaction.
10. Is the following reaction endothermic or exothermic? How do you know?
CaCO3 + Heat
CaO + CO2
Endothermic because heat is required to start the reaction. Heat is a reactant.
11. Is the following reaction endothermic or exothermic? How do you know?
2SO2+O2
2SO3 + Heat
Exothermic because heat is given off or released. The heat is a product.
12. Why do we balance chemical equations? What law does it support?
We balance equations because you have to the same materials at the beginning and end. This
is because of the law of conservation of matter/mass. The law states that matter can’t be
created or destroyed. This means that we have to balance equations because you can’t make
stuff appear out of nowhere. If it was a reactant than it should be present in the same amount
in the products, now it doesn’t look the same, but it is definitely there.
13. Write the correct formulas for the following compounds. Remember about the valence
electrons. Draw a lewis dot structure, if necessary.
Sodium chloride
potassium bromide
carbon monoxide
NaCl
KBr
Dihydrogen monoxide
CO
magnesium fluoride
H2O
MgF2
beryllium oxide
BeO
14. What is a synthesis reaction?
A synthesis reaction takes 2 elements and combines them to form 1 product
15. What is a decomposition reaction?
A decomposition reaction breaks a single compound down into smaller compounds or
elements.
16. What is a single replacement reaction?
Single replacement reactions replaces one ion in a compound with another element. (starts
with 1 compound and 1 element)
17. What is a double replacement reaction?
Double replacement reactions switch 2 elements from one compound to another. (starts with 2
compounds)
18. Identify the following reactions as synthesis, decomposition, single replace or double
replacement and justify your answer. (you don’t have to balance these)
1. ____AlBr3 + ____Cl2
____AlCl3 + _____Br2----single replacement
2.
____Al2(SO4)3 + _____Ca(OH)2
replacement
3. _____Cu + _____AgNO3
_____ Al(OH)3 + _____CaSO4 ----double
_____Cu(NO3)2 + ____Ag-----single replacement
4. _____KClO3
5. ____P4 +
____KCl + _____O2-----decomposition
_____O2
_____P2O5 ----synthesis
6. ____AlI3 + _____HgCl2
7. _____NaClO3
8. ____H2 +
____AlCl3
_____NaCl
____O2
+ _____HgI2---double replacement
+ ____O2 ----decomposition
_____H2O----synthesis
19. In the following chemical equation, which compounds are the reactants?
____AgNO3 + _____K3PO4
____Ag3PO4 + ____KNO3
AgNO3 and K3PO4 are the reactants
20. In the following chemical equation, which compounds are the products?
____AlI3 + _____HgCl2
____AlCl3
+ _____HgI2
AlCl3 and HgI2 are the products
21. Draw a graph of the energy in an endothermic reaction.
Energy (J)
Time (s)
22. Draw a graph of the energy in an exothermic reaction.
Energy (J)
Time (s)