Chapter 9 TEST STUDY GUIDE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
What is the force that holds two atoms together called?
A chemical bond
How do substances form during a chemical reaction?
Chemical bonds break, atoms rearrange, and form new bonds to make new substances / props.
What causes chemical bonds in molecules to break?
Molecules bump into each other.
What is needed for a chemical bond to break?
Energy
When chemical bonds break, what do atoms do?
Rearrange
What happens in an exothermic reaction?
Energy (heat) is released
What happens in an endothermic reaction?
Energy (heat) is absorbed
List the ways you know a chemical reaction is happening and not a physical change?
∙ Color change,
∙ formation of a gas or solid (precipitate)
∙ release (EXOthermic) or absorption (ENDOthermic) of heat
What is a diatomic molecule?
Two identical atoms bonded together - H2
How many atoms are represented in the formula C 11H22O11?
11 carbon + 22 hydrogen + 11 oxygen = 44 TOTAL atoms
How many oxygen atoms are in one molecule of calcium carbonate CaCO3.?
Three
Carbon dioxide is a covalent compound. How many oxygen atoms are in a carbon dioxide molecule?
“Di” means “two;” 2 oxygen atoms
The law of conservation of energy states that energy cannot be created or _____?
Destroyed
What does the law of conservation of mass say about chemical equations? Why?
The number of each element’s atoms in the reactants must equal the number of product atoms.
Because the total mass of the atoms is the same before and after a chemical reaction.
How can you tell if a chemical equation is balanced?
The number of each element’s atoms are the same in the reactants and product (each side of the arrow.
If a chemical symbol in a chemical formula has no subscript, what does that mean?
There is only one atom of that element.
What does a prefix (coefficient) in a chemical formula represent?
The prefix or coefficient multiplies the entire molecule: (2H2O means 2 water molecules.)
The subscript 3 means that there are two of that element’s atoms: (NH3 has 1 N and 3 H atoms.)
What is the product in the chemical equation C + O2  CO2?
The product comes after the arrow: CO2
Know how to use coefficients and subscripts correctly to balance chemical equations.
K
K ++ C
Cll222 
 K
KC
Cll
1
2

1 ++
2
 1
11
1
Potassium (K) balances, but Chlorine (Cl) does not;
Choose the 1 Cl on the right side and multiply it by 2 to match the 2 on the other side.
K
K ++ C
Cll222 
 2
2((K
KC
Cll))
1
2
1 ++
2 
 2
2((1
11
1))
1
2
2
1 ++
2 

22
2
Now the Chlorines Cl balance, but the potassium atoms (k) do not.
Choose the smaller number of potassium atoms to increase to match the larger number of
potassium atoms on the other side.
K
K ++ C
Cll222 
 2
2K
KC
Cll
1
1 ++ 2
2 
 2
22
2
2
(
1
)
+
2

2
2
2 (1 ) + 2  2 2
2
2 ++ 2
2 
 2
22
2
2
2K
K ++ C
Cll222 
 2
2K
KC
Cll
Now all elements are equal on both sides of the arrow, and the equation is balanced.