Chapter 24
Chemical Reactions
In a chemical Reaction . . .
Reactants
Products
• Substances reacting
• New substances produced
•Any state of matter
•Follow law of conservation of mass
Example: Which are the reactants? Which are the products?
NaCl Na+ + Cl-
2HgO O2 + 2Hg
NiCl2 + 2NaOHNi(OH)2 + 2NaCl
Law of Conservation of Mass
• In the late 1700s
• Antoine Lavoisier
• Mass is changed; NOT created or destroyed
Example: 2HgO O2 + 2Hg
10.0g = 0.7g + 9.3g
Try: Zn + 2HCl  H2 + ZnCl2
12.0g
15.0g + 3.2g = 6.2g + _____
Chemical Changes in Equations
• Table 1 on page 740
• We use formulas and equations to shorten the
writing process
• It helps us see how many atoms are involved
Balancing Equations - Nuts and Bolts Lab Revisited
1. Build these compounds if
Boltium (Bo) and Nutter (Nu)
Bo2Nu3
BoNu
Nu
How many of each compound to balance
Bo2Nu3  BoNu + Nu
Balancing Equations - Nuts and Bolts Lab
Revisited
2. Build these compounds
BoNu2
Bo3
Nu
How many of each compound to balance
BoNu2  Bo3 + Nu
Balancing Equations - Nuts and Bolts Lab
Revisited
3. Build these compounds
Bo2Nu2
Bo3
Nu
How many of each compound to balance
Bo3 + Nu  Bo2Nu2
Balancing equations
Example
Steps
1. Write chemical
1. Lithium metal treated with
equation with balanced
water, a hydrogen gas and a
molecules (cheat sheet
lithium hydroxide are produced:
for poly + diatomic)
Li (s) + H2O  LiOH + H2 (g)
2. Check equation for
2. Li 1
= 1
atom balance
H
2
=
1 + 2
O
1 = 1
Balancing equations
Steps
3. Choose coefficients to
balance it
4. Recheck number of
atoms
Example
3. Li (s) + H2O  LiOH + H2 (g)
4Li (s) + 4H2O  4LiOH + 2H2 (g)
4. Li 4
=
4
H
8
=
4 + 4
O
4 = 4