1. Chapter 5 Chemical Quantities and Reactions
5.3
Chemical Reactions and Equations

2. Chemical Changes A chemical change
occurs when a substance is converted into one or more substances with different formulas and different properties
may be observed by the formation of bubbles, a change in color, or production of a solid

3. Visible Evidence of a Chemical Reaction

4. Learning Check Which of the following represent a chemical change?
A. burning a candle
B. ice melting
C. toast burns
D. water turns to steam

5. Solution Which of the following represent a chemical change?
A. burning a candle chemical change
B. ice melting
C. toast burns chemical change
D. water turns to steam

6. Writing a Chemical Equation

7. Symbols Used in Chemical Equations
To write a chemical equation
an arrow indicates reactants form products
reactants are written on the left side of the arrow
products are written on the right side of the arrow
multiple reactants or products are separated by a + sign
the delta {Δ} sign indicates that heat is used to start the reaction

8. Symbols Used in Chemical Equations

9. Identifying a Balanced Equation
In a balanced
chemical equation,
no atoms are lost or gained
the number of reacting atoms is equal to the number of product atoms

10. Balancing a Chemical Equation

11. Balancing a Chemical Equation: Formation of Al2S3
Step 1 Write an equation using the correct formulas of the reactants
and products.
Al(s) S(s) Al2S3(s)
Step 2 Count the atoms of each element in the reactants and products.
Reactants
Products
1 atom Al
2 atoms Al Not balanced
1 atoms S
3 atoms S Not balanced

12. Balancing a Chemical Equation: Formation of Al2S3
Step 3 Use coefficients to balance each element. Starting with the most complex formula, change coefficients to balance equation.
2Al(s) S(s) Al2S3(s)
Step 4 Check the final equation to confirm it is balanced. Make sure coefficients are the lowest ratio.
Reactants
Products
2 atoms Al
2 atoms Al Balanced
3 atoms S
3 atoms S Balanced

13. Learning Check State the number of atoms of each element on the
reactant side and the product side for each of the
following balanced equations.
A. P4(s) + 6Br2(l) PBr3(g)
B. 2Al(s) + Fe2O3(s) Fe(s) + Al2O3(s)

14. Solution State the number of atoms of each element on the reactant
side and the product side for each of the following balanced
equations.
A. P4(s) + 6Br2(l) PBr3(g)
Reactants
Products
P atoms 4
Br atoms 12

15. Solution State the number of atoms of each element on the reactant
side and the product side for each of the following balanced
equations.
B. 2Al(s) + Fe2O3(s) Fe(s) + Al2O3(s)
Reactants
Products
Al atoms 2
Fe atoms
O atoms 3

16. Learning Check Balance the following equation,
Fe3O4(s) + H2(g) Fe(s) + H2O(l)
Reactants
Products
Atoms Fe
Atoms O
Atoms H

17. Solution Balance the following equation,
Fe3O4(s) + H2(g) Fe(s) + H2O(l)
Step 1 Write an equation using the correct formulas of the reactants and products.
Fe3O4(s) + H2(g) Fe(s) + H2O(l)

18. Solution
Step 2 Count the atoms of each element in the reactants and products.
Fe3O4(s) + H2(g) Fe(s) + H2O(l)
Reactants
Products
Atoms Fe 3 1
Atoms O 4
Atoms H 2

19. Solution Step 3 Use Coefficients to balance each element.
Fe3O4(s) + 6H2(g) Fe(s) + 3H2O(l)
Step 4 Check the final equation to confirm it is balanced.
Reactants
Products
Atoms Fe 3 1
Atoms O 4
Atoms H 2

20. Balancing Equations with Polyatomic Ions

21. Balancing Equations with Polyatomic Ions
When balancing equations with polyatomic ions, balance each
polyatomic ion as a unit.
2Na3PO4(aq) + 3MgCl2(aq) Mg3(PO4)2(s) + 6NaCl(aq)
Reactants
Products
PO43− ions 2
Na+ ions 6
Mg2+ ions 3
Cl− ions

22. Learning Check
Balance and list the coefficients from reactants to products.
A. __Fe2O3(s) __C(s) __Fe(s) __CO2(g)
1) 2, 3, 2, ) 2, 3, 4, ) 1, 1, 2, 3
B. __Al(s) + __FeO(s) __Fe(s) __Al2O3(s)
1) 2, 3, 3, ) 2, 1, 1, ) 3, 3, 3, 1
C. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)
1) 3, 2, 1, ) 2, 3, 1, ) 2, 3, 2, 3

23. Solution A. 2) 2, 3, 4, 3 2Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g)
B. 1) 2, 3, 3, 1
2Al(s) + 3FeO(s) Fe(s) + 1Al2O3(s)
C. 2) 2, 3, 1, 3
2Al(s) + 3H2SO4(aq) Al2(SO4)3(aq) + 3H2(g)