4. A physical change is a process that alters the
physical state of a substance without changing its
composition.
A chemical change/ chemical reaction converts one
substance into another.
5. What is Chemical Reaction?
A chemical reaction is in which the bonds are
broken within the reactant molecules, and new
bonds are formed within product molecules in
order to form a new substance.
6. Parts of Chemical Reaction
Reactants Products
Reactants: Substances that are destroyed by
the chemical change (bonds break)
Products: Substances created by the chemical
change (new bonds form)
The arrow ( ) as “yields”
7. ( s ) – solid
( l )- liquid
( g ) – gas
( aq ) – aqueous solution ( the substance is
dissolved in H2O)
“+” separates two or more reactants or
products
“ “ yield sign separates reactants from
products
Other symbols in chemical reaction
8.
9. 5 Evidences of a Chemical Reaction
1. Evolution of light or heat.
2. Temperature change (bubbling or an odor other
than boiling)
10. 3. Formation of gas (building or an odor) –
other than boiling
4. Color change – due to the formation of a new
substance
5. Formation of a precipitate – a new solid form
from the reaction of a two aqueous solutions.
11. Word Equations
Statements that indicate the reactants and products in a chemical
reaction.
The Chemical equation
2Fe ( s ) + 3Cl2 ( g ) 2FeCl3
Word Equation
Iron (s) + chlorine (g) iron (III) chloride (s)
2H2 ( g ) + O2 ( g ) H2O ( g)
12. Converting Word Equations into Skeleton Equations
A symbolic way to represent the correct formula for all reactants and products in a
reaction.
It does not necessarily show the correct quantity/ratios. “missing coefficients describing
correct particle ratio”
The word equation:
Tin + chlorine ( g ) tin ( IV ) chloride
The skeleton equation:
Sn + Cl2 ( g ) SnCl4 Sn4+ Cl1-
13. 6 Na ( s ) + Fe2O2 ( s ) 3 Na2O ( s ) + 2 Fe ( s )
The numbers preceding the chemical formula are coeffecients. They are
used to balance the reaction.
The numbers within the chemical formula are subscripts.
You can read the above balanced reaction as:
o 6 atoms of solid sodium plus 1 formula unit of solid iron (III) oxide yields 3
formula units of solid sodium oxide and 2 atoms of solid.
o 6 moles of solid soduim plus 1 mole of solid iron (III) oxide yields 3 moles of
solid sodium oxide plus 2 moles of solid iron.
o
14. Conservation of Mass
During a chemical reaction, atoms are neither created nor destroyed.
Hydrogen and oxygen gas react to form a water
H2 ( g ) + O2 ( g ) H2O ( I )
According to conservation of mass, the proper way to write this reaction is:
2H2 ( g ) + 1O2 ( g ) 2H2O ( I )
The red coefficients represented the # of a molecules (the # of moles) of each
reactant or product.
15. CONSERVED NOT CONSERVED
Mass
Types of Atoms
Number of each atom
Color
Physical state ( solid, liquid, gas )
Volume
Number of moles of
reactants/moles
