Transcript Question to answer… - Rochester Century High School

Intro video
- shorthand way to describe chemical
reactions using symbols and formulas
Instead of writing:
“When you add solid silver to hydrogen
sulfide gas, you get solid silver (I) sulfide
and diatomic hydrogen gas.”
You can just write:
Ag(s) + H2S(g) --> Ag2S(s) + H2 (g)

Reactants:



Products:



On the left side of the equation
Substances that are altered in the course of a
chemical reaction (what you start with)
On the right side of the equation
New substances created as a result of a
chemical reaction (what you end up with)
→


“Yeilds” or produces
Similar to an equal sign in an equation
“In a chemical reaction, matter (consisting of
atoms) is not created or destroyed.”
–
number placed in front of items in a chemical
equation to tell how many of each are taking
part in the reaction
–
Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3
- equation with the same number of atoms of
each element on both sides of the equation
(atoms are rearranged)
If you don't balance your equations, you're not
following the law of conservation of mass! It
looks like you're making or destroying atoms!
- To balance the equation, you CANNOT
change subscripts. You can only change
coefficients.
Does the following equation
follow the law of conservation of
mass? Explain your answer.
Ag(cr) + H2S(g)  Ag2S(cr) + H2(g)
Ag
H
S
1 Ag 2
2 H 2
1 S 1
2
2
1 Ag 2
2 H 2
1 S 1
1.
2.
3.
4.
5.
Coefficients will always be whole numbers.
Leave oxygen and hydrogen until last.
If you have to add coefficients to more than 1
item, leave single elements like Ag or H2
If you get stuck, try balancing the metals first.
Make sure the equation is in the simplest form
by reducing.
GCD = 2
Divide all coefficients by GCD (2)
4 Al + 3 O2  2Al2O3
2 H2O  2 H2 + O2
2 H2O  2 H2 + 1O2
O2 + H2  H2O
NaOH  Na2O + H2O
Ag2O  Ag + O2
SO2 +
Al +
MnO2  Mn +
AgNO3 + Ni 
KI +
O2  SO3
Br2
Ag
+
 KBr +
Al2O3
Ni(NO3)2
I2

Bi2S3 + HCI

PbO2

FeS

Al

+
+
O2
HCI
BiCI3 + H2S

PbO +


O2
Fe2O3 + SO2
AICI3 +
H2
 “Word
Equations” are transIations of the
names of chemicaI compounds or eIements
into chemicaI formuIas. ExampIe:
 Carbon
pIus iron (III) oxide makes Carbon
dioxide and iron.


C +
C +
Fe3+O2-  CO2 + Fe
Fe2O3  CO2 + Fe
 Barium
nitrate plus Sodium sulfate makes
barium sulfate and sodium nitrate.