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Chemical Reactions, Formulas, & How to Balance Equations

Unit 3: Introduction to Chemistry
by

Carmen Rodriguez

on 16 November 2016

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Transcript of Chemical Reactions, Formulas, & How to Balance Equations

4. A
double replacement
reaction- two different compounds exchange positive ions (cations) and form new compounds.

AB + CD AD + CB
NaOH + HCl NaCl + H2O

5. A
combustion
reaction- when a substances reacts rapidly with oxygen producing heat and light. (fire)
3. A
single replacement
reaction- where one element replaces another elements in a compound from the same activity series.

A + BC B + AC
2Na + H2O 2NaOH + H2


A song to end...
Chemical Reactions, Formulas, & How to Balance Equations
Balancing Chemical Equations
1. H2 + O2 → H2O

2. H2 + N2 → NH3

3. Al2O3 → Al + O2

4. KClO3 → KCl + O2
Types of Reactions:
1. A
synthesis
: two or more substances react to form a new compound.

A + B AB
S + 02 SO2
Chemical Equations
A way to show a chemical reaction in which the
reactants
and
products
are expressed as a formula. Using symbols instead of words.
Reactants
- substances that undergo a change in a chemical reaction. (LEFT of arrow)
Products
- new substances formed in a chemical reaction. (RIGHT of arrow)
-->
- called a yield sign--means to react or make

The mass of the reactants always equals the mass of the products in a chemical reaction.

States that matter in a chemical reaction does not change, it is neither created nor destroyed.

Meaning the total mass of the products must equal the total mass of the reactants.
In order to show that mass is conserved during a chemical reaction, a chemical equation must be balanced.
When balancing a chemical equation you always change the
coefficients
, never the subscript next to an element.
- show the number of molecules present in a reaction.
Balancing a Chemical Equation:

In order to show that mass is conserved during a reaction, a chemical equation must be balanced.
Coefficients: the number before the formula

1. Draw a vertical line dividing the
products
from the reactants.
2.
List
your individual elements.
3. Count how many
atoms
you have of each individual element.
4. Pick an element that is not equal on both sides of the equation. Begin
process
with the most complicated-looking group.
BIG RULE: You can only change
coefficients
, do not touch
subscripts
.
5. Add a
coefficient
in front of the formula with that element and adjust your
count
.
6. Save the elemental (single elements) reactant and products for
last
.
7. Continue adding coefficients to get the same number of
atoms
of each element on each side.
2. A
decomposition reaction
: a single compound breaks down into two or more simpler substances.

AB A + B
2H2O H2 + O2


-
subscripts
- show the number of atoms in a molecule.
https://phet.colorado.edu/en/simulation/balancing-chemical-equations
Try these problems:

___ CH4 + ___ O2 ___CO2 + ___ H2O

___ Na+ + ___ Cl2 ___ NaCl
Chemical Formula
A combination of symbols that represent the elements in a compound.
Law of Conservation of Mass
Molecules vs. Compounds
A
molecule
is more than one atom of the same element.
A
compound
is two or more elements combined.
Counting Atoms in Molecules
2
4
2
3
6
3
12
4
4
8
24
Other Parts of the Chemical Formula

Element Symbol= a code for a chemical element (first letter always capitalized)

Coefficients= shows the number of molecules present in a reaction

Subscripts= shows the number of atoms in a molecule
A chemical reaction is a change in matter that produces one or more new substances!
Activity Series=
a reference table that lists elements in order of their reactivity

It's used to determine if a single replacement occurs.
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