Chemical Equation Writing

Writing Equations1) Word Equations

(ex) methane + oxygen -----> carbon dioxide + water

- states the name(s) of the reactants (what you start

with = left side of arrow) and the name(s) of the

products (what you end with = right side of arrow).

- does not state quanity!!!

2) Chemical equation

(ex) CH4 (g) + 2O2 (g) -----> CO2 (g) +

2H2O (l)

- states reactants and products

- states quantities!!!

- the letters in parentheses indicate the physical state

of each substance involved:

(g) = gas

(l) = liquid

(s) = solid

(aq) = aqueous = dissolved in water

(cr) = crystalline solid

- the coefficient (large number out front) tells us:

1) number of moles

2) number of molecules

3) volume iff a gas and STP (standard T & P)

4) number of atoms when mult. by the

subscript.

- when writing a chemical equation the Law of

Conservation of Atoms must be obeyed!

- Law of Conservation of Atoms:

- the total number of atoms of reactants must

equal the total number of atoms of products.

***** NOTE: When the following elements are

standing alone they combine with themselves in order to become

stable (in the following manner):

- H2, I2, N2, Cl2, Br2, O2, F2

- P4

- S8

Types of Reactions1) Binary Composition:

- occur when 2 elements combine to form a binary

compound.

general form: element + element -----> binary compound

X0 + Y0 -----> XY- elements that stand alone have an oxidation state

of zero!

- compound’s name will end in -ide (binary)

- use the lowest oxidation state for the metal unless:

1) metal = Cu2+

2) metal = Hg2+

3) or there is an excess of the nonmetal

(ex) lithium + bromine ----->

lithium + bromine -----> lithium bromide

Li + Br2 -----> LiBr

2Li + Br2 -----> 2LiBr

(ex) iron + sulfur ----->

iron + sulfur -----> iron (II) sulfide

Fe + S8 -----> FeS

8Fe + S8 -----> 8FeS

(ex) copper + oxygen ----->

copper + oxygen -----> copper (II) oxide

Cu + O2 -----> CuO

2Cu + O2 -----> 2CuO