Chemical Reactions

· explain the Law of Conservation of Mass

· differentiate between subscripts and coefficients

· balance skeleton equations by adding coefficients

· move between word equations and chemical reactions

Reactants Products

Coefficient Subscript

Solid state Liquid state

Gas state Aqueous state

Law of Conservation of Mass

Key Words

subscript

Chemical formula - show the type and amount of each atom present in a compound.

HH O

HH O H

H O

HH O

H2O3

form 3 molecules of water.6 atoms of hydrogen and 3 atoms of oxygen

Compound Number of particles

Total of each element

KHCO3 1 formula unit K – 1 H – 1 C – 1 O – 3

AlCl3 3 formula units Al – 3 Cl – 9

CBr4 6 molecules C – 6 Br – 24

H2SO4 5 formula units H – 10 S – 5 O – 20

C11H22O12 4 molecules C – 44 H – 88 O – 48

Some covalent compounds can act as ions – these compounds are called polyatomic ions.

Polyatomic ions carry a known charge.

Cl

Na -1

+1 -1

-1

The nitrate ion, NO31-, consists of 1 nitrogen atom

and 3 oxygen atoms.

These atoms form a covalent group that takes one electron and carries a charge of -1.

+1

Na

-1+1

Na Na(NO3)

Mg+2 NO3-1

Mg(NO3)2

1 atom of magnesium, 2 atoms of nitrogen, and 6 atoms of oxygen.

Chemical reaction – substances react to produce one or more new substances.

Chemical equation – contains all necessary information about a reaction (like a recipe).

reactants products

A + 2 B C

+ 2

H + O H2O

Chemical reactions can be shown as word equations:

Hydrogen gas and oxygen gas react to form water vapour

diatomic

(g) (g) (g)2 2

“aqueous” – compound is dissolved in water.

State (phase) of the substance is always shown as small subscripts after the numbers.

l = liquid g = gas s = solid aq = aqueous

Coefficients indicate the ratio of the substances in the chemical reaction.

Two molecules of hydrogen react with one molecule of oxygen to yield two molecules of water.

H2 (g) + O2 (g) H2O (g)

HOH

HH

O

2 2

HH

O

HH

O

The Law of Conservation of Mass:

In any chemical reaction matter cannot be created or destroyed.

Atoms will rearrange to form new compounds, but the number and type of atoms will not change during the reaction.

1000 kg 1000 kg

H2 (g) + O2 (g) H2O (g)2 2

Coefficients subscripts (phase/state)

reactants products

In any chemical reaction matter cannot be created or destroyed.