OB: intro to chemical reactions (5) and the creation of five demo diagrams.

In a chemical reaction bonds are broken and new ones form. New substances form, these new substances have their own properties. There are a variety of kinds of reactions which we will learn about, learn to recognize, and then to write balanced chemical equations for.

The first kind of reaction is called the SYNTHESIS REACTION. In a synthesis reaction, smaller reactants combine to form larger products.

A + B ABReactants form into products

Examples of word equations…

Hydrogen and oxygen synthesize into water

Carbon and oxygen combine into carbon monoxide

Carbon monoxide and oxygen synthesize into carbon dioxide

Iron and oxygen form into iron (III) oxide (or rust)

In each case, smaller reactants form into larger products.

When bonds form, energy is released.

To break bonds, energy must be absorbed.

Take out a separate sheet of paper now, not your notes. We will make a set of demo diagrams, diagramming each of the five kinds of chemical reactions.

You will be expected to memorize this, able to rewrite it from memory.

This is your example for synthesis (1 of 14 kinds of reactions this year).

This will be collected (all 5 together) for a grade. Do it because you care about yourself.

Demo Diagram #1 Synthesis Reactions Get a new sheet of paper for these, name on top

Hydrogen

Oxygen in air

With a flame, we will ignite the hydrogen, allowing it to combine with the oxygen in the air, synthesizing into water (in a FAST AND LOUD WAY!)

SYNTHESIS REACTION – Demo diagram #1

Abstract examples: A + B AB or X + YZ XYZ

Word equation: hydrogen and oxygen yields water

Skeleton:

Balanced Equation:

Balanced Thermochemical Equation:

SYNTHESIS REACTION – Demo diagram #1

Abstract examples: A + B AB or X + YZ XYZ

Word equation: hydrogen and oxygen yields water

Skeleton: H2 + O2 H2O

Balanced Equation: 2H2 + O2 2H2O

Balanced Thermochemical Equation: 2H2 + O2 2H2O + Energy

A synthesis reaction always has two or more smaller reactants combining into larger products.

Today’s reaction was exothermic, but sometimes these reactions can absorb energy (heat) and are called endothermic.

We start with a skeleton, then work out the balancing.

We cannot “fix” subscripts, they are set by formula rules. We can adjust ratios by adding coefficients.

From the word equation, write the skeleton equation, then balance the chemical reaction. Add phase symbols where ever you can.

Sodium + chlorine yields sodium chloride

From the word equation, write the skeleton equation, then balance the chemical reaction. Add phase symbols where ever you can.

Sodium + chlorine yields sodium chloride

Na + Cl2 NaCl

2Na(S) + Cl2(G) 2NaCl(S)

For the next few slides, write the word equation, under it write a skeleton equation, then write a balanced chemical equation.

Iron + Oxygen synthesizes to iron III oxide (rust)

Iron + Oxygen synthesizes to iron III oxide (rust)

4Fe(S) + 3O2(G) 2Fe2O3(S)

Aluminum + Nitrogen synthesize to aluminum nitride

Aluminum + Nitrogen synthesize to aluminum nitride

2Al(S) + N2(G) 2AlN(S)

Potassium and chlorine make potassium chloride

Potassium and chlorine make potassium chloride

2K(S) + Cl2(G) 2KCl(S)

Examples of skeleton equations…

H2 + O2 H2O

C + O2 CO

CO + O2 CO2

Fe + O2 Fe2O3

Examples of Balanced equations…

2H2 + O2 2H2O

2C + O2 2CO

2CO + O2 2CO2

4Fe + 3O2 2Fe2O3