The Dance of the Elements:Simple Chemical Reactions

5 types of reactions

1. Synthesis (S)

2. Decomposition (D)

3. Single replacement (SR)

4. Double replacement (DR)

5. Combustion (C)

Visualizing chemical reactions is much like imagining the elements involved in a simple dance.

At a dance, people can pick a partner, separate and take a break, change a dance partner or change both dance partners.

At the beginning of a dance, partners join together.

When elements combine to form a new compound, this is called a SYNTHESIS REACTION.

Synthesis Reactions

Elements combine to form a new compound that has different properties than the elements alone. Synthesis means “to make” and what happens in this reaction is that smaller parts create a new more complex compound.

Reaction

Recognizing a Synthesis Reaction

All synthesis reactions follow the pattern

A + B AB

Looking at a real reaction, like one below, two or more different elements/compounds combine to form one new compound

2Na (s) + Cl2 (g) 2NaCl (s)

There comes a time for partners to stop dancing and take a break.

When chemical compounds divide and break down into smaller components, this is called a DECOMPOSITION REACTION.

Decomposition Reactions

Decomposition occurs when a compound breaks down from a complex molecule into simpler substances. Decomposition means “to break down” or “decay.”

Reaction

Recognizing a Decomposition Reaction

All decomposition reactions follow the pattern

AB A + B

In an actual reaction, one larger compound breaks down into two or more smaller substances.

HgCl2 (s) Hg (l) + Cl2 (g)

Dancers sometimes change partners

When chemical compounds change one partner for another, this is called a SINGLE DISPLACEMENT REACTION.

Single Displacement Reactions

In this reaction, a more reactive ion replaces a less reactive ion and a new compound is produced.

Reaction

Recognizing a Single Displacement Reaction

This reaction follows the pattern

AB + C AC + B

An actual single displacement reaction would free one ion and take up another ion

Mg (s) + 2 H2O (l) Mg(OH)2 (l) + H2 (g)

Dancers can also change both partners

When two chemical compounds both exchange a partner, it is called a DOUBLE DISPLACEMENT REACTION.

Double Displacement Reactions

Reaction

In this reaction, the more reactive ions pair to form a new compound and the less reactive pair also form a new compound.

Recognizing a Double Displacement Reaction

This reaction follows the pattern

AB + CD AD + CB

A double displacement reaction would free ions to change partners

AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq)

It’s that simple!

Chemistry isn’t always difficult. By learning to recognize the four simplest types of chemical reactions, you have taken a big step towards learning how different chemicals interact with one another.

HOMEWORK

• READ lab CAREFULLY!!!!• HANDOUT: front : tell type for 1—6 , 8—14• Back : tell type for 1—15•  • Finish ch. 8 reading guide AND webquest for a

late grade!!• BE READY FOR QUIZ ON TYPES OF

REACTIONS NEXT CLASS PERIOD!!

 

http://www.youtube.com/watch?v=JQVl1-RDFWI

(you tube: types of chemical reactions intro.wmv)