Types of Reactions

The symbols A, B, C and D can be used to represent ions, atoms or compounds (we’ll use them like variables in math)

Synthesis reaction Synthesis reactions occur when two substances (generally elements) combine and form a compound. General form: A + B  AB Example: C + O 2  CO 2 Example: 2H 2 + O 2  2H 2 O

What about A + B + C  ABC? Is this a synthesis reaction?

Pg 222 Synthesis reactionequation

Also called… Combination reactions Construction reactions Composition reactions

One last thing! In a synthesis reaction, the product is always more complex than the reactants… Example: 2H 2 + O 2  2H 2 O

Practice Predict the products. Write and balance the following synthesis reaction equations. Sodium metal reacts with chlorine gas Na (s) + Cl 2(g)  Solid Magnesium reacts with fluorine gas Mg (s) + F 2(g)  Aluminum metal reacts with fluorine gas Al (s) + F 2(g) 

Decomposition Reactions Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds 1 Reactant  Product + Product General form: AB  A + B Example: 2 H 2 O  2H 2 + O 2 Example: 2 HgO  2Hg + O 2

Decomposition reactions usually absorb energy from an external source. This energy is used to convert reactants into products. Ex – hydrolysis of water!

Some examples Decomposition reactionequation

Ms. Erdelyi’s decomposition reaction: Elephant toothpaste!

practice Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation: N 2(g) + O 2(g)  BaCO 3(s)  Co (s) + S (s)  NH 3(g) + H 2 CO 3(aq)  NI 3(s) 