The process in which the physical and chemical properties of the original substances change to new substances with different properties  atoms are rearranging in new ways Chemical Reaction

Characteristics of chemical reactions Reactant= a substance that enters into a chemi- cal reaction Product= a substance that is produced by a chemi- cal reaction

Energy of chemical reactions An endothermic reaction: -A chemical reaction in which energy is absorbed (is a reactant). It gets cold! -The energy absorbed is stored in the molecules of the products. An exothermic reaction: -A chemical reaction in which energy is released (is a product). It gets hot! -The energy released was originally stored in the molecules of the reactants

The Dance

Types of Interactions at the Dance Synthesis(combination) Decomposition Single-replacement Double-replacement Combustion

Synthesis: A + B  AB One example of a synthesis reaction is the combination of iron and sulfur to form iron (II) sulfide: Fe + S 8  FeS See movies

Decomposition: AB  A + B The opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. One example is the electrolysis of water to make oxygen and hydrogen gas: H 2 O ---> H 2 + O 2 See movies

Single replacement: A + BC ---> AC + B One example of a single replacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas: Mg + H 2 O ---> Mg(OH) 2 + H 2 Another example is when fluorine gas replaces iodide in potassium iodide. F 2 + KI  I 2 + KF

It’s a bit like cutting in at a dance!!

Note: –In single replacement reactions, “Like replaces like!” –What this means, is that metals replace metals or cations, nonmetals replace nonmetals, or anions!!

Double replacement: AB + CD  AD + CB One example is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate: Pb(NO 3 ) 2 (aq) + KI (aq)  PbI 2 (s) + KNO 3 (aq) Again, “Like replaces like.”

It’s like changing your partners in square dancing!!

5 th Type (the last one) Combustion-a hydrocarbon combines with oxygen gas to produce carbon dioxide and water. C x H y + O 2  CO 2 + H 2 O It is also called “burning.”

Types of Interactions at the Dance Synthesis(combination) 2 or more reactants combine to produce a new substance Decomposition 1 reactant breaks down into 2 or more new substances Single-replacement an element replacing a similar element in the other reactant Double-replacement cations and anions of two different compounds change places

Now let us see if you can apply these 5 types of reactions to the equations listed below: 1) 2NaOH + Cu(NO 3 ) 2 --> 2NaNO 3 + Cu(OH) 2 2) CH 4 + 2O 2 --> CO 2 + 2H 2 O 3) Fe + 3NaBr --> FeBr 3 + 3Na 4) MgSO 4 + BaCl 2 --> MgCl 2 + BaSO 4 5) NH 4 OH + HBr --> H 2 O + NH 4 Br 6) 2Pb + O 2 --> 2PbO 7) Na 2 CO 3 --> Na 2 O + CO 2

More Examples For each of the movies shown: Write the balanced chemical equation

Other Stuff = Dissociation Shows what happens when an ionic salt dissolves in water. Ex. NaI(s) ----> Na + (aq) + I - (aq) HgCl 2 (s) ----> Hg 2+ (aq) + 2Cl - (aq) *Notice ions are free floating and do not form diatomic molecules

Precipitation- occurs when an insoluble substance (something that is not able to dissolve in water) is produced when two solutions are mixed. It “rains” out of solution! This is called a double-replacement reaction with precipitation.

Let’s see what happens when we combine solutions of sodium iodide and mercury(II) chloride Example What is the identity of the precipitate? NaI(aq) + HgCl 2 (aq)  NaCl(aq) + HgI 2 (s)