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)