Types of Reactions

Classifying Reactions How can you predict the products if you are given the reactants? Must know the types of reactions

Types of Reactions Addition (Synthesis) Decomposition Single Displacement (Replacement) Double Displacement (Replacement) Combustion Acid Base

Addition (Synthesis) Two or more reactants combine to form a new product A + B  AB Example: Rust formation: Fe(s) + O2(g)  Fe2O3

Decomposition Compounds are broken down into two or more smaller compounds AB  A + B SiCl4  Si + Cl2

Single Displacement One element replaces another in a compound AX + B  BX + A Ca + HCl  CaCl2 + H2

Double Displacement Ions switch places; two elements switch places AB + CD  AD + CB AgNO3 + NaCl  AgCl + NaNO3

Combustion Carbon compound combines with oxygen to release carbon dioxide and water and energy Carbon cmpd + O2  CO2 + H20 + energy! C2H6 + O2  CO2 + H20

Acid Base Reactions The reactants will always be an acid and a base producing 2 specific products; Water and a Salt. Acids always start with an H- Bases always end in an –OH Water is H20 HCl + NaOH  H20 + NaCl

Let’s practice- Type _______ HgO → Hg + O2 _______ CH4 + O2 → CO2 + H2O _______ NaCl + AgNO3 → NaNO3 + AgCl _______ Mg + HCl → MgCl2 + H2 _______ Zn + H2SO4 → ZnSO4 + H2 _______ C6H12O6 + O2→ CO2 + H2O _______ NaOH + HCl → NaCl + H2O _______ Al2(SO4)3 + Ca(OH)2 → Al(OH)3 + CaSO4 _______ H2 + O2 → H2O _______ Cl2 + NaBr → NaCl + Br2 _______ KClO3 → KCl + O2 _______ C2H2 + O2→ CO2 + H2O _______ Na2O + CO2 → Na2CO3

Categorizing Chemical Reactions All chemical reactions involve something moving, so we can categorize the types of reactions we just learned to help us predict the products in a reaction! Moving electrons = synthesis, decomposition, single displacement, combustion. Moving ions = double displacement Moving protons = acid/base reaction (we’ll get into this in a later unit)

Moving Electrons In the following reactions, one or more electrons move from one atom to another This allows the atoms to act differently than in their original compounds, and we form new substances. Ex: Mg + Br2  MgBr2 NaCl  Na + Cl2 Zn + CuSO4  Cu + ZnSO4

In the first example, think about the Lewis Structures that we’ve drawn. The Magnesium atom loses electrons and the Bromine atom gains electrons. There is a transfer of electrons to create the ionic bond.

In the second example, we break apart the compound by transferring the electrons back to the individual elements.

Zn + CuSO4  Cu + ZnSO4 Remember CuSO4 is an ionic compound, so it really is made of Cu+2 and SO4-2 ions. Zn is starting off neutral in the reactants. During this reaction, Zn transfers its electrons to Cu+2 ion. Zinc loses electrons and becomes a Zn+2 ion and Cu gains electrons to become neutral. Now that Zn+2 has a charge, it will form the ionic compound with SO4-2 because the opposite charges ions will attract.

In this case, did the sulfate ion see an change of electrons? No, so these electrons were not involved in the reaction and were not shown. This is an example of something called a “Spectator Ion” and we’ll talk about it later.

Reduction and Oxidation In these reactions, one atom or element is reduced and the other is oxidized. So you’ll hear these called Redox. A substance that is reduced has gained electrons and the charge is reduced. (more negative) A substance that is oxidized has lost electrons and the charge is increased. (more positive)

2 Fun Ways to Remember Oxidation Is Losing elections Reduction OIL RIG LEO the lion says GER Oxidation Is Losing elections Reduction Gaining electrons Losing Electrons is Oxidation Gaining Reduction

And now, the tricky part… A substance that has been oxidized is called a reducing AGENT because it caused another element to take their electrons. A substance that has been reduced is called an oxidizing AGENT because it caused another element to give up its own electrons

Br starts with 0 charge and ends with -1 The charge has gone down, because Br has gained electrons. Mg starts with 0 charge and ends with +2 The charge has gone up, because Mg has lost electrons. This means Br has been ______ and is the _______ agent. reduced oxidizing This means Mg has been ______ and is the _______ agent. oxidized reducing

Na starts with a +1 charge, ends with 0 charge Charge has gone down because it gained electrons Cl starts with a -1 charge, ends with 0 charge Charge has gone up because it lost electrons This means Na has been _______ and is the ______ agent. reduced oxidizing This means Cl has been ______ and is the _______ agent. oxidized reducing

Zn started with 0 charge, ended with +2 Charge has gone up because it lost electrons Cu started with +2 charge, ended with 0 Charge has gone down because it gained electrons SO4 started and ended with -2, no electrons changed here Zn has been oxidized and is the reducing agent Cu has been reduced and is the oxidizing agent SO4 wasn’t really involved in the reaction. (Spectator)