Types of Reactions

I. Synthesis reactions – have only one product.

General Form: A + X AX

EX: •2 Na(s) + Cl2(g) 2 NaCl(s)•2 H2(g) + O2(g) 2 H2O(l)•CaO(s) + CO2(g) CaCO3(s)

*Metals combine with non-metals in synthesis rxns to form ionic compounds.

EX: Mg + Br2 MgBr2

Synthesis Reactions

Examples:

N2 (g) + 3 H2 (g) 2 NH3 (g)

C3H6 (g) + Br2 (l) C3H6Br2 (l)

2 Mg (s) + O2 (g) 2 MgO (s)

• Two or more substances react to form one product

• Also called“combination rxns”

Practice• Predict the products then write and balance the

following synthesis reaction equations.

• Sodium metal reacts with chlorine gas

• Solid Magnesium reacts with fluorine gas

• Aluminum metal reacts with fluorine gas

Na(s) + Cl2(g)

Mg(s) + F2(g)

Al(s) + F2(g)

II. Decomposition Reactions

• Examples:

CaCO3 (s) CaO (s) + CO2 (g)

2 KClO3 (s) 2 KCl (s) + O2 (g)

2 NaN3 (s) 2 Na (s) + 3 N2 (g)

• Have only one reactant• General Form:

AX A + X• One substance breaks down

into two or more substances

Electrolysis – decomposing a compound by runningan electric current through it.

2 H2O 2 H2 + O2

Special decomposition rxns:

a) Decomposition of metal carbonatesproduces the metal oxide and CO2

EX: MgCO3 MgO + CO2

Write the equation for the decomposition of Na2CO3

Na2CO3 Na2O + CO2

* The decomposition of binary compoundsproduces the two elements in the compound.

EX: 2 NaCl(l) 2 Na(s) + Cl2(g)

N2O4 N2 + 2 O2

b. Decomposition of metal hydroxidesproduce the metal oxide and water.

EX: Mg(OH)2 MgO + H2O

Write the equation for thedecomposition of KOH.

KOH K2O + H2O2

c. Carbonic acid rapidly decomposes upon its formation:

H2CO3(aq) H2O(l) + CO2(g)

Practice• Predict the products then write and balance the following decomposition

rxn equations:• Solid Lead (IV) oxide decomposes

• Aluminum nitride decomposes

• Calcium carbonate is decomposed by heating

• Copper(II) hydroxide is decomposed

PbO2(s)

AlN(s)

CaCO3

Cu(OH)2

III. Single Replacement Reactions

An element replaces another element in a compound.

General forms:

A + BX B + AX (metal takes place of metal)

or

Y + BX X + BY (nonmetal takes place of nonmetal)

These rxns usually occur in solution.

EX: Cu(s)+ 2 AgNO3(aq) 2 Ag(s) + Cu(NO3)2(aq)

Cl2(g) + 2 NaBr2(aq) Br2(l) + 2 NaCl(aq)

*** For a single replacement rxn to occur, an element must be more reactive

than the element it replaces***

See the “Activity Series of Elements” on the back of your periodic table. In order for an elementto replace another element in a compound, it must be higher than that element on the activity series.

Cu(s)+ 2 AgNO3(aq) 2 Ag(s) + Cu(NO3)2(aq)

Occurs - Copper is more reactive than silver

Cl2(g) + 2 NaBr2(aq) Br2(l) + 2 NaCl(aq)

Occurs - Chlorine is more reactive than bromine

Al(s) + NaCl(aq)

Aluminum is LESS reactive than sodium.

No Rxn

Br2(l) + NaCl(aq) No Rxn

Remember that metals replace metals,and nonmetals replace nonmetals.

Bromine is LESS reactive than chlorine

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If the following rxns occur, write the products andbalance the equation; if no reaction occurs, write “No Rxn”

1. Mg(s) + ZnCl2(aq)

2. Al(s) + Pb(NO3)2(aq)

3. Fe(s) + AlCl3(aq)

4. I2(s) + NaCl(aq)

5. F2(g) + LiBr(aq)

Zn(s) + MgCl2(aq)

Pb(s) + Al(NO3)3(aq)2 3 3 2

No Rxn

No Rxn

Br2(l) + LiF(aq)2 2

Write the equation for the rxn of potassium and water.

Special Single Replacement Reactions

a) Group 1 metals and Ca, Sr, and Ba will replace one of the hydrogens in water, producing hydrogen gas and the metal hydroxide.

Ex: Ca + 2 H2O H2 + Ca(OH)2

2 K + 2 H2O H2 + 2 KOH

b) Metals can replace the hydrogen in acids.

Ex: 2 Al(s) + 6 HCl(aq) 3 H2(g) + 2 AlCl3(aq)

Write the equation for the rxn between nitric acidand magnesium metal.

Mg + 2 HNO3 H2 + Mg(NO3)2

*note that hydrogen is listed with the metalson the Activity Series

IV. Double-Replacement Rxns

- the ions of two aqueous compounds“switch places” to form two new compounds.

General Form: AX + BY AY + BX

EX: AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

In order for a double replacement rxn to occur,one of the products must remove its ions from aqueous solution. This can occur when:

1) One of the products is insoluble (forms a solid) in water. A precipitate forms.See the solubility chart on back of periodic table.

Pb(NO3)2(aq) + Na2CrO4(aq) PbCrO4(s) + 2NaNO3(aq)

Check to see if one of the products does not dissolvein water (an “s” on the solubility table). If so, that substance is the precipitate and the rxn occurs. If both products are soluble, no rxn occurs.

Predict the products and balance the equations for the following rxns; if no reaction occurs write “no rxn”

1. AlCl3(aq) + Na3PO4(aq)

2. KNO3(aq) + MgBr2(aq)

AlPO4 + NaCl(s) (aq)3

No Rxn

3. NaCl(aq) + Pb(NO3)2(aq)

4. KNO3(aq) + CaCl2(aq)

5. BaI2(aq) + Na2CO3(aq)

6. CuSO4(aq) + K3PO4(aq)

7. (NH4)2S(aq) + ZnCl2(aq)

2

No Rxn

BaCO3(s) + 2 NaI(aq)

PbCl2(s) + NaNO3(aq)

2. A double replacement rxn occurs if one of the products is water (H2O).

Ex: HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)

2 HNO3(aq) + Mg(OH)2(s) H2O(l) + 2 Mg(NO3)2(aq)

(these rxns occur when an acid reacts with a base –they’re called neutralization rxns)

Predict the products and balance the following rxn:

H2SO4(aq) + KOH(aq)

3. A double replacement rxn occurs if one of the products is a gas.

Ex: 2 HCl(aq) + Na2CO3(aq) H2CO3(aq) + 2NaCl(aq)

2 HCl(aq) + Na2CO3(aq) H2O(l) +CO2(g) + 2NaCl(aq)

*metal carbonates react with acids to produceH2O, CO2, and a salt.

Predict the products and balance the following rxn:

H2SO4(aq) + CaCO3(aq)