Chemical Reactions

Types of Reactions

Types of Reactions

1. Combination reactions

2. Decomposition reactions

3. Displacement reactions

4. Precipitation reactions

You need to be able to identify each type.

A. Combination

the combination of 2 or more substances to form a compound

only one product forms

A + B AB2P + 3Br2 2PBr3

E.g. Combination Reaction

B. Decomposition

a compound breaks down into 2 or more simpler substances

only one reactant

AB A + B2H2O2 2H2O + O2

E.g. Decomposition Reaction

C. Displacement

one element replaces another in a compoundmetal replaces metal (+)nonmetal replaces nonmetal (-)

A + BC AC + B

Zn + 2HCl ZnCl2 + H2

E.g. Displacement Reaction

D. Precipitation

ions in two compounds “change partners”

cation(+) of one compound combines with anion(-) of the other

AB + CD AD + CB

2KOH + CuSO4 K2SO4 + Cu(OH)2

Exchange Reactions

Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together

Example:

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

Another example:

K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s) 2

Precipitation

Predicting the products

1) Identify the likely reaction type based on the reactants:

Combination - often 2 elements Decomposition - 1 compound Displacement - 1 compound & 1

element Precipitation - 2 compounds

Predicting the products 2) Use the information in your

notes about likely products to help you determine the products Combination- put the 2 elements

together-look at the charges and use the crisscross method

Decomposition- pull the compound apart- for us, it will usually be the 2 elements that make up the compound

Pay attention to the diatomics

Predicting Products 2) continued

Displacement- look at the activity series to see if the element can replace one of the elements in the compound If the reaction occurs, find the charges of

the each of the elements. Trade the places of the metals Write the new formula of the compound using

the crisscross method Eliminate the charge from the new lone

element and write it alone.

Predicting products 2) Continued

Exchange - trade the cations of the compounds Pay attention to charge of your ions and use the

crisscross method to write the formula. Look at your solubility table on the back of your

periodic table to determine which product is solid (the insoluble one is the solid) and which is aqueous

– Be sure to indicate state of matter for every compound in exchange reactions

– If both are aqueous (soluble), no reaction occurs.

– Water is a liquid

Predicting Products 3) Balance the equation.

Practicing exchange reactions Predict the products.

1. HCl(aq) + AgNO3(aq)

2. Pb(NO3)2(aq) + BaCl2(aq)

3. FeCl3(aq) + NaOH(aq)

4. KOH(aq) + CuSO4(aq)

AgCl (s) + HNO3(aq)

PbCl2(s) + Ba(NO3)2(aq)

Fe(OH)3(s) + NaCl(aq)3 3

K2SO4(aq) + Cu(OH)2(s)2

Mixed Practice

State the type & predict the products.

1. BaCl2 (aq)+ H2SO4(aq)

2. Zn(s) + CuSO4(aq)

3. Cs(s) + Br2 (l)

4. FeCO3(s)

1. Exchange reaction

BaCl2(aq) +H2SO4(aq) BaSO4(s) + HCl(aq) 2

What you would see:

•Two solutions are mixed and a white solid (precipitate) forms on mixing

2. Displacement reaction

Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s)

What you would see:

•Copper sulfate solution fades in colour…gets less blue•Zinc metal disappears as it reacts•Brown/orange copper metal appears

3. Combination reaction

Cs(s) + Br2 (l) CsBr (s)

What you would see:

•Explosion…lots of energy given off …Cs is a group one metal!•Brown/red bromine liquid would disappear quickly as it reacts•Silvery Cs metal would quickly disappear as it reacts•A white crystalline solid is left behind

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4. Decomposition reaction

1. FeCO3(s) FeO (s) + CO2(g)

What you would see:

You would need to heat this for the reaction to take place• green powder turns black• gas given off could be bubbled through limewater to test for carbon dioxide