Types of Reactions

Chapter 7

Synthesis(Combination) Reaction

• Na (l) + Cl2(g) --> NaCl(s)– Balance the reaction.

• You know you have a synthesis reaction when…

• 2 Reactants, 1 Product• Reactants are elements or simpler compound• Product is a compound

Decomposition Reaction

• Cu(NO3)2 (aq) --> NO2 (g) + O2 (g)+ CuO (s)

• Balance the reaction

• You know you have a decomposition reaction when…

• 1 Reactant, 2+ products

Single Replacement

• Al (s) + Fe2O3 (s) --> Al2O3 (s) + Fe(l)– Balance the equation

• You know you have a single replacement reaction when…

• Element + compound element + compound

Combustion

• CH4(g) + 2O2(g) CO2 (g) +2H2O(g)

• You know you have a combustion reaction when…

• Oxygen is a reactant and carbon dioxide + water are the products.

Double Replacement

• NaOH (aq) + AgNO3 (aq) --> AgOH (s) + NaNO3(aq)

• You know you have a double replacement reaction when…

• Compound + Compound Compound + Compound

Back to ions…

• What is an ionic compound?• What happens when an ionic compound

dissolves in water?– The compound dissociates, or separates into the

individual ions.

So…

• When mixing two dissolved ionic compounds, you are really mixing the ions together.

• A chemical reaction can occur!• A precipitation reaction: reaction in which a

solid forms and separates from the solution.

How do precipitation reactions work?

• Example: Let’s mix potassium chromate solution and barium nitrate solution together

• What is the chemical equation (reactants only) for this reaction?

• K2CrO4 (aq) + Ba(NO3)2 (aq)

• But these are ionic compounds, so it’s really the ions dissolved in water

• 2K+ (aq) + CrO42- (aq) + Ba2+ (aq) + 2NO3

- (aq)

The reaction

But what are the products?

• Experimental evidence tells us that one product is a solid. A solid must be electrically neutral, a cation with an anion– What are the options?

• K2CrO4 ; Ba(NO3)2

• KNO3 ; BaCrO4

• But which one is the solid?

Use solubility rules!

What does it all mean?

• Nitrate and potassium salts are soluble, so potassium nitrate cannot be a precipitate.

• Therefore, barium chromate is the solid.

How do you write all of this

• Molecular (undissociated) equation• K2CrO4 (aq) + Ba(NO3)2 (aq) KNO3(aq) + BaCrO4 (s)

• Complete ionic equation (any ionic “aq” broken up into ions.

• 2K+(aq) + CrO42-(aq) + Ba2+(aq) + 2NO3

- (aq) 2K+(aq) + 2NO3-

(aq)+BaCrO4 (s)

• Net ionic equation(eliminate spectator ions)• CrO4

2-(aq) + Ba2+(aq) BaCrO4 (s)