UNIT VITypes of Chemical Reactions

Lesson 2

VI.5 TYPES OF CHEMICAL REACTIONS

When we classify reactions by how atoms are rearranged, there are 5 MAJOR TYPES of reactions:

http://www.youtube.com/watch?v=i-HHvx1VC_8

VI.5 TYPES OF CHEMICAL REACTIONS

1. Synthesis - is the combination of two or more substances to form a _____________________________.

 A + B → AB

 Examples: 2H2 (g) + O2(g) → 2H2O (g) 

CaO(s) + H2O(l) → Ca(OH)2 (s) 

2Fe(s) + O2(g) → 2FeO(s)  How to predict the products: assume product is

made of the two reactants joined together. http://www.youtube.com/watch?

v=A5H6DVe5FAI&feature=related

VI.5 TYPES OF CHEMICAL REACTIONS

2. Decomposition – is the opposite of synthesis; one substance breaks down to form two or more ________________________________.

 AB → A + B

 Examples: CO2 (g) → C(s) + O2(g) 

2Ag2O(s) → 4Ag(s) + O2(g)   How to predict the products: the products will be

the elements that make up the original compound.

http://www.youtube.com/watch?v=ezsur0L0L1c&feature=related

VI.5 TYPES OF CHEMICAL REACTIONS3. Single Replacement – occurs when one element is replaced

by another element in a compound.  

A + BC→ AC + B Examples: Cl2 (aq) + 2KBr(aq) → 2KCl(aq) + Br2 (aq) 

Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) *This is when an ELEMENT reacts with a compound and

REPLACES an element in the compound. How to predict the products: replace metal with metal OR

replace nonmetal with nonmetal. CuI2 + Fe → FeI2 + Cu (Cu is replaced by Fe – METAL)CuI2 + Br2 → CuBr2 + I2 ( I is replaced by Br – NONMETAL)http://www.youtube.com/watch?

v=hKtynbVtMKc&feature=related

VI.5 TYPES OF CHEMICAL REACTIONS

4. Double Replacement – occurs when the elements in a solution of reacting compounds ______________ places, or ________________ each other.

 AB + XY→ AY + XB

  Examples:

ZnBr2(aq) + 2AgNO3(aq) → 2AgBr(s) + Zn(NO3)2 (aq)   *This is when TWO COMPOUNDS react – pay close

attention to CHARGE on ions. http://www.youtube.com/watch?v=opY3FLrPTa4

VI.5 TYPES OF CHEMICAL REACTIONS

4. Double Replacement  AB + XY→ AY + XB

 

ZnBr2(aq) + 2AgNO3(aq) → Zn(NO3)2 (aq) + 2AgBr(s)  Note that compounds are made of ions put together.

What you will do is take a positive ion on the reactant side and exchange it with the positive ion on the product side.

BE VERY careful about the charges and how you combine the ions together to make a new compound.

 http://www.youtube.com/watch?v=opY3FLrPTa4

VI.5 TYPES OF CHEMICAL REACTIONS A special type of double replacement

reaction...  Neutralization – reaction between an ACID and

a BASE (the H in the acid and the OH in the base form H2O)

  the products are always WATER and SALT 

Acid + Base → Salt + Water 

HB + XOH → XB + HOH Examples:

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

VI.5 TYPES OF CHEMICAL REACTIONS A special type of double replacement

reaction...  Neutralization  Example:

VI.5 TYPES OF CHEMICAL REACTIONS

5. Combustion – chemical reaction that usually gives off a large amount of energy in the form of heat or light

involves the reaction of a substance with OXYGEN (O2)

hydrocarbons (compounds made of H and C) are involved

carbon dioxide and water are produced

CxHy + O2 → CO2 + H2O

Ex: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)  http://www.youtube.com/watch?v=UygUcMkRy_c

VI.5 TYPES OF CHEMICAL REACTIONS5. Combustion ---Special notes

CxHy + O2 → CO2 + H2O

If you have an organic compound with O, you get the same thing

+ O2 → CO2 + H2OIf you have an organic compound with S, you get:

Sulphur dioxide reacts with water to form sulphurous acid(acid rain)

 

-----Nice SUMMARY on p. 118 of your Hebden textbook----- http://www.youtube.com/watch?v=tE4668aarck

VI.5 TYPES OF CHEMICAL REACTIONS

Predicting Products 1. Synthesis (2 elements form one compound)

Mg + I2 →

2. Decomposition (1 compound breaks into elements)

HgO →

VI.5 TYPES OF CHEMICAL REACTIONS

Predicting Products

3. Single Replacement (interchange metal or non-metal)

   Mg + AlCl3 →

 4. Double Replacement (interchange positive

ions in compound)   FeCl2 + K2S →

VI.5 TYPES OF CHEMICAL REACTIONS

Predicting Products

5. Combustion (products will be carbon dioxide and water)

 C6H14 + O2 →

  

VI.6 ENERGY CHANGES IN CHEMICAL REACTIONS In a chemical reaction, BONDS are broken

and new bonds are formed. ENERGY is required to break these bonds.

Endothermic Reactions ABSORB heat (energy) from the surroundings

Ex: HCl + energy → H + Cl energy appears on the REACTANT side there is more energy at the end of the

reaction (as reaction proceeds, more energy is required to break the bonds)

VI.6 ENERGY CHANGES IN CHEMICAL REACTIONS

Endothermic Reactions

VI.6 ENERGY CHANGES IN CHEMICAL REACTIONS

Exothermic Reactions GIVES OFF heat (energy) to the surroundings

Ex: H + Cl → HCl + energy  energy appears on the PRODUCT side there is more energy at the beginning of

reaction (as reaction proceeds, energy is lost to the surroundings)

VI.6 ENERGY CHANGES IN CHEMICAL REACTIONS

Exothermic Reactions

VI.6 ENERGY CHANGES IN CHEMICAL REACTIONS

∆H = change in enthalpy (the heat contained in the system)

Endothermic Rxn: ∆H is positive

Ex: A + 45kJ → B

A → B ∆H = + 45kJ

VI.6 ENERGY CHANGES IN CHEMICAL REACTIONS

Exothermic Rxn: ∆H is negative

Ex: C → D + 65kJ

C → D ∆H = - 65kJ

 Summary: HEAT on LEFT -----> ∆H = +ve

HEAT on RIGHT -----> ∆H = -ve

VI.6 ENERGY CHANGES IN CHEMICAL REACTIONS

∆H of the products and reactants:

 

LET US TRY (INTRO TO UNIT 7 )

C12H22O11 + 12O2 12CO2 + 11H2O + 5638 kJ

How much heat is released during the formation of 9.6 moles of CO2?

HOMEWORK Balancing & Types of rxns:

Questions: p. 118 # 65 -66 (every 3rd), 67 (every 2nd one)

Endo vs Exo Questions: p. 120 #68 - 80