Chemical Reactions
SCH3U - Unit 2
Chemical ChangeChemical Change = any change in which a new substance is formed
Evidence of Chemical Change:Change in colourChange in odourFormation of gas/solidRelease/absorption of heat
Collision-Reaction Theory A theory stating that chemical reactions
involve collisions and rearrangements of atoms or groups of atoms and that the outcome of collisions depends on the energy and orientation of the collisions No reaction occurs if:
Molecules don’t have enough energy Molecules don’t collide in the right orientation
Orientation The molecules must be in a certain 3-D
arrangement to allow a reaction e.g. CH2=CH2 + HCl -> CH3CH2Cl
Energy Required A reaction doesn’t occur unless the particles
collide with a certain minimum energy called the activation energy of the reaction
Activation energy is the minimum energy required before a reaction can occur. You can show this on an energy profile for the reaction. For a simple over-all exothermic reaction, the energy profile looks like this:
Activation Energy Profile
Chemical Equations Chemical Equation = a
representation of a chemical reaction that indicates the: Chemical formulas Relative number of entities States of matter of the reactants and
productsReactants Products
Chemical EquationsIn general: Reactant A + Reactant B Product C
Reactant = is a chemical that is used up in a chemical reaction
Product = is a product that is created during a chemical reaction.
Chemical Formulas A chemical formula uses subscripts to indicates
the number of atoms in a compound
Example: H2O Has 2 atoms of H And 1 atom of O
Example: C6H12O6 Has 6 atoms of C Has 12 atoms of H And 6 atoms of O
Relative # of Entities Coefficient = a whole number
indicating the ratio of molecules of each substance involved in a chemical reaction The large number on the left side of a
molecule’s formula
Example: Mg + 2 Cl MgCl2 Example: 6 K + N2 2 K3N
State of Matter Solid = (s) Liquid = (l) Gas = (g) Solution = (aq)
Example: 6 K(s) + N2(g) 2 K3N(s)
Catalysts A catalyst is a substance which speeds up a
reaction, but is chemically unchanged at the end of the reaction .e.g conc. H2SO4 in many different reactions
Adding a catalyst has exactly this effect on activation energy. A catalyst provides an alternative route for the reaction. That alternative route has a lower activation energy
Draw a standard energy profile and then draw a new line to represent the inclusion of a catalyst
5 Types of Chemical Reactions1. Combustion2. Synthesis3. Decomposition4. Single Displacement5. Double Displacement
5 Types of Chemical ReactionsGeneralizations:Combustion: AB + oxygen oxides of A &
B + heatSynthesis: A + B CDecomposition: AB A + BSingle Displacement: A + BC AC + BDouble Displacement: AB + CD AD + CB
Combustion Reactions Combustion Reaction: the reaction of
a substance with oxygen, producing oxides and energy
Also know as burning
For a combustion reaction to occur 3 things must be present:1. Fuel2. Oxygen3. Heat
Combustion Reactions C
Type of Reaction: Synthesis
Example C + O2
OO C + O O C
OO COO C OO C OO C OO
C OO
C OO
CO
O
C OO
C O
O C O
O C OO C
OO C OO C
General: A + B AB
Synthesis Reaction Characteristics Two or more substances (elements or
compounds) react to form ONE product. Combination of smaller atoms/molecules into larger molecules.
Usually exothermic (energy is produced) Can occur naturally or by an initial application
of energy (heat, flame, UV light, use of catalyst)
Predicting Products of Synthesis Reactions Metal + oxygen → metal oxide (basic oxide)
EX. 2Mg(s) + O2(g) → 2MgO(s) Nonmetal + oxygen → nonmetallic oxide (acidic oxide)
EX. C(s) + O2(g) → CO2(g) Metal oxide + water → metallic hydroxide (base)
EX. MgO(s) + H2O(l) → Mg(OH)2(s) Nonmetallic oxide + water → acid
EX. CO2(g) + H2O(l) → ; H2CO3(aq) Metal + nonmetal → salt
EX. 2 Na(s) + Cl2(g) → 2NaCl(s) A few nonmetals combine with each other.
EX. 2P(s) + 3Cl2(g) → 2PCl3(g) These two reactions should be remembered:
N2(g) + 3H2(g) → 2NH3(g) NH3(g) + H2O(l) → NH4OH(aq)
Type of Reaction: Decomposition
Example: NaCl
General: AB A + B
Cl Na Cl + Na
Type of Reaction: Decomposition
Example 2HgO
O Hg
O Hg
Hg
O O Hg
+
General: AB A + B
Decomposition Reaction Characteristics ONE reactant produces two or more products.
Splitting of large molecules into elements or smaller molecules.
Usually endothermic (requires energy) Can require energy in the form of heat,
electricity, catalyst, UV light *some decomposition rxns occur at room
temperature
Predicting Products of Decomposition Reactions
Metallic carbonates, when heated, form metallic oxides and CO2(g). EX. CaCO3(s) → CaO(s) + CO2(g)
Most metallic hydroxides, when heated, decompose into metallic oxides and water.
EX. Ca(OH)2(s) → CaO(s) + H2O(g) Metallic chlorates, when heated, decompose into metallic chlorides and
oxygen. EX. 2KClO3(s) → 2KCl(s) + 3O2(g)
Some acids, when heated, decompose into nonmetallic oxides and water. EX. H2SO4 → H2O(l) + SO3(g)
Some oxides, when heated, decompose. EX. 2HgO(s) → 2Hg(l) + O2(g)
Some decomposition reactions are produced by electricity. EX. 2H2O(l) → 2H2(g) + O2(g) EX. 2NaCl(l) → 2Na(s) + Cl2(g)
Type of Reaction: Single Displacement
Example: Zn + CuCl2
ZnClCl Cu +
General: AB + C AC + B
ClCl Zn Cu+
Type of Reaction: Double Displacement
Example: MgO + CaS
General: AB + CD AD + CB
SOMg Ca+
O S
Mg Ca+
Chemical Reactions
combustion: AB + oxygen oxides of A & Bsynthesis: A + B Cdecomposition: AB A + Bsingle displacement: A + BC AC + Bdouble displacement: AB + CD AD + CB