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UNIT VITypes of Chemical Reactions
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 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
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
-----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 →
Questions: p. 118 # 65 -66 (every 3rd), 67 (a,c,e only)
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 **If you know ∆H of the products and
reactants:
Questions: p. 120 #68-75 & p. 122 #76,77