Chemical Reactions: An Introduction. Indicators of a Chemical Reaction A color change A solid forms...
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Transcript of Chemical Reactions: An Introduction. Indicators of a Chemical Reaction A color change A solid forms...
Chemical Reactions:An Introduction
Indicators of a Chemical Reaction• A color change
• A solid forms (precipitate)
• A gas forms
• The temperature changes (hot OR cold)
Chemical EquationsReactants – what goes INTO the rxn
Products – what comes OUT OF the rxn
Reactant A + Reactant B Product A
Law of Conservation of MassIn a chemical reaction, atoms are neither
created or destroyed
All atoms in the reactants MUST be accounted for in the products.
Physical StatesAfter each reactant and product is a symbol
representing the physical state of the element or compound
(s) – solid(l) – liquid(g) – gas(aq) – aqueous (dissolved in water)
Balancing Chemical EquationsDone by trial and error
1. Balance elements that only appear once2. Keep polyatomic ions together if possible
3. ***NEVER EVER EVER EVER CHANGE A SUBSCRIPT!!!***
4. Balance hydrogen and oxygen last
Diatomic Molecules• 7 elements exist in nature as diatomic
molecules (2 atoms)– Hydrogen (H2)– Oxygen (O2)– Nitrogen (N2)– Fluorine (F2)– Chlorine (Cl2)– Bromine (Br2)– Iodine (I2)
C2H5OH (l) + O2(g) CO2(g) + H2O(g)
Fe2O3(s) + HNO3(aq) Fe(NO3)3(aq) + H2O(l)
H2S(g) + Pb(NO3)2(aq) PbS(s) + HNO3(aq)
Types of Reactions
Objectives1. Give general equations for types of
reactions2. Classify reactions3. List 3 types of synthesis and 6
decomposition reactions4. List 4 types of single-replacement and 3
types of double-replacement reactions5. Predict products of reactions given the
reactants
Synthesis ReactionsGeneral Formula:
A + X AX
Synthesis with OxygenWith metals form metal oxides
Ex – Mg(s) + O2(g) MgO(s)
K(s) + O2(g) K2O(s)
2Fe(s) + O2(g) 2FeO(s)
4Fe(s) + 3O2(g) 2Fe2O3
S8(s) + 8O2(g) 8SO2(g)
C(s) + O2(g) CO2(g)
Synthesis with SulfurWith metals produce metal sulfides
Ex- 16Rb(s) + S8(s) 8Rb2S(s)
8Ba(s) + S8(s) 8BaS(s)
Metals with HalogensGroup 1: M + X2 2MX
Ex – Na(s) + Cl2(g) 2NaCl(s)
Group 2: M + X2 MX2
Ex – Mg(s) + F2(g) MgF2(s)
Metal Oxides with WaterGroup 1 & 2 form hydroxides
Ex – K2O(s) + H2O(l) 2KOH(aq)
CaO(s) + H2O(l) Ca(OH)2(l)
Non-metal Oxide with WaterForm oxyacids
Ex – SO2(g) + H2O(l) H2SO3(aq)
P2O5(s) + 3H2O(l) 2H3PO4(aq)
Decomposition ReactionsAX A + X
Decomposition of Binary CompoundsBreaks down into its elements
(g)O (g)2H O(l)2H 22yelectricit
2
Process called electrolysis
Decomposition of Metal CarbonatesForm metal oxides and carbon dioxide
(g)CO CaO(s) (s)CaCO 23
Decomposition of Metal HydroxidesForm metal oxides and water
O(g)H CaO(s) (s)Ca(OH) 22
Decomposition of AcidsBreak down into non-metal oxides and water
O(g)H (g)CO (aq)COH 2232
O(l)H (g)SO (aq)SOH 2342
Single ReplacementGeneral Formula
A + BX AX + B
Metal Replaces Another MetalAluminum is more reactive than lead
(aq))2Al(NO 3Pb(s) (aq))Pb(NO 2Al(s)
33
23
Replacement of Hydrogen in Water by a MetalMore Active Metals
(g)H 2NaOH(aq) O(l)2H 2Na(s) 22
Less Active Metals
(g)4H (s)OFe O(g)4H 3Fe(s) 2432
Replacement of Hydrogen in an Acid by a MetalMetals more active than hydrogen
(aq)MgCl (g)H 2HCl(aq) Mg(s) 22
Replacement of HalogensEach halogen can replace the halogen below it
on the periodic table
reaction no 2NaCl(aq) (g)I(g)Cl 2KF(aq) 2KCl(aq) (g)F
(g)Br 2KCl(aq) 2KBr(aq) (g)Cl
2
22
22
Double ReplacementAX + BY AY + BX
• Formation of a precipitate• Formation of a gas• Formation of water
Formation of a Precipitate
An insoluble product forms
(aq)2KNO (s)PbI (aq))Pb(NO KI(aq)2 3223
Formation of a GasInsoluble gas forms
Example
(aq)FeCl S(g)H 2HCl(aq) FeS(s) 22
Formation of WaterWater forms during reaction
Combustion ReactionSubstance reacts with oxygen to release heat
and light
Products are often carbon dioxide and water
Neutralization ReactionHA + BOH AB + HOH
Usually these are acid-base reactions
Products include salt and water
Activity Series
Objectives1. Explain the significance of an activity series
2. Use an activity series to predict if a reaction will take place
Metals vs. NonmetalsGreater activity of a metal indicates how easily
it loses electrons
Greater activity of a nonmetal indicates how easily it gains electrons
In a single-replacement reaction, if an element with lower activity is to be replaced, the reaction will take place.