Chemical Reactions
description
Transcript of Chemical Reactions
Representing Chemical Equations
reactant 1 + reactant 2 → product 1 and product 2
produces
Product(s) must be different than the reactants
Representing Chemical Equations
Simply a “recipe”
+ + →
Eggs and butter and flour produce a cake
Word equations name the reactants and products.
What is missing from this recipe? AMOUNTS!!!
• + →
• Iron (II) and oxygen produce iron oxide• Fe (s) + O2 (g) → FeO (s)
• What is missing?• Amounts! • How do you figure out the amounts needed and
produced?
Representing Chemical Equations
Balancing Equations
• Based on the Law of Conservation of Mass
• “Matter is not created or destroyed in a reaction, just rearranged.”
• Fe + O-O → Fe O
• What is wrong here?
• an oxygen atom is missing
Balancing Equations
• Atom inventory Fe + O2 → Fe O
• Reactant side Product side
Fe O Fe O
1 2 1 1
Fe + O2 → Fe O
Final equation: Fe + O2 → Fe O
Balancing Equations
Steps:
• 1. Write the skeleton equation (can’t escape formula writing)
• 2. Count atoms in reactants
• 3. Count atoms in products
• 4. Change coefficients to make atom counts match. Never change subscripts.
• 5. Reduce coefficients if necessary.
Practice Problems
____ AlBr3 + ____ K ____ KBr + ____ Al
____ AlBr3 + 3 K 3 KBr + ____ Al
____ P4 + ____ Br2 ____ PBr3
____ P4 + 6 Br2 4 PBr3
Symbols used in Equations
+ separates two reactants or two products
→ “Yields” separated reactants from products
(s) Designates a reactant in the solid state
(t) Designates a reactant in the liquid state
(g) Designates a reactant in the gaseous state
(aq) Designates a reactant in the aqueous state
→ → indicates that heat is supplied to a reaction
→ Indicates that a catalyst is used (here, platinum)
Symbols used in Equations#1 separates two reactants or two products
#2 “Yields” separated reactants from products
#3 Designates a reactant in the solid state
(l) Designates a reactant in the # 4 state
(g) Designates a reactant in the # 5 state
#6 Designates a reactant in the aqueous state
# 7 indicates that heat is supplied to a reaction
→ Indicates that a # 8 is used (here, platinum)
# 9 name the diatomic elements
Classifying Chemical Reactions
• Five general types• Synthesis one new product• Solid sodium and chlorine gas form solid sodium chloride
2Na(s) + Cl2(g) → 2NaCl(s)
+ →
http://jchemed.chem.wisc.edu/jcesoft/cca/cca0/Movies/NACL1.html
http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/04chemrxnpage/chemicalreactions.htm
Classifying Chemical Reactions
Combustion Must have O2 as a reactant
2 Mg + O2 → 2 MgO
+ →
Combustion reactions are exothermic; energy is produced.
Classifying Chemical Reactions
• Combustion of hydrocarbons (compounds containing hydrogen and carbon)
• CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
• Most fuels are hydrocarbons
Classifying Chemical Reactions
• Decomposition Only one reactant• Hydrogen peroxide decomposes to release
oxygen gas and leave water on your skin
H2O2(aq) → O2 (g) + H2O(l)
2 H2O2(aq) → O2 (g) + 2 H2O(l)
Classifying Chemical Reactions
• Single replacement reactions One reactant is an element
• Copper reacts with silver nitrate to produce silver and copper nitrate.
• Cu(s) + AgNO3(aq) → Ag(s) + Cu(NO3)2(aq)
Single replacement reactions
• Activity Series of Metals
Lithium Iron
Rubidium Nickel
Potassium Tin
Calcium Lead
Sodium Copper
Magnesium Silver
Aluminum Platinum
Manganese Gold
Zinc
Classifying Chemical Reactions
• Double replacement reactions both reactants are ionic compounds
• A gas, liquid, or solid must be producedSilver nitrate and sodium chloride react to produce sodium nitrate and silver chloride
AgNO3 (aq) + Na Cl (aq) → NaNO3 (aq) + AgCl (s)
Ag+
Cl-
Na+ NO3- AgCl
Na+ NO3-
Summary Reaction Classification
Class of Reaction Reactants Probable products
Synthesis Two or more substances
One compound
Combustion Some substance and oxygen
An oxide
H20 and CO2 for hydrocarbon combustion
Decomposition One compound Two or more (elements or compounds)
Single-replacement An element and a compound
A new compound and the replaced element
Double-replacement Two compounds Two different compounds including a s, l, g
Reactions in Aqueous Solutions
• Review:
• Solution – homogeneous mixture
• Solute – substance dissolved
• Solvent – most plentiful substance in the solution
• Water is the “universal solvent”
• Other substances can also be solvents
Reactions in Aqueous Solutions
• How does water dissolve ionic compounds? Water is a polar molecule.
• http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf
http://programs.northlandcollege.edu/biology/Biology1111/animations/dissolve.html
Reactions in Aqueous Solutions Reactions that form solids
• Lead nitrate and potassium iodide
• Two clear solutions – mix – precipitate
forms
Pb +2
NO3 -
K+
I-
Reactions in Aqueous Solutions Reactions that form solids
• What happened on an atomic level?
• + →
• Lead and iodide form a new compound• Nitrate and potassium are still dissolved ions –
they did nothing but “watch” – spectator ions
NO3 –
Pb +2
K+
I-
K+
NO3 –
PbI2
Reactions in Aqueous Solutions Reactions that form solids
• Complete ionic equation• Pb +2 + NO3
- + K+ + I- → PbI2 + NO3 - + K+
• Spectator ions
• Net ionic equation• Pb +2 + I- → PbI2
Reactions in Aqueous Solutions Reactions that form liquids
• HBr (aq) + NaOH(aq) → H2O (l) + NaBr(aq)
Complete ionic equation .H+
(aq) + Br-(aq) + Na+
(aq) + OH -(aq) → H2O(l) + Na+
(aq) + Br-(aq)
Net ionic equation H+
(aq) + OH -(aq) → H2O(l)