Post on 14-Jan-2016
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Chemical ReactionsPotassium iodide (aq) reacts with lead nitrate (aq)
producing a yellow precipitate of lead iodide
Chemical Formulas
1. Empirical formula
2. Molecular formula
3. Structural formula
Formulas?
Empirical• Metal and non-metal• Ionic - lacking discrete unit,
or molecule• Simplest whole number ratio
• Metal and non-metal• Ionic - lacking discrete unit,
or molecule• Simplest whole number ratio
• Covalent compounds• Molecular and empirical
formulas can be different– Glucose:
molecular C6H12O6 versus empirical CH2O.
• Covalent compounds• Molecular and empirical
formulas can be different– Glucose:
molecular C6H12O6 versus empirical CH2O.
Molecular
Formula Weight
• General term ; Molecular Weight used more often • “Sum” of the atomic weights of all the atoms in a chemical formula• General term ; Molecular Weight used more often • “Sum” of the atomic weights of all the atoms in a chemical formula
Hydrocarbons and Carbohydrates(Organic Chemistry)
• Hydrocarbons– Composed of H and C– Some simple ; some complex– Examples: C3H8 (propane)
C4H10 (butane)– Complete “combustion” yields:
• CO2, H2O + energy
• Carbohydrates– Composed of H, C, and O– Sugars, starches, cellulose– Examples: C12H22O11 (sugar)– Complete “oxidation” yields:
• CO2, H2O + energy.
• Hydrocarbons– Composed of H and C– Some simple ; some complex– Examples: C3H8 (propane)
C4H10 (butane)– Complete “combustion” yields:
• CO2, H2O + energy
• Carbohydrates– Composed of H, C, and O– Sugars, starches, cellulose– Examples: C12H22O11 (sugar)– Complete “oxidation” yields:
• CO2, H2O + energy.
Chemical Reactions
• Occur through formation and breaking of chemical bonds between atoms
• Involve changes in matter, creation of new materials, and energy exchange
• Chemical equations – Concise representation of chemical reactions.
• Occur through formation and breaking of chemical bonds between atoms
• Involve changes in matter, creation of new materials, and energy exchange
• Chemical equations – Concise representation of chemical reactions.
Chemical Equations
• Reactants - substances existing before reaction• Products - substances existing after reaction• Chemical symbols and formulas needed for
quantitative purposes.
Balancing Equations
• Law of conservation of mass: atoms are neither created nor destroyed in chemical reactions– Mass of reactants = mass of products (i.e. balanced)
• To balance a chemical equation – Change coefficients in front of chemical formulas – Do not change the subscripts (numbers within formulas).
• Law of conservation of mass: atoms are neither created nor destroyed in chemical reactions– Mass of reactants = mass of products (i.e. balanced)
• To balance a chemical equation – Change coefficients in front of chemical formulas – Do not change the subscripts (numbers within formulas).
Subscripts vs Coefficients
Fig 10.5
Example: Fig. 10.6
Stepwise balancing procedurepage 279
Like an Inventory or “Bean Counting” 1. Law of conservation of mass (atoms are conserved)
2. Don’t change subscripts of formulas (compounds)
3. Multiply everything within a compound by the Coefficient
• Look for the most complex reactants and products – Try to balance atoms within them first
• Treat “Polyatomic” ions that appear on both sides as independent units with a charge
• Cross-over technique and use of fractional coefficients top find least common multiple to balance the equation
– See the next few examples: 10.5, 10.6, and 10.7
Like an Inventory or “Bean Counting” 1. Law of conservation of mass (atoms are conserved)
2. Don’t change subscripts of formulas (compounds)
3. Multiply everything within a compound by the Coefficient
• Look for the most complex reactants and products – Try to balance atoms within them first
• Treat “Polyatomic” ions that appear on both sides as independent units with a charge
• Cross-over technique and use of fractional coefficients top find least common multiple to balance the equation
– See the next few examples: 10.5, 10.6, and 10.7
Chemical ReactionsPotassium iodide (aq) reacts with lead nitrate (aq)
producing a yellow precipitate of lead iodide
Classifications of Chemical Reactions
1. Combination reactions2. Decomposition reactions3. Replacement reactions
(1-3 = redox reaction subclasses)
4. Ion exchange reactions
1. Combination reactions2. Decomposition reactions3. Replacement reactions
(1-3 = redox reaction subclasses)
4. Ion exchange reactions
Bal Eq
Combination Reactions
Rust: Fig 10.10
4 Fe(s) + 3 O2(g) 2 Fe2O3(s)
• Two or more substances combine to form a single compound
• Two or more substances combine to form a single compound
Decomposition Reactions
• Breakdown into simpler compounds or elements
• Usually require some form of energy for Rx to occur
• Breakdown into simpler compounds or elements
• Usually require some form of energy for Rx to occur
2 HgO (s) 2 Hg (s) + O2 Δ
Example: Replacement Reaction
2 Al (s) + 3 CuCl2 (aq) 2 AlCl3 (aq) + 3 Cu (s)
Fig 10.13
Replacement ReactionFig 10.12
• Occur because some elements have a stronger electron-holding ability • More active metals (Li, K, Ca, Na) give up electrons to elements lower on the list
• Occur because some elements have a stronger electron-holding ability • More active metals (Li, K, Ca, Na) give up electrons to elements lower on the list
Ag (s) + CuCl2 (aq) No Rx2 Al (s) + 3 CuCl2 (aq) 2 AlCl3 (aq) + 3 Cu (s)
Ion Exchange Reaction
AX + BY AY + BX
3 Ca(OH)2 (aq) + Al2(SO4)3 (aq) 3 CaSO4 (aq) + 2 Al(OH)3
• Ion Exchange: ions of one compound interact with ions of
another compound
• Possible results: 1. Solid precipitates: ↓2. Gas forms: ↑ 3. Water formed: H2O (l)
• No ion exchange reaction occurred if both products are soluble (See appendix B) “ S ” versus “ i ”
• Ion Exchange: ions of one compound interact with ions of
another compound
• Possible results: 1. Solid precipitates: ↓2. Gas forms: ↑ 3. Water formed: H2O (l)
• No ion exchange reaction occurred if both products are soluble (See appendix B) “ S ” versus “ i ”
Information from Chemical Equations
• Atoms are conserved• Mass is conserved• Law of combining
volumes (gases)– Gases at the same
temperature and pressure contain equal numbers of molecules
• Atoms are conserved• Mass is conserved• Law of combining
volumes (gases)– Gases at the same
temperature and pressure contain equal numbers of molecules
Units of Measurement used with Equations
• Atomic mass unit (u) = 1/12th mass of carbon-12
• One mole of a substance contains Avogadro’s number (6.02x1023) of the basic chemical unit of that substance (atoms, molecules, ions, …)
• Example: A mole of carbon-12 atoms is defined as having 6.02 x 1023 atoms totaling a mass of 12.00g
• Atomic mass unit (u) = 1/12th mass of carbon-12
• One mole of a substance contains Avogadro’s number (6.02x1023) of the basic chemical unit of that substance (atoms, molecules, ions, …)
• Example: A mole of carbon-12 atoms is defined as having 6.02 x 1023 atoms totaling a mass of 12.00g
Molar Weights
• Gram-atomic weight: mass in grams equal to atomic weight
• Gram-formula weight: mass in grams equal to formula weight
• Gram-molecular weight: mass in grams equal to molecular weight
• Gram-atomic weight: mass in grams equal to atomic weight
• Gram-formula weight: mass in grams equal to formula weight
• Gram-molecular weight: mass in grams equal to molecular weight
Quantitative use of Equations
Next Time: Water and Solutions