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