AP chem unit 4: chemical reactions

4.1: introduction for reactions

physical change: a physical property of a substance changes without changing the composition

• ex) freezing/melting, seperations of mixures, making solutions, etc.

• atoms are not rearranged, physical properties(shape, color, density, mass) are

chemical change: a property of a substance changes(breaking of bonds and formation of new ones)

• what to look for:t

  • precipitate forming

  • color change

  • light

  • temp. change

  • sound

  • gas production

  • new substance formed

• difficult to reverse

• double ionic replacement includes acid/base neutralization and precipitation reactions

• can be considered RedOx reactions(except for double replacement)

4.2: net ionic equations

physical and chemical reactions can be represented by balanced equations

• must be balanced!!!

diatomic elements should always be in diatomic form(H2, N2, O2, F2, Cl2, Br2, I2)

overall ionic equations show how ionic compounds dissociate into their ions when dissolved in water

only changes substances that are ionic and aqueous

net ionic equations shows the particles that change in the reaction

• cancels out spectator ions

4.3: representation of reactions

chemists use diagrams as a way to represent chemical reactions

• solid particles should be close together, liquid particles showing a bit of disorder, and gas particles spread out far

• aqueous solutions sometimes only shows the solvent particles

  • ions should be dissociated & include charge

  • solvent particles should orient dipoles in the correct way

4.4: physical and chemical changes

a physical process occurs when a substance undergoes a change in properties but not a change in composition(phase change, mixture separation)

• ex) H2O(s) → H2O(l)

  • when the water melts the chemical properties do not change, but the physical properties do

• ex) mixture separation(chromatography, distillation, filtration)

a chemical process occurs when a substance is transformed into a substance with a different composition

• ex) Na + Cl → NaCl

• ex) synthesis, decomposition

4.5: stoichiometry

stoichiometry: conversions that involve mole ratios from a balanced chemical equation

information about >1 reactants signals that you will have a limiting reagent(the reactant that runs out first)

theoretical yield: predicted/calculated mass

actual yield: experiment determined mass

percent yield = (actual yield/theoretical yield)*100

4.6: introduction to reactions

titration: lab technique where a volume and molarity of a titrant is dispensed from a buret to a flask containing a measured quantity of the analyte

• moles of titrant can be determined at the equivalence point(when the moles of titrant and analyte are the stoichiometrically the same)

  • usually indicated by color change

types of common titrations:

• acid base titrations: either acid or base can be the titrant

  • acid base indicator used for end point

• redox reactions: color change when oxidation state of a metal ion changes

• precipitation titrations: precipitate formed or a color change

  • when titrant reacts with ions in the analyte

4.7: types of chemical reactions

acid base reactions involve transfer of 1 or more protons between substances

acids are proton donors, bases are proton acceptors

• protons are hydrogen ions

• hydronium(H3O+) ions form when a hydrogen reacts with water

• conjugate acid: a base that has gained one proton

• conjugate base: an acid that has lost one proton

acids and bases are described as strong or weak

• strong means that the substance will completely separate into its ions

  • strong acids: H2So4, HI, HBr, HNO3, HCl, HClO3, HClO4(So I Brought No Clean Clothes)

  • strong bases: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

oxidation reduction reactions involve transfer of one or more electrons between substances

• oxidation: loss of electrons

• reduction: gain of electrons

oxidation numbers!!!

• hydrogen is always +1

  • except for hydride, -1

• oxygen is always -2

  • except for peroxide, -1

4.8: introduction to acid base reactions

an acid base reaction is a reaction where a proton(H+) is transferred from an acid to a base

• an acid becomes a conjugate base when it transfers a proton to a base

  • make a conjugate acid base pair(that always differs by one proton)

  • water can be either a base or an acid

• ex) HA + H2O → H3O+ + A-

  acid base CA CB

a strong acid/base will ionize completely and is represented by a single arrow(→), a weaker acid/base will not ionize completely is represented by a double arrow(<->)

a stronger acid will form a weaker conjugate base, and vise versa

4.9: oxidation reduction(redox) reactions

1. redox is the transfer of electrons from one element to another

2. oxidation reaction cannot occur without reduction

3. all chemical reactions(except double replacement(precipitation reactions) and neutralization reactions) are redox