CHEM 1210 Exam Review: Stoichiometry, Thermochemistry, Electron Configuration and Bonding

Terms in this set (30)

1. How many particles are in one mole?Avogadro's number, 6.022 x 10^23 particles (atoms, molecules or formula units).
2. Convert 36.0 g of water (molar mass 18.02 g/mol) to moles.n = mass / molar mass = 36.0 g / 18.02 g/mol = 2.00 mol H2O.
3. How do you find the limiting reactant?Convert each reactant to moles, divide by its coefficient in the balanced equation (or compute product each could form); the reactant giving the least product is limiting.
4. Percent yield formulaPercent yield = (actual yield / theoretical yield) x 100%. Theoretical yield comes from stoichiometry using the limiting reactant.
5. Empirical formula vs molecular formulaThe empirical formula is the simplest whole-number ratio of atoms (CH2O); the molecular formula is the actual count, a whole-number multiple of it (C6H12O6).
6. Define molarity and give its formula.Molarity M = moles of solute / liters of solution. Example: 0.50 mol NaCl in 0.250 L gives 2.0 M.
7. Dilution equationM1V1 = M2V2: initial concentration times initial volume equals final concentration times final volume, since moles of solute stay constant.
8. What is a net ionic equation?An equation showing only the species that actually react, with spectator ions (present unchanged on both sides) removed. E.g. Ag+(aq) + Cl-(aq) -> AgCl(s).
9. In a redox reaction, what is oxidized and what is reduced?Oxidation is loss of electrons (oxidation number increases); reduction is gain of electrons (oxidation number decreases). Mnemonic: OIL RIG.
10. Ideal gas law: state it and define each symbol.PV = nRT. P pressure, V volume, n moles of gas, R gas constant (0.08206 L*atm/(mol*K)), T absolute temperature in kelvin.
11. A gas at 1.00 atm occupies 4.0 L. At constant T, what is its volume at 2.00 atm?Boyle's law P1V1 = P2V2: V2 = (1.00 x 4.0)/2.00 = 2.0 L.
12. What is Dalton's law of partial pressures?Total pressure of a gas mixture equals the sum of each gas's partial pressure; each partial pressure equals its mole fraction times total pressure.
13. Endothermic vs exothermicExothermic processes release heat to the surroundings (delta H < 0). Endothermic processes absorb heat (delta H > 0).
14. Formula for heat absorbed by a substance, with symbols.q = m*c*delta T. m mass, c specific heat capacity, delta T = T_final - T_initial.
15. What does Hess's law state?The enthalpy change of a reaction is the same whether it occurs in one step or many, so you can add the delta H values of steps that sum to the overall reaction.
16. How do you calculate delta H of reaction from standard enthalpies of formation?delta H rxn = sum of n*delta Hf(products) - sum of n*delta Hf(reactants). Elements in their standard states have delta Hf = 0.
17. Relationship between wavelength, frequency and energy of lightc = lambda*nu and E = h*nu. Shorter wavelength means higher frequency and higher energy per photon.
18. What do the four quantum numbers n, l, ml and ms describe?n: energy level and size. l: subshell shape (0=s, 1=p, 2=d, 3=f). ml: orbital orientation (-l to +l). ms: electron spin (+1/2 or -1/2).
19. Write the ground-state electron configuration of oxygen (Z = 8).1s2 2s2 2p4.
20. State the Pauli exclusion principle and Hund's rule.Pauli: no two electrons in an atom share all four quantum numbers, so an orbital holds at most 2 with opposite spins. Hund: electrons fill degenerate orbitals singly before pairing.
21. Periodic trend for atomic radiusRadius decreases across a period (higher effective nuclear charge) and increases down a group (more electron shells).
22. Periodic trend for first ionization energyIncreases across a period and decreases down a group; it is the energy needed to remove the outermost electron from a gaseous atom.
23. Ionic vs covalent bondsIonic bonds form by electron transfer between a metal and nonmetal (large electronegativity difference). Covalent bonds form by sharing electrons, usually between nonmetals.
24. How do you calculate formal charge?Formal charge = valence electrons - nonbonding electrons - (bonding electrons / 2). The best Lewis structure minimizes formal charges.
25. What is resonance?When more than one valid Lewis structure can be drawn, the real molecule is an average (hybrid) of them, e.g. the equal N-O bonds in nitrate.
26. VSEPR: geometry of a molecule with 4 electron domains and 2 lone pairs (like H2O)?Electron geometry is tetrahedral; molecular shape is bent, with a bond angle a bit less than 109.5 degrees (about 104.5 degrees in water).
27. Why is CO2 nonpolar though its C=O bonds are polar?It is linear, so the two bond dipoles point in opposite directions and cancel, giving no net dipole moment.
28. What hybridization does the central atom have with 3 electron domains?sp2, trigonal planar arrangement with about 120 degree angles. 2 domains is sp, 4 is sp3.
29. Rank intermolecular forces from weakest to strongest.London dispersion < dipole-dipole < hydrogen bonding (H bonded to N, O or F). Stronger forces give higher boiling points.
30. Sigma vs pi bondsA sigma bond forms from head-on orbital overlap; a pi bond from side-by-side p overlap. A single bond is 1 sigma, a double is 1 sigma + 1 pi, a triple is 1 sigma + 2 pi.