CHEM 102 Exam Review: Atomic Structure, Bonding, Stoichiometry, Gases and Equilibrium

Terms in this set (28)

1. Avogadro's number and what it means6.022 x 10^23 particles per mole. One mole of any substance contains that many atoms, molecules or formula units.
2. How do you convert grams to moles?Divide the mass by the molar mass: n = m / M. Example: 36.0 g of water / 18.0 g/mol = 2.00 mol.
3. Limiting reactantThe reactant that runs out first and therefore sets the maximum amount of product. Find it by converting each reactant to moles of product and taking the smallest amount.
4. Percent yield formulaPercent yield = (actual yield / theoretical yield) x 100%.
5. Molarity definition and formulaMolarity M = moles of solute / liters of solution. Dilution: M1*V1 = M2*V2.
6. Mini-problem: how many grams of NaOH (40.0 g/mol) are in 250 mL of 0.200 M NaOH?moles = 0.200 mol/L x 0.250 L = 0.0500 mol; mass = 0.0500 x 40.0 = 2.00 g.
7. Empirical vs molecular formulaThe empirical formula is the simplest whole-number ratio of atoms (CH2O). The molecular formula is the actual number of atoms (C6H12O6 for glucose), a whole-number multiple of the empirical formula.
8. Relationship between energy, frequency and wavelength of lightE = h*nu and c = lambda*nu, so E = h*c / lambda. h = 6.626 x 10^-34 J*s, c = 3.00 x 10^8 m/s. Shorter wavelength means higher energy.
9. 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), from 0 to n-1. ml: orbital orientation, from -l to +l. ms: electron spin, +1/2 or -1/2.
10. Pauli exclusion principle vs Hund's rulePauli: no two electrons in an atom share all four quantum numbers, so an orbital holds at most two electrons of opposite spin. Hund: electrons fill degenerate orbitals singly with parallel spins before pairing.
11. Ground-state electron configuration of Fe (Z = 26)1s2 2s2 2p6 3s2 3p6 4s2 3d6, or [Ar] 4s2 3d6.
12. Periodic trend: atomic radiusRadius decreases left to right across a period (greater effective nuclear charge) and increases down a group (more electron shells).
13. Periodic trend: first ionization energyIncreases left to right across a period and decreases down a group. Small exceptions: B is lower than Be, and O is lower than N.
14. Electronegativity and bond polarityElectronegativity is an atom's pull on shared electrons; F is highest. A large electronegativity difference gives a polar covalent bond; a very large one gives ionic bonding.
15. How do you calculate formal charge?Formal charge = valence electrons - nonbonding electrons - (bonding electrons / 2). The best Lewis structure keeps formal charges near zero, with negative charge on the more electronegative atom.
16. What is resonance?When more than one valid Lewis structure can be drawn, the real molecule is an average (hybrid) of them. In ozone or nitrate, all equivalent bonds have the same length.
17. VSEPR: geometry for 4 electron domains with 0, 1 and 2 lone pairs0 lone pairs: tetrahedral (109.5 deg, CH4). 1 lone pair: trigonal pyramidal (NH3). 2 lone pairs: bent (H2O).
18. Hybridization for 2, 3 and 4 electron domains2 domains: sp (linear). 3 domains: sp2 (trigonal planar). 4 domains: sp3 (tetrahedral).
19. Sigma vs pi bondsA single bond is one sigma bond. A double bond is one sigma plus one pi. A triple bond is one sigma plus two pi. Pi bonds come from side-by-side p orbital overlap.
20. Rank the intermolecular forces from weakest to strongestLondon dispersion forces < dipole-dipole < hydrogen bonding (H bonded to N, O or F). Stronger forces mean higher boiling points.
21. Ideal gas law and its unitsPV = nRT. R = 0.08206 L*atm/(mol*K) or 8.314 J/(mol*K). Temperature must be in kelvin.
22. Dalton's law of partial pressuresTotal pressure is the sum of partial pressures: P_total = P_A + P_B + ... Each partial pressure P_A = X_A * P_total, where X_A is the mole fraction.
23. Kinetic molecular theory: what does temperature measure?Temperature is proportional to the average kinetic energy of gas particles. At the same temperature, lighter gases move faster (rms speed = sqrt(3RT/M)).
24. Equilibrium constant expression for aA + bB <=> cC + dDK = [C]^c [D]^d / ([A]^a [B]^b). Pure solids and liquids are left out.
25. Q vs K: which way does the reaction shift?If Q < K the reaction goes forward toward products. If Q > K it goes in reverse toward reactants. If Q = K the system is at equilibrium.
26. Le Chatelier: effect of adding reactant or raising pressureAdding reactant shifts toward products. Raising pressure by shrinking volume shifts toward the side with fewer moles of gas.
27. Does a catalyst change K?No. A catalyst speeds up the forward and reverse reactions equally, so equilibrium is reached faster but its position and K are unchanged. Only temperature changes K.
28. How do you relate Kp and Kc?Kp = Kc*(RT)^(delta n), where delta n = moles of gaseous products - moles of gaseous reactants.