Periodic Trends
What is the period trend for ionization energy?
Increases across period and up a group.
What is K for this reaction?
2KI (aq) + Pb(NO3)2 (aq) --> 2KNO3 (aq) + PbI2 (s)
Double Replacement Reaction
H2(g) + Br2(g) --><-- 2HBr(g)
At a certain temperature, the value of the equilibrium constant, K, for the reaction represented above 2.0 * 10^5. What is the value of K for the reverse reaction at the same temperature?
ANS: 5.0 * 10^-6
if you reverse the reaction, you flipped the positions of the products and reactants in the chemical equilibrium equation, thus you also flipped their positions in the new Kreverse expression, which is equivalent to taking the reciprocal of 2.0 × 10^5 which is 5.0*10-6.
What is the periodic trend for electron affinity AND electronegativity?
Electronegativity: Increases across a period and decreases down a group.
Electron Affinity: Increases across a period and decreases down a group.
For the reversible reaction
N2 (g) + 3 H2(g) --> <-- 2NH3 + Heat. The equilibrium shifts in the forward direction by ...
Increasing pressure and decreasing temperature
Of the following compounds, which is the most ionic?
A) SiCl4; B) BrCl; C) PCl3; D) Cl2O; E) CaCl2
ANS: E
Ionic compounds contain a metal-nonmetal combination. Only CaCl2 contains a metal-nonmetal combination. All the other choices are combinations of nonmetals, thus covalently bound.
Describe why sometimes there is a drastic leap in the magnitude of an Ionization energy when going from 1st to 2nd, or 2nd to 3rd, or 3rd to 4th etc. Give an example.
After losing valence electrons, much higher energy needed to take off more electrons because a stable configuration has been achieved.
Ex: Ca, leap between 2nd and 3rd ionization energy
Indicate the effect of a catalyst, pressure, temperature and concentration on speed
catalyst presence increases speed
pressure direct relationship
temperature direct relationship
concentration direct relationship
A flask contains 0.25 mole of SO2(g), 0.50 mole of CH4(g), and 0.50 mole of O2(g). The total pressure of the gases in the flask is 800 mm Hg. What is the partial pressure of the SO2(g) in the flask?
ANS: 160 mmHg
Since the quantity of moles given are related by a factor of 0.25...simplify! Think: 1 part SO2 + 2 parts CH4 +2 parts O2 = 5 total parts. Divide the total pressure of 800 mm Hg by 5 (Avogadro’s Law--equal moles of gases exert equal pressures at constant T and P. ) Each part is equal to 160 mm Hg and SO2 is only one “part” of the mixture, so its pressure is 160 mm Hg
What determines the position and the height (intensity) of each peak in a photoelectron spectrum?
The position of each peak is identified by the ionization energy, the height of each peak identifies the ratio of electrons in each level or orbital.
Dinitrogentetraoxide partially decomposes according to the following equilibrium: N2O4 (g) --> 2NO2 (g) A 1.000-L flask is charged with 3.00 * 10^-2 mol of N2O4. At equilibrium, 2.36*10-2 mol of N2O4 remains. Keq for this reaction is __________.
6.93 * 10^-3
Which of the following compounds is LEAST likely to exist?
PCl5, PBr3, NF3, NI5, SbF5
NI5.
Aluminum and gallium have almost identical 1st ionization energies even though they are in different periods. Why?
Aluminum is in the third period of the table, which does not have transition metals. The difference between alluminum and Gallium, however, is in the fourth period of the table, which does include transition metals. Filled D shell and new P shell makes it more difficult to remove the electron in the P-shell.
4HCl(g) + O2(g) --> <-- 2Cl2(g) + 2H2O(g)
Equal numbers of moles of HCl and O2 in a closed system are allowed to reach eqilibrium as represented by the equation above. Which of the following must be true at equilibrium.
A) [HCl] must be less than [Cl2]; B) [O2] must be greater than [HCl]; C) [Cl2] must equal [H2O].
B and C ONLY.
B. Per the ICE table, the [O2] must be larger than [HCl] because equal moles were initially added to the system and the change in HCl per stoichiometry is larger than O2.
C. Per the ICE table, they must be equal as they both start with 0.0 and have the same change.
In which of the following species does sulfur have the same oxidation number as it does in H2SO4?
a) H2SO3; b) S2O32-; c) S2-; d) S8; e) SO2Cl2
ANS: E
First calculate the oxidation number of sulfur in sulfuric acid. H is always + 1 and O is always –2 (unless in a peroxide). So far, that is 2(+1) + 4(–2) = –6. Since this is a neutral compound, and only one S is present, we are looking for a compound where the oxidation number of sulfur in it is +6. H2SO3 oxidation number of S = +4 S2O3 2– oxidation number of S = +2 S2– oxidation number of S = –2 S8 oxidation number of S = 0 (this is an allotrope of the element sulfur) SO2Cl2 oxidation number of S = +6