A few selected practice questions: VSEPR & Equilibrium

1) Experimentally the azide ion, N₃^-, is found to be linear, with each adjacent nitrogen-nitrogen distance equal to 116 pm. a) Draw two resonance forms for the Azide ion. b) Include the formal charge for each respective nitrogen atom in both resonance forms. c) Estimate the bond order of the respective nitrogen-nitrogen bonds. d) Briefly explain why the bond lengths are all equal.

2) The electronic structure of the H₃O⁺ ion with lone pairs is

3) How many pairs of electrons from from the correct Lewis drawing of HOCH₂CH₂OH are involved in bonding vs.non-bonding (free pairs of electrons)? (Bonding /Non-bonding)

4) In hemoglobin the heme group provides four electron pairs in a square arrangement. Two additional electron pairs (one above the other below the center of the square) complete the interaction with the iron. What is the electronic geometry of the resulting iron complex including electron pairs?

5) Identify the molecular geomtery of the following molecules and if it is polar or non-polar

(a) ICl3 Geometry: ________ (_) polar (_) nonpolar

(b) SiF4 Geometry: ________ (_) polar (_) nonpolar

6) What is the NO bond order in H₃CNO?

7) Write the equilibrium expression and calculate the equilibrium constant value (Kc) for the following reaction.

2SO₂(g) + O₂ (g) 2SO₃(g)

The concentrations of each species at equilibrium are as follows: [SO₂] = 0.40 mol/L, [O₂] = 0.80 mol/L, [SO₃] = 0.20 mol/L

8) Consider the following endothermic reaction in the gas phase: H₂ + I₂ 2 HI; If the temperature is increased

A. the value of the equilibrium constant will decrease and more HI will be produced

B. the value of the equilibrium constant will decrease and less HI will be produced

C. the value of the equilibrium constant will increase and more HI will be produced

D. the value of the equilibrium constant will increase and less HI will be produced

9) The equilibrium constant, Kp, is 2.4 x 10³ at a certain temperature for the following reaction.

2 NO(g) N₂(g) + O₂(g)

a) Calculate the value of the reaction quotient, Q, using the data below, and b) select the correct description that goes with it.

PNO = 0.010 atm, PN₂ = 0.11 atm, PO₂ = 2.0 atm

Q =

(_) Q < Kp so the reaction shifts right.

(_) Q > Kp so the reaction shifts right.

(_) Q < Kp so the reaction shifts left.

(_) Q > Kp so the reaction shifts left.

(_) Q = Kp so the reaction is at equilibrium.

10) a) Kc = 6.9 x 10–3 for N2O4(g) 2 NO2(g) at 300 K and 1 atm. Determine the concentrations of both species at equilibrium if the reaction is initiated by placing 1.00 mole of N2O4 in a 1000.0 mL reaction vessel. ( Solving by approximation is OK.)

b) Briefly describe what effect that doubling the pressure while keeping the temperature constant would have on the respective concentrations of N2O4 and NO2.