General Chemistry 2

Equilibrium

100

This letter represents the constant for an equilibrium equation when the rate of the forward reaction is the same as the rate of the backwards reaction.

k

200

HCOOH + OH^- -> H₂O + HCOO^-

If more of the formate ion (HCOO^-) is added to this reaction, which direction will the reaction shift?

To the left/reactants.

300

N_2(g) + 3H_2(g) -> 2NH_3(g)

The above reaction is endothermic and occurs in a container. Where will the reaction shift if the container suddenly becomes smaller?

To the right. Decreased volume = increased pressure, goes to the side with less moles of gas

400

The partial pressures of S₂O, O₂, and S₂O₄ are currently 0.174atm, 0.225atm, and 0.419atm respectively. Determine if the reaction is at equilibrium or if it will shift to the right or to the left. Kp = 110.8

2S₂O(g) + O₂(g) → S₂O₄(g)

K = 61.51 

Shifts right

500

2HI -> I₂ + H₂

If there is 0.75M of HI initially in the mixture, and the equilibrium concentration of I₂ is 0.3M, what is the equilibrium concentration of HI?

0.15M

    2HI   ->   I₂ + H₂

I   0.75M     0M   0M

C   -2x        +x   +x

E  0.75-2x    0.3M   0.3M

x=0.3M so 0.75M - 2x = 0.15M

Solubility

100

The Ksp's of several compounds are given

Al(OH)₃                                                      Ksp= 3x10^-34

Cd(IO₃)₂                                                    Ksp= 2.5x10^-8

Cu₃(AsO₄)₂                                   Ksp= 7.95x10^-36

Which compound is the least soluble?

Cu₃(AsO₄)₂ [Copper(II) Arsenate]

200

If ∆S is negative, and ∆H is positive, when is the reaction spontaneous?

At low temperatures

300

Keq is 1.83x10^-12 for a reaction at 372K. What is ∆G for this experiment?

83.6 KJ/mol

∆G = -RTln(k)

400

If ∆H _rxn = −82 kJ/mol and ∆S = 109 J/mol · K, what is ∆G _rxn for this reaction at 54°C? Is the reaction spontaneous?

∆G _rxn = -117.6, reaction is spontaneous 

500

For a generic process A → B, ΔH°_sys = -174 kJ/mol and ΔS°_surr = 243 J/K-mol. Assuming that ΔH°_sys and ΔS°_surr do not change with temperature, at what temperature in °C does the reaction go from being non-spontaneous to spontaneous?

716K

Electrochemistry

100

If a molecule is a reducing agent in a reaction, is it accepting or producing moles of electrons?

Producing moles of electrons.

A reducing agent is BEING oxidized, therefore its charge is increasing, therefore it is producing electrons.

200

Hg2+(aq) + 2e- -> Hg(l)                          E^o=0.85V

Cu2+(aq) + 2e- -> Cu(s)                         E^o=0.34V 

Based on the half-cell potentials, what is the cell potential for the reaction? Write the complete reaction?

Hg²⁺(aq) + Cu(s) --> Hg(l) + Cu²⁺(aq)

Cell Potential: 0.51

300

Ce³⁺ + Pb → Ce + Pb⁴⁺

How many moles of electrons are transferred in the reaction above?

12 moles of electrons

400

Fe³⁺(aq) + 3e^- -> Fe(s)                    E^o=0.04V

Ag⁺(aq) + e^- -> Ag(s)                      E^o=0.80V

Which of the half-cells listed would gain mass in a galvanic cell?

Ag - It has a higher reduction potential (the cathode), cathode's gain mass during electrolysis.

500

2Cr₂O₇^2- + 14H⁺ + 6Cl^- -> 2Cr₃⁺ + 3Cl₂ + 7H₂O

Which molecule is the reducing agent in this full-cell reaction?

6Cl^- -> 3Cl₂ + 6e^-

Acids and Bases

100

Which of these are strong acids?

HCl, HCN, HCOOCH, HNO₃, HF, HClO₃, H₃PO₄

HCl, HNO₃, HClO₃

200

What is the equilibrium volume of a titration of 0.0974M NaOH have been added to 57.0mL of 0.0466M HClO4

27.27mL

300

If 0.25M of HCOOH yields 6.71x10^-3M of both H₃O⁺ and COOH^-, what is the Kb of HCOOH?

5.6x10^-11

Ka=[H₃O⁺][COOH^-]/[HCOOH]

Ka=1.8x10^-4

Kw/Ka=Kb

400

Calculate the pH of a 0.25 solution of HC₂H₃O₂ if the Ka of acetic acid is 1.8x10^-5.

2.67

1.8x10^-5= [H₃O⁺][C₂H₃O₂^-]/[HC₂H₃O₂]

1.8x10^-5= [x][x]/[0.25-x] (drop the x in reactants)

x=0.002121, -log(x)=2.67

500

Calculate the pH of a solution if 30.5g of NaF is dissolved in 650mL of water. The Kb of F^- is 

1.471x10^-11.

8.61

30.5g x 1g/42mol x 1/0.65L = 0.117M

Ka = [HF][OH^-]/[F^-]

1.471x10^-11=[x][x]/[0.117-x] (drop the x)

x=4.05x10^-6 -log(x)=5.39

14-5.39=8.61

MISC

100

What are the oxidation numbers in K2CO3?

K = +1

C = +4

O = -2

200

How many intermediates and transition states are there? Is this reaction endothermic or exothermic? 

B, D, F = transition states 

C, E = intermediates 

reaction is exothermic 

300

A piece of zinc is dropped into 1.00 L of 0.100 M HCl and the following data was obtained:

Time                Mass of Zinc

0s                    0.016g

4s                    0.014g

8s                    0.012g

12s                  0.010g

16s                  0.008g

20s                  0.006g

Calculate the Rate of Reaction in grams and moles of Zn consumed per second. 

grams of Zn = 5.0 x 10^-4 g/s

moles of Zn = 7.65 x 10^-6 mol/s

400

What is the standard potential for the voltaic cell using the Pb²⁺/Pb and Mg²⁺/Mg half reactions. Which metal is the cathode

Pb²⁺ + 2e^- --> Pb   E = -0.124 V

Mg²⁺ + 2e^- --> Mg   E = -2.37 V 

Cathode: Pb²⁺/Pb

Standard Potential = 2.246 V

500

Look at this Table for 2NO₂ + O₂ -> N₂O₄:

[NO₂]       [O₂]       Reaction Rate

0.1M        0.1M      0.000125M/s

0.2M        0.1M      0.000500M/s

0.1M        0.2M      0.000250M/s

What is the Rate law expression?

rate = k[NO₂]²[O₂]