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 is added to this reaction, which direction will the reaction shift?

To the left/reactants.

300

NH₄⁺ + H₂O -> NH₃ + H₃O⁺

If this reaction is endothermic, will more ammonia or ammonium be produced if the heat is decreased?

Ammonium

400

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

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

Which of these solvents would dissolve the most CaCl₂?

NaCl aqueous solution

Deionized Water

CaF₂ aqueous solution

Deionized water. The other's have a common ion.

200

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]

300

As the temperature increases for a solubility reaction, the solubility decreases. What does this mean about the enthalpy of the reaction?

It is exothermic/ DeltaH is -

400

Give the solubility equilibrium equation for this reaction:

Fe₂(HPO4)₃ -> 2Fe³⁺+3HPO₄^2-

K_sp = [4s²][27s³] OR

K_sp = [108s⁵]

500

Look at the following equation:

NaCl₂ -> Na⁺ + 2Cl^-

Given K_sp = 32, what is the final molarity of Na⁺?

2M

Ksp = [Na][Cl]²

32 = [s][4s²]

s=2M

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)                          Eo=0.85V

Cu2+(aq) + 2e- -> Cu(s)                         Eo=0.34V 

Does the top half-cell or bottom half-cell represent the molecule being reduced?

Top half-cell

300

3 As₂O₃ + 4 NO₃^- + 7 H₂O + 4 H⁺ -> 6 H₃AsO₄ + 2 N₂O₂

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

4 moles of electrons

400

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

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

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

Bottom, the silver

It has a higher reduction potential, so it is reduced, so it is 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

Regarding concentrations, when can you use the Henderson-Hasselbach equation to find pH?

When the concentration of products is equal to the amount of reactants (or the equivalence point)

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

Miscellaneous

100

If a given reaction produces more products than reactants, what does that say about DeltaG?

It is negative/spontaneous

200

What numerical value of R is used in the Arrenhius equation?

8.314 J/(mol K)

300

If DeltaS is negative, and DeltaH is positive, when is the reaction spontaneous?

At low temperatures

400

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

83.6 KJ/mol

DeltaG= -RTln(k)

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]