Equilibrium & Thermo
The value of Kc for a particular reaction is 3.80*10-5. Which of the following statements about this reaction must be true at equilibrium?
a. There are more products than reactants
b. There are more reactants than products
c. The reactants and products are about equal
d. We cannot conclude anything from this value
b. There are more reactants than products
The acid dissociation constant (𝐾𝑎) of acetic acid (CH3COOH) is 1.80x10-5. Determine the pH for a 0.56 M solution of lactic acid.
2.50
In a phase diagram, what is the triple point?
The temperature and pressure at which solid, liquid, and gas phases all coexist in equilibrium (all 3 curves meet).
Consider the following reaction:
3HNO2(aq) + 5H+(aq) + Cr2O72-(aq) --> 3NO3-(aq) + 2Cr3+(aq) + 4H2O(l)
What is being oxidized in this reaction?
N
Substance Y decomposes by first order kinetics with a rate constant of 0.65 s−1. If we start with 15.9 moles of the substance Y initially, how much will you have after 4.0 seconds?
1.2 moles
Ammonia (NH3) and oxygen can react as follows:
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) ΔHrxn= -906 kJ/mol
Suppose a mixture of these gases has come to equilibrium. According to Le Châtelier's principle, which of the processes below will shift the equilibrium to the left (i.e. towards the reactants)? Select all that apply.
a. Decreasing the volume of the container
b. Increasing the temperature
c. Removing oxygen
d. Decreasing the temperature
e. Removing water
a. Decreasing the volume of the container
b. Increasing the temperature
c. Removing oxygen
A weak acid (HF) is titrated with a strong base (NaOH).
The titration curve begins around pH 2, rises gradually through a buffer region (pH 4–7), then increases sharply near the equivalence point (around pH 8), and finally levels off in the high-pH region (pH 10–12) after excess NaOH has been added.
In this post-equivalence region (where NaOH is in excess), which species (aside from water) are present in significant quantities?
(Select all that apply.)
a. HF
b. F⁻
c. OH⁻
d. Na⁺
e. H⁺
b. F⁻
c. OH⁻
d. Na⁺
A substance’s phase diagram shows the gas region on the right side at high temperature and relatively low pressure. In this region, what can you conclude about the relationship between average molecular kinetic energy and intermolecular forces?
a. The average molecular kinetic energy is stronger than the intermolecular forces
b. The intermolecular forces are stronger than the average molecular kinetic energy
c. The kinetic energy and intermolecular forces are approximately equal
d. Nothing can be concluded
a. The average molecular kinetic energy is stronger than the intermolecular forces
Let’s say that we have some ocean water that has a 22.0% by mass concentration of NaCl. Assuming NaCl is the only solute, calculate the mole fraction (x) of water in this solution.
0.920
A galvanic cell is constructed using a silver electrode in a silver nitrate solution and a copper electrode in a copper(II) nitrate solution. The two half-cells are connected by a U-shaped tube filled with an inert electrolyte that allows ions to migrate and maintain electrical neutrality as the reaction proceeds.
Which component of the cell is this U-shaped ion-conducting pathway?
The salt bridge
The first step to balancing a redox reaction is to balance each half reaction separately. How many electrons are lost/gained when the half-reaction below is balanced?
Cr2O72- --> 2Cr3+
six gained
On a titration curve of hydrofluoric acid (HF) with NaOH, what calculation method would you use to calculate the pH of this titration before the equivalence point?
Henderson Hasselbalch
Substance G is a crystalline solid at 25°𝐶 with the following properties:
· A high melting point
· Brittle (breaks easily when struck)
· Soluble in water
What type of crystalline solid would you expect Substance Q to be?
ionic solid
The mechanism for the decomposition of ozone is below.
O3(g) --> O2(g) + O K1
O + O3(g) --> 2O2(g) K2
Assuming that the first step is the slowest, write the correct experimentally-observable rate law for the overall chemical reaction.
Rate = k1 [O3]
A galvanic cell is constructed using a silver electrode in Ag⁺(aq) and a copper electrode in Cu²⁺(aq). Using standard reduction potentials, Ag⁺/Ag has the higher reduction potential and is therefore where reduction occurs.
Which component of the cell is the cathode?
The silver electrode
17. When lithium hydroxide (LiOH) is dissolved in water, the temperature of the liquid changes from 20°C to 25°C. Which of the following statements must be true for this solution? Select all that apply.
a. Δ𝐻solution < 0
b. |Δ𝐻𝑚𝑖𝑥|>|Δ𝐻𝑠𝑜𝑙𝑢𝑡𝑒+Δ𝐻𝑠𝑜𝑙𝑣𝑒𝑛𝑡|
c. |Δ𝐻𝑚𝑖𝑥|<|Δ𝐻𝑠𝑜𝑙𝑢𝑡𝑒+Δ𝐻𝑠𝑜𝑙𝑣𝑒𝑛𝑡|
d. Δ𝐻solution > 0
e. Δ𝐻𝑚𝑖𝑥 > 0
a. Δ𝐻solution < 0
b. |Δ𝐻𝑚𝑖𝑥|>|Δ𝐻𝑠𝑜𝑙𝑢𝑡𝑒+Δ𝐻𝑠𝑜𝑙𝑣𝑒𝑛𝑡|
Which of the following are possible definitions for an base? Select all that apply.
a. A proton donor
b. A proton acceptor
c. An electron pair acceptor
d. An electron pair donor
e. A substance that produces OH- when dissolved in water
b. A proton acceptor
d. An electron pair donor
e. A substance that produces OH- when dissolved in water
Why do molecules with greater molecular masses tend to have higher boiling points?
Increasing polarizability increases magnitude of dispersion forces.
When 2.43 g of a certain molecular compound Z are dissolved in 55. g of cyclohexane (kf=20.8 C/m), the freezing point of the solution is measured to be 1.7 degrees C. Given that the normal freezing point of cyclohexane is 6.7 degrees C, what is the molar mass of compound Z?
180 g/mol
In which of the following aqueous solutions would you expect PbCl2 to have the lowest solubility?
a. 0.020 M BaCl2
b. 0.020 M Fe2Cl4
c. 0.020 M NaCl
d. 0.010 M AgCl2
e. pure water
b. 0.020 M Fe2Cl4
If we have a reaction that has a K of 0.189 at 25℃, what is the standard Gibbs free energy change for this process?
4.13 kJ/mol
Calculate the pH at 25 C of a 0.82 M soluiton of potassium acetate (KCH3COO). Note that acetic acid (CH3COOH) is a weak acid with Ka= 1.74 x 10-5.
9.3
This intermolecular force is generally strongest under typical conditions
a. London dispersion b. Dipole–dipole c. Hydrogen bonding d. Ion–dipole e. None of the above
ion-dipole
Given the following data, determine the rate law for the reaction:
Experiment [H2] (M) [I2] (M) Initial Rate (M s-1)
1 1.10 2.18 6.00 x 104
2 3.35 2.18 5.57 x 105
3 1.10 4.70 1.29 x 105
rate = k[H2]2[I2]
A sealed 2.00 L container holds 3.50 g of an unknown gas at 27 °C. When the gas is cooled to –33 °C at constant volume, the pressure drops from 1.20 atm to 0.720 atm. Assume the gas behaves ideally at both temperatures.
What is the molar mass of the gas?
36 g/mol