Atoms + Compounds (Units 1-2)
A student has a 1 g sample of each of the following compounds: NaCl, KBr, KCl. List these in order of increasing number of moles per sample.
KBr < KCl < NaCl
2F2(g) + 2NaOH(aq) → OF2(g) + 2NaF(aq) + H2O(l)
A 2mol sample of F2(g) reacts with excess NaOH(aq) according to the equation above. If the reaction is repeated with excess NaOH(aq) but with 1 mol of F2(g), what is true of the amount of OF2(g) produced?
The amount of OF2(g) produced is halved.
For a classroom demonstration, a chemistry teacher puts samples of two different pure solid powders in a beaker. The teacher places the beaker on a small wooden board with a wet surface, then stirs the contents of the beaker. After a short time the students observe that the bottom of the beaker is frozen to the wood surface. Make a claim about the observation and to justify your claims.
An endothermic chemical change has occurred because the temperature of the surroundings of the reaction has decreased significantly.
H2O(l) + H2O(l) ⇄ H3O+(aq) + OH−(aq)
At 5.0°C, the value of Kw for the equilibrium shown above is 1.9×10−15 and the value of pKw is 14.73. Solve for [H30+].
[H30+] = square root(1.9x10-15)
Write the ground-state electron configuration for an atom of selenium.
1s12s22p63s23p64s23d104p4
A gas mixture at 0°C and 1.0atm contains 0.010mol of H2, 0.015mol of O2, and 0.025mol of N2. Assuming ideal behavior, what is the partial pressure of hydrogen gas (H2) in the mixture?
0.20 atm (H2 makes up about 20% of the total moles in the mixture)
HCl(aq) + H2O(l) → H3O+(aq) + Cl−(aq)
For the dissolution of HCl in water represented above, which species are the Brønsted-Lowry bases?
H2O(l) and Cl-(aq)
For an experiment, 50.0g of H2O was added to a coffee-cup calorimeter. The initial temperature of the H2O was 22.0°C, and it absorbed 300.J of heat from an object that was carefully placed inside the calorimeter. Assuming no heat is transferred to the surroundings, which of the following was the approximate temperature of the H2O after thermal equilibrium was reached? Assume that the specific heat capacity of H2O is 4.2 J/(g⋅K).
23.4 degrees C
Draw a Lewis Diagram for the substance HNO2
O=N-O-H, (2 lone pairs on each O, 1 lone pair on N)
How many grams of CaCl2 (molar mass =111g/mol) are needed to prepare 100.mL of 0.100M Cl−(aq) ions?
0.555 g
C2H4(g) + H2(g) --> C2H6(g)
When C2H4(g) reacts with H2(g), the compound C2H6(g) is produced, as represented by the equation above. Which type of reaction is represented by the above scenario? (Acid-Base, Precipitation, Decomposition, Redox)
Redox reaction because H2(g) is oxidized.
Fe3+(aq, Colorless) + SCN−(aq, Colorless) ⇄ FeSCN2+(aq,Red)
When colorless solutions containing Fe3+(aq) ions and SCN−(aq) ions are combined, a deep-red complex ion, FeSCN2+(aq) quickly forms, as shown in the net ionic equation above. Explain the observation that adding a few additional crystals of KSCN(s) results in the red color of the solution becoming deeper?
The added KSCN(s) dissolves, causing the reaction system to respond by producing more product to partially consume SCN−(aq) and reduce its concentration.
A student pours a 10.0mL sample of a solution containing HC2H3O2(pKa=4.8) and NaC2H3O2 into a test tube. The student adds a few drops of bromocresol green to the test tube and observes a yellow color, which indicates that the pH of the solution is less than 3.8. Based on this result, what is true about the relative concentrations of HC2H3O2 and NaC2H3O2 in the original solution?
[HC2H3O2]>[NaC2H3O2]
Name an element that has a significant jump between the second and third ionization energies.
Be, Mg, Ca, Sr, Ba
A 1L sample of helium gas at 25°C and 1atm is combined with a 1L sample of neon gas at 25°C and 1atm. The temperature is kept constant. What is true of the average kinetic energies of the gases when they are combined?
The average kinetic energies do not change because the temperature is kept constant.
Step 1: H2(g) + ICl(g) → HI(g) + HCl(g) (slow)
Step 2: HI(g) + ICl(g) → HCl(g) + I2(g) (fast)
Write the rate law for the overall reaction mechanism.
Rate = k[H2][ICl]
2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
ΔH°=−1120 kJ/molrxn
Based on the reaction represented by the chemical equation shown above, what is the amount of heat released when 4.00mol of H2S(g) reacts with 9.00mol of O2(g)?
-2240 kJ
HCN(aq) + H2O(l) ⇄ H3O+(aq) +CN−(aq)
Ka=[H3O+][CN−]/[HCN] =6.2×10−10
The equilibrium reaction shown above represents the partial ionization of the weak acid HCN(aq). A 0.200M HCN(aq) solution has a pH≈4.95. If 0.049g (0.010mol) of NaCN(s) is added to 100mL of 0.200M HCN(aq), what explains how and why the pH of the solution changes?
The pH will be higher than 4.95 because adding CN− will disrupt the equilibrium, resulting in an increased production of HCN that decreases the concentration of H3O+.
Which of the following complete Lewis diagrams represents a molecule containing a bond angle that is closest to 120°? CO2, NH3, CH4, C2H4O2 (draw Lewis diagrams for each to visualize)
C2H4O2 (H3-C-C-O2)
The electron cloud of HF is smaller than that of F2 , however, HF has a much higher boiling point than F2 has. What best explains how the dispersion-force model of intermolecular attraction does not account for the unusually high boiling point of HF?
HF has dispersion forces AND hydrogen bonding between molecules, requiring more energy to overcome its IMFs than the dispersion forces between F2 molecules.
NH4+(aq)+OH−(aq)→NH3(aq)+H2O(l)
When 0.20 M NH4Cl(aq) and 0.20 M NaOH(aq) are mixed, the reaction represented by the equation above occurs and a strong smell of ammonia, NH3, is observed. Based on this information, what is true concerning the acids in this reaction?
NH4+ is a stronger acid than H2O.
CuBr(s) ⇄ Cu+(aq)+Br−(aq)
Shown above is the chemical equation for the dissolution of the slightly soluble salt CuBr(s). Its Ksp value in pure water was experimentally determined. CuBr was found to be much less soluble in a 0.001M NaBr solution than in pure water. What correctly explains the decrease in solubility of CuBr in 0.001 M NaBr?
The presence of additional Br− ions already in the solution means equilibrium will be reached when much less CuBr has dissolved.
N2(g) + 3H2(g) ⇄ 2NH3(g)
K= 5.6×105 at 298K
ΔH°rxn=−91.8 kJ/molrxn
The synthesis of NH3 is represented by the equation above. Based on the equilibrium constant, K, and ΔH°rxn given above, justify that the reaction is thermodynamically favorable at 298K and constant pressure.
ΔG = -RTln(K) < 0 because K >> 1