Safety Minute/Molecule of the Day
Stoichiometry/Reactions
Gases
Thermochemistry
MO Theory/Bond Order/Bond Character
100
What are 3 safety requirements for gas cylinders?
Secure at all times, store in cool areas, place where its not in the way,close valves,tighten caps, inspect for leaks, check support brackets, move using specific equipment, and report leaks
100
Based on the following reaction, which element is being reduced? Which is being oxidized?
Fe2O3 + 2Al → 2Fe +Al2O3
Fe: +3→ 0 Fe is reduced
O: -2 → -2
Al: 0 → +3 Al is oxidized
100
Determine the density of O2 gas at 25℃ and a pressure of 0.400 atm. Assume oxygen is an ideal gas and obeys the ideal gas law. The molecular weight is 31.998 grams per mole. Give your answer in units of g/L.
Potentially helpful information: R=0.08206 Latm/(Kmol).
PV = nO2RT = mO2MO2
D = m O2V= (P)(MO2)RT
= (0.400 atm)(31.998 g/mol)
——————————--- 0.0523 g/L
(0.8206 LatmKmol)([25 +273] K)
100
Is energy required or released when bonds break?
This happens because for a bond to break, it needs energy to be put into the molecule to break it since the bond wants to be held together. The energy is what breaks it, therefore it is required for the bond to go against what naturally wants to do. This is a common misconception, and bond formation is when energy is released as this saves energy. This follows the fundamental principle of energy minimization, and the energy is then released during the formation.
100
What is the bond order of O2?
2
10 bonding electrons - 6 non binding pairs of electrons = 2
2
200
Draw the organic chemist’s lewis structures of dimethyl sulfide and dimethyl disulfide.
200
Identify each acid/base and its corresponding conjugate acid/base in the reaction between perchloric acid and sodium hydroxide. Is this reaction strong or weak?
HClO4 + NaOH ---> NaClO4 + H2O
Acid: HClO4
Conjugate base: NaClO4
Base: NaOH
Conjugate acid: H2O
This is a strong reaction because HCLO4 is a strong acid, allowing for complete dissociation.
200
Given the following reaction:
H2(g) + Cl2(g) → 2HCl (g)
If 40.0 L of H2 reacts with 65.0 L of Cl2 at a temperature of 25℃ and a pressure of 3.00 atm, what is the limiting reactant? Assume that H2 acts ideally. (Additional information: The density of Cl2 is 2.898 g/L.)
Answer:
nH2 = PV/RT = (3.00 atm)(40.0 L) / (0.08206 L*atm/mol*K) (298 K) = 4.91 mol H2
nCl2 = (65.0L) x (2.898 g/L) x (1 mol/ 70.9 g) = 2.66 mol Cl2
Mole ratio (H2/ Cl2) = 4.91 mol/2.66 mol = 1.85
Stoich ratio (1 H2/ 1 Cl2) = 1
Since 1.85 > 1, Cl2 is the limiting reactant.
200
What are five of the state functions and variables and the two path functions we have discussed? What are the definitions of “state function” and “path function?”
State functions/variables: U, H, A, G, V, P, T, n (only 5 needed)
Path functions: q, w
Definitions: State function: a function that depends only on the state of a system but not on the path through which the state is reached
Path function: a function that is dependent on the path a system is taking to change between states
200
What is the lewis structure and bond order of NO3 - ? Round to 3 significant figures.
Take the average of the bond orders. N=O has a bond order of two, and both N-O bonds have a bond order of one. Adding these together and dividing by the number of bonds (3) reveals that the bond order of nitrate is 1.33 (4/3).
300
When operating an autoclave, correct PPE is required such as:
Eye protection, face shield, lab coat and/or apron, heat-insulating gloves
300
How many atoms of NaCl are produced from 23.000 g of MgCl2? Don’t forget to balance the equation!!
Answer:2.9096x10^23 atoms
Work: Balanced Equation: MgCl2 + 2NaOH -> 2NaCl + Mg(OH)2
Grams of MgCl2 to moles: 23g/(95.205 g/mol) ->0.24158 moles MgCl2
Moles of MgCl2 to NaCl: 0.24158 moles MgCl2 x 2 (due to mole ratio, 1 mole MgCl2 to 2 mole NaCl) = 0.48317 moles NaCl
Moles NaCl to atoms: 0.48317 x 6.022E23 (Avogadro’s Constant) = 2.9096E23 atoms
300
Determine if true or false based on the Maxwell Distribution & explain:
Pmax (3000K) > Pmax (2000K) for Ne(g)
Answer: false; Pmax (3000K) < Pmax (2000K) for Ne(g) because, the higher the temperature results in more particles moving at higher speeds. As a result, the Pmax for 3000K is smaller.
300
2 HA(aq) + MX2(aq) → MA2(aq) + 2 HX(l)
Substance
ΔHf° (kJ/mol)
HA(aq)
678.899
HX(l)
-298.765
MA2(aq)
223.546
MX2(aq)
214.559
What is the standard enthalpy of reaction in kJ?
Answer:
[223.546 + 2(-298.765)] - [2(678.899) + 214.559)] = -1946.34 kJ
300
What 3 things can be predicted by LCAO (Linear Combination of Atomic Orbitals)?
1. Bond Order 2. Bond Length 3. Bond Strength
LCAO is the mathematical process of combining atomic orbitals to generate molecular orbitals.
400
List some of the hazards associated with liquid nitrogen use in the lab
Burns (similar to frostbite/thermal burn), asphyxiation (from oxygen deficiency), and risk of explosions
400
Permanganate is reacted in an acidic solution to produce Mn^2+ ions. Write and balance each of the half reactions for the acidic solution.
Answer: MnO4-+8H+ +5e- yields Mn2-+4H20
Work:
Reaction to start is: MnO4- (aq) yields Mn2+ aqueous
MnO4- + H+ yields Mn2- +H2O
Balance
MnO4-+8H+ yields Mn2-+4H2O
Mn=7 Mn=2+
O=2-
H=1
So
MnO4-+8H+ +5e- yields Mn2-+4H20
400
Name at least 3 of the 5 assumptions made for the ideal gas model
Gases are made up of many microscopic particles (atoms, molecules, etc.)
The gas particles have mass but negligible volume.
There are no long-range attractive or repulsive forces between the particles.
The molecules are constantly in random motion.
The gas molecules obey Newton's laws of motion.
400
For a calorimetry experiment, a student weighs out 8.455 grams of an unknown metal and brings it to a boil at 120.℃. The metal is then placed in a styrofoam cup with 20.0 grams of water at 25℃, and the final temperature is measured to be 33.0℃. What is the specific heat capacity of the unknown metal?
qmetal= - qwater
q= mcΔt
(8.455g)(c)(33℃-120℃) = - (20.0g) (4.184J/g℃) (33℃-25℃)
-735.585 g℃ (c) = - 669.44 J
c = - 669.44 J / -735.585g℃
c = 0.910 J/g℃
400
What is the molecular electron configuration of Be2?
(σg2s)2 (σ∗u2s)2
500
Draw the lewis structure of ethanol and name one thing it can be used for.
Primary ingredient in alcoholic beverages, can be used as fuel, used in medical wipes and antibacterial hand sanitizer gels as an antiseptic.
500
Each year, the United States throws away about 1.3 billion pounds (650,000 short tons) of pumpkins. As municipal waste decomposes into methane gas, the U.S. Department of Energy has in recent years expressed their concern over these pumpkins’ contribution to climate change. They have instead proposed an alternative solution: to use the pumpkins as a source of renewable energy. This would be done by gathering pumpkins and capturing the methane gas released from their decomposition (at approximately 38°C), then using the energy created from the combustion of methane. One short ton of pumpkins produces about 90.6 m^3 of methane gas, and the combustion of methane gas releases 891 kJ/mol.
In 2018, the average annual electricity consumption for a house was 39,499,200 kJ. How many houses could the pumpkins power per year? (Assume all energy released by the combustion of methane is captured.)
Potentially helpful information:
Density of methane gas at 38°C: 0.6295 g/L
A: 52,000 houses
Mass of methane:
V CH4 = (90.6 m3 / 1 short ton) * 650000 short tons * (1000 L / 1 m^3) = 5.889e10 L
m = d*V
(0.6295 g/L) * (5.889e10 L)
m = 3.7071255e10 g
Moles of methane:
3.7071255e10 g * (1 mol / 16.042 g) = 2310887358 mol
Energy produced by pumpkins via methane combustion:
CH4(g) + 2O2(g) —> CO2(g) + 2H2O(g)
ΔH = -891 kJ/mol
(891 kJ / 1 mol ) * 2310887358 mol = 2.059000636e12 kJ
Houses powered by pumpkins: 2.059000636e12 kJ / 39499200 kJ = 52127.65413 houses / 1 year (to 2 sig figs)
52000 houses
500
Nigel ate too much Halloween candy, and now he has a stomach ache. Nigel’s stomach, when empty, has a volume of 0.075 L and an intragastric pressure of 6.25 mm Hg. He ate about half of his gallon-sized bucket of candy. What is the total increase in intragastric pressure necessary to empty Nigel’s stomach, thus relieving him of his stomachache? Assume a constant core body temperature of 37.6°C and specify your answer in mm Hg.
A: 6.0 mm Hg
P1V1 = P2V2
Vi = Vcandy + Vempty
Vcandy = (1 gal * (3.785 L/1 gal))/2 =1.8925 L
Vi = 1.8925 L + 0.075 L = 1.9675 L
(1.9675 L) * (Pi)= (0.075 L) * (6.25 mm Hg)
Pi = 0.238246505717916 mm Hg
ΔP = 6.25 mm Hg - 0.238246505717916 mm Hg =
6.011753494282084 mm Hg (to 2 sig figs)
500
Equal amounts of heat are absorbed by 100 g samples of various solid metals with differing specific heat values. Compare the temperature change in a higher and lower specific heat capacity.
According to the q = mcΔT equation, as long as the provided masses of metal solids are the same, the metal with the greatest specific heat will undergo the smallest change in temperature for a given heat energy value.
500
When observing the orbital diagrams for molecules such as diatomic oxygen and fluorine, there is an apparent switching between the sigma and pi bonds for the bonding orbitals. What phenomenon results in this switch? How does linear combination involved in this phenomenon?
This switch in orbital ordering occurs because of a phenomenon called s-p mixing. s-p mixing does not create new orbitals; it merely influences the energies of the existing molecular orbitals. The σs wave-function mathematically combines with the σp wave-function, with the result that the σs orbital becomes more stable, and the σp orbital becomes less stable.