CHEMISTRY COMMUNITY

AngelaZ 1J

I know a guy who cooled himself to -273.15C.

He was 0K.

AngelaZ 1J

Why do chemists like nitrates so much?

Because they're cheaper than day rates.

AngelaZ 1J

What do you call a tooth in a glass of water?

A one molar solution.

AngelaZ 1J

If the Queen farts, is it a noble gas?

AngelaZ 1J

Organic chemistry is difficult.

Those who study it have alkynes of trouble.

AngelaZ 1J

What kind of fish is made out of 2 sodium atoms?
2 Na

AngelaZ 1J

A neutron walks into a bar. He asks the bartender, “How much for a beer?” The bartender offers him a warm smile and says, “For you, no charge”.

AngelaZ 1J

Why are chemists great for solving problems?
They have all the solutions.

AngelaZ 1J

A photon checks into a hotel and is asked if he needs any help with his luggage. He says, "No, I'm traveling light."

AngelaZ 1J

Someone threw sodium chloride at me.
I yelled, “That’s a salt!”

AngelaZ 1J

What do dipoles say in passing?
"Have you got a moment?"

AngelaZ 1J

Two atoms are walking down the street…
One atom says to the other, “Hey! I think I lost an electron!” The other asks, “Are you sure?”
“Yes, I’m positive!”

AngelaZ 1J

Why can you never trust atoms?
They make up everything!

AngelaZ 1J

Why can you never trust atoms?
They make up everything!

AngelaZ 1J

Why did the acid go to the gym?
To become a buffer solution.

AngelaZ 1J

Why did the acid go to the gym?
To become a buffer solution.

AngelaZ 1J

What do you do with a dead chemist?

Barium.

AngelaZ 1J

Why did the noble gas cry?
Because all his friends Argon.

AngelaZ 1J

Can someone please explain why delta G is less than 0 for the following two processes?

The precipitation of snowflakes inside a cloud at -10 C and 0.839 atm.
The sublimation of dry ice in a warm room.

AngelaZ 1J

An alternative way to balance redox reactions in basic solutions is just to balance it like you would for an acidic solution, then add OH- for every H+ there is on both sides of the equation, and then use H+ + OH- -> H2O so that there are only OH- and H2O molecules in the final balanced equation.

AngelaZ 1J

∆S = q(rev)/T at constant temperature and q = ∆H at constant pressure. Thus, ∆S = ∆H/T at constant temperature and pressure.
This equation is applicable to changes in entropy of phase changes.

AngelaZ 1J

I don't believe the outlines include derivation of the formulas but I think knowing them is helpful in understanding when to apply which formulas.

AngelaZ 1J

The change in internal energy is a function of only the initial and final states.

AngelaZ 1J

Change in enthalpy (delta H) is the amount of heat (q) absorbed or released at constant pressure.

AngelaZ 1J

Enthalpy is the amount of heat released or absorbed at constant pressure.

AngelaZ 1J

If pressure is increased by decreasing volume, then concentration increases (C=n/V). We can calculate Q using the new concentrations and compare that with K to see which way the reaction shifts. In this case, we can look at [O2]^3/[O3]^2 to know that increasing concentration would cause Q>K and the ...

AngelaZ 1J

It's also important to note that we're comparing only the number of moles of gases.

AngelaZ 1J

The strong acids and bases can be found on F83 in the 6th edition textbook:

Strong acids: HBr, HCl, HI, HNO3, NClO4, HClO3, H2SO4
Strong bases: Group 1 hydroxides, alkaline earth metal hydroxides (Ca(OH)2, Sr(OH)2, Ba(OH)2), Group 1 and Group 2 oxides

AngelaZ 1J

Lavelle was giving an example of how a reaction responds to minimize the effect of increasing pressure (by decreasing volume). If P doubled (V halved), then there would be new initial concentrations (since concentration=moles/volume). Q would then be solved for these new concentrations so that we co...

AngelaZ 1J

Kc is the equilibrium constant calculated using molar concentrations of the products and reactants. Kp is the equilibrium constant using partial pressures of the products and reactants. You can write either the Kc or Kp for a problem involving gases only.

AngelaZ 1J

R is a constant that will be given to us on tests. T is not a constant but must be given to us to use the ideal gas law.

AngelaZ 1J

They're ring structures that are formed by polydentate ligands bonding to a transition metal.

AngelaZ 1J

You can look at the structure or you can memorize which ligands are polydentate (there's a list of ligands we need to know on Lavelle's website).

AngelaZ 1J

Easiest way would be to memorize the common polydentate ligands.

AngelaZ 1J

Correct

AngelaZ 1J

If it's identifying the hybrid orbitals used by an atom, I think it's just sp, sp2, sp3, etc.

AngelaZ 1J

There's a picture of it here: https://en.wikipedia.org/wiki/Cisplatin

AngelaZ 1J

SO2 reacts with water vapor to form acidic rain. (SO2 comes from burning petroleum products, coal, etc.)
SO2(g) + H2O(l) → H2SO3(aq)

AngelaZ 1J

From the lecture slides:
Sulfur dioxide + water → sulphurous acid
SO2(g) + H2O(l) → H2SO3(aq)
SO2(g) comes from burning petroleum products, coal, etc.
SO2(g) reacts with water vapor to form acidic rain.

AngelaZ 1J

HCl is a stronger acid because the bond between H and Cl is weaker than the bond between H and F (this is because Cl has a greater atomic radius). HClO is a stronger acid than HBrO because the resulting anion of HClO is more stable as a result of Cl having a greater electron withdrawing power than Br.

AngelaZ 1J

viewtopic.php?t=8826

AngelaZ 1J

CH2Cl2 has a tetrahedral shape, so the dipole moments that are formed between the Cl's and the C don't cancel out.

AngelaZ 1J

The lone pairs should be placed so as to minimize electron-pair repulsions. Since H2O has a tetrahedral electron arrangement, the lone pairs will always be next to each other no matter where you place them. XeF4 has an octahedral electron arrangement, so placing the 2 lone pairs on opposite sides of...

AngelaZ 1J

What's the correct lewis structure for S2O3 2-? I know that the double bonds don't matter for the shapes and bond angles, but I'm getting varied answers on the internet.

AngelaZ 1J

If the electron geometry is an octahedral and there are 2 lone pairs, then the molecular shape will be square planar.

AngelaZ 1J

Here's a visual: https://www.dlt.ncssm.edu/tiger/diagram ... w_a_3D.jpg

AngelaZ 1J

The molecular shape looks at the bonded atoms only, while the electron geometry includes the bonded atoms and lone pairs.

AngelaZ 1J

Intermolecular forces determine boiling point, but I don't believe intramolecular forces (bonds) do.

AngelaZ 1J

Polarity refers to the unequal sharing of electrons between atoms depending on their differing electronegativities. A dipole moment is created as a result of these polar bonds.

A molecule may have a dipole moment depending on the geometry of the polar bonds.

AngelaZ 1J

It is an attractive force.

AngelaZ 1J

Metals tend to form cations and nonmetals tend to form anions.

AngelaZ 1J

An electron configuration with a full (or half full) 4d-orbital is more stable than a partially filled 4d-orbital.

AngelaZ 1J

Actually, the phenomenon also applies to Ag and Au which are in the 5th and 6th periods. Tungsten and the heavier elements in the Cr group are just more stable without promoting an s electron to half fill a d-orbital: viewtopic.php?t=22959

AngelaZ 1J

For isoelectronic atoms, the size would be dependent on the number of protons.

AngelaZ 1J

I think elements in the same group will generally be more similar since they have the same number of valence electrons. This similar electron configuration gives them similar chemical and physical properties.

AngelaZ 1J

An electron configuration with a completely full or half full 3d subshell is more stable.

AngelaZ 1J

Schrodinger's equation uses a wave function to describe an electron, with its wavelike properties and indeterminacy in momentum and position. The wave function squared tells us the electron density distribution in an atom.

AngelaZ 1J

n1 should be smaller than n2. Another way to think of the equation is R * (1/n(final)^2 - 1/n(initial)^2), assuming that the electron transitions from a higher to lower energy level.

AngelaZ 1J

We don't need to know the derivation process - it's difficult and you would learn it in a graduate school course.

AngelaZ 1J

All objects have wavelike properties, but it is only noticed for moving objects with extremely small mass. For the purpose of this class, anything with a de broglie wavelength smaller than 10^-18 m is considered not measurable.

AngelaZ 1J

For part a, calculate the frequency by using the Rydberg formula and plugging in n(initial) = 4 and n(final) = 2. Then, solve for the wavelength by using c/v. For part b, you know that the electron transitions from a higher energy level to n=2. This is all you need to know to determine whether the t...

AngelaZ 1J

If you are looking at the wave model of light, then increasing the intensity of the light increases its amplitude. If you are viewing light as a particle, increasing the intensity of light increases the number of photons. It is when frequency of the light is increased that energy is increased and el...

AngelaZ 1J

If you're doing a multi-step calculation with various operations and have to add/subtract numbers in one of the steps, the number of sig figs could change to be less than the least number of sight figs given in the problem. Would we use that number of sig figs for our final answer?

AngelaZ 1J

As Andrew said, 9.8 mL of KMnO4 is poured into a beaker and water is added up to the 250 mL mark. So, the stock solution is being diluted with water, and the concentration of the solution is decreased since there is now the same amount of solute in more water.

AngelaZ 1J

Finding the mass percentage would not be needed for this question. Unless the question asks for the mass percentages, I wouldn't take an extra step to find it when the moles can be calculated directly from the masses given. However, it doesn't hurt to calculate the mass percentage, so it can be up t...

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