CHEMISTRY COMMUNITY

Shanmitha Arun 1L

Did you know that you can cool yourself to -273.15˚C and still be 0k?

Shanmitha Arun 1L

There wouldn't be any cases where you would need to use log. It's usually easiest to go by the given equation.

Shanmitha Arun 1L

At boiling point, temperature and pressure are constant. Therefore, the change in enthalpy would be zero.

Shanmitha Arun 1L

The oxidation number for an atom in its elemental form is always zero. It is not always a solid.

Shanmitha Arun 1L

For problems like this that give % of the initial like 10%, it would be ln(1/0.1) which ends up being ln(10). For 15%, it would be ln(1/0.15) since its ln of [A]/[Ao]

Shanmitha Arun 1L

You would do ln(1/0.1) which is the same as ln(10).

Shanmitha Arun 1L

The change in concentration is proportional to the rate because the rate is dependent upon the concentration. This is why we can use the proportionality to figure out the order.

Shanmitha Arun 1L

Make sure to look at the correct temperature in the table. Generally on tests though, I assume the k will be given but you should still know how to find it based on a table.

Shanmitha Arun 1L

Simply put, kinetics deals with the rate of a reaction and thermodynamics deals with favorability of the reaction.

Shanmitha Arun 1L

Just make sure all your units match but other than that, I don't think the answer has a preferred unit.

Shanmitha Arun 1L

We want to work with positive numbers so you should make sure the rate is positive.

Shanmitha Arun 1L

The tests should be clear with whether it is acidic or basic.

Shanmitha Arun 1L

Mostly, Pt is used when there is no conducting metal in the reaction.

Shanmitha Arun 1L

The tests would explicitly say what you need to find and will be really clear.

Shanmitha Arun 1L

I believe sig figs should not matter too much this quarter but just use the smallest number given in the problem.

Shanmitha Arun 1L

Most likely, it will be given so you don't need to worry about it. However, it can be determined by looking at the equation and whether it has H+ or OH- in it.

Shanmitha Arun 1L

Simply put, it matters when P and T are constant. Based on that, certain equations are used.

Shanmitha Arun 1L

You do not need to know integrals and how to derive the functions. It is helpful to understand as a way to change equations around and understand it. Rather than memorizing different equations, you could calculate it yourself.

Shanmitha Arun 1L

It's easiest to choose equations based on the problem. You can tell by what they give what equation to use. Also, as mentioned, it depends on whether it is reversible or irreversible.

Shanmitha Arun 1L

Gibbs free energy of a solid changes more slowly with respect to a temperature change, which means its entropy is lower than the entropy of the liquid. This is related back to the strength of the intermolecular forces and the correspondence with the rigidity of the substance overall.

Shanmitha Arun 1L

Look at the signs in entropy as a change rather than positive and negative entropy.

Shanmitha Arun 1L

For entropy, delta S is basically a measure of the change in order/disorder of the reaction. Increasing order gives us a negative delta S value, and decreasing order gives a positive delta S value. ΔU is the change in internal energy U of the system.

Shanmitha Arun 1L

For many cases, Kelvin is used but it really just depends on the problem and the units given.

Shanmitha Arun 1L

If the system allows neither energy or matter transfer, then it is an isolated system. However, if it allows only energy transfer, it is a closed system.

Shanmitha Arun 1L

https://www.youtube.com/watch?v=eJXL0IrbtqE

This video gives a good, simple explanation of endothermic and exothermic reactions.

Shanmitha Arun 1L

The heat of an object is the total energy of all the molecular motion inside that object. Temperature, on the other hand, is a measure of the average heat or thermal energy of the molecules in a substance.

Shanmitha Arun 1L

A mercury thermometer is a closed system because matter cannot enter or leave it.

Shanmitha Arun 1L

Simply put, Q is positive if heat is added to the system, and negative if heat is removed.

Shanmitha Arun 1L

https://www.youtube.com/watch?v=1CygQUIJodc

This is a really helpful video that explains ΔU and ΔH.

Shanmitha Arun 1L

Heat is the flow of thermal energy between two objects of different temperature whereas the thermal energy tells about how much is the transfer of energy due to temperature difference between two bodies. Hence thermal energy in transit gives heat.

Shanmitha Arun 1L

It would be best to know the enthalpy of fusion and the enthalpy of vaporization as it is used in calculations.

Shanmitha Arun 1L

Graphite and diamond are both large molecules made of carbon, but have different connectivity. The carbon in graphite are bonded to 3 other carbon neighbors, but in diamond carbon bonds with 4 neighbors. Therefore, it would be a chemical change.

Shanmitha Arun 1L

Dr. Lavelle's lecture went over pH and pOH but additionally watching this video may help. It gives a clear explanation.

https://www.youtube.com/watch?v=eoM1nzYFy8k

Shanmitha Arun 1L

An example of this would be BF3 + F- ---> BF4-
BF3 is a lewis acid
F- is a lewis base

Neither are Bronsted acid/bases because there is no transfer of protons.
Also, all Bronsted acid/bases are Lewis acid/bases.

Shanmitha Arun 1L

I was confused about this problem from the module.

13. For the unbalanced reaction, CO (g) + H2 (g) ⇌ CH3OH (g), the equilibrium concentrations are [CO] = 0.0911 M, [H2 ] = 0.0822 M, [CH3OH] = 0.00892 M. What is the value of the equilibrium constant? Does the equilibrium favor reactants or products?

Shanmitha Arun 1L

First, there are two types of bonds: ionic and covalent. Based on the type of bond, chemical formulas are written differently. I put a link below that explains how to name the compounds in depth and would highly recommend watching it.

https://www.youtube.com/watch?v=mQpNjm7xB30

Shanmitha Arun 1L

If you are confused with topics, I would highly recommend watching videos in order to clarify things. The link below clearly explains what ligands are and you may find it very useful. Hope that helps!

https://www.youtube.com/watch?v=011Bj5USal8

Shanmitha Arun 1L

High polarizing power is based on size and charge so Group 2 would have a higher polarizing power compared to Group 1. Also as you go up, polarizing power increases due to a smaller size. As for being the most polarizable, larger anions are more polarizing. It increases as you go up the group.

Shanmitha Arun 1L

A dipole moment is a measurement of the separation of two opposite electrical charges.
Watching a video might help explain it better:
https://www.khanacademy.org/science/che ... ole-moment

Shanmitha Arun 1L

2-D representations show the atoms in the molecule and the connections between them but leave out other important factors. In order to draw a 3-D structure, first you must understand the different symbols such as normal bonds, dashed bonds, and wedged bonds. Dashed bonds are used to represent bonds ...

Shanmitha Arun 1L

There are some common elements such as H, C, N, and O that we are expected to know electronegativity for in order to determine polarity. Other than that, we can base it off trends since we know electronegativity increases as we go higher up and to the right.

Shanmitha Arun 1L

Michael Cheng 1B wrote:How do you know if an electron will be spin up of spin down?

After determining the number of electrons and drawing the electron configuration, you would distribute the electrons using up and down arrows in order to show spin.

To see it visually:
http://www.graylark.com/eve/c-configs.svg

Shanmitha Arun 1L

Quantum number ml is the magnetic quantum number. It determines the number of orbitals and their orientation within a subshell. In the s orbital, there is only one possible orientation which is 0. For example in the p orbital, it would be 1 0 -1. Based on the electron, it would be one of those integ...

Shanmitha Arun 1L

I think it would be okay to leave it in meters but changing it to picometers would just be better to understand.

Shanmitha Arun 1L

Elements of the same period share the same principal quantum number. Atoms do not change principal quantum numbers as you move from left to right across the periodic table.

Shanmitha Arun 1L

In 1.13, it states that the transition is from n=4 to n=2 so wouldn't that make n1=4 and n2=2? However, the solutions manual switches it around. Does anyone understand why?

Shanmitha Arun 1L

I don't really understand what Rydberg's formula is about and the meaning of the different levels. Also, will the series we are starting from and jumping to be given?

Shanmitha Arun 1L

I like to watch videos sometimes in order to understand and remember concepts. This video helped me and may be useful for you too. I also included a diagram with arrows that clearly show all the trends. Hope this helps! https://www.youtube.com/watch?v=XK-WTYncldA https://sciencenotes.org/periodic-ta...

Shanmitha Arun 1L

When light shines on a metal, electrons can be emitted from the surface of the metal. This is what is known as the photoelectric effect. From experiments, we have learned that intensity of the light does not affect the energies of the emitted electrons.

Shanmitha Arun 1L

Energy is "quantized" because light comes in packets of energy defined by its frequency and planck's constant. Quantization has to do with it only being able to have discrete values.

Shanmitha Arun 1L

A mole would be 6.022 x 10^23 molecules. So, a mole is a unit quantity that is used to measure the quantity of molecules. A molecule is just 2 or more atoms combined by a chemical bond.

Shanmitha Arun 1L

I assume it would just be be based on what would be easier to balance first. I think it's just a strategy, not really a rule.

Shanmitha Arun 1L

The reason you may be getting the wrong answer is because the molar mass you calculated is wrong. The molar mass of Ca5(PO4)3F is 504.3, which is what you got, but the molar mass of Ca5(PO4)3OH is actually 502.31. Now if you subtract 502.31 from 504.3 and divide that overall by 504.3, you will get 0...

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