CHEMISTRY COMMUNITY

Chance Herbert 3A

Work is similar to heat in that is not an internal property of a system and it is dependent on the path taken to obtain a specific state.

Chance Herbert 3A

Since in this context of heat capacity delta t is used, the conversion is not necessary as a change in 1 degree Kelvin is the same as 1 degree Celsius. However, when you are working with specific temperatures you should keep units consistent with the provided information.

Chance Herbert 3A

I think the most important thing to remember here is that for an endothermic reaction, the energy required to break the bonds of the reactants will be greater than the energy released during the formation of bonds for the product. In the provided table, those with the strongest bond require the most...

Chance Herbert 3A

I believe I read that it can be classified as both depending on which book you read, but in the scope of this class HClO3 is a strong acid.

Chance Herbert 3A

A neutralization reaction typically occurs when an acid and the base with the same magnitude of strength react to produce neutral products. In this example, the strong base NaOH reacts with the strong acid HCl to produce neutral salt NaCl and H20.

Chance Herbert 3A

The acid/base dissociation constant is used specifically when dealing with equilibrium concentrations of an acid/base in water.

Chance Herbert 3A

I think Anna summarized this well. Temperature is a value that can be added and subtracted, especially in the case of comparing final and initial values. Heat is not an internal property of a system and is dependent on the path taken to obtain a specific state. For example, multiple pathways can be ...

Chance Herbert 3A

Yes! Endothermic reactions will always have a positive delta H as the system absorbs energy while exothermic reactions release energy from the system, resulting in a negative delta H

Chance Herbert 3A

You are correct. The graph provided in the 1/20 lecture illustrates this best. When the the temperature remains constant and heat is still supplied to the system, this energy functions as phase change energy (opposed to temp increase) that results in the breaking or formation of bonds.

Chance Herbert 3A

I also referred to the provided list of strong acids and bases. You must first look at both anions and cations and determine if they are derived from strong acids or weak bases. I believe you can say that if the salt has both anions and cations that are conjugates of a strong acid or base, the salt ...

Chance Herbert 3A

As long as you are consistent with units throughout your ice table you should be fine! I prefer to convert (if needed) to mol/L at the beginning to ensure that I do not forget to do so at the end!

Chance Herbert 3A

Usually, when I find two roots that are positive, the best way for me to determine which is the correct one is by actually plugging them in for x. In all of the cases I have encountered, one of the values will result in a negative equilibrium concentration for either the product or reactant (or both...

Chance Herbert 3A

"P" is used instead of brackets to indicate that the measurement is using partial pressure as opposed to concentration when calculating the equilibrium constant. This is also a key difference between Kp and Kc.

Chance Herbert 3A

Yes! ICE tables can be used with partial pressures or concentrations!

Chance Herbert 3A

The first thing you will want to do is create an ICE table. You are given the initial pressure of 0.0750 bar for PCl5. The initial pressure will be 0 for PCl3 and PCl2. The change in pressure will be +x for both PCl3 and PCl2 and -x for PCl5 since there is a 1:1 molar ratio for each of the reactants...

Chance Herbert 3A

A concentration or Molarity is the number of moles per Liter. It is not possible to have a concentration that is less than zero because this would imply that it is possible to have a negative number of moles or liters.

Chance Herbert 3A

The overall reaction would be used in determining if a system has heterogeneous or homogeneous equilibrium. Despite solids and liquids not being included in the expression of the equilibrium constant, these phases are still present and do not change concentration or pressure in reactions. Because th...

Chance Herbert 3A

Kelvin is the correct unit to use. Using dimensional analysis, you will see that the units of Kelvin cancel out in calculations with ideal gas law! If provided Celsius, you can calculate the temperature in Kelvin by adding 273.15 to this value!

Chance Herbert 3A

Molarity is measured in moles/Liter. In the expression n/V, n represents moles, and volume (V) is measured in liters. Dividing moles by liters provides the units of Molarity or concentration!

Chance Herbert 3A

These both can be used interchangeably; however, it is important to understand that physical "shifting" does not actually occur in a system at equilibrium.

Chance Herbert 3A

Lewis Acids/Bases deal with the transfer of electron pairs where:
-A Lewis Acid accepts a lone pair of electrons
-A Lewis Base donates a pair of electron

Bronsted Acids/Bases deal with the transfer of protons:
-A Bronsted Acid donates a H⁺
-A Bronsted Base accepts a H⁺

Chance Herbert 3A

The number of regions of electron density is equal to the number of hybrid orbitals. We can determine the shape and number of regions on electron density from as VSEPR Formula. Keep in mind lone pairs and bonded atoms both count as regions of electron density. I found this quizlet which provides a n...

Chance Herbert 3A

I do think it would be beneficial to know the acids and bases discussed in lecture. Can gives a good list of these. Another example I can think of off the top of my head is acetic acid, CH₃COOH and the deprotonated conjugate base acetate, CH3COO^-

Chance Herbert 3A

Ionization energy is the amount of energy required to remove an electron from an atom. Oxygen is the first element in the p-block to have a paired electron. It is slightly easier to remove an electron from oxygen than it is in nitrogen and fluorine because this one paired electron is subject to a gr...

Chance Herbert 3A

It is most energetically favorable for lone pairs to be the furthest distance away from bonded atoms due to their relatively high magnitude of repulsion. Essentially, they will exist where the least amount of atoms are present. Tatyana uses a great example of this with the see-saw in which the lone ...

Chance Herbert 3A

I remember in Dr. Lavelle's lecture on types of bonds he held a marker in his hands parallel to demonstrate how pi bonds do not allow for rotation. If rotation were to occur, the bond would have to be broken which was represented by the marker falling from his hands. I am totally visual as well and ...

Chance Herbert 3A

When drawing your Lewis structure, to get the most stable structure, you should choose the structure that minimizes formal charge for each atom in the structure. Formal charge can be calculated by subtracting the sum of the number of nonbonding valence electrons and half the number of bonding electr...

Chance Herbert 3A

Lone pairs exert a slightly greater magnitude of repulsion than another bonded atom (take for example AX 3 E compared to AX 4 ), which would result in two molecules with the same electron geometry (tetrahedral) and different molecular geometry (trigonal pyramidal vs tetrahedral) with slighlty differ...

Chance Herbert 3A

The coordination number is a value representing the number of atoms, molecules, or ions that are held by a central transition metal atom. It is important to note that denticity can vary and you count only the number of atoms inside brackets held by the transition metal!

Chance Herbert 3A

I believe that the textbook mentions that the ligands should be written in alphabetical order when there is more than one; however, I do not know that this is necessary. As already said, I think it is more important that the cation comes before the ligands.

Chance Herbert 3A

It is also to consider the shape of the molecule. For example, polar bonds arising from differing electronegativities of central and bonded atoms may form on a molecule with a trigonal planar shape; however, this molecule will be nonpolar given the fact that electrons are evenly distributed about th...

Chance Herbert 3A

There are only four regions of electron density which results in the hybridization of sp 3 . It is important to note that we only consider bonding electron pairs and lone pairs as regions of electron density. This molecule would have the VSEPR formula AX 4 , meaning that there are four regions of el...

Chance Herbert 3A

Adding on to my last response, it would be impossible to know the bond angles for every molecule given that bonding atoms will have different properties that make their properties slightly different from the general bond angles; however, these values listed above give a great idea of understanding t...

Chance Herbert 3A

I think Alexa put this very nicely. Knowing that bond angles 109.5° for tetrahedral shape, 120° for trigonal planar, and 180° for linear will definitely help in comparing molecules. I feel like these might be used as a reference for different molecules. For example, comparing an AX 4 to an AX 3 E wo...

Chance Herbert 3A

Since the electronegativity difference between Carbon and Hydrogen is relatively small (approximately 0.35), the electrons will be more likely to be evenly distributed between the two atoms. In response to Joanna, the properties of hydrogen are unique in that hydrogen is likely to attract the one el...

Chance Herbert 3A

In terms of memorizing, it helped me a lot to be able to visualize each of the molecular shapes. I really like the PHET simulator I linked because it allows you to experiment with a variety of molecules and observe both molecular and electron geometry for each! https://phet.colorado.edu/en/simulatio...

Chance Herbert 3A

I think that we are more expected to know periodic trends relating to electronegativity. For example, electronegativity increases across a period and decreases as you go down a group or column.

Chance Herbert 3A

I believe that any polyatomic ion ending with "ite" will always have one less Oxygen than those ending with "ate".

Chance Herbert 3A

I think by definition hydrogen bonds only occur with N, O, and F so there shouldn't be any exceptions!

Chance Herbert 3A

For a trigonal bipyramidal structure like PCl₅, it is most energetically favorable for three of these electrons in one plane and the other two domains will be 90 degrees to this plane to allow for the most distance between repelling valence electrons of each atom.

Chance Herbert 3A

From everything I have seen so far, the bond length is usually given. I think it would be more beneficial to know what factors contribute to bond length. For example, size of an atom may increase the bond length. Also know that the greater the bond length, the weaker the bond will be.

Chance Herbert 3A

You can also check through myUCLA! Click on the classes tab and it will be under the grades and homework section as "exam and homework grades" :)

Chance Herbert 3A

Coordinate covalent bonds exist when one atom shares two of its own valence electrons with another atom to form a covalent bond.

Chance Herbert 3A

Coordinate covalent bonds exist when one atom shares two of its own valence electrons with another atom to form a covalent bond.

Chance Herbert 3A

There is a stronger attraction that arises from a greater number of electrons and attractive force exerted by the nuclei which would in turn decrease the bond length.

Chance Herbert 3A

For hydrogen, the octet rule does not apply since the atom can only have a maximum of two electrons in its outermost/valence shell! All successive levels can have a maximum of 8 with the exceptions you listed.

Chance Herbert 3A

Lone pairs are valence electrons that exist in pairs and are not shared or bonded with another atom.

Chance Herbert 3A

The first ionization energy is the amount of energy required to remove the first valence electron. This will vary depending upon the depending on the magnitude of electrostatic attraction towards the nucleus. Oxygen has a greater degree of electron-electron repulsion in its subshell than Nitrogen (2...

Chance Herbert 3A

I just finished a show called Biohackers on Netflix and really enjoyed it!

Chance Herbert 3A

The most important thing to understad is that electron shielding is the same as repulsion. For each subsequent shell or period, there is an added ring or shell outside of the inner shells containing electrons. These electrons on the inside will repel the outer valence electrons, resulting in an over...

Chance Herbert 3A

The second ionization energy will be greater after the first electron is removed. When there are fewer valence electrons, there is a lesser magnitude of repulsion between these valence electrons which would increase the overall center seeking force resulting in a higher ionization energy or amount o...

Chance Herbert 3A

Adding on to the last response, as you increase energy levels, you also have a greater number of shielding electrons betweeen the outer valence electrons and the nucleus of the atom. This would in turn result in a lower ionization energy as there is a lessened center-seeking force along with an incr...

Chance Herbert 3A

The "ground state" is the most stable and lowest energy state of an atom. Using the term excited would imply that the electron has been increased in energy level.

Chance Herbert 3A

here is the link for anybody needing it! https://www.saplinglearning.com/ibiscms/login/

Chance Herbert 3A

When you click on the provided link, you will see that the enthalpy of fusion of water is 333.6 J/g. You will multiply this number by the provided mass of 445 g to calculate the amount of energy required to melt the ice. You then need to calculate the amount of energy per photon using the equation E...

Chance Herbert 3A

nayha a 1L wrote:Everyone in this thread is mentioning Avogadro's number, but as I look through my notes, I can't seem to find anything about it. Does anyone know which lecture talked about this?

Avogadro's Constant is referenced near the beginning of the October 2nd Lecture! (Listed in Week 1 I believe)

Chance Herbert 3A

I believe the 2_px state would correspond to n=2,l=1, and m_l=-1! If m_l were equal to +1 I believe this would be 2_pz

Chance Herbert 3A

If we manipulate other equations based on the values given, and we set the two equal to each other, does it matter that the one equation has a greater than or equal to symbol? For example, if we have delta p = m(delta v), and delta p is greater than or equal to h/(delta x)(4pi), can we still substi...

Chance Herbert 3A

The formula for Kinetic Energy is 1/2(m)(v^2). In this problem, the velocity is provided as 6.61x10^5 m/s. Here you would not use molar mass as you are considering the velocity for a sole electron and this would not provide you with the correct units for Kinetic Energy (keep in mind Joules are kgm^2...

Chance Herbert 3A

I have been using a printed version of the periodic table provided on the class website. Will this be the same one we are able to use on exams?

Chance Herbert 3A

I have a TI-nspire cx.. it hadn't occurred to me we might not be able to use certain calculators! Have you heard anything about this calculator or just the rules if there are any for calculators during exams? I have a TI-nspire cx as well! Not sure either if the TI-84 is approved or not, but the TI...

Chance Herbert 3A

Actually was included in the last email sent out! Here is the link! https://lavelle.chem.ucla.edu/wp-conten ... equest.pdf

Chance Herbert 3A

I was told today during my discussion that an email would be sent out later this week addressing the webcam requirements!

Chance Herbert 3A

My understanding is that light intensity is simply how bright a light is, and increasing the intensity increases the amount of photons being emitted by that light source. The wavelength and frequency are independent of the amplitude, and are instead dependent on the length of a wave. So changing th...

Chance Herbert 3A

You are correct! When you calculate the molar mass of an element or molecule you will not multiply this by the stoichiometric coefficient; however, stoichiometric coefficients are relevant in determining the number of moles of each reactant and product present in a reaction. Take for example the rea...

Chance Herbert 3A

On this same topic, is there a maximum amount of limiting reactants an equation can have? Thanks! It is highly unlikely that there will be more than one limiting reactant since this would require that the moles of two or more different reactants are exactly equal and completely react with each othe...

Chance Herbert 3A

Hope I am answering this question correctly, but I believe you are asking about the process of using the calculated moles of each element in a molecule to determine the empirical formula. If we use the example of being given a mass percent composition, we can first determine the number of grams of e...

Chance Herbert 3A

I believe it is safe to assume based on the wording on Sapling that it is due tomorrow night at 11:59 PM.

Chance Herbert 3A

From my understanding, to not have a limiting reactant would be nearly impossible even if the number of moles of each reactant and stoichiometric coefficients appeared to be the same. Thinking back to Avogadro's Constant which defines a mole as having 6.022x10^23 particles or "things" woul...

Chance Herbert 3A

Thank you guys so much for sharing these acronyms! I was definitely in need of these as well and will be using them this year! :))

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