CHEMISTRY COMMUNITY

Jonathan Shyu 3L

A reaction mechanism is the steps a reaction undergoes to make that reaction. These include catalysts and intermediates,

Jonathan Shyu 3L

Molarity is in the units of mol/L so it's just the same thing.

Jonathan Shyu 3L

There are study rooms that can be booked, places such as the learning centers in de neve or sunset are also great places to use with good wifi and for the most part quiet space.

Jonathan Shyu 3L

I personally like doing achieve and making sure I understand the questions 100%. Then I really like going through the outline that Dr. Lavelle posts on his website. Then to supplement all of that I go through the textbook questions.

Jonathan Shyu 3L

The exam should follow very similar formats to the midterms this year and tests last year in 14A. The test would be multiple choice and proctored, and last quarter it was 25 questions instead of 15.

Jonathan Shyu 3L

The exam should follow very similar formats to the midterms this year and tests last year in 14A. The test would be multiple choice and proctored, and last quarter it was 25 questions instead of 15.

Jonathan Shyu 3L

Extensive properties are characteristics that are dependent on the amount of substance in a sample. This includes things such as mass and volume.

Jonathan Shyu 3L

A bomb calorimeter is completely isolated. This means no matter or energy enters or exists in the bomb calorimeter. This also means that any pressure or temperature change would not result in any work done since the volume is constant. A normal calorimeter can have work done to it and can have energ...

Jonathan Shyu 3L

You would check the units that either the equations you are using give you or the units of the answer you are looking for. If equations or your solution is in Celsius, you keep it celsius. If your equations or solution is in Kelvin, you add 273 to celsius to convert to kelvin.

Jonathan Shyu 3L

You would use the formula delta S = nRln(V2/V1). This formula is used when volume is being changed but temperature is constant. V2=1, V1=3, n=1, mole, R= 8.314 J/molK, and you just solve!

Jonathan Shyu 3L

It starts after 1st law. but 1st law is still relevant content to know.

Jonathan Shyu 3L

How Dr. Lavelle described it in class, state property is a property that does not change regardless of the path taken. So if you are climbing a mountain, if you took the direct path to the top or if you circled the mountain 5 times before climbing to the top, state property would be the height trave...

Jonathan Shyu 3L

These are only used for ideal monatomic gases.

Jonathan Shyu 3L

Yes if it the reaction results in a positive delta S as well as is done in a high temperature. Using the equation delta G = delta H - T* delta S, if delta H is positive, for G to be negative, delta S has to be positive and temp has to be high.

Jonathan Shyu 3L

ΔGº is the free energy available at 25ºC/298ºK and 1atm (standard conditions). ΔG is the free energy under current conditions.

Jonathan Shyu 3L

For this question: Consider the following reaction at 298 K. 4Al(s)+3O2(g)⟶2Al2O3(s)ΔH∘=−3351.4 kJ Calculate the following quantities. Refer to the standard entropy values as needed. Why would you calculate Delta S of the system using the the table and doing Delta S of products - Delta S of reactant...

Jonathan Shyu 3L

You would use w = -P∆V is used for irreversible expansion when the pressure is constant and volume changes and you would use w = –nRTln(V2/V1) for reversible expansions that vary in pressure.

Jonathan Shyu 3L

You use this equation to find the work done on a system in constant pressure but changing volume. This equation can also be substituted for -delta n(R)(T).

Jonathan Shyu 3L

The official equation is U=q+w. However, the situation that w is subtracted or negative comes from whether work is being done by the system or on the system. It is better to think of U=q+w, that way if work is being done on the system and w is positive, it is just added. If work is being done by the...

Jonathan Shyu 3L

Both equations can be used interchangeably, it really just depends on what units the question or situation gives you as well as what you are trying to solve for. If the question gives you mass in grams then you use m. If the question gives you number of moles, then use n.

Jonathan Shyu 3L

HAPPY VALENTINES DAY!

Jonathan Shyu 3L

Because they are so similar, for this class they are interchangeable. Dr. Lavelle also stated this.

Jonathan Shyu 3L

Endothermic means that the products have a higher "heat" than reactants, thus adding heat or increasing temperature would favor products because it has higher "heat." This also means that endothermic reactions take in heat for the reaction because products require it, and so the ...

Jonathan Shyu 3L

Enthalpy can be defined as the energy in the form of heat that is transferred. So H, being the variable for enthalpy, if ∆H is positive, that means your system is gaining heat. If ∆H is negative, that means your system is giving off heat/losing heat energy.

Jonathan Shyu 3L

The R constant values you use will depend on what units you are given or you want to produce. For R=8.314, it is J/(K*mol) so you would use it when finding Joules or if you already have those units. R=8.206x10^-2 is in (L*atm)/(K*mol) so you would use it if you were given L or atm. R=8.314x10^-2 is ...

Jonathan Shyu 3L

Paper for scratch is the only thing allowed, but you don't have to turn it in!

Jonathan Shyu 3L

q in thermo is the heat transferred in a reaction. q is also measured in joules/kilojoules. When q is negative means that the reaction is changing from a higher heat to a lower heat, thus a reaction is exothermic. Vice versa with q + means the reaction is going from low heat to high heat, making the...

Jonathan Shyu 3L

Endothermic means that the products have a higher "heat" than reactants, thus adding heat or increasing temperature would favor products because it has higher "heat." This also means that endothermic reactions take in heat for the reaction because products require it, and so the ...

Jonathan Shyu 3L

The R constant values you use will depend on what units you are given or you want to produce. For R=8.314, it is J/(K*mol) so you would use it when finding Joules or if you already have those units. R=8.206x10^-2 is in (L*atm)/(K*mol) so you would use it if you were given L or atm. R=8.314x10^-2 is ...

Jonathan Shyu 3L

So this equation is specifically q (of system) = -q (of surrounding). Conceptually, if your system is receiving heat from the surrounding, q of the system would be + because it is receiving, and q of the surrounding would be - because it is giving off heat. On the contrary, if your system was produc...

Jonathan Shyu 3L

In outline 3 for the midterm 1, it says Understand the environmental impact of burning fossil fuels, and the use of alternative fuels as energy sources. What exactly are we supposed to know for this?

Jonathan Shyu 3L

I also got [Ha] ≠ [H3O+] as my answer!

Jonathan Shyu 3L

I believe endothermic and exothermic literally refer to energy released and absorbed. However, most if not all of the time, the energy released or absorbed is in the form of heat. Thus endothermic reactions are reaction that absorbed energy in the form of heat and exothermic reactions are reactions ...

Jonathan Shyu 3L

Simply put, enthalpy refers to the total heat content of the system. This means that when there is a positive change in enthalpy, products have higher heat content compared to reactants, thus the reaction requires more heat. On the contrary, if a reaction has a negative change in enthalpy, the react...

Jonathan Shyu 3L

Melting is endothermic because it takes heat to melt. With water, going from a solid (ice) to a liquid (normal water) requires heat, thus a positive delta h and an endothermic reaction.

Jonathan Shyu 3L

Baking a cake is endothermic because it requires heat to begin the physical "baking" process. You can think of endothermic as requiring heat and exothermic as reducing heat. In terms of cake batter being liquid becoming a solid cake, I believe this doesn't have to do with the endothermic t...

Jonathan Shyu 3L

Yes I believe vapor just means gas, they are interchangable. Vaporization means the change of liquid to gas so it is safe to assume vapor is gas.

Jonathan Shyu 3L

Sublimation is the change of a substance from a solid phase directly to a gas phase. Thus, simply put, it is kind of like going from solid to liquid, then liquid to gas. Solid to liquid is called fusion, and liquid to gas is called vaporization. When you combine the enthalpy of fusion with the entha...

Jonathan Shyu 3L

Sublimation is the process of changing a substance from a solid directly to a gas. Because of this, it takes energy to break apart or loosen the bonds of a solid, thus taking in energy is endothermic.

Jonathan Shyu 3L

When calculating K, typically you do not include solids such as salts (e.g. NaCl) or liquids such as water (H2O). Unless H2O is in gas form, you do not include it.

Jonathan Shyu 3L

The first midterm is 2/2 (Week 5) at 6-7pm. The second midterm is 2/28 (Week 9) at 6-7pm.

Jonathan Shyu 3L

K is the ratio of concentrations at equilibrium. Q is the ratio of concentrations at any one point chosen during the reaction. This could mean the beginning, the end, the middle, 3 seconds in, or anything. Q can also include K.

Jonathan Shyu 3L

It is only with water because water is always neutral or very close to neutral. Thus, with the equation Ka*Kb=Kw=14, Ka and [H30+] are the same. But in other acid-base reactions, Ka will be different than [H30] because when calculating Ka, there will be more factors in the equation for normal acid-b...

Jonathan Shyu 3L

K=10^-3 is the biggest that you can approximate, but you also have to ensure that the equilibrium concentration is less than 5% of the initial to ensure your approximation is accurate. To be safe, Dr. Lavelle said to estimate with K=10^-4 or smaller.

Jonathan Shyu 3L

You're right, they are exactly the same thing. Not sure the exact reason Dr. Lavelle chooses mol*L^-1, but I know he likes to specify units a lot and the units for Molarity is just moles of liters.

Jonathan Shyu 3L

In general, reactants side is always negative and product side is always positive. Think of it like you're using up reactants (negative change) to create the products (positive change). Yes they are interchangeable since reactions are typically reversible with equilibrium, but the general rule is re...

Jonathan Shyu 3L

K is the ratio of the concentration of products to the concentration of reactants AT EQUILIBRIUM. Q is the ratio of the concentration of products to the concentration of reactants at any one point of the reaction. This could be the beginning, the end, the middle, equilibrium, or any other time of th...

Jonathan Shyu 3L

ICE method is used to find the concentrations of either reactants or products at equilibrium. With the reaction and the initial concentrations, you can use them and the Kc or Kp to calculate concentrations, or you can use the concentrations to calculate Kc or Kp.

Jonathan Shyu 3L

In the equation for K, where K=[Products]/[Reactants], K is equilibrium. Q is the same thing but reflecting a specific point of the reaction that does not have to be when it is at equilibrium. When K<Q, that means that there are too much products, since a higher numerator and a lower denominator wou...

Jonathan Shyu 3L

Yes, you keep the same login and password and same account. The only thing different is you follow the instructions on Dr. Lavelle's website for changing your username to match the discussion that you are in. Your posts do carry over when you switch your name.

Jonathan Shyu 3L

It is the same format as the previous password, updated with the current class info!

Jonathan Shyu 3L

They are exactly the same!

Jonathan Shyu 3L

Lewis acids and bases focus on the transfer of electrons, while the bronsted acids and bases focus on the transfer of protons

Jonathan Shyu 3L

This is a very general question, but how much do we have to memorize for the final in terms of specific ligand names, which ones are monodentate, bidentate, etc? There is a lot and there is not much specificity around which ones we need to know or just all of them.

Jonathan Shyu 3L

One thing to note is the "dentateness" does not contribute to the coordination number. Despite having more bonds, the coordination number is only determined by how many ligands are bonded, not how many bonds are between the ligand and the central metal atom.

Jonathan Shyu 3L

Does any know any details about the final such as how many questions, if it is cumulative or just units past the 2nd midterm, or when details are going to be sent out? Also is it going to be completely multiple choice just like the midterms?

Jonathan Shyu 3L

A coordination compound is a molecule that has a central metal ion with ligands bound to it. The ligand is attached to the central metal atom through a coordinate bond, which means the ligand shares 2 of its electrons and the metal atom doesn't share any. A coordination number is just how many ligan...

Jonathan Shyu 3L

Yes! Coordination number is counting the number of atoms bonded without regarding how many times an atom is bonded (monodentate, bidentate, etc.)

Jonathan Shyu 3L

Ligands are atoms or molecules that bond to a central metal ion atom through a coordinate bond. A coordinate bond is produced as the ligand shares 2 of its electrons to the metal ion instead of ligand sharing one and the metal sharing 1. A ligand does not have to be polyatomic, but it commonly is.

Jonathan Shyu 3L

Adding on, specific oxidation numbers are set, such as chlorine, fluorine, or sodium. However, there are elements non in group 1 or 2 or the other rules that require a bit of calculation to determine the oxidation number which is the transition metals. The metals have to be put into a compound and f...

Jonathan Shyu 3L

I believe coordinate compounds can only occur with metal ions. The transition metals are found in the d block on the periodic table.

Jonathan Shyu 3L

Single Bond has 1 pi bond. Double bond has 1 pi bond and 1 sigma bond. Triple bond has 1 pi bond and 2 sigma bonds. Pi bonds only attach at 1 point, which means the molecule can rotate/twist. Sigma bonds are attached at 2 points so twisting/rotating the molecule at the bond will break the bond.

Jonathan Shyu 3L

So in sp2 vs sp3, sp2 has a higher s-characteristic because if you think about it in proportions, the s to p ratio is 1:2 in sp2 vs 1:3 in sp3. Thus the less p there is, the more s-characteristic there is. sp2 is then also characterized by a 120 bond angle and sp3 has a 109.5 bond angle. Thus, the h...

Jonathan Shyu 3L

Normally we would just use, bi, tri, tetra, penta, etc. However, if a compound needs 2 different prefixes, instead of using bi twice, we would use bis and bi to make it more clear and reduce repetition or any confusion that comes with it.

Jonathan Shyu 3L

I was wondering what the definition of a coordination compound and coordination bond is. Also if someone could provide an example that would be great.

Jonathan Shyu 3L

I was just wondering what the definition of ligand and chelate was. Also if anyone could give examples. Thanks!

Jonathan Shyu 3L

I2 is a bigger molecule than Cl2. When an atom is bigger with the same type of force acting upon them, in this case both are LDFs, the bigger molecule allows for more polarizability because electrons are farther away from the nucleus. The more polarizability there is in a molecule, the strong the in...

Jonathan Shyu 3L

A single bond is longer than a double bond. This is because single bonds are weaker than double bonds, thus when a bond is weaker, it holds atoms together less tightly, increasing the distance and length of the bond.

Jonathan Shyu 3L

This would stay the same across all elements of the periodic table and all bonds. For all elements, single bonds are composed of 1 sigma bond, double bonds are composed of 1 sigma and 1 pi bond, and triple bonds are composed of 1 sigma and 2 pi bonds.

Jonathan Shyu 3L

Sigma bonds bond two atoms together through 1 point of contact. Because it's only 1 point that is bonded, it can rotate. Pi bonds attach atoms at 2 points, and because of this, the atoms cannot rotate or else they will break the bond.

Jonathan Shyu 3L

Simply put, sigma bonds are in all 3 types of bonds. Single bond is composed of 1 sigma bond. Double bonds are composed of 1 sigma bond and 1 pi bond, and Triple bonds are composed of 1 sigma bond and 2 pi bonds.

Jonathan Shyu 3L

I am trying to study for Midterm 2, and I am doing the Focus Exercises in the textbook. The answers for the normal exercises are found in the back of the book contents in "odd-number" exercises. Where could I find the answers for the Focus Exercises to check my work?

Jonathan Shyu 3L

Determining if a molecule exhibits only London Forces depends on the polarity of the molecule. All molecules exhibit London Dispersion forces, but only nonpolar molecules display only London. Polar molecules display London as well as dipole forces. Looking at the question, the nonpolar molecules are...

Jonathan Shyu 3L

In a hydrogen bond, the H molecule would be covalently attached to an N, O, or F already in a single molecule. The hydrogen bond part comes from when that H is a bonding point with another N,O, or F. So an example would be O-(covalent)-H ---(hydrogen bond)--- O.

Jonathan Shyu 3L

Simply put, a Lewis Acid is the atom that receives the electron, while the Lewis base is the one donating the electron.

Jonathan Shyu 3L

Answering Milli's Question, I believe the midterm will be multiple choice again, but the answers might be of lewis dot structures and you have to choose the best one to answer the question. Hopefully that makes sense.

Jonathan Shyu 3L

Covalent bonds are formed between 2 nonmetals, and Ionic Bonds are formed between a metal and a nonmetal.

Jonathan Shyu 3L

Single bonds only contain sigma bonds, so they are referred to as sigma bonds. Double bonds have both sigma and pi bonds, so they can be referred to as pi bonds to differentiate from single bonds.

Jonathan Shyu 3L

Yes those are the exceptions because H and He only have 1 shell for electrons which the first shell can only hold 2 electrons, thus no octet rule. Li and Be on the other hand have 2 shells for electrons, but due to ionization energy and electron affinity, its easier to remove those electrons from th...

Jonathan Shyu 3L

There are assignments on achieve under the "no due date" section posted on the first week that are tutorial assignments on how to navigate around doing the assignments of achieve. In one of those assignments is a tutorial assignment on how to draw molecules on achieve. Hope this helps!

Jonathan Shyu 3L

Ionic bonds tend to be much stronger than covalent bonds because ionic bonds are characterized by the coulombic attraction between ions with opposite charges (cations and anions). Covalent bonds are just a simple sharing of pairs of electrons, thus ionic bonds are much stronger.

Jonathan Shyu 3L

Yes! Ionic bonds are all salts and all salts contain ionic bonds. Ionic bonds are formed between a metal and nonmetal and is also characterized by a bond between a cation and an anion. Thus, all ionic bonds are salts.

Jonathan Shyu 3L

I believe yes, the sig figs would be the same. Also, I believe in general how many sig figs any question uses would be the amount of sig figs your answer should be. As others have stated, the mid term is multiple choice so it should make things easier.

Jonathan Shyu 3L

As you go down the groups in the periodic table (horizontally), the amount of electron shells/the distance between the valence shell and the nucleus remains the same. But as you go down, you increase protons and electrons, thus increasing the attraction between the two and decreasing the atomic radi...

Jonathan Shyu 3L

For the Chem 14A midterms and finals, are there grade curves or no? I don't think the homeworks or assignments are curved at all, so I don't think there are curves for tests, but I was just wondering.

Jonathan Shyu 3L

I was also wondering the same thing. I believe it should be the school week following the test date of the midterm. Hopefully Dr. Lavelle or TAs will also clarify in lectures, discussions, or emails in the following week.

Jonathan Shyu 3L

Yes! Right on the money! Because of C=Lambda*Frequency, when wavelength decreases, frequency increases. Because of E=hv, the greater the frequency, the greater the energy of a photon.

Jonathan Shyu 3L

I do not believe we will need to draw anything on the midterm. I recall hearing that the midterm is fully multiple choice so there would not be any hand drawing. There might be questions asking about the shape/orientations of the different orbitals. S has no nodal planes, it's just a sphere. D has a...

Jonathan Shyu 3L

As others have stated, all material from Week 0-Week 3. A good "study guide" would be the Learning Outcomes on Professor Lavelle's Chem14A website. We covered Outline 1 and 2 for content, and on the actual pages of those links, there are things that you should be able to do. I will be usin...

Jonathan Shyu 3L

Just adding onto what has been stated before, simply stated, half and full filled d-orbital is more stable and thus the electron from say 4s2 would jump to the d-orbital to make 3d5 4d1 for Chromium or 3d10 4d1 for Copper. It is just a general rule/principle that happens and needs to be memorized. A...

Jonathan Shyu 3L

So there is S, P, D, and F blocks. If you google "Electron Configuration Periodic Table," it's a good source of visuals corresponding to each element. It starts with S which can hold one pair or two electrons, then P which can hold 3 pairs or 6 electrons, and then D block which can hold 5 ...

Jonathan Shyu 3L

So from Schrodinger's Wave Equation, the three quantum numbers are n, l, and Ml. Letter n corresponds to the energy level or electron level, l refers to the shape (s,p,d,f), and Ml refers to the orientation. However, I'm not quite sure what it means by orientation. So if Ml=1, what does that mean?

Jonathan Shyu 3L

A good way to think about it is the equation for Kinetic Energy. Kinetic Energy (Ke) is measured in joules, and the equation is Ke=1/2MV^2. Velocity is meters (m) per second (s) so m/s, and we can replace V in the equation to become Ke=1/2M(m/s)^2, which is the same equation for joules.

Jonathan Shyu 3L

We use Kgs to allow for calculations across formulas not only in chem but physics and any other subjects that apply to be applicable. Kgs are a part of the SI units, which are the standard units that everyone utilizes during calculations to allow for consistent and accurate outcomes.

Jonathan Shyu 3L

Polarity can be determined in two ways: first way is to see what a molecule is composed of, and second way is to view the bonds/electron sharing of the molecule. If a molecule is composed of the same element and share electrons evenly, then it is nonpolar, while if a molecule is made up of different...

Jonathan Shyu 3L

Electron mass in general is commonly viewed as negligible because it is so small, so when it comes to questions that have to do with general atomic mass or questions with a scale much larger than electrons, then there is no need to include electron mass. However, in certain equations such as the De ...

Jonathan Shyu 3L

I am no psychology major or stress relief specialist by any means, but I find that like lots of people, having a routine and a plan helps a lot. You can only control what is in your power, and anything outside your control you shouldn't stress about. This means you should focus on things pertaining ...

Jonathan Shyu 3L

I'm not sure what Professor Lavelle wants, whether he wants sig figs to be rounded or truncated. However, when solving mathematical equations for problems, numbers should always be rounded or enough sig figs should remain in order to get the most accurate final answer.

Jonathan Shyu 3L

So just to clarify, using proper sig figs is only for final answer, but when solving the problem we use any amount of sig figs to avoid improper rounding.

Jonathan Shyu 3L

I just tried searching it up "Average Molar Mass Practice" on google, and many websites/images with answers popped up. Khan Academy and Youtube probably have lots, but just googling it will get you more if you need.

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