CHEMISTRY COMMUNITY

Sara Richmond 2K

I dont think so. But where is the information for this topic in the textbook?

Sara Richmond 2K

Does the cell flow from anode to cathode or cathode to anode? which has the higher concentration anode or cathode?

Sara Richmond 2K

My confusion is with part A. How do we determine which part is the slowest? Which affects the rate law?

Sara Richmond 2K

How are we supposed to know if something is an elementary reaction? What exactly is different from an elementary reactions and a classic reaction?

Sara Richmond 2K

Is it true that coefficients to dont influence rate laws for elementary reactions?

Sara Richmond 2K

Termolecular reactions are when three molecules are involved in a rate law such as A+A+A=C or A+B+B=C

Sara Richmond 2K

Instantaneously was rate decreases with time. If you think about it, it makes sense that the reaction would slow as more of the reactants have been used up;.

Sara Richmond 2K

As far as I can tell zero order reactions are not that common, but they proceed when the rate of the reaction is independent of the concentration of the substances.

Sara Richmond 2K

a) You must pick metals that are below titanium in the electrochemical series. Meaning they are stronger reducing agents. For example aluminum or magnesium. b) cost, availability, and environmental impact c) Iron (Fe) is a stronger reducing agent so it could act as the anode of an electrochemical ch...

Sara Richmond 2K

I've attached an image of a rule chart that I use. But basically you set up an algebraic equation for each compound and solve for the elements whose oxidation number you do not know.

Sara Richmond 2K

The question will usually specify acidic or basic solution. If no solution is specified assume acidic.

Sara Richmond 2K

Why does the answer key use two electrons in the cathode reaction? Wouldn't one electron be sufficient to balance the charge from 3+ to 2+.

Sara Richmond 2K

When is a reducing agent an anode or cathode? I thought the general rule was that oxidation= anode and reduction=cathode but If you look at the screen shot this problem uses the reverse. I am confused.

Sara Richmond 2K

This one was very confusing for me as well, but I think since Cl2 has to serve as both the oxidizing and reducing agent, if Cl is getting oxidized in Cl2 --> HClO, then the Cl2 also needs to get reduced somehow. The easiest way for this to occur would be to make the other half reaction Cl2 --> 2 Cl...

Sara Richmond 2K

The answer key converts Cl2 on the products side of the equation to 2Cl-. Why does it do this? How would I know to do this is a similar problem?

Sara Richmond 2K

Why does the answer key use 2 electrons for the oxidation reaction when the oxidation number only changes by 1? Why does the answer key use 6 electrons for the reduction reaction when the oxidation number only changes by 3?

Sara Richmond 2K

Bond enthalpy denotes the amount of energy necessary to break or form a given bond. Thus the higher the bond enthalpy the tighter the bond.

Sara Richmond 2K

An easy way to decide which heat capacity to use is to write the c value last. Then choose the C value in which the correct units cancel. This is also applicable to deciding which R constant to use.

Sara Richmond 2K

You first must draw out all of the Lewis structures. Then count all the bonds on the left side of the equation and all of the bonds on the right side of the equation. Then do bonds broken- bonds formed.

Sara Richmond 2K

The units for Enthalpy or delta H are in KJ/mol. If they are written in just KJ, 1 mole is assumed or there is a predefined mass.

Sara Richmond 2K

The unit for Delta H are KJ/mol. If the problem just says KJ, 1 mol is assumed or a predefined mass has already been stated.

Sara Richmond 2K

I know a negative delta g means the reaction is spontaneous. A positive delate g means the reaction is not spontaneous. But does a negative delta g means the reaction favors products and a positive delta g means the reaction favors reactants.

Sara Richmond 2K

Matt Sanruk 2H wrote:Since it's at STP, the value must at the a value of 273.15k

What is STP?

Sara Richmond 2K

Why did the solution manual use 273K rather than the 298K discussed earlier?

Sara Richmond 2K

How do you determine the number of orientations for these cis/ trans structures?

Sara Richmond 2K

SO are the units of Delta H KJ per mole while the units of Q are just KJ.

Sara Richmond 2K

The equations the solution manual uses are combustion reactions. Because we are told the substances’ enthalpy of combustion we can first write out those combustion reactions as the solution manual did. A combustion reaction happens when a substance reacts with water and produces CO2 and H2O. You go...

Sara Richmond 2K

Photos

Sara Richmond 2K

Hey guys I had a question on a home problem. I’ve included the textbook, my work, and the solution manuals work. As you can see, I get a positive answer while the solution manual gets a negative one. The solution manual uses equations and I am not sure where they found them. Please help/ explain wha...

Sara Richmond 2K

What are the different formulas for calculating enthalpy at a constant pressure vs calculating enthalpy at a constant volume.

Sara Richmond 2K

For part B how do we calculate the change in enthalpy? It is not included in the answer key

Sara Richmond 2K

Remember that Kb corresponds to bases and Ka corresponds to acids so it can be difficult to compare. First consider that K is [Products]/[Reactants]. So anytime K is very very small it means that there are way more reactants than there are products thus the solution is very weak. This reasoning work...

Sara Richmond 2K

Usually you will get partial credit on tests. But it may depend on your TA.

Sara Richmond 2K

ABombino_2J wrote:All acids/bases have a Ka or a Kb but strong acids and bases have such large Ka and Kb's that they are considered to fully dissociate.

I agree. The larger of the value of these constant would indicate strong acids/bases.

Sara Richmond 2K

% ionization is calculated by dividing the [H30] or [OH] concentration by the concentration of the original acid/ base. Essentially, the higher the concentration of the OH or H30 ions the higher the percent ionization.

Sara Richmond 2K

JesseAuLec1Dis1G wrote:If I make the assumption because K is less than 10^-3, but the x value is less than 5% do I have to go back and use the quadratic formula to calculate x?

If the value is less than 5% you are good to go. If the value is more than 5% you would need to go back and use the quadratic formula.

Sara Richmond 2K

A reaction is exothermic when it releases heat. Exothermic reactions have a negative (DELTA H) value. When exothermic reactions are heated they will favor the production of the reactants. Another way to phrase this is that when an exothermic reaction is heated the reaction will move in the reverse d...

Sara Richmond 2K

I understand that autoprotolysis is the transfer of an H+ from an acid to a base in an equation (I think), I'm unclear on how pKW = pH + pOH is derived from it though. The PkW=Pka+Pkb equation is derived from autoprotolysis because autoprotolysis is the simplest example of acid and conjugate base p...

Sara Richmond 2K

Autoprotolysis is the transfer of H+ ions within two identical molecules such as two H2O molecules. In this reaction two H2O molecules react to form one molecule of H30 and one molecule of OH

Sara Richmond 2K

In the solution Manuel it says "Ka2<< Ka1., the second ionization energy can be ignored"

What does this mean? When can the second ionization energy be ignored?

Sara Richmond 2K

You should know that strong acids dissociate completely, which is why they don't have Ka constants, and thus result in solutions with higher H+ concentrations. Thus, if you are comparing two strong acid solutions, you can expect the one with a higher molarity to be more acidic. So is there a chart ...

Sara Richmond 2K

Yes, I am sure that I am looking at the right solution manual question. The answer to part A is actually 5. I have included a screen shot of my work to show how to get 5 for part A.

Sara Richmond 2K

Approximation can be used for weak acids and bases problems when the K value is less than 10^-3. This means it is so small that it is not going to make a difference when calculating concentrations. After you use approximation, you should use the 5% rule to check if your calculation was valid/ if the...

Sara Richmond 2K

Please explain the reasoning behind this problem. The solution Manuel has no calculations just general reasoning including the strength of the acid or the conjugate base. What information from the problem is important to know/understand?

Sara Richmond 2K

Here are the photos sorry.

Sara Richmond 2K

Can you explain to me why in the solution Manuel the Cl3 is replaced by (H20)6?

Sara Richmond 2K

Thank you both.

I have one more question regarding this problem. I've included both my work and the answer key's work for finding the equilibrium constant. My question is "How would I have known to divide by 100 when finding the equilibrium constant?"

Sara Richmond 2K

Please explain how to do this problem? I do not even know where to begin. or how to read the graph?

Sara Richmond 2K

In the case of this problem, why doesn't reducing the volume result in the production of more X molecules? The solution manual says that it would result in the production of more X2 molecules which doesn't make sense to me as in the equation there are more moles on the right side of the equation.

Sara Richmond 2K

I don't think we have gotten this far in class yet, but generally if ∆G < 0 then the reaction is exothermic, and if ∆G > 0 then the reaction is endothermic. The reaction is Δ G = Δ H − T Δ S. (I only know this from bio so I'm not sure if this will be the same or not for chem but I'm sure we'll lear...

Sara Richmond 2K

Le Chatelier's Principle can be used to determine how changes in a specific constraint of a reaction in equilibrium will affect the other constraints of the reaction. The principle can be best understood if you look at it like a fraction, as Kc is written in fraction form. (A/B=C) In situation, C ne...

Sara Richmond 2K

Solids are not included when calculating the equilibrium constant. So in the case of this problem, C is ignored. Thus there are 2 moles on the right side of the equation, and only 1 mole on the left side of the equation.

Sara Richmond 2K

Le Chatelier's Principle can be used to determine how changes in specific constraints of a reaction in equilibrium will affect the other constraints of the reaction. The principle can be best understood if you look at it like a fraction. (A/B=C) In situation, C never changes. So if A is increased, t...

Sara Richmond 2K

How do you determine if a reaction is endothermic or exothermic?

Sara Richmond 2K

The major contributor is the most stable resonance structure, where the central atom's charge is closest to 0. To determine charge of a molecule add all of the formal charges together.

Sara Richmond 2K

I have heard on past chem finals, students have had to draw cisplatin. So maybe be familiar with the chemical formula and shape.

Sara Richmond 2K

amphoteric: Can act as both an acid and a base
amphiprotic: Can donate or accept protons
ionic: has ionic character. Has to do with bonding.
polyprotic: can donate or accept multiple protons

Sara Richmond 2K

What specific biological examples would we know for the final? And what should we know about them?

Sara Richmond 2K

I am so confused by this problem. I have included two photos. One of my work and one of the solution guide's work. Where did the solution guide get the equation they used? What is wrong with the equations I used?

Sara Richmond 2K

Q6.A. Magnesium ions are a known cofactor in over 300 enzymatic reactions. What are the possible angular momentum quantum numbers of the highest energy electrons in these magnesium ions? Indicate the corresponding subshell of each angular momentum quantum number. The electron configuration of Mg is ...

Sara Richmond 2K

Q5C. Calcium ions are important in the process of neurotransmitter release at the neuromuscular junction. Write the full electron-configuration for the ground-state of a calcium ion. Answer: Ca2+ 2pt 1s2 2s2 2p6 3s2 3p6 2pt How would we have know to write the electron configuration of calcium 2+? Wh...

Sara Richmond 2K

Double bonds do not affect hybridization because a double bond still represents a single location of electron density. An easy way to determine what type of hybridization is to use steric numbers. Steric Number= number of bonded atoms + number of lone pairs. Notice that the number of bonds is not in...

Sara Richmond 2K

Typically strong acids have a greater difference in electronegativity than weak acids. While weak bases have a smaller difference in electronegativity than strong bases.

Sara Richmond 2K

Yes, by referencing the periodic table you can tell which compounds are amphoteric. Semi metals are typically amphoteric. Meaning that if they lay on the jagged diagonal line they are amphoteric. In addition to this information. We can use the periodic table to determine which elements are solely a...

Sara Richmond 2K

Yes, by referencing the periodic table you can tell which compounds are amphoteric. Semi metals are typically amphoteric. Meaning that if they lay on the jagged diagonal line they are amphoteric.

Sara Richmond 2K

danielruiz1G wrote:is it possible to determine the shape of a molecule if you're only given the AXE formula, if so how do you do it?

The only real way to do it, is to memorize the chart. This chart is especially helpful because it includes hybridization and shape and polarity.

Sara Richmond 2K

Can someone please explain Denticity to me? I do not understand how we are supposed to be able to determine if a molecule is polydentate, mono dentate, or didentate.

Sara Richmond 2K

AXE notation is the same as saying "What is the Vsepr formula?" Each of the letter stand for something: A= the central atom. Some chemistry courses will require you to write the central atom in the formula, but Dr Lavelle does not require this nor does he prefer that you do. On exams just ...

Sara Richmond 2K

I believe hybridization is based on molecular geometry. This chart can help you understand the relationship of hybridization and molecular geometry.

Sara Richmond 2K

Are one of these bonds stronger than the other? Pi bond vs Sigma? If so, why? Sigma bonds are stronger than pie bonds because the orbitals of a sigma bond overlap more during hybridization than the orbitals of a pie bond. It can be difficult to understand sigma and pie bonds without reading through...

Sara Richmond 2K

Sigma bonds are single bonds. Pie bonds are in double and triple bonded atoms. In a double/ triple bonded atom, one bond is always a sigma bond and the others are pie bonds.

Sara Richmond 2K

This chart is extremely useful. I would recommend memorizing the sheet for your test 2.

Sara Richmond 2K

Will you have a review session this weekend to prepare for Test 2?

Sara Richmond 2K

I believe that I read in the textbook that the VSEPR formula for molecules of the same atom result in a linear shape.

Sara Richmond 2K

What does VSEPR stand for? How do we determine a molecules VSEPR formula for a molecule.

Sara Richmond 2K

I went to a UA workshop last week. She said that we will be expected to memorize all of the shapes. She also suggests we memorize the VSEPR model.

Sara Richmond 2K

What material will we be tested on for test 2 that occurs during Week 8?

Sara Richmond 2K

Use these equations:
(delta p)(delta x) = (1/2)(h/4 PIE)
(deltap) = m( delta v)

Sometimes this type of problem can be confusing because they dont give you the delta p equation.

Also remember to multiply the delta v uncertainty by 2 because it is plus or minus a certain amount.

Sara Richmond 2K

I find it useful to take a nap before a midterm or final. especially when they are night midterms. To be honest after studying for weeks (like I do for chemistry exams), I can be really distracted and nervous before an exam. By taking a nap, I recharge my brain. But really you will need to find what...

Sara Richmond 2K

Thank you, the process makes more sense now. I was missing the equation for delta P. "ΔP is equal to mΔv because mass is constant and velocity is the only thing that changes. Set up the equation Δp=mΔv on the side to solve for Δp". Now that I know this, it makes more sense.

Sara Richmond 2K

For number 4 part b on the extra practice problems, why doesn't boron have to complete it's octet? In your answer key, boron only has 6 electrons accounted for in the lewis structure

Sara Richmond 2K

I am kind confused when it comes to the Heisenberg uncertainty principle. Can you help me calculate this problem? It is from a worksheet made by the UA Karen Leung

Sara Richmond 2K

Usually in terms of Chemical bonds, we usually just include the s and p orbitals when defining the number of valence electrons in the valence shells. You should definitely check out the other posts on this topic.

Sara Richmond 2K

M2+ is not actually an element. The problem is asking you to name the 2+ ions with those electron configurations. Imagine M as x in an algebraic function.

Sara Richmond 2K

AN easy way to calculate formal charge of an atom is:

# of valence electrons for that element- number of dots-number of lines=formal charge

Sara Richmond 2K

Do bonds count as one or two valence electrons in a Lewis Structure?

Sara Richmond 2K

When do the electrons from a future s orbital transfer to a d orbital to stabilize the electron configuration.

Sara Richmond 2K

I had a questions on a chemistry concept relating to determining the electron configuration of an ion- do you move left or right on the periodic table for charge? For example: 1. Is the electron configuration of Fe^+ the same as the electron configuration of Mn (move left) or the same as Co (move ...

Sara Richmond 2K

Electron shells are divided into subshells and subshells are divided into orbitals. In terms of quantum numbers, n denotes the shell, l denotes the subshell, and ml denotes the orbital. Each orbital typically houses 2 electrons of opposite spin./

Sara Richmond 2K

Why fo the elements of Cr and Cu have different electron configurations than the rest of the elements in the 3d block? For instance why is Cr's electron configuration: [Ar]3d^5 4s^1 instead of [Ar]3d^4 4s^2? What other elements are an exception to the expected electron configuration? Will we need to...

Sara Richmond 2K

Sometimes its difficult to know what order to write the orbitals. The best one to remember which orbitals have higher or lower energy is with this chart. Follow the arrows from bottom to top and when your done return to the bottom of the next arrow.

Sara Richmond 2K

Hey the order of electron shell energy is difficult to understand. The only way that I can remember the order of the energy is with this chart. Follow the arrows from bottom to top and then return to the bottom of the next arrow.

Sara Richmond 2K

Hund's rule states that: Every orbital in a sublevel is singly occupied before any orbital is doubly occupied. All of the electrons in singly occupied orbitals have the same spin (to maximize total spin). It is easier to understand if you picture electrons as magnets, two negatively polled magnets w...

Sara Richmond 2K

Molarity is a measure of concentration. The higher a substances molarity the more solutes. For example, if one sample of salt water has a molarity of 0.1M and another sample has a molarity of 0.9M, then the 0.1M water would be less. salty than the 0.9M sample.

Sara Richmond 2K

I went to your workshop last Sunday, and I found it extremely useful. Thank you for all the help. I will see you next week!

Sara Richmond 2K

Will we be expected to derive Bohr's equation on the midterm like Dr. Lavelle did in class?

Sara Richmond 2K

Every week my chemistry community account locks me out. I am forced to reset my password each week. Has anyone else experienced this? Each week a reset my password to the same thing and it still locks me out the next week.

Sara Richmond 2K

For the first midterm will we need to memorize the electromagnetic spectrum?

Sara Richmond 2K

There is a short section in the textbook about Wein's law that helped me better understand this. You should check out section 1B of the textbook.

Sara Richmond 2K

I am having trouble understanding the difference between when light acts like wave and like a particle. Any advice for reading material/ videos?

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