CHEMISTRY COMMUNITY

Annabelle Jeon 3K

So I was looking over factors that affect the rate of reaction. So for temperature, I understand that it generally increases reaction rate by increasing particle speed which increases the force and frequency of collisions. However, is this also the case even for exothermic reactions? (Because genera...

Annabelle Jeon 3K

Do you mean like the written notation or the drawn out diagrams? Either way, anodes should always be to the left and cathodes should always be to the right. For written notation, the solids conducting the electrons should always be located in the outermost part of the notation. Each element should b...

Annabelle Jeon 3K

The anode components are always on the left while the cathode components are always on the right. The solids (or on occasions liquids like Hg) being conducted is always located on the outer edge of the notation. We use commas instead of vertical bars to separate substances of the same element and st...

Annabelle Jeon 3K

So how I'd go about this problem is just converting the pH to pOH so then you can solve for molarity. So for this example pOH = 14 - 9.771 = 4.229. Then you can solve for molarity of OH- using exponents: M = 10^-4.229 = 5.902*10^-5M. Then you make an ice chart. Set the left hand amine solution to 5....

Annabelle Jeon 3K

So in the lecture, they mentioned the concept of microscopic reveresibility, meaning that we can assume for any given reaction, the reverse reaction takes the same pathway or mechanism as the forward reaction. This does NOT mean that the activation energy for the reverse reaction is the same as the ...

Annabelle Jeon 3K

combined gas law is when we use PV = nRT to find a missing variable by setting two set of the same gaseous substances under different conditions equal to each other. Here are some example formulas: P1V1/(n1*T1) = P2V2/(n2*T2) P1V1 = P2V2 In the context of chem14b, I can see us having to use it for s...

Annabelle Jeon 3K

n should be the number of moles of electrons being transferred in your balanced redox equation.

Annabelle Jeon 3K

You should just typically know that the units of k for.. zero order = M/s 1st order = 1/s 2nd order = 1/(M*s) 3rd order = 1/(M^2*s) so on and so forth. If you want to know the reasoning why, we want our unit for our rate to ultimately be M/s. So for example, if a reaction is second order, then our u...

Annabelle Jeon 3K

An intermediate is a substance that's used up and made in the same reaction so it's not considered either as part of the reactant or product. For example, in our lectures, we use the reaction 2NO +O2 -> 2NO2, which is broken into two steps: 1. NO + NO -> N2O2 2. N2O2 + O2 -> NO2 +NO2 Since N2O2 is l...

Annabelle Jeon 3K

Did the solutions say that the 3rd flask is not equilibrium? Because I think you're right that it is, and we can tell because the number of diatomic molecules and atoms of X stay the same in the 4th flask, meaning that it's reached equilibrium. The 4th flask just represents the passage of time. Each...

Annabelle Jeon 3K

Adding onto that, delta G° is delta G under standard conditions as stated (298K or 25C at 1 atm). While delta G is just G at any given condition. Delta G is equal to zero at equilibrium, hence we set the equation: delta G = delta G° -RTlnK to 0 = delta G° -RTlnKat equilibrium. (Note that we're using...

Annabelle Jeon 3K

For the March 11th lecture on Arrhenius Equations, I was confused as to where we got the unique rate for step two from (1/2 d[NO2]/dt). Are we supposed to know this? It was mentioned that the 2 was because the reaction produces 2 molecules of NO2. Is this the case for all reactions? For example, if ...

Annabelle Jeon 3K

I was wondering for this question, since it states to calculate the solubility product of Hg2Cl2, if we should automatically know the formula for the reaction, given those key phrases? Is this something that we're supposed to have memorized, and if so, are there other general formulas and their name...

Annabelle Jeon 3K

Whenever there's a single reactant with multiple products, we can usually assume that both products result from the same reactant. So how I'd go about this problem is by setting two skeleton equations: 1. Au+ -> Au (s) 2. Au+ -> Au3+ then you balance the charges accordingly. You only have to worry a...

Annabelle Jeon 3K

For part a, why don't the half reactions balance out? For example, both the cathode and the anode reaction must have electrons to the left of the reaction in order for the cell potential sum to be positive. How does this work out?

Annabelle Jeon 3K

part A of this question asks to write out the half reaction of a cell with a redox reaction of potassium permanganate (KMnO4) and Iron (II) chloride (FeCl2). How do we know what the products are? The textbook answer has MnO4- + 8H+ +5e- -> Mn2+ + 4H2O and Fe 2+ -> Fe 3+ + e- as the half reactions. A...

Annabelle Jeon 3K

I was wondering why for part d of 6L.3 we don't simply the final reaction and leave the coefficient as is: 4H20 -> 4H+ + 4OH= instead of dividing it by four to make it H2O -> H+ + OH-

Annabelle Jeon 3K

Hi, I was wondering for part c, why the notation for Ce3+ and Ce4+ is separated by a comma rather than a vertical bar and if there are any other exceptions we should know about for shorthand notations of galvanic cells. Same with part b which has C (gr) for the anode metal.

Annabelle Jeon 3K

I'm having trouble figuring out how to even set up the redox reactions. How do we know whether to add H+ or H2O or some other substance to balance the reaction? For example, in the textbook, question 3 is throwing me off because at a first glance, it looks like MnO4- is getting oxidized into Mn2+ si...

Annabelle Jeon 3K

I have two questions about this achieve problem. How do we keep track of the sign changes, and what's an easy way to keep track of the different steps of the equation. For example, how do we know to only do a single step, using mcΔT to solve for the final temperature, whereas in other problems, you ...

Annabelle Jeon 3K

Yeah. For example if you're given a certain equation and you need to reverse the order to cancel out the reactants and products, you should inverse the sign as well when adding the change in enthalpy. Other rules to remember is multiplying the enthalpy by the mole coefficient. For example, if you ne...

Annabelle Jeon 3K

How do we keep track between what formula to use and when? I know that there's two different formulas for change in entropy when pressure is constant and when volume is constant, but how can we tell from the wording of the problem which formula to use?

Annabelle Jeon 3K

I'm having a hard time distinguishing between reversible and irreversible reactions. How do we tell them apart and what formula do we use for each type of problem? Thanks.

Annabelle Jeon 3K

So change in gibbs free energy is given by: change in G = -RTlnK at non-equilibrium conditions and change in H - T*change in S. In either case, enthalpy and entropy of reactants and products are fixed values, so the only thing we can really change is temperature or the amount of available heat and a...

Annabelle Jeon 3K

We can determined residual entropy by comparing the number of orientations or microstates possible. All the molecules except for NO given are symmetric and therefore only have a single orientation. NO will have residual entropy because it is asymmetric and therefore has more than one orientation pos...

Annabelle Jeon 3K

The only formula we need to know for achieve question 9 is that: change in S of a system = change in S of products = change in S of reactants, since the values are already given to us by chart. We may sometimes have to manipulate the values by multiplying it by the number of moles used or adding a n...

Annabelle Jeon 3K

The higher flexibility in framework is likely referring to the number of available microstates, which we can determine by looking at the shape and symmetry of a molecule. 1-pentene is a linear, asymmetric molecule so it will have more available microstates than cyclopentane, which is a symmetric pen...

Annabelle Jeon 3K

I'm not sure about the possible questions they might use on the test. But an example of a reaction in real life where the signs in the changes of enthalpy and entropy are opposite is an explosion. Such reactions release energy meaning a negative change in enthalpy since energy released by products i...

Annabelle Jeon 3K

You probably don't need to know about the equipartition theorem in this level of detail for the midterm because all the problems we've done so far, they usually also give us the Cp or Cv like in #20 of Week 3/4 achieve. But if you want to be thorough, the theorem states that the thermal energy of a ...

Annabelle Jeon 3K

First off, residual entropy is the difference in entropy between a non-equilibrium state and crystal state of a substance close to absolute zero. And the amount of residual entropy of a substance is determined by how many different microstates it's able to take. The more microstates, the more entrop...

Annabelle Jeon 3K

deltaG=deltaH-TdeltaS If we're just thinking about this mathematically, negative deltaG means a spontaneous relationship so for G to be more negative we would want a higher temperature if delta S is positive and a lower temperature if delta S is negative. We can also think about this in terms of an ...

Annabelle Jeon 3K

I ran into the same problem at first but you can use the same answer more than once. So the reaction would be spontaneous at both points since on the left, Q < K meaning that the reaction will want to go forward in order to make more products so that Q increases to approach K, while on the right, th...

Annabelle Jeon 3K

I'm not sure where you're getting integrals from but the main formulas you'll use for problems like these where you're heating or cooling water to different states/temperatures in relation to entropy is: change in entropy = Cp*ln(T2/T1), where Cp is heat capacity for the substance you're heating. We...

Annabelle Jeon 3K

In the textbook it states that the human body is an example of a closed system but a plant is listed as an open system. I understand the logic behind the plant because it contains stomatas that periodically open to exchange gas with the outside the system but would the same not be true for the human...

Annabelle Jeon 3K

I'm not entirely sure of the exact process you used unless you sent me a screenshot of your calculations but from what I can tell, your mistake was when you calculated pOH from pH because you start out with Kb, which is for a base. Make sure that you use pH when setting your reaction quotient equal ...

Annabelle Jeon 3K

By textbook definiton, work is the energy required to move an object against a force. And vice versa, energy is defined as the capacity to do work. The formula we use is work = -pressure x change in volume for irreversible work or -nrT x ln(v2/v1) for reversible work, where v1 is the initial volume ...

Annabelle Jeon 3K

Hi, I'm still having a hard time understanding how to set up problems with acids that have a second round of dissociation like H2SO4. Also, in monoprotic reactions with weak acids, we can estimate the calculation and leave off x if its Ka is less than 10^-3 or ionization percent is less than 5%. How...

Annabelle Jeon 3K

You can usually tell by how the problem is worded. For example, in a lot of the achieve assignments, they tell you that you start out with let's say "M" amount of an acid or base in the form of molar concentration. You can then set up your equation: HA + H2O <-> A- + H3O+ or B + H2O <-> BH...

Annabelle Jeon 3K

So I understand that if the Ka or Kb value of an acid or base respectively is 10^-3 or less, we can usually estimate, so when we are solving for x--(for example, the denominator is the molarity concentration - x) we can leave off x since it is assumed to be such an insignificantly tiny amount. Howev...

Annabelle Jeon 3K

Adding onto that exothermic reactions are usually also spontaneous. This is because the free energy of the products are lower than that of the reactants resulting in a negative net gibbs free energy. On the other hand, endergonic reactions require energy hence they absorb heat.

Annabelle Jeon 3K

Adding onto that exothermic reactions are usually also spontaneous. This is because the free energy of the products are lower than that of the reactants resulting in a negative net gibbs free energy. On the other hand, endergonic reactions require energy hence they absorb heat.

Annabelle Jeon 3K

The last two problems of the achieve assignment gives a solution and a salt of acidic or basic nature and then asks us to calculate the ionization rate given the molarity of the solution. How do we know whether it is the salt or the solution that is relevant. I am also confused as to how to interpre...

Annabelle Jeon 3K

It's actually the opposite. The reaction tends toward the forward reaction (i.e. creates more products) when Q < K and tends toward the reverse reaction when Q>K. To explain why, Q basically tells us the concentration of the products over reactants when the reaction is NOT in equilibrium while K tel...

Annabelle Jeon 3K

Yes, a change in partial pressure will disturb the equilibrium just as a change in the concentration would. This is because a change in partial pressure is given by the formula PV=nRT -> P = nrt/V which would either imply a change in the volume (V) of the container, the temperature (T), or the conce...

Annabelle Jeon 3K

The textbook states that increasing pressure will favor the reverse reaction, but is this always the case? Are there ever any exceptions? I understand that if there are the same number of moles on each side of the reaction equation, the tendency to shift remains neutral. However, would the reverse r...

Annabelle Jeon 3K

So I've been doing the problems on the homework and textbook and so far, though there are temperatures mentioned, we haven't had to take any of them into account into the reaction when applying PV=nRT. Will this always be the case? Will there be problems when we have to manually solve for the partia...

Annabelle Jeon 3K

To what extent do acids like that of copper nitrate that go through labile or short-lived reactions and rapidly exchange molecules affect pH when dissolved in water. Does the short-lived-ness of the reaction and constant exchange of molecules lessen the effect of the acid because it "balances o...

Annabelle Jeon 3K

There's an explanation posted in the solutions. I don't think it was really emphasized in lecture, but if we look at the Lewis structure, HCCCH2 lies on a different plane because the H atoms of H2CCCH2 are perpendicular to each other as a result of the double C pi bond. The general rule for the shap...

Annabelle Jeon 3K

Resonance structures should generally share the same shape and hybridization. The three structures we drew out for this question each possess a fundamentally different shape and hybridization.

Annabelle Jeon 3K

The rapid exchange of ligands is due to the instability of the complex, which makes sense since it is labile, therefore short-lived, a common characteristic of unstable compounds.I assumed the instability is due to the unfilled outer orbitals of the copper atom of the [Cu(OH2)6]2+ complex since copp...

Annabelle Jeon 3K

How important is the concept of autoprotolysis and are there any other notable examples of a molecule being able to transfer a proton to another of the same kind besides water? Also, what is the significance of this phenomenon and why is it important to distinguish?

Annabelle Jeon 3K

I remember briefly going over the possible orientations of orbitals like how the different ways they could lie on the x, y, z plane. Will we have to know how to illustrate these and how many variations there are for the final?

Annabelle Jeon 3K

I was also wondering why the strength of a bond decreases as more atoms are attached to the central hydrogen atom in week 10's achieve question 12. Is this because there are less electrons to be shared?

Annabelle Jeon 3K

How should we go about identifying less obvious bases and acids such as those in question of 7 of week 10's achieve like K2CO3 and Na2S. Why/how are these compounds considered basic or able to donate electrons? Also why is K2CO3 basic while KCl is neutral?

Annabelle Jeon 3K

Hi, I was wondering if there are any compounds that might fit one or two definitions of the types of acids/bases above but not fit another and whether we will have to differentiate between the types of acids and bases on the final.

Annabelle Jeon 3K

So amphoteric means that a substance can act as both an acid and base using the bronsted lowry or lewis definition. So we should look for whatever part of the molecule can both accept/donate electrons or protons. 1. identifying the base -- look for an atom that would allow for the donation of electr...

Annabelle Jeon 3K

You basically add the two reactions together. Compounds on opposite sides cancel out which is why HCO3- is omitted in the overall reaction since it appears as the product in the first reaction and a reactant in the second reaction. The logic behind this is that at some point it's made in the reactio...

Annabelle Jeon 3K

Ionic bonds are formed between ions with opposite charges, which are basically atoms or molecules with a net positive or negative charge as a result of the gain or loss of electrons i.e. Na+ SO4 2- , NH4+ Essentially, they happen between anions and cations and are a result of the COMPLETE transfer o...

Annabelle Jeon 3K

Pt 2+ and Au 3+ have a square planar arrangement because they have bigger d-orbitals which allows them to hold more electrons. This also means more space for the electrons to distribute themselves across. This is important because bond angles are a result of the repulsion of lone pairs on the centra...

Annabelle Jeon 3K

The atoms don't move on the resonance structure per se. We use the dotted lines to represented delocalized regions of electron density. I'm not entirely sure what you mean by when to start counting. But resonance structures are the possible variations of a molecule. The overall charge should be the ...

Annabelle Jeon 3K

Ion-ion interactions are the attraction between exclusively ions usually between anion and cations as the respective negative and positive charge attract each other. Ion-dipole interactions are between an ion and a polar covalent molecule. The polarity is important because this allows for the moveme...

Annabelle Jeon 3K

Adding onto that the prefixes di, tri, tetra, etc... are used for monodentate compounds while bis, tris, etc.. is used for polydentate substances. And to confirm, they denote the number of the given ligand.

Annabelle Jeon 3K

They're used interchangeably. H3O+ in particular usually denotes the product of an acid-base reaction since the hydrogen proton binds to water molecules to form H3O+

Annabelle Jeon 3K

So remember amphoteric means that a substance can act as both a proton donor and acceptor while amphiprotic means that it can act as both a proton donor and acceptor. So a substance that meets both definitions would basically meet the definition for both a Bronsted base and acid. An example of such ...

Annabelle Jeon 3K

Transition metals are able to form complexes with anionic ligands because the t-metals contain empty orbitals that can then be occupied or accept electron pairs from the anionic ligands. This is also why a lot of anions are considered bases because they easily donate electron electrons.

Annabelle Jeon 3K

Adding onto that, it might be useful to know the basic shape of the molecule, which is a modified trigonal bipyramidal shape since the 4 ammine groups form a square planar shape. It then forms a modified octahedral shape when an oxygen molecule attaches directly to the central iron atom.

Annabelle Jeon 3K

Yes to the first question but I think repulsive forces, would be a more apt description in the context of bond angles. Angled structures are created when a lone pair of electrons push down on the central atom, and the atoms it is bonded to, forcing it to condense. This is because electrons repel eac...

Annabelle Jeon 3K

Adding onto the previous answer, on top of the strength of intramolecular forces, you should also take into account the size of the molecule being compared. For example, if compound A is bound by nonpolar covalent bonds while compound B is bound by ionic bonds, A could still be a more stable structu...

Annabelle Jeon 3K

To add onto that, we can use hybridization to determine the type of bonds used. For example, hybridized orbitals are formed through sigma bonds while unhybridized orbitals are formed through pi bonds, which makes sense since sigma bonds are formed through the direct overlap of regions of electron de...

Annabelle Jeon 3K

There aren't too many of them to memorize so probably. For reference, here are the seven most common strong acids: HCl, HBr, HI, HNO3, H2SO4, HClO4 and seven most common strong gases: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 A general rule of thumb, you can kind of infer the strength of an acid or...

Annabelle Jeon 3K

Usually just means a general rule of thumb, not always. I assume they say that because most compounds that starts in an H is usually bonded to an anion, which it is readily able to "let go of" when dissolved in water. For example, acids like HCl are acids because it takes less energy for t...

Annabelle Jeon 3K

I'm still having a hard time wrapping my head around polydentate structures. I understand that polydentate bonds arise from multiple a ligand bonding to the central atom through more than one bond and this increases the stability of the structure, but how can we tell what type of ligands can be poly...

Annabelle Jeon 3K

The question's worded a little strangely because technically both the cation and anion could be considered an acid or base based on the Lewis definition as one of them would inevitably accept an electron while the other would donate an electron. But I assume it's using the Bronstead definition, whic...

Annabelle Jeon 3K

The dissociation of acids and bases refers to the separation of the compounds within the acids, when exposed to water, which provides an environment favorable to the transferring of H+ ions. This allows acids like HCl to dissociate or separate into H+ and Cl- as the H+ ion is stripped from HCl and b...

Annabelle Jeon 3K

I just had a question about question 2 on week 9's achieve. So I get how to determine the coordination number for most of the compounds except K3[CoF6]. All the other compounds seem quite intuitive because there is an obvious central atom and the central atom happens to be the cation as it does for ...

Annabelle Jeon 3K

In lecture we went over how humans are able to tolerate a wide range of acids from lemon juice to soda, which is almost at the extreme end of the scale with a pH of 2. However, something even slightly base like soap with a pH of 7 to 8 is unpleasant and even harmful to ingest. Why is this the case? ...

Annabelle Jeon 3K

In lecture we went over how humans are able to tolerate a wide range of acids from lemon juice to soda, which is almost at the extreme end of the scale with a pH of 2. However, something even slightly base like soap with a pH of 7 to 8 is unpleasant and even harmful to ingest. Why is this the case? ...

Annabelle Jeon 3K

Why aren't strong acids able to dissociate completely at a 100% rate? I understand from the lecture strong acids (i.e. HCl) dissociate almost completely so we estimate a roughly 1:1 ratio of acid to ions but that's just an estimation, not what actually happens. Would it be possible for a compound to...

Annabelle Jeon 3K

How would one go about forming the VSEPR model for a large molecule like a hydrocarbon?

Annabelle Jeon 3K

An atomic orbital is just referring to an atom's orbital in general. Hybrid orbital refers to overlaps in orbitals between different atoms when they form a bond to form a molecule (i.e. sp3 is a hybridized orbital for a carbon atom in a CH4 molecule).

Annabelle Jeon 3K

An atomic orbital is just referring to an atom's orbital in general. Hybrid orbital refers to overlaps in orbitals between different atoms when they form a bond to form a molecule (i.e. sp3 is a hybridized orbital for a carbon atom in a CH4 molecule).

Annabelle Jeon 3K

I noticed that questions asking for the lewis structure of molecules with formal charges on achieve like questions #3 took quite some time. I know to use general rules of thumb like that nitrogen usually only forms 3 bonds or otherwise creates a formal charge and after you create a rough outline, yo...

Annabelle Jeon 3K

I'm sure you can find a list on the internet but as a general rule of thumb, you can just use the periodic table to eyeball the charges. For example, the oxidation number of Na+ is +1 and you know because it's in the 1st column of the periodic table. Similarly, carbon usually has a +4 or -4 charge d...

Annabelle Jeon 3K

I understand hydrogen bonding is a type of dipole-dipole bonding, which requires polar molecules, but would it still be possible for a nonpolar molecule with bonds that each have evenly distributed charge, to still form a hydrogen bond with another molecule if that molecule is extremely polar? Could...

Annabelle Jeon 3K

Why does the atom with lower ionization energy end up as the central atom? How does having lower ionization energy make it more primed to form more bonds?

Annabelle Jeon 3K

The central atom should be the one with the lowest ionization energy. Carbon has a lower ionization energy than oxygen, meaning that it requires less energy for a gaseous carbon atom to eject an electron, therefore it is the central atom. You can determine which atom to use as ionization energy decr...

Annabelle Jeon 3K

This is just more of a theory question rather than how to solve an actual problem. I was wondering if there was a reason why we write spin down first when filling up orbital diagrams and if that is reflective of the actual orientation of electrons or if that's just what people decided on when they c...

Annabelle Jeon 3K

You look for the noble gas located at the rightmost side of the periodic table located the row above whatever element you're writing the notation for. Keep track of the atomic number of that noble gas and the target element. For example, if you wanted to write the notation for silver, you would use ...

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