CHEMISTRY COMMUNITY

Juliet Carr 1F

In general, raising the temperature will increase the rate constant of the reaction with the higher activation barrier more than the rate constant of the reaction with the lower activation barrier.

Juliet Carr 1F

Termolecular is used to describe an elementary reaction that involves the collision of three reactant molecules.

Juliet Carr 1F

I'm not positive but I think this example might include stead-state approximation which Dr. Lavelle mentioned we were not going to cover. Instead, we are focusing on examples that use the pre-equilibrium approach to combining rate laws for elementary steps of a mechanism.

Juliet Carr 1F

Unique average rates are important because they can be used to describe the rate for any species in the equation. They minimize ambiguity related to the different ways of reporting a reaction rate. Since the unique rate is the same for each species, what differs are the stoichiometric coefficients i...

Juliet Carr 1F

My understanding is that for differential rate laws, we consider the whole reaction equation. This equation itself, (even with stoichiometric coefficients greater than 1), does not tell us anything about the speed/rate of reaction. Therefore, we need to conduct experiments to obtain data that will a...

Juliet Carr 1F

As the reaction proceeds, the instantaneous rate will decrease. This is due to reactants being used up as the reaction proceeds, so the rate becomes slower as there are less reactants able to form products. Furthermore, if you look at a graph of concentration versus time, the slope of the tangent li...

Juliet Carr 1F

The example used in lecture to explain the difference between kinetics and thermodynamics controlling a reaction is the reaction of carbon diamond to carbon graphite. This reaction has a negative deltaG value, therefore based on what we learned about thermodynamics, this is a favorable/ spontaneous ...

Juliet Carr 1F

Going off of the information on the syllabus, I think the only sections we need to be worried about for focus 6O is 6O.1 which doesn't cover much in depth about electrolysis, only about electrolytic cells. Also the only problem listed on the syllabus for this section is problem 3 where we need to co...

Juliet Carr 1F

This is not required for this specific question but might be for others, but you could also write out both of the oxidation and reduction half equations in full. This way, you can balance the two half equations to ensure that the electrons transferred are the same for each half equation and will can...

Juliet Carr 1F

In order to determine which is the anode and cathode you have to look at the list of reduction potentials in the appendix. For this question though you only need to look up the standard reduction potential for Sn(NO3)2 since the reduction potential for H+ is always zero. Then compare the reduction p...

Juliet Carr 1F

If using the direct reduction potential values you can use the equation cathode - anode. You can also use the equation that just adds the two reduction potentials together, however you have to make sure you flip the sign of the reduction potential for the equation showing oxidation before you add th...

Juliet Carr 1F

Anions from the salt bridge flow towards the anode and cations from the salt bridge flow towards the cathode.

Juliet Carr 1F

Yes, this is why it is important to first write out the half equations, then balance the elements on the reactant and product side, and adding H2O, H+, or OH- accordingly. Then once you have made these changes, the charges on each side of the equation need to be balanced. This is done by adding elec...

Juliet Carr 1F

For me, it is best to first write out the half equations to clearly determine which species is being oxidized and which is being reduced. Then, to determine the oxidizing and reducing agents I just switch the species being oxidized and reduced since the oxidizing agent is the species that itself is ...

Juliet Carr 1F

I had the same issue. For the first question of #5 sapling kept defaulting to the format issue and accepted the answer with the issue for me. For the second problem, it would only accept the answer if I put the compound in the brackets before the other compounds on the reactant side. Other questions...

Juliet Carr 1F

The stoichiometric coefficients do not affect the oxidation number of individual elements or molecules, however it is important to consider them when calculating and balancing the reaction's overall charge.

Juliet Carr 1F

Yes I learned OILRIG too :) , and it clears up any confusion in case you were unsure of/ mixed up oxidation and reduction.

Juliet Carr 1F

I don't think it matters the side of the anode and cathode as it would be different for two people standing across from each other looking at the same cell diagram. The important thing to remember is that oxidation occurs at the anode, reduction occurs at the cathode, and electrons flow from the ano...

Juliet Carr 1F

The example used in lecture was the oxidation of zinc and reduction of copper. I don't think this example is specific to galvanic cells. Though I think the requirements for the substances used in galvanic cells are that two different metals are used, oxidation occurs at the anode, reduction occurs a...

Juliet Carr 1F

The purpose of the salt bridge is to allow for ion transfer so that the solutions remain neutral.

Juliet Carr 1F

This question is confusing because it doesn't make it clear to refer to the table of enthalpies of formation given in the textbook. Once you have written out the chemical equation of the reaction, you can use the equation: (sum deltaHf[products]) - (sum deltaHf[reactants] ) and the values given in t...

Juliet Carr 1F

I think Dr. Lavelle wrote the equation sheet so that the integral part is shown, then the same equation not involving calculus is written out next to it. I think the integral equations are shown so that we can relate the equation we are using to its initial derivation.

Juliet Carr 1F

On the basis of structure, only NO and N2O would be likely to have residual entropy. Cl2 and CO2 would not have residual entropy because both of these molecules are symmetrical, so orienting the molecules in different ways does not contribute to increased disorder. Both NO and N2O could be ordered i...

Juliet Carr 1F

In order to calculate the change in entropy of the system, you can use the equation (sum of standard molar entropy of products) - (sum of standard molar entropy of reactants) using the values linked where is says "refer to standard entropy values as needed". Next, to find the change in ent...

Juliet Carr 1F

Since the question is asking to calculate the entropy of vaporization at a temperature other than the boiling point and entropy is a state function, you need to calculate the entropy at three different points and add them together. The first calculation is the change in entropy heating the water to ...

Juliet Carr 1F

Hi! For path A, the question says that it is an isothermal, reversible expansion. So we use the equation w = -nRTln(V2/V1). We have the V2 and V1 given in the equation (V2 = 8.96L, V1 = 2.84L), and we also have the T (298K) and the R which is a constant. So, we need to calculate the number of moles...

Juliet Carr 1F

In the textbook problems, we used Cp and Cv as heat capacities for ideal gasses. Cp is the heat capacity of an ideal gas at constant pressure, and Cv at constant volume. According to the constants and equations sheet, Cp for an ideal gas = (5/2)R and Cv = (3/2)R. Section 4C in the textbook better de...

Juliet Carr 1F

Work can be described by the equation w = -(delta(n))RT, where negative work indicates work done by the system onto the surroundings. So in order to find the equation that represents work done onto the surroundings (-w), delta(n) needs to be a positive value. Also it is important that when calculati...

Juliet Carr 1F

I think it'll definitely be helpful to have a strong understanding of calorimeters and for the most part, have the diagram memorized. Hannah's explanation above about the bathtub is a great trick to use! What exactly is the purpose of a calorimeter? The purpose of a calorimeter is to measure the tr...

Juliet Carr 1F

Sapling writes this for the relationship between Cv and Cp: "The change in internal energy deltaU that corresponds to a temperature change deltaT is given by deltaU=n(Cv)(deltaT) where Cv is the constant‑volume molar specific heat of the gas. Cv is related to Cp by (CV = CP-R) = (5R/2 - R) = (3...

Juliet Carr 1F

It also depends on the information given and the specific problem being solved. For example, a requirement for calculating bond enthalpies is that the substances are in gas state. If this is not the case, and the substance is in a different state you also have to consider the enthalpy involved with ...

Juliet Carr 1F

Things to remember with endothermic and exothermic reactions in equilibrium: Endothermic (+): Increasing the temperature/adding heat shifts towards production of products Decreasing the temperature/cooling shifts towards production of reactants Exothermic (-): Increasing temperature shifts towards p...

Juliet Carr 1F

To my understanding, heat depending on the path refers to the heat/energy transferred between the system and surroundings during some heat exchange process. Since this exchange depends on the ways in which the process occurs, heat cannot be a state function.

Juliet Carr 1F

You can also tell if a certain phase change is endothermic or exothermic based on whether the original substance was heated or cooled to complete the phase change. If the substance is heated, such as ice to water (solid to liquid), this is endothermic. If a substance is cooled, such as gas to liquid...

Juliet Carr 1F

I've also read that substances with caffeine can be purified through processes including sublimation.

Juliet Carr 1F

With questions involving Hess' law I would say the most important things to remember are: -if you flip the chemical equation, change the sign of the enthalpy value -if you multiply the whole equation by a coefficient, multiple the enthalpy value by the same coefficient -make sure all the required co...

Juliet Carr 1F

I think using bond enthalpies is just one of the three methods used to calculate the change in enthalpy of a reaction. The three main methods discussed in lecture were using Hess' method, bond enthalpies, or standard reaction enthalpies such as enthalpy of formation. In terms of those three methods,...

Juliet Carr 1F

I think a phase change is just a change in the state of matter.
For example:
-When you heat liquid water, it undergoes a phase change from liquid to gas
-When you cool liquid water, it undergoes a phase change from liquid to solid
-etc.

Juliet Carr 1F

I would also suggest graphing the quadratic equation on your calculator and then finding the zeros that way for the values of x because it is very easy to make mistakes when inputing the quadratic formula on a calculator due to signs, correct parentheses use, square root, etc.

Juliet Carr 1F

I don't think you should disregard the x in this question since you need to solve for the initial concentration in order to find the percent protonation. Also, a way to check if u can disregard the x is if you get an answer 5% or greater because in that case you are unable to approximate.

Juliet Carr 1F

Adding onto what others have already said, you can think of the equilibrium chemical reaction like a scale that wants to be balanced. For example, if the equilibrium is disturbed by adding more product, the reaction will shift to the production of reactants as if it was evening back out the scale. S...

Juliet Carr 1F

When changing the pressure of a system make sure to only focus on the moles of gas to see the effects on the reaction. Do not account for the moles of solid, liquid, or aqueous compounds when examining the effects of altering the pressure/ volume.

Juliet Carr 1F

When Dr. Lavelle was explaining this concept he showed the potential energy diagrams for an endothermic versus exothermic reaction. The endothermic reactions had reactants lower than products with a positive enthalpy (moving left to right on the graph), and the exothermic reaction had reactants high...

Juliet Carr 1F

In general: -pH is the -log[hydrogen ion concentration] -Ka is the acidity constant for the equilibrium reaction of a weak acid in solution [products/reactant, or in many cases (hydronium ion concentration)x(conjugate base concentration)/ (weak acid concentration)] -pKa is just the -log[Ka] -Both pK...

Juliet Carr 1F

so i understand that if the equilibrium constant is less than 10^-4, approximation is okay. i am a bit confused/curious though as to why 10^-4 is the baseline or value that allows for approximation. is that just something memorize or is there reasoning behind it? To add onto what someone else said,...

Juliet Carr 1F

Yes! The same process for finding either the initial, change, or equilibrium concentrations using an ICE table can also be used for finding pressure amounts.

Juliet Carr 1F

You need to use an ICE table. You know the Kc value from Table 5G.2. Plug all the expressions from the ICE table into the Kc expression and set it equal to the value from Table 5G.2. Using the quadratic formula, solve for x. Knowing this x value, you will be able to evaluate the concentrations at e...

Juliet Carr 1F

Yes only a change in temperature will change the value of K. When there is a change in the amount of reactant or product, the chemical reaction will readjust itself to reach equilibrium again, and when it does the ratio of concentrations of products to reactants remains the same. Similarly, the orig...

Juliet Carr 1F

Like others have said, the answer would be B. Right away you are able to eliminate answers C and D. This is because the equilibrium constant (K) is calculated using equilibrium concentrations, instead of initial concentrations. If the concentrations are not those when the reaction has reached equili...

Juliet Carr 1F

To answer the second question, the ideal gas law equation can be manipulated in order to find concentration or pressure to eventually find Kc or Kp.
For example:
PV=nRT, becomes
P=(n/V)RT, where (n/V) is concentration. So,
P=(conc.)RT

Juliet Carr 1F

You would use kelvin as it is the SI unit for temperature.

Juliet Carr 1F

In module 4, we learned that when more of a reactant is added, more product will form until the original product/reactant ratio is attained.

I was wondering if there would be any effect on the chemical reaction if you added more of the reactant that was already in excess?

Thanks :)

Juliet Carr 1F

I think the answer key shows Al(H2O)6^3 and Cu(H2O)6^2 to show how the reaction of the cation that makes up the salt (the conjugate acids of the weak bases) interacts with the solution to affect the pH.

Juliet Carr 1F

Oxalate follows the general formula lone pair - spacer - spacer - lone pair, so it can be a polydentate ligand. In this case, it is a bidentate ligand because the two -1 charged oxygens can make coordinate covalent bonds with two transition metals, or form a chelate bonding to the same transition me...

Juliet Carr 1F

Yes I think it is important to know the following things about the ligands: -en is a neutral, bidentate ligand -dien is a neutral, tridentate ligand -oxalato is a 2- charge, bidentate ligand -edta is a 4- charge, hexadentate ligand In general, anything on the naming coordination compounds worksheet ...

Juliet Carr 1F

Yes I think we are expected to memorize all of the ligands and their ion charges on the naming coordination compounds worksheet on the class website.

Juliet Carr 1F

I think the important takeaways from solving problems with PH and POH are:
[H3O+][OH-] = 1 x 10^-14
pH + pOH = 14
pH = -log[H3O+]
pOH = -log[OH-]

So being able to apply these concepts and doing the textbook problems are probably sufficient enough.

Juliet Carr 1F

The carbonate ion is a monodentate ligand when one of the single bonded oxygens with -1 charge makes a coordinate covalent bond with a transition metal. It is a bidentate ligand when both of the single bonded oxygens with -1 charge make a coordinate covalent bond to the same transition metal in a ri...

Juliet Carr 1F

In addition to drawing the structure out, I think it would be helpful to memorize whether common ligands are mono, di, tri, polydentate etc. Also, it would be beneficial to remember the formation lone pair - spacer - spacer - lone pair for polydentate ligands. Another rule when determining the numbe...

Juliet Carr 1F

To add onto what others have said, in a UA session they said you can also typically tell if a ligand is polydentate if it follows the form: lone pair - spacer - spacer - lone pair.

Juliet Carr 1F

Yes, your thought process is correct :) This same thought process can be also be applied to any element in groups 1-8, just not the transition metals. For example, you can assume a halogen has a -1 oxidation number, an alkali earth metal +2, and alkali metal +1, etc. Then, you multiply these oxidati...

Juliet Carr 1F

Some differences between sigma and pi bonds include their formation. Sigma bonds form when two orbitals each with one electron overlap end-to-end. This overlap can occur between two s orbitals, s and p, p and p, etc. The overlap of orbitals in a sigma bond creates electron density with cylindrical s...

Juliet Carr 1F

Like others have said, you should first count the regions of electron density around the central atom in question. Single bonds, double bonds, and triple bonds count as one region of electron density. Lone pairs also count as one region of electron density. Then, that number corresponds to the hybri...

Juliet Carr 1F

A molecule forms a bent shape when it either has three total regions of electron density with 2 regions bonded and one lone pair, or four total regions of electron density with 2 regions bonded and 2 lone pairs. The bent shape of the molecule is due to the greater repulsion strength of the lone pair...

Juliet Carr 1F

When they ask about relative positions, I think they are talking about the positions of atoms in relation to one another in a 3D space, using the lewis structure to help create the model. Lewis structures are 2D, but the actual model of the molecule is in 3D. For instance, the lewis structure for C...

Juliet Carr 1F

Yes you are correct! In this example, the acetate ion is formed when the H is lost from the OH. This makes the single bonded oxygen a -1 charge, and now electron rich. Two acetate ions are able to bond to each of the N in ethylene, which are both also electron rich with a lone pair. So, the final st...

Juliet Carr 1F

Based on how it was described in the lecture, I think coordination number has to do with the number of bonds instead of general regions of electron density, and does not include lone pairs.

Juliet Carr 1F

Electron rich species are those that have valence lone pairs that can be donated. Some examples of electron rich species are negatively charged ions and lewis bases.

Juliet Carr 1F

I think the answer is referring to the molecule as a whole and the net vectors. For example in COF2 the vectors point towards the oxygen and two fluorine atoms because they are more electronegative compared to the carbon. However, since the electronegativity difference between carbon and fluorine is...

Juliet Carr 1F

Hi, going off of this, I understand how to determine the polarity of a molecule but I am a little confused how to determine if an individual bond is polar or non-polar. Is it simply a large difference in electronegativity between the two atoms? My understanding of individual bonds being polar is th...

Juliet Carr 1F

Oh I understand. Thank you for clarifying!

Juliet Carr 1F

I think it is because the s orbital is closer to the nucleus than the p orbital. So the electrons in the s orbital experience a greater effective nuclear charge than the electrons in the p orbital as the p orbital is further away from the nucleus and the electrons in s orbital shield some of that ch...

Juliet Carr 1F

I had the same question about this problem. I'm thinking maybe Mn includes the valence electrons in the d block because it falls in the d block of the periodic table. Then for Sb they don't include the valence electrons in the 4d subshell because Sb doesn't exist in the d block on the periodic table...

Juliet Carr 1F

Textbook problem 1E.25 b) says to give the notation for valence shell configuration (including outermost d electrons) of Group 5 transition metals. The answer given was (n-1)d^5 ns^2. It appears that (n-1)d^5 ns^2 gives the valence shell configuration for group 7 on the periodic table which includes...

Juliet Carr 1F

It is really important to consider VSEPR when determining polarity because VSEPR will show symmetry in the shape of the molecule. So, if there are unequal pulls on the central atom in different directions by the dipole moments surrounding it, then the dipole moments cannot cancel and the molecule is...

Juliet Carr 1F

The partial negative exists on the more electronegative atom, and in this example that is oxygen. So the oxygen exists as partially negative making the S exists as partially positive. This creates two dipole moments, and the reason why these moments do not cancel out is because of the lone pair elec...

Juliet Carr 1F

I think the important take aways from this equation is that the interaction potential energy (Ep) is inversely proportional to the radius. As the radius gets larger, the Ep gets smaller and vise versa. So, the molecules have to be close to one another in order to cause a strong interaction between t...

Juliet Carr 1F

Coordinate covalent bonds are also common between lewis acids and bases. Since lewis acids are electron pair acceptors and lewis bases are electron pair donors, the lewis base will donate both of its electrons to form a coordinate covalent bond with the lewis acid.

Juliet Carr 1F

Ya it might seem like OH is a radical because if you add up the valence electrons to make the lewis structure it is 7e- (6e- from O and 1e- from H), which would leave one electron unpaired. However, OH exists as OH-, so a total of 8e- (6e- from O + 1e- from H + 1e-), making OH- not a radical.

Juliet Carr 1F

Formal charge definition states that it is the charge of an atom in a molecule, so it must be bonded to other atoms. Also if the atom was not bonded then there would be an important part of the formula missing, and it could not be calculated.

Juliet Carr 1F

For the exceptions to the octet rule it is more important to maintain a formal charge closer to zero. However when you are trying to draw the correct lewis structure it is important to make sure that all the elements follow the octet rule first (for example that's why we sometimes have to make singl...

Juliet Carr 1F

If you follow the periodic table you can see that from left to right the 4s subshell comes before the 3d subshell. So when you are adding electrons to elements after Ar the 4s is filled first, but once Sc is reached and electron are added to the 3d subshell it has lower energy than 4s and it written...

Juliet Carr 1F

How I would approach this problem: 1)Since it is asking for a metal then it would narrow my answer mostly to elements in the s or d block, and some of the p block. 2)Also since it says its a 3+ ion that means 3 electrons were lost from the metal in question. 3)Then I would look at the electron confi...

Juliet Carr 1F

The nucleus interacts with more electrons in double bonds than in single bonds, so it is able to pull the electrons closer resulting in shorter bonds.

Juliet Carr 1F

I have not watched the lecture yet so I'm not completely sure what he's referring to but in general there is a formula 2n^2, where n is the principal quantum level/shell, and this formula gives the maximum amount of electrons that can occupy each shell.

Juliet Carr 1F

I think m(l) itself is a quantum number, so I don't know if you could have three different quantum numbers for m(l), but instead you could have three different values for the quantum number m(l). I'm pretty sure if the last electron falls in in p(x) m(l) is -1, 0 for p(y), and 1 for p(z). So, I thin...

Juliet Carr 1F

In simple terms, I just think of electron affinity as the opposite of ionization energy. Ionization energy is a measure of the energy required to remove an electron from an atom. Instead, electron affinity is a measure of the energy required to put an electron in the outer shell of an atom.

Juliet Carr 1F

Similar to what others have explained, as you move down a group the atomic and ionic radii increase. This is because more energy shells are being added to the atoms moving down the group to account for the increase in electrons. As additional energy shells are added, they are further away from the n...

Juliet Carr 1F

The elements on the periodic table with 'low' first ionization energy values (compared to the other elements) are metals, and metals conduct electricity well. So, that could be used to explain how low ionization energy ensures that atom conducts electricity. I'm sure there are other factors that can...

Juliet Carr 1F

To the above question about how to know if the sparks were caused by the photoelectric effect or not (I don't know how to reply to a reply lol): There should be second part to the question that gives the frequency that the microwave radiates. Then, convert that number to wavelength, and if the wavel...

Juliet Carr 1F

Similar to what other students have explained, the photoelectric effect can only work on metals because of the nature of metallic bonds. Metallic bonds create a 'sea of electrons', which can be easily emitted from the metal when the energy of the photons in the light shone is greater than or equal t...

Juliet Carr 1F

In this case you cannot use E = hv to solve for the e-s kinetic energy because this equation is used to solve for the energy of one photon. The kinetic energy of the electron is the energy of the photon minus the threshold energy. The kinetic energy can be calculated using the equation Ek = 1/2(m)(v...

Juliet Carr 1F

I don't think we need to know black body radiation for the exam because Lavelle has mentioned multiple times that we won't be going into detail about it, however, I think it would be good to have a general understand of a black body being an object that absorbs and emits all frequencies of radiation...

Juliet Carr 1F

My TA said you can use the front an back of the constants and periodic table sheets and as much scratch paper as you need as long as you show the front and back of every paper before the exam begins.

Juliet Carr 1F

In one of the workshop sessions a UA mentioned that in a classical wave model increasing the intensity means increasing the amplitude, and increasing the amplitude of a wave usually means higher energy. Although, I'm not sure if this relationship can be used to describe the wave model of light becau...

Juliet Carr 1F

The equation is -hR/n^2 with the negative sign meaning that bound electrons have lower energy than free electrons. The question was asking to calculate frequency of light emitted by an H-atom when an electron makes a transition from the fourth to the second principal quantum level. Since the electro...

Juliet Carr 1F

Similar to another response, I interpreted extent of change as relating to the amplitude and size/width of the wave. So, if frequency decreases, then wavelength has increased. Now within a certain region, the wave extends bigger than it did when the frequency was increased in this region. So, within...

Juliet Carr 1F

Which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning. (a) The speed of the radiation decreases. (b) The wavelength of the radiation decreases. (c) The extent of the change in the electrical field at a given point decreases. (d) The energy o...

Juliet Carr 1F

I think we are expected to know the order of electromagnetic radiation for tests and exams because there was a question about it in one of the topic 1A exercises that Lavelle assigned (not graded), and I remember the syllabus explaining how test/exam questions are directly related to homework proble...

Juliet Carr 1F

Thank you everyone! Now I understand

Search found 107 matches