CHEMISTRY COMMUNITY

Madilyn Schindler 3E

Carolina 3E wrote:If you use -Ea/R then it is (1/T2 - 1/T1)
If you use Ea/R then it is (1/T1 - 1/T2)

Ohh that makes so much sense. Thank you so much!

Madilyn Schindler 3E

The rate constant of the reaction between CO2 and OH- in aqueous solution to give the HCO3- ion is 1.5×10^10 L⋅mol−1⋅s− at 25˚C. Determine the rate constant at human body temperature (37˚C), given that the activation energy for the reaction is 38 kJ⋅mol^-1. I'm keep getting the same wrong answer and...

Madilyn Schindler 3E

A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential or passivity at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis? Would someone mind e...

Madilyn Schindler 3E

6N.23 (a) Suggest two metals that could be used for the cathodic protection of a titanium pipeline. (b) What factors other than relative positions in the electrochemical series need to be considered in practice? (c) Often copper piping is connected to iron pipes in household plumbing systems. What i...

Madilyn Schindler 3E

I just did this problem and I have the same question. I think the answer key might be wrong and that it should be Au+(aq) on the anode side, but I'm not entirely sure.

Madilyn Schindler 3E

When looking at a cell diagram, how do you tell which substances are reactants and which are products? Also, how do you know whether a substance that is included in the diagram is actually included in the half reactions? For example, question 6L.3 (d) asks for the half reactions of: Pt(s) | O2(g) | ...

Madilyn Schindler 3E

If a problem tells you that a reaction takes place in basic solution, can you add H+ to balance the equation out, and if a reaction takes place in acidic solution, can you add OH- to balance it out? I originally thought you couldn't add H+ to a reaction happening in basic solution and vice versa. If...

Madilyn Schindler 3E

I think the best thing to do is review the textbook problems. It's almost impossible to redo every single one of them, so I recommend just doing one problem of each type from the topics we've already been tested on (unless there's a specific concept that you're struggling with) and all of the ones f...

Madilyn Schindler 3E

ΔE is 0 at equilibrium because the reactant quotient Q isn't changing (lnQ is 0). Hope that helps!

Madilyn Schindler 3E

To add on, the rate of the reaction A + B + C -> P is equal to k[A]^N [B]^M [C]^L. N, M, and L are the orders of the reactants, so you can see how increasing/decreasing them would affect the reaction rate. Hope that helps!

Madilyn Schindler 3E

Adding a catalyst will cause the activation energies of both the forward and reverse reactions to decrease, and it will cause the reaction rates of both the forward and reverse reactions to increase. There's a sapling problem that tests this exact question too! Hope that helps!

Madilyn Schindler 3E

The anode is where oxidation happens and the cathode is where reduction happens. The electrons will flow from the anode to the cathode (my trick for remembering this is that A for anode comes before C for cathode in the alphabet if that helps haha).

Madilyn Schindler 3E

I think we're safe assuming that we don't have to memorize any specific values and that any values we need to solve a problem will be given.

Madilyn Schindler 3E

The reduced molecule (one that gains electrons) is the oxidizing agent and the oxidized molecule (one that loses electrons) is the reducing agent.

Madilyn Schindler 3E

I'm happy with my score but I still know I could've done better. Honestly, the conceptual ones threw me off a little bit because I was expecting mostly calculations. The final is going to be really stressful knowing exactly how many points you can miss for an A haha.

Madilyn Schindler 3E

I randomly crave the type of things that are good straight out of the oven, like warm cookies or brownies and things like that. Also beignets are really good but hard to find (and kinda hard to make lol).

Madilyn Schindler 3E

You basically just add H2O to whichever side of the reaction has less oxygen in order to balance it out. This is also affected by whether the reaction is in acidic or basic solution (when you are adding either H or OH).

Madilyn Schindler 3E

Hi! First of all, I don't understand why there are numbers in the answer key when the problem doesn't ask for any value answers. And second, I don't understand the steps to figuring this problem out. (Also, are we supposed to know whether we're dealing with decomposition or formation?) If someone co...

Madilyn Schindler 3E

Hi! Would someone mind writing a step by step explanation for part a of this problem? I'm a little confused as to why it is considered stable. Thanks! Determine which of the following compounds are stable with respect to decomposition into their elements under standard conditions at 25°C (see Append...

Madilyn Schindler 3E

It's probably just for practice! If a problem like that was on the midterm, I doubt the answer would be given the same way that answer could be found in the Appendix. I remember another textbook problem I did where I had to solve for a value that was already given on the constants and formulas sheet...

Madilyn Schindler 3E

Hi! I was able to do the first part of the problem, but I'm confused on part b. I tried using the ideal gas equation (U = 3/2 nRT) but didn't get the right answer, so I'm assuming I'm not supposed to use that equation. Any help would be appreciated! An experimental automobile burns hydrogen for fuel...

Madilyn Schindler 3E

Hi! Would someone mind explaining part a step by step (I'm pretty sure I'd be able to figure out part b if I understood part a? 4A.7 (a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its temperature from 20.0°C to the boiling point o...

Madilyn Schindler 3E

I would focus on just memorizing it because I can't see how there would be a question requiring you to know the derivation. However, the derivation could be helpful when you're trying to memorize it. So I think it could be helpful, but it's not absolutely necessary. Hope that helps!

Madilyn Schindler 3E

An open system allows anything (matter or energy) to pass in and out, a closed system only allows energy to pass in and out, and an isolated system doesn't allow anything to pass in or out. I think it could matter but it varies from problem to problem. Any question that requires you to know what can...

Madilyn Schindler 3E

The only things I can think of that K could stand for is potassium, Kelvin, or the equilibrium constant haha. However, a lowercase k could stand for the Boltzmann constant. Hope that helps!

Madilyn Schindler 3E

No, I don't think there's a way to tell whether a reaction is favorable or not based on ΔU. A reaction is thermodynamically favorable if ΔG is negative or if ΔH is negative and ΔS is positive. Hope that helps!

Madilyn Schindler 3E

I understand how to do this problem: The molar heat capacity for carbon monoxide at constant volume is Cv, m=20.17 J/(K·mol). A 14.00-L fixed-volume flask contains CO(g) at a pressure of 8.00 kPa and a temperature of 25.0°C. Assuming that carbon monoxide acts as an ideal gas and that its heat capaci...

Madilyn Schindler 3E

Only gases can change volume. Solids and liquids can't change volume so their Cp and Cv are the same, leaving them with only one heat capacity as opposed to two. Hope that helps!

Madilyn Schindler 3E

Personally, I like to do the textbook problems during the week leading up to the day of the exam and then review all of them on the day of the exam to make sure I know how to do all of them. I also read the textbook and find helpful YouTube videos on topics that I'm not 100% comfortable with. Anothe...

Madilyn Schindler 3E

Hopefully I'm not misunderstanding your question, but I substituted both T finals for x and then just solved for x algebraically by distributing. I think it might be easier for you to set the problem as one equation instead of multiple. This is how I did it: heat to melt ice + heat to warm melted ic...

Madilyn Schindler 3E

Hey! I'm struggling a little bit to fully understand the topics that Dr. Lavelle covered in last week's lectures (on thermodynamics) and all of the new equations. I was wondering if anyone has any recommendations for outside resources that might help. Thanks!

Madilyn Schindler 3E

Hi! I'm having a little bit of trouble with this problem: An ice cube with a mass of 47.2 g at 0.0 C is added to a glass containing 407 g of water at 45.0 C. Determine the final temperature of the system at equilibrium. The specific heat capacity of water, Cs, is 4.184 J/g⋅C, and the standard enthal...

Madilyn Schindler 3E

When pressure increases, the equilibrium shifts towards the side of the reaction that has less moles of gas. When pressure decreases, the equilibrium shifts towards the side that has more moles of gas. However, increasing pressure by adding inert gas doesn't affect the equilibrium at all. Hope that ...

Madilyn Schindler 3E

Hey! Usually it's just easier to use whatever gas constant corresponds to the units you are given in the problem, or whichever units are given in the answer choices. Otherwise, you can always convert units if you have to. Just make sure you are being consistent with your units throughout every probl...

Madilyn Schindler 3E

The K value increases for an endothermic reaction when the temperature increases because an endothermic reaction requires heat in order to produce its products. Therefore, when you increase the temperature, you are increasing the amount of heat that the reaction can use, meaning that the reaction is...

Madilyn Schindler 3E

Hey! I'm working part-time as well and I honestly feel like I easily fall behind in some of my classes. I find that the best way for me to stay on top of things is to multitask. When I'm getting ready in the morning, I'll have a lecture playing with my notes out, and I'll do the same thing when I'm ...

Madilyn Schindler 3E

Your question was already answered, but if you have any similar questions I recommend Khan Academy! They have lots of videos on enthalpy and other topics that we are covering.

Madilyn Schindler 3E

From past experience, textbook problems seem to be the most similar to the types of test questions that are usually on the exams. Also don't forget to study the conceptual parts!

Madilyn Schindler 3E

Ka and pH have an inverse relationship. If Ka decreases then pH increases, and if Ka increases the pH decreases.

Madilyn Schindler 3E

Could someone clarify how we check our “x” after using the 5 percent rule? Also, is the 5 percent rule a part of Le chatelier’s principle? Thanks The 5% rule basically just means that if the percent ionization if below 5% then x can be ignored, but if it's above 5% then you have to use the quadrati...

Madilyn Schindler 3E

We can assume the x value is insignificant if the equilibrium constant is less than 10^-3 (safer if less than 10^-4 as Dr. Lavelle mentioned in lecture) and if the ionization percentage is below 5%.

Madilyn Schindler 3E

The difference is that a strong acid 100% dissociates into ions, while a weak acid does not. I'm pretty sure it doesn't matter whether it is weak or strong in those types of calculations.

Madilyn Schindler 3E

Your calculations are correct! It's totally okay to get a negative pH value, as not all pH values are positive (Dr. Lavelle mentioned this in a lecture). Hope that helps! (I see that a lot of people have commented otherwise, but I assure you, there are pH values that are below 1 and above 14) I actu...

Madilyn Schindler 3E

Something to keep in mind here is that the pH decreasing doesn't equate to water actually becoming more acidic when temperature increases. The reason the pH decreases is because the neutral value for pH changes as temperature changes. For example, at 100 degrees C, the neutral pH is 6.14 instead of ...

Madilyn Schindler 3E

When the temperature increases, the system is able to absorb more heat that can be used for the endothermic reaction (whether it be the forward reaction or the reverse reaction). This causes the endothermic reaction to be favored over the exothermic reaction, causing K to shift depending on whether ...

Madilyn Schindler 3E

I'm pretty sure there can only be a negative on the product side and a positive on the reactant side when the reaction is leaning left, and the reverse reaction is favored over the forward reaction. In other words, the substances on the right side can be used to make substances on the left side, eve...

Madilyn Schindler 3E

For part (a), you wanna find the change in A, B, and C. Because A decreases, it is a reactant, and because B and C increase, they are products. A decreases by 10, B increases by 5, and C increases by 10. Thinking back to our ICE box, this gives the ratios that exist in the chemical equation. Therefo...

Madilyn Schindler 3E

Yes, you're correct. Adding inert gases doesn't affect the reaction because the partial pressures of the reactants and products remain the same.

Madilyn Schindler 3E

A change in concentration causes the forward and reverse reactions to occur at different rates, causing the system to be out of equilibrium. However, the system will eventually return to equilibrium and have the same K value. The K value only changes when there is a change in temperature.

Madilyn Schindler 3E

Yes, both Q and K are calculated using the same method. The only difference is that K is the ratio of concentrations when the system is at equilibrium. Q is the ratio of concentrations when the system isn't at equilibrium.

Madilyn Schindler 3E

Yes, you only include the gases in your calculations anyways, so it doesn't matter whether the numbers are given in terms of concentration or in terms of partial pressure.

Madilyn Schindler 3E

From what I've heard, the last day to post to get your 5 points for a week is on Sunday. I think you can make up missing points by posting a really thorough post in the following weeks. Hope that makes sense!

Madilyn Schindler 3E

Could someone please explain this? Identify the salt that is produced from the acid–base neutralization reaction between (a) potassium hydroxide and acetic acid, CH3COOH;CH3 COOH; (b) ammonia and phosphoric acid; (c) calcium hydroxide and bromous acid; (d) sodium hydroxide and hydrosulfuric acid, H2...

Madilyn Schindler 3E

Thank you so much!

Madilyn Schindler 3E

How do we determine whether a bond is polar or not when we aren't given the actual electronegativity values (and therefore can't find the difference in electronegativity to tell whether it's polar or not)?

Madilyn Schindler 3E

I'm pretty sure we only need to understand acid rain from a chemistry perspective rather than a biological one, so I wouldn't worry about learning its biological application and just focus on how it is formed, etc.

Madilyn Schindler 3E

First, start out with Heisenberg's Uncertainty Principle. Since the uncertainty of speed of the electron is given in the problem (165 x 10^3 m/s) and you already know the mass of an electron, you can multiple those two values together to find the uncertainty in momentum (about 1.5 x 10^-25 kgm/s). S...

Madilyn Schindler 3E

I would definitely memorize all of the ligands on that sheet, especially the ones that are more commonly seen. I don't know of any memorization tricks for this, but I would recommend looking at them a lot and doing practice problems with them over the next few days.

Madilyn Schindler 3E

A Bronsted acid is a proton donor and a Bronsted base is a proton acceptor. In relation to Lewis acids, all Bronsted acids are Lewis acids, but not all Lewis acids are Bronsted acids. The only way to determine whether a substance is a Bronsted acid or base is to observe it in a reaction. Hope that h...

Madilyn Schindler 3E

A neutral salt is formed when a strong acid and a strong base react (this reaction is reversible so the same thing applies to the products of the reaction between salt and water). For example, NaCl is neutral because the reactants to form it are a strong acid (HCl) and a strong base (NaOH). On the o...

Madilyn Schindler 3E

So just to clarify, the alphabetical order is completely based off of the ligand name and not the greek prefix attached right? Yes, I believe the alphabetical order is based on the ligand name. The greek prefix can be attached after the ligands have already been put in alphabetical order when namin...

Madilyn Schindler 3E

Electron geometry basically describes the arrangement of electron groups while molecular geometry describes the arrangement of atoms in relation to the central atom. Hope that helps!

Madilyn Schindler 3E

An angle is slightly less due to the presence of lone pairs, which have strong repulsion against other atoms and lone pairs. For example, a tetrahedral shape with 4 bonded atoms and 0 lone pairs will have 109 degree angles. On the other hand, a trigonal pyramidal shape with 3 bonded atoms and 1 lone...

Madilyn Schindler 3E

Yes, the bond angle would be 180 degrees. I think if a molecule has a linear shape, its bond angle is always going to be 180 degrees.

Madilyn Schindler 3E

What is the easiest way to identify anions from a chemical formula when naming a coordination compound?

Madilyn Schindler 3E

The d-orbital is more stable when it has either 5 electrons or 10 electrons (either half filled or filled entirely). Therefore, whenever the d-orbital seems like it should have 4 electrons or 9 electrons, an electron is taken from the s-orbital to make that number either 5 electrons or 10 electrons ...

Madilyn Schindler 3E

P3- is the largest ion followed by S2- and Cl-. This is because P has the least number of protons and Cl has the greatest number of protons. They all have the same number of electrons, but as the number of protons decreases, the strength of attraction between the positively charged protons and the n...

Madilyn Schindler 3E

It's basically a state of matter that's between a liquid and a solid. It has the molecular characteristics of solid crystal, but it can change shape like a liquid. Hope that makes sense!

Madilyn Schindler 3E

I'm not entirely sure, but yes I do believe that all expanded octets contain hybrid orbitals because elements need access to the d orbital in order to have more than an octet.

Madilyn Schindler 3E

Yes, every bond and lone pair are considered regions of electron density. However, a double bond is only one region of electron density and a triple bond is only one region of electron density. Hope that makes sense!

Madilyn Schindler 3E

How do you determine the shape of CH2Cl2 for #7 on the Sapling homework? Originally I thought that the dipole moments would cancel out because I thought it was symmetrical, making it nonpolar. However, they don't cancel out due to the shape, and I was wondering if anyone could explain how to figure ...

Madilyn Schindler 3E

Since BrF3 has 2 lone pairs and 3 atoms bonded to it, the shape of the molecule is somewhat t-shaped. Therefore, the dipole moments don't cancel out with one another and the molecule is polar. Hope that helps!

Madilyn Schindler 3E

Just to make sure I'm not forgetting anything when I study, how many different molecular shapes are there that we need to know and what are they?

Madilyn Schindler 3E

If I'm understanding your question correctly, there are 14 because the first elements of the lanthanide and actinide series are part of the d-block. So La and Ac would actually be 5d1 and 6d1, leaving the other 14 to be parts of the f subshell. Hope that helps!

Madilyn Schindler 3E

The valence electrons are just the number of electrons that are in the outmost shell. Since 3d is the only orbital in the outmost shell, 3, and there are 3 electrons in it, the number of valence electrons is 3. Hope that helps!

Madilyn Schindler 3E

The ionic character simply depends on how evenly the electrons are shared between the atoms of a molecule. There may be a correlation between the size of the molecule and ionic character, but I don't think it would be reliable and I don't think it has a direct affect.

Madilyn Schindler 3E

Two of the oxygen atoms have a negative charge, three lone pairs, and a single bond, while the other oxygen atom is neutral with only two lone pairs and a double bond. Hope that helps!

Madilyn Schindler 3E

I believe lone pairs take up more space than a bonded pair of electrons because a bonded pair has two different nuclei attracting it, making the bond smaller. On the other hand, lone pairs are only being attracted to one nucleus, therefore attracted less strongly, allowing the density of the electro...

Madilyn Schindler 3E

As the strength of the intermolecular forces decrease, vapor pressure increases. This is because when a liquid has weak intermolecular forces, it can evaporate more easily and therefore it has a higher vapor pressure. Hope that helps!

Madilyn Schindler 3E

For the specific question you gave: Co3+ is a lewis acid because the central atom doesn't have a complete octet. AlCl3 is a lewis acid because the central atom doesn't have a complete octet. CO2 is a lewis acid because the central atom doesn't have a complete octet. O2- is a lewis base because it ha...

Madilyn Schindler 3E

I would definitely check out Khan Academy! They have videos on pretty much everything we're learning and practice problems as well, including conceptual ones. It's a super good resource. Hope you find it useful!

Madilyn Schindler 3E

Hey! A Lewis structure contributes more to the structure of an ion if the formal charges are minimized. Therefore, the structure with the least formal charges would contribute the most. Hope that helps!

Madilyn Schindler 3E

The number of valence electrons for elements in the d block are much less straightforward than those in the other blocks. The difference is that transition elements have an incomplete inner sub shell, which allows for valence electrons that aren't in the outer shell. This enables transition metals t...

Madilyn Schindler 3E

A Lewis base is basically just any substance that has the ability to donate a pair of electrons. So yes, I believe that all anions are considered Lewis bases. However, this doesn't mean that all Lewis bases are anions. Lewis bases can be either negatively charged or neutral. Hope that helps!

Madilyn Schindler 3E

I would look at it this way. There are 3 general exceptions to having an octet: 1. When the molecule has an odd number of valence electrons. 2. When the molecule has a central atom with more valence electrons than needed to get to 8. 3. When the molecule has a central atom with too few valence elect...

Madilyn Schindler 3E

Unfortunately, I'm pretty sure there's only one way to calculate the formal charge (number of valence electrons of neutral atom - number of electrons in lone pairs - number of covalent bonds). Just keep practicing finding the formal charge and eventually you'll be able to do those problems faster.

Madilyn Schindler 3E

There are four orbits in the n=2 shell. I'll list them: n=2, l=0, m=0 n=2, l=1, m=-1 n=2, l=1, m=0 n=2, l=1, m=1 As you can see, there are four different combinations. The n=2 shell includes both s and p orbitals. There is only one s orbital and there are 3 p orbitals. Therefore, there are four tota...

Madilyn Schindler 3E

1B.5 The γ-ray photons emitted by the nuclear decay of a technetium-99 atom used in radiopharmaceuticals have an energy of 140.511 keV. Calculate the wavelength of these γ-rays. I initially tried solving this problem by finding the velocity using Ek=1/2mv^2, and then plugging it into the equation la...

Madilyn Schindler 3E

An atom with a higher electron affinity can more easily accept electrons, and when an atom accepts an electron, energy is released.

Madilyn Schindler 3E

I don't think there is a literal cutoff for rounding. In most cases, it should be fairly obvious whether or not the number should be rounded up or not, as the numbers are usually less than 0.2 away from a whole number. Just go with your gut and you'll be fine.

Madilyn Schindler 3E

This problem is essentially saying that 1 meter was equivalent to 1,650,763.73 wavelengths, meaning that each wavelength was (1 meter)/(1,650,763.73 wavelengths). That should help you start off the problem. Hope that helps!

Madilyn Schindler 3E

In the lecture, Dr. Lavelle used the Heisenberg Indeterminacy Equation to show that an electron could not be in the nucleus of an atom and that it must be on the outside. The explanation for this was that the uncertainty in the electron's velocity was greater than the speed of light. This may just b...

Madilyn Schindler 3E

Because you know the wavelength, you are able to find the frequency of the light emitted using the equation c=lambda*v. Knowing the frequency, you can find the energy using the equation E=hv. Then, you will need to use the empirical equation for hydrogen which is En = -hR/n^2 for n = 1,2,..infinity....

Madilyn Schindler 3E

The maximum number of electrons would just be the total energy divided by the work function. To explain further, the work function is the amount of energy needed to remove one electron. Therefore, knowing the total energy, you can figure out how many electrons could be ejected. Hope that helps!

Madilyn Schindler 3E

I'm not sure if I'm explaining this correctly, but I don't think you can use the equation c=lambda*v for this scenario, c being the speed of light, because we aren't calculating the energy of a photon. However, you may be able to use the equation c=lambda*v if you substitute the speed of light (c) w...

Madilyn Schindler 3E

One line (on both the atomic absorption spectrum and the atomic emission spectrum) represents a wavelength of light that can be either absorbed or emitted by the specific element or molecule when an electron's energy level changes. The difference between the atomic absorption spectrum and the atomic...

Madilyn Schindler 3E

In summary, Max Planck basically realized that energy was quantized instead of continuous when it came to photons and wanted to figure out the exact number that related the amount of energy that a photon carries with the frequency of the wave that it is part of. Scientists have used varying experime...

Madilyn Schindler 3E

I'm pretty sure we don't need to memorize any historical figures, but I'm not 100% sure, so it would probably be best if you ask your TA.

Madilyn Schindler 3E

Kilograms is probably used because that is the SI unit of mass. The velocity of the electron is important because it is needed to find the momentum of the electron, and therefore needed to find the wavelength of the electron. Hope that helps!

Madilyn Schindler 3E

You can find the wavelength of an electron using this equation: wavelength=Planck's constant/momentum. To find momentum, multiple the mass of the electron with the velocity of the electron.

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