CHEMISTRY COMMUNITY

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Hi quick question, is 1 kPa equal to one Joule?

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Hi, Identify the oxidizing and reducing agents in the skeletal (unbalanced) reaction. Then, balance the reaction, including the phase (solid, liquid, etc.) of each species. The reaction takes place in basic aqueous solution. Pb(OH)2−4(aq)+ClO−(aq)⟶PbO2(s)+Cl−(aq) I really don't understand how to wor...

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One of the most recognizable corrosion reactions is the rusting of iron. Rust is caused by iron reacting with oxygen gas in the presence of water to create an oxide layer. Iron can form several different oxides, each having its own unique color. Red rust is caused by the formation of iron(III) oxide...

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Kaethe Zappacosta 2L wrote:You are just stating which species are in the anode and which species are in the cathode. It is a basic shorthand notation, so you do not have to put coefficients, as the coefficients are found FROM writing out and balancing the shorthand notation!

Thank you!

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In the solution to this problem, they do not flip the sign of the standard reduction potential of the Cr half reaction even though I can see from the table that the reaction is flipped. Why is this? I thought we were supposed to change the sign to make it +0.91 as opposed to -0.91 because the reacti...

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Hi, the reaction that is written for Ag in the standard reduction potential table is opposite/flipped in comparison to the reaction that is given in the Achieve problem. Does this mean that I should flip the sign of the E knot value?

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Arrange these species by their ability to act as an oxidizing agent: Mg2+, Cr2+, I2, F2. It says that I arranged the species from highest to lowest oxidation potential. However, I thought that the best oxidizing agent would be the species most likely to be reduced (gain electrons). I assumed this w...

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Arrange these species by their ability to act as an oxidizing agent: Mg2+, Cr2+, I2, F2. It says that I arranged the species from highest to lowest oxidation potential. However, I thought that the best oxidizing agent would be the species most likely to be reduced (gain electrons). I assumed this wo...

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For your second question, the flow of anions and cations is looking at the salt bridge. When electrons are leaving the anode (X), there will eventually be a positive charge buildup, preventing further electron transfer as the electrons would be pulled towards the positive charge buildup. The same g...

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Okay thank you! How do we know Mn has a charge of +7? Is this just something I should memorize? I know the trends for the oxidation states of the alkali metals and the halogens, but transition metals are trickier.

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Hi, why don't we include coefficients in the cell diagram? Thanks.

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Hi, I have a few questions about this problem: 1) What does "X is more reactive" mean? 2) Why would anions (negatively charged molecules) flow into the X electrode if it is in the process of having electrons flow away from it? And same goes for the Y electrode, why would cations (positivel...

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I'm having trouble understanding why both species aren't considered reducing agents because both MnO4- and S2- go from having a negative charge to a neutral charge. Can someone explain why MnO4- is considered an oxidizing agent?

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The solution says that the element that is oxidized is oxygen. However, Cl's oxidation state is +7, when I originally thought that it's oxidation state was -1. So I thought Cl was oxidized (losing more electrons and becoming positively charged). Can someone help me out?

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Calculate the standard entropy of vaporization of water at 85°C, given that its standard entropy of vaporization at 100°C is 109 kJ/mol and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 kJ/mol and 33.6 kJ/mol, respectively, in this range. I don't really unde...

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Assuming that the heat capacity of an ideal gas is independent of temperature, calculate the entropy change associated with raising the temperature of 1.00 mol of ideal gas atoms reversibly from 37.6°C to 157.9°C at (a) constant pressure and (b) constant volume. How do I find the heat capacity of th...

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A human body generates heat at the rate of about 100W. (a) At what rate does your body heat generate entropy in your surroundings, taken to be at 20 degrees C? (b) How much entropy do you generate each day? (c) Would the entropy generated be greater or less if you were in a room kept at 30 degrees C...

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Hello, the answer key uses Hess's Law and breaks each part of the reaction into another chemical reaction. However, I thought it was correct to subtract the sum of the reactant enthalpies from the sum of the product enthalpies to obtain a value of +312 (the textbook answer says -312). What does ever...

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The answer sheet gives a thorough explanation, but I'm having a hard time following it, especially when it comes to incorporating density. Can someone break this answer down a little bit more for me please?

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A piece of copper of mass 20.0 g at 100°C is placed in a vessel of negligible heat capacity but containing 50.7 g of water at 22°C. Calculate the final temperature of the water. Assume that no energy is lost to the surroundings. The answer key sets the heat lost by copper = - heat gained by water. W...

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Hi, can someone please explain to me why we disregard the molarity and liters given in this problem? So much extra information is given and I'm trying to understand why we don't use most of it.

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Hi! The solution of this problem says that the constant‑volume molar specific heat of the gas is related to C(pressure) by CV=CP−R. Just to cover all my bases, are there any other relationships of specific heat that I should know for our exams?

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Hi! For the second part of the question, I need to convert L x atm to J. How can I use the equation sheet we're given to do this?

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This Is Us is an amazing show on Hulu about a very unique family. It's incredibly emotionally charged and will most likely make you cry every episode so do not watch if you want an easy-going show.

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Hi :) I've found that mindless activities help a lot. I've found that painting by numbers is a great way to decompress. Also making picture collages with cutouts from magazines. Creative activities that take no brain power are the best way I re-gather myself and relax!

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Hi, in a workshop we talked about reversible and irreversible expansion of a system. What is the difference and how do I approach each type of scenario?

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I'm confused by the idea that you can add heat but it won't change the temperature. How is this possible? It seems like we talk about heat and temperature directly affecting each other instantaneously.

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Hello, can someone please explain to me the concept of internal energy being a state property? I'm confused about what a state property is.

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Hi, is there any way to cross over between Ka/pKa and pH? And the same for bases? It seems like there is no direct conversion and I'm wondering if we will ever have to.

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Hi all, can someone explain to me the reasoning behind why an atom in its elemental form has an enthalpy at standard state of 0? I like to know the "why" behind everything and can't find this one out by myself.

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Muscles produce lactic acid, CH3CH(OH)COOH(aq) , during exercise. Calculate the percent ionization (deprotonation), pH, and pOH of a 0.1164 M solution of lactic acid. The acid‑dissociation (or ionization) constant, Ka, of this acid is 8.40×10−4 . I did all the proper steps (ICE table and the quadrat...

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A weak base, B, is ionized forming its conjugate acid ( BH+ ) according to the reaction B(aq)+H2O(l)↽−−⇀BH+(aq)+OH−(aq) The conjugate acid BH+ has a pKa=8.63. For this weak base, the predominant species present at pH 10.85 is -charged -neutral -unknown I know how to approach these problems when the ...

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NH3 is a weak base ( Kb=1.8×10−5 ) and so the salt NH4Cl acts as a weak acid. What is the pH of a solution that is 0.081 M in NH4Cl at 25 °C? Questions like this are difficult for me because I think that you have to write two equations to account for both NH3 and NH4Cl, but I have a hard time writin...

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Among these three molecules, which has the strongest conjugate base?
CF3COOH
CH3COOH
H2SO4

I don't know how to rank these. Can someone please explain what my thought process should be?

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Hi, I'm having difficulty interpreting this graph and making an equation for a reaction for it. I'm particularly confused about how I should know what amount of moles are on both sides of the equation, if you even have to take that into account. Please help, thanks!

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According to Le Chatelier's principle, do catalysts shift the reaction?

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Hi 14B students! I'm struggling to recall my knowledge of acids and bases from 14A - I thought this section was really hard last quarter. Can people please weigh in on how you've figured out how to identify an acid, base, or salt? Do you use a periodic table? Is there a good website with lists of ac...

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Dr. Lavelle explicitly stated in lecture that inert gases have no effect on equilibrium when they are added to a system. However, in a UA workshop, the UA said that inert gases shift equilibrium when they are added to a *closed* system. Can someone - maybe Professor Lavelle or a TA - weigh in on how...

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For this problem, I don't understand how we are supposed to use the reactions in the table to calculate K because none of them match up with the reaction that the problem gives. Can someone help me solve this problem? I'm lost.

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I understand that the answer to part A is just the inverse of K=41. But I do not know how to calculate K for parts B and C when the amount of moles are changed and the molar concentrations are not provided. Please help!

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I do not understand when to assign "x" as positive or negative in the "Change" part of the ICE box. Can someone please explain to me when the "x"s for the reactants are positive or negative and when the "x"s for the products are positive or negative?

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The question is: Consider the reaction of NH3 and I2 to give N2 and HI. 2NH3(g)+3I2(g)↽−−⇀N2(g)+6HI(g) Using two or more of the given equations, determine the equilibrium constant, K , for the reaction of NH3 with I2. H2(g)+I2(g)↽−−⇀2HI(g) Ka=160 I2(g)↽−−⇀2I(g) Kb=2.1×10^−3 N2(g)+3H2(g)↽−−⇀2NH3(g) K...

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I understand all parts of this question except part D, which says "If one starts with higher concentrations of reactants, the equilibrium concentrations of the products will be larger." Can someone explain to me why this statement is true?

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Also, how do I calculate percentage deprotonation?

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For this problem, I'm stuck on part A. I am calculating the pH of CH3COOH by first finding the pOH. Here is my work...
pOH = -log(0.2M)
pOH = 0.7
pH = 14 - 0.7
pH = 13.3
But my answer does not match up with the textbook. What am I doing wrong?

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A careless laboratory technician wants to prepare 200.0 mL of a 0.025 M HCl(aq) solution but uses a volumetric flask of volume 250.0 mL by mistake. (a) What would the pH of the desired solution have been? (b) What will be the actual pH of the solution as prepared? Can someone please help me with thi...

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I honestly don't know where to start with this question. I don't understand how molar concentration, pH, and dilution are related and how to calculate change in pH from this. I originally thought that pH would not be affected because HCl is a strong acid and water is neutral, but there actually is a...

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Hello, this problem asks if oxalate is polydentate. From the Lewis structure, I can see that there are two double bonds from each carbon to an oxygen atom. Therefore, there are 10 lone pairs of electrons on all four of the oxygen atoms. The answer says it is bidentate. Does this mean that only the s...

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Also I forgot to mention that this question is in reference to part B.

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When I was solving this question, I originally put cobalt outside the brackets but the answer puts chlorine outside the brackets. Also, I'm just having a really hard time understanding how to work backwards to assign the charges with (III). Can someone please walk me through this problem?

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Do you identify the coordination compound of [M(NH3)4F2] based on the central atom or the total amount of ligands?

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A bidentate ligand can form two bonds to a metal ion, but how can I identify that a molecule I'm looking at is a metal? Do I get this information from periodic trends?

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What does the "en" mean in [Co(en)2(CO)2]?

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Practice problems, practice problems, practice problems! Then get out some nervous energy before the exam with light exercise :) It makes me feel better.

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In lecture, Professor Lavelle discussed relative acidity and that the resulting anion must be stable. How can I identify stability? Is it based on the bond size or delocalizing electrons? I'm confused and didn't piece together this part of the lecture.

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Hello, I need clarification from lecture. What is an oxidation state and why is it good for energy transfer? Thank you in advance!

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This is clarification I need from lecture. Am I correct in saying that a salt has both a cation and an anion in its molecular makeup? Can salts be identified according to periodic trends?

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Can someone please explain to me what a delocalized pi bond is in comparison to a regular pi bond?

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The last part of this question discusses the molecules being "coplanar." Does coplanar mean that each part of the molecule is the same shape? In this case, the shape of the molecules can be split up as trigonal planar. I'm confused and could use help clarifying what coplanar means.

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I was under the impression that tetrahedral shapes are always polar because even if the atoms surrounding the central atom are all the same, they are not directly across from each other. Rather, the bond angles are 109.5 degrees. Why is the answer nonpolar in #20?

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What would the speed of each particle be if it had the same wavelength as a photon of green light (wavelength=500.0 nm)?

Can someone help me solve this problem?

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Chemical Principles seventh edition by Atkins, Jones, and Laverman. M H E Freeman presented by Macmillan Learning. The electron affinity of thulium has been measured by a technique known as laser photodetachment electron spectroscopy. In this technique, a gaseous beam of the anions of an element is ...

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A liquid is exposed to infrared radiation with a wavelength of 5.80×10−4 cm.
Assume that all the radiation is absorbed and converted to heat. How many photons are required for the liquid to absorb 24.96 J
of heat?

I’m confused about how to calculate the number of photons?

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What are spectral lines and how do we determine how many there are?

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Conceptually, can someone explain to me why photons can't have kinetic energy but can still have regular energy?

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Conceptually, can someone explain to me why photons can't have kinetic energy but can still have regular energy?

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Watts came up in a textbook question. What are watts and how do you convert them to J/s?

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Conceptually, why can't two electrons spinning in the same direction be in the same orbital?

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This question comes from an example Professor Lavelle came up with in class. If we are given that n=2, l=1, and ml=-1, how do we know that e- is in 2Px state (I am specifically confused in regards to the x).

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Can someone please help me solve this problem?

For the following equation, determine the limiting reagent if 21.4g NH3 is reacted with 42.5g of 02.

4(NH3) + 5(02) --> 4NO + 6(H20)

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Can someone please explain the correct answer to me among the answer choices? What do chemical equations represent? A. They are symbolic short-hand representation of a chemical reaction. B. They are equations you need in order to solve for final mass of the product. C. They represent ratios of total...

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Can someone help me solve this problem?

Nicotine has mass percentage composition 74.03% C, 8.70% H, and 17.27% N and a molar mass of 162.23 g.mol^-1. Determine the molecular formula of nicotine.

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Can someone help me solve this problem?

Xylitol, a sugar substitute, has a mass composition of C 39.43%, O 52.58%, H 7.88%, and a molar mass of 152.15 g.mol^-1. What is its molecular formula?

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Can someone explain how to do this problem?

L-Dopa, a drug used for the treatment of Parkinson's disease, is 54.82% C, 5.62% H, 7.10% N, and 32.46% O, and has a molar mass of 197.19 g/mol. What is the molecular formula of L-dopa?

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