CHEMISTRY COMMUNITY

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O2 and O3 has an oxidation number of 0, but O in any other compound or molecule has an oxidation number of -2.

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You can use the experimental method when they give you a table of concentrations of reactants for different experiments and their rates to cancel and find the order. You can use graphs if given: - first order should be a straight negative slope plotted over ln[A] vs. time - second should be a straig...

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You use the pre-equilibrium method when the earlier step is the fast step and the later step is a slow step. You can then think of the fast step as being almost at equilibrium and use that to solve.

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If you use the equation ln[A] = -kt + ln[A]0 you can see this will happen. You should be subtracting over the ln[A]0 before dividing and with laws of natural logs, if you subtract two logs you are basically taking the natural log of the two divided so that's why you are dividing 0.085/0.153 and then...

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Yes you ignore it. I got the answer without using it.

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Make sure to convert the hours into seconds so the units match up correctly!

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You just need two experiments that have the same concentration for both experiments so you can cancel them to find the order of the one with different concentrations.

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The rate determining step is the slow step. You can think of it this way. If two runners are tied together, one who is a track star and one who has never run before, even if the track star can outrun the slower runner, they are prevented because they are tied together. They can only move as fast as ...

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What equation are they using in this problem?

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Are the values for A given to us somewhere or is there a way to calculate them?

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In 7B.3 it tells us that the reactions are all first order but in part c the reaction is 2A > B + C which I thought would be a second order reaction. Do we not use the coefficients to find the order of the reaction?

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You write out the rate law for the first-order reaction, then you find that [A] decreased by .068M over 115 seconds as the rate, then you can plug in all the information you know, leaving the k constant as the only unknown since you know [A], the rate, and that the reaction is first-order, and solv...

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How do you do this problem or other problems similar to this when they give you only the initial concentration of the reactant and then a later concentration of a product? For the first-order reaction A > 3B + C, when initial concentration of A = 0.015 mol/L, the concentration of B increases to 0.01...

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How do you do part c of this question.( i.e. how do you find concentration of A) Determine the rate constant for each of the following first- order reactions, in each case expressed for the rate of loss of A: c) 2A > B + C [A]0 = 0.153 mol/L after 115s the concentration of B rises to 0.034 mol/L

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How do we know what can be used for electrodes based on the other metals given. (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 consid- ered in practice? (c) Often co...

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This is how you balance for both: 1. determine the oxidation and reduction half reactions. 2. Balance both half reactions: a) Balance elements other than H or O b) Balance O elements by adding H2O molecules to match the number of O molecules you have. c) Balance H elements by adding H+ (aq) FOR BASE...

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It does matter.
The anode is always on the left and the cathode is on the right with a salt bridge symbolized by "||" in the middle.

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YES! They are different. Here's what my TA said for the difference: 1. determine the oxidation and reduction half reactions. 2. Balance both half reactions: a) Balance elements other than H or O b) Balance O elements by adding H2O molecules to match the number of O molecules you have. c) Balance H e...

RRahimtoola1I

This is how you balance for both: 1. determine the oxidation and reduction half reactions. 2. Balance both half reactions: a) Balance elements other than H or O b) Balance O elements by adding H2O molecules to match the number of O molecules you have. c) Balance H elements by adding H+ (aq) FOR BASE...

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An oxidizing agent is one that oxidizes and thereby gets reduced.

A reducing agent is one that reduces and thereby gets oxidized.

RRahimtoola1I

you can also use "AN OIL RIG CAT" which means oxidation is loss of electrons at the anode and reduction is gain of electrons at the cathode.

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E naught is when the cell is at 1M, 1atm, and 25*C. E naught is standard cell potential.

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anode on the left
cathode on the right
separate phases by "|" going from solids on the outside to gases on the inside

RRahimtoola1I

Anode is on the left, cathode is on the right separated by || (Salt bridge).

You separate phases by "|" putting solids on the outside and working in towards gases.

RRahimtoola1I

You just plug in the standard cell potential they give you into E* = E*(cath) -E*(an). So it would be the way you did it first if you are not changing any of the signs given in the table.

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I'm not sure but you can also look at electronegativity of an atom. The lower the electronegativity the stronger reducing agent it will be because it will be losing electrons (oxidation).

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Why is Pt(s) only added on one side of a galvanic diagram sometimes. For example, in 6M.5 part a, the cell diagram in the solution manual is:

Hg(l) | Hg2^2+(aq) || NO^3-(aq), H^+(aq) | NO(s) | Pt(s)

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How do you do this problem with the equilibriums?

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In what case do you add platinum and when do you not when drawing cell diagrams?

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A galvanic cell requires no input of energy because the reactions are spontaneous and favorable. Electrons and cations travel from the anode to the cathode producing energy. A galvanic cell, overall, turns chemical energy into electrical energy.

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The | separates phases (Solid, aqueous, gas) and the || means a salt bridge and can also separate the anode and cathode.

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The cations move through the salt bridge or the porous disk because of the reasons ^^^. They are attracted to the negative cathode.

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You add the H2O to balance out the oxygens and then add H+ to balance out the hydrogens and then the same amount of OH- as H+ you added. Then you combine them to form water.

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The test will be in week 9 during discussion.

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I would also like to know how to differentiate between acidic and basic reactions.

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The reaction of 1.40 g of carbon monoxide with excess water vapor to produce carbon dioxide and hydrogen gases in a bomb calorimeter causes the temperature of the calorimeter assembly to rise from 22.113 8C to 22.799 8C. The calorimeter assembly is known to have a total heat capacity (calorimeter co...

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Can someone explain how to differentiate between which heating curve is correct?

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How do you break this problem down to solve for the ice melting and the water heating. The solution manual is not making sense? An ice cube of mass 50.0 g at 0.0 8C is added to a glass containing 400.0 g of water at 45.0 8C. What is the final tempera- ture of the system (see Tables 4A.2 and 4C.1)? A...

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Is the correct answer the one in the back of the book? I keep getting 342.8K for my final temperature. Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820 mol Kr(g) at 298 K and 1.00 atm (a) at constant pressure; (b) at constant vol- ume. T...

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How do you do this problem? I was using q = nH and q = mH but I am not getting the correct answer. "(a)Atitsboilingpoint,thevaporizationof0.579molCH4(l) requires 4.76 kJ of heat. What is the enthalpy of vaporization of methane? (b) An electric heater was immersed in a flask of boiling ethanol, ...

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Can someone please explain this problem. The solution manual is using 101.325J as a conversion but I'm not sure where they are getting it from. Other than that, I still don't understand the problem.

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Outline 1 and 2 except for 6E.

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Yes that's right! Also remember that it's not like pH where the higher the number the stronger the base and the lower the number the stronger the acid. For both acids and bases, the lower the pKa or pKb the stronger the acid or base.

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Make sure you are using -14 not -4!

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Set up a K expression using an ICE table and solve for x setting the expression equal to Ka, Kb, or Kc.

RRahimtoola1I

The following is stated on Outline 1 as things we have to know...

"Biological examples. For example: ATP hydrolysis; osmotic pressure"

Can anyone tell me what we have to know about it because I don't recall going over this?

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In high school chem I learned that the way the reaction shifts based on an increase or decrease of pressure depends on the amount of moles on each side of the reaction. I know Prof. Lavelle said there was another way that was better to determine which way the reaction shifts, but I don't remember it...

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It says on outline 1 that we have to know when to differentiate between using partial pressure and concentration for the equilibrium constant. How do we know which one to use when there are only gases but they don't give any other information like concentration or partial pressure?

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Here are the different gas constants. It depends on the units you are using in the equation. For PV=nRT you would usually use the 0.082.

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Will we have to know how to factor a complicated problem like this one where there is a quadratic over a quadratic for tests?

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Aqueous solutions have measurable and changeable concentrations. Liquids don't have significantly changeable concentrations and solids don't have measurable concentrations.

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This is true because of LeChatelier's principle that a reaction will try to minimize change to equilibrium. If more reactants are added the reaction shifts towards the products producing more product in the same ration that K was initially.

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Basically, because we don't have access to a graphing calculator, anything that you can't do without it like a cubic function for example can be simplified.

RRahimtoola1I

I'm pretty sure you are correct that if K < 10_-5 you can use approximation.

RRahimtoola1I

I believe only gases are included when finding equilibrium constants. Also, can someone explain how to ask a question on Chem Community? I cannot figure out how to. Thanks You have to go to a certain topic and then click on new topic in the top left corner. Name the subject something that people ca...

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Can someone explain how to understand this question? "A sample of ozone, O3, amounting to 0.10 mol, is placed in a sealed container of volume 1.0 L and the reaction 2 O3(g) S 3 O2(g) is allowed to reach equilibrium. Then 0.50 mol O3 is placed in a second container of volume 1.0 L at the same te...

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It's a possibility because we went over it in the notes, but I also don't think it would need to be detailed because it never showed up on the HW and the exams usually follow the format of the HW.

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Also why are there two hybridizations written for each bond even though they are the exact same thing? And why is the pi bond hybridization different from the sigma bond hybridization?

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Can someone please explain the transition between a normal atomic orbital and the hybrid orbital? I mean when we write the electron configuration with the arrows and how it changes in hybrids.

Can someone also explain it in terms of ethene because the notes I took are not making sense to me?

RRahimtoola1I

When counting charge clouds does it matter whether it's a single, double, or triple bond or does it always count as 1 charge cloud?

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Just a clarification because I thought hybridization would be more complicated. Do we just have to draw the Lewis structure, count the amount of charge clouds, and memorize the hybrid orbitals for each amount of charge cloud and write it down?

Does it get more complicated than this for this course?

RRahimtoola1I

A single bond is a sigma bond and every other bond after that is a pi bond. For example, in a double bond, there's one sigma and one pi bond and in a triple bond there's one sigma and two pi bonds.

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What is considered a hydrogen bond site on a molecule?

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I understand that CH2Cl2 is polar because a tetrahedral shape isn't completely symmetrical. However if a shape is symmetrical like a square planar would it be considered nonpolar? For example if it was a square planar with two Cl and two H atoms around a central atom, would it be considered non polar?

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Could you say that it would only be nonpolar if all the atoms around the central atom were the same?

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How do you do part a from 2E.21? It asks to draw the Lewis structure and give approximate bond angles of C2H4. Maybe I'm drawing it wrong but what is the central atom? I have the carbons bonded with two hydrogens bonded to each.

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It's better to determine whether a molecule is polar or non polar based on VSPER rather than Lewis Structure because it isn't always clear with the Lewis Structure. For H2O for example it seems like it would be non polar because it's symmetrical but the VSPER structure shows it's polar because of th...

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They are two completely different shapes. Trigonal planar has no lone pairs and 3 bonded pairs while trigonal pyramidal has 1 lone pair and 3 bonded pairs.

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Will we need to know how to draw the molecular structures in this way for the test?

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What is an example of a lone-bonding pair?

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Are the molecules that are considered polar the ones with no lone electron pairs? So only linear, tetrahedral, trigonal planar, etc.?

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What would the VSPER formula for a compound with a tetrahedral shape look like?

Do we just not include "E" when writing the formula?

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Do we have to know how to identify molecular shapes based on just a VSPER formula or will he most likely give us a compound that we have to find the Lewis Structure of to determine the VSPER shape?

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It's probably easiest to just memorize a chart with all the bond angles stated, but for the test he said we just have to be able to say that a trigonal pyramidal shape has a smaller bond angle than a tetrahedral because of the lone pair having more repulsion than the bonded pair.

RRahimtoola1I

OClO has 19 valence electrons so it's a radical. Do we count the extra electron even though it's not in a pair when determining shape?

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Are you supposed to use an expanded octet if you can make a Lewis Structure without it? For example, in ClO would I give Cl 9 electrons by making a double bond or leave it with 7 with a single bond even though the single bond gives Cl a -1 formal charge?

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Line structures omit lone electron pairs and just show bonds while Lewis structures have both.

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I'm pretty sure the stability of a Lewis structure is based off of formal charge and which atoms have what formal charges. Typically, the more electronegative atoms rather have a negative formal charge than less electronegative atoms.

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Can someone explain this by using a Lewis structure too?

Ashley, I think they are important because they are highly reactive and exist for a short time.

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How do you know what is ionic and what isn't?

For part b and c it's obvious because there's a metal involved, but for ammonium chloride, they are all nonmetals.

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So I went to the UA review session on Friday and they discussed using formal charge to determine the best way to draw a Lewis Structure. I've been trying to use that but it isn't working and I keep getting the wrong answer for the homework. Is there a certain time when we should or shouldn't use the...

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I'm confused as to how to find how many valence electrons are present for these ions. I usually just count back on the periodic table because they're all cations and then determine the amount of valence electrons for the element I land on, but I keep getting them wrong. Is there another way to do th...

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"Give the number of valence electrons (including d electrons) for each of the following elements: (a) Sb; (b) Si; (c) Mn; (d) B." For part c, do you count the d electrons because the subshell is not full because for the rest you also count subshells that are full if the shell isn't full? H...

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How do you find the kinetic energy of the electrons emitted? "In a recent suspense film, two secret agents must penetrate a criminal's stronghold monitored by a lithium photomultiplier cell that is continually bathed in light from a laser. If the beam of light is broken, an alarm sounds. The ag...

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Does anyone know if we could answer this question by saying that nitrogen has one electron in each orbital which has a higher stability and that fluorine has a high electron affinity because it wants an octet and doesn't want to lose an electron instead?

Do we have to mention electron repulsion?

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I used E=hc(wavelength) too but I got 753668J for my final answer. I'm confused on what we're both doing wrong. Can someone help?

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What rule is part C of this question violating that makes it an excited state?

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Can someone please explain this entire question...why each is true/false? I don't understand. "Which of the following statements are true for many-elec- tron atoms? If false, explain why. (a) The effective nuclear charge Zeffe is independent of the number of electrons present in an atom. (b) El...

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For ∆x, I got 6.6 x 10^-36m also, but the answer in the back of the book and the solution manual is 1.3 x 10^-36m. Which is the correct answer?

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"How many orbitals can have the following quantum numbers in an atom:(a)n=2, l=1; (b)n=4, l=2, ml=22; (c)n=2; (d)n=3, l=2, ml=1?" For a, is the number of orbitals only dependent on the subshell (p) and the amount of orientations possible for it? For b and d, is it only 1 because the orient...

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I don't understand what to use given in the problem to get the answer. I thought b was 11 because if n=6 and l=5, then shouldn't ml = -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5? Also can someone explain c and d too?

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2 questions:

For the mass of protons, neutrons, and electrons can we just look it up online or is there a certain value the book wants us to use and where would I find these values?

For tests, will we be given the mass of these particles?

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"The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 3 103 km?s21. (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50 3 1016 Hz. How much energy is re...

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I don't understand how the answer given answers the question. Can someone please explain? Why is grouping the series related to the base energy level?

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Here's an electromagnetic spectrum I found for reference. A wavelength of 340 nm would be suntanning because the sun emits UV rays. A wavelength of 1m or 1x10^9 nm would be microwaving popcorn because that wavelength falls under microwave radar. A wavelength of 2.5 nm would be x-ray because of the s...

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Particles have discreet energies with only certain stable wavelengths allowed in a circular standing wave around the nucleus. Professor Lavelle was specifically talking about electrons as being the particle in a box. An electron bound to an atom is like a particle in a box in that it has to stay amo...

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This can be helpful for converting between the prefixes to get to the base units on the metric system.

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"A reaction vessel contains 5.77 g of white phosphorus and 5.77 g of oxygen. The first reaction to take place is the formation of phosphorus(III) oxide, P 4 O 6 : P 4 (s) + 3 O 2 (g) > P 4 O 6 (s). If enough oxygen is present, the oxygen can react further with this oxide to produce phosphorus(V...

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When doing empirical formula problems, after you divide by the smallest number of moles, sometimes you get a decimal which you have to convert into a whole number for the formula. I know how what to multiply by when they're simple decimals like 0.5, 0.33, 0.66, 0.25, but how do I know what number to...

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For Question 3, Section H, I balanced the equation and got:

SiH₄ + 2H₂O > SiO₂ + 4H₂

but the answer doubles all the coefficients, even though the way I did it above is balanced. Is there a reason for this?

Thank you in advance!

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