CHEMISTRY COMMUNITY

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When you want to know the effect on K with the change in temperature

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Does anyone know yet if the final will be multiple choice or will be free response?

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Can someone explain why/how in the answer key it says that since concentration of H+=10^pH, and the given pH is 4, which gives us a concentration of [10^-4]^16 (because the stoichiometric coefficient of H+=16) the end result is [10^66]? Wouldn’t it be [10^64]?

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On homework question 6M.1 they are asking us to find the value of E(M2+/M). Im confused because they say we are given a standard Cu(s)|Cu2+ half cell, which I thought was an oxidation but when they give us the formed cell it’s actually on the right making it a reduction.When I look up its standard c...

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Can someone please explain what the difference and meaning of “kinetic control” and “thermodynamic control”. I am not sure how to use those terms to answer the question they are asking.

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You first get the concentration by finding the Molar mass of N2O5 which is 108g, you then use the formula C=m/M*V and plug in the values they gave you in the problem.

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For homework problem 7A.15 how do we know which experiment to divide by? I thought that it was by the experiment with the largest initial rate is this true?

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Can someone explain how they answered part b to homework 7A.11?

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Are we expected to know when to include a product into the rate law?

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Why is the rate of consumption of NH3 solely equal to kr the (rate constant) and independent of the concentration of NH3?

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How can we derive the ph by using the Nernst equation? Would you have to use log rather than lnQ?

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The reducing agent will be the agent that pretty much causes another substance to reduce so in other words the agent that donates electrons, and the oxidizing agent will be the agent that accepts or gains electrons. I remember it as being the opposite from each other.

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Yes it is the same, the right side consist of the reduction reaction (cathode) and the left side consist of the oxidized reaction (anode)

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You can determine if the equilibrium constant of a reaction is greater than or less than one, by plugging all the necessary values into the Nernst equation, by doing this you can isolate lnK to one side in order to find what the value of K is. Usually if the voltage is positive, and the delta G is n...

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Both galvanic and concentration cells have a positive voltage, but the difference between both is that in concentration cells contain the same chemical species but in different concentrations, the difference in concentration drives movement of electrons, and the voltage tends to be very low. In galv...

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Can someone please explain how concentration affects cell potential? And how Le Chatelliers principle plays a role in this?

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Why is max cell potential directly related to the free energy difference between reactants and products in cell/redox reaction?

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You use platinum when there is no other metal solid being used, platinum is used to conduct these electrons.

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The main difference is that when balancing acidic solutions you balance oxygen with water and hydrogen with H+ protons, and in basic solutions you balance oxygen with OH- molecules and balance hydrogen with water.

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In acidic solutions you first balance oxygen with water an then balance the hydrogens with protons (H+).

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If you have work being done on the system then work will be positive, and if work is being done by the system then work will be a negative value.

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If delta G (Gibbs free energy) is negative then you know that it was spontaneous.

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Intensive properties do not depend on the quantity of matter , and expensive properties do depend on the amount of matter.

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When calculating equilibrium concentrations we do not include the units in the brackets but concentration is measured using moles/liters.

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Going off what happened in 14A and in his syllabus, he does not curve the midterm but a 50% in the class is a C, so in that way he does curve the final grade to help those that are close to failing.

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It is a spontaneous reaction when delta G is negative, because it means that the free energy of the reactant is higher than the product.

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He mentioned in class that only the first page of outline 4 would be on the midterm.

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Will we only be using the Gibbs change in free energy equation? And when do we know to use it instead of just G=H-TS?

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How Is standard reaction entropy different from the entropy state function? Why is it considered an extensive property?

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When you are calculating the standard enthalpy do you only use formation enthalpy or can you use bond enthalpies?

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Yes you can, you would just have to email that PLF and ask them if you can attend their session :)

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I order to change the energy of a system you can do 3 things
1. Add or remove heat
2. Add or remove mass
3. Do work on the system

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Steam releases more energy as opposed to boiling water, the steam releases about 40 kJ of energy.

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Why do things that fo to a lower energy level happen by themselves?

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In terms of delta U, why does it remain 0. Why does work + heat equal 0 in isolated systems?

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Under what circumstances should you assume there is a constant pressure?

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I’d start with whatever addresses enthalpy first since we just learned about it on Wednesday.

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Reverse reactions are exothermic because heat is not required, in fact heat is released when going in the reverse reaction.

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Why is work not a state property and what are different types of work?

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Why is enthalpy only a state property? Why does the path towards that state not matter?

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Steam burns more because if you look at the diagram he showed us in lecture , it releases a lot more energy to go back down to its liquid phase. The release in energy is much more than if you touched boiling hot water.

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Can anyone explain why we need to multiply the kA and kB in order the get the Kw for weak acid and base reactions?

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Inert gases are those gases that do not react, and therefore do not change the reaction, therefore you can use noble gases as an example as they usually do not react with other elements.

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They both essentially mean the same thing, and you can use them interchangeably.

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Why is energy released as new bonds are formed?

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Can someone please explain why : 1. If a reaction requires Heat, (is endothermic) while forming products, then heating will favor P (product) formation when additional heat is used. 2. If a reaction gives off heat, (is exothermic) while forming products, then heating will favor R formation when addi...

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Kc is the equilibrium constant used for aqueous solutions, because they have concentration values. Kp is the equilibrium constant for gases, since they have partial pressures.

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For question 5G.11 it asks to write the reaction quotient for the reactions given. I know that to calculate the Q you do the same thing as when you are calculating for K, but in the answer key it states that the Q= 1/(PBCl3)^2.
Why would it not be (PB2Cl4)(PHg2Cl2)/(Pcl3)^2(PHg)^2?

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Because it contains aqueous solution we would use Kc instead of Kp which is just for gases.

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Q is not at equilibrium, it is just products over reactants at any given time during the reaction. K is the equilibrium constant of the products over her reactants.

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The reaction quotient is the amount of products over reactants at any time during the Rxn, it is calculated the same way as K but it is not at equilibrium.

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I hope this is true! But yeah I have heard that his final grades are curved but test aren’t.

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Will we be asked to measure the ph and PoH of weak acids and bases?

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So if there is a lot of co2 in the blood it will cause there to be more carbonic acid in the blood which in turn creates more H30+ molecules increasing the pH?

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Does anyone know what we will have to know about titrations? Or will that not be on the final?

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For part a in 6D. 11 it asks whether an aqueous solution of each of the following salts has a pH equal to, greater than or less than 7. How would you determine this?

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Can any biological compound with a lone pair act as a base? Or is this only true for Nitrogen?

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You can use either one, but for now I would use the bronsted definition as it mentions protons which is what we are focusing on in this section.

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What are amphoteric compounds and why are they important? Would h20 be considered an amphoteric compound?

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Strong acids and bases will fully ionize and disassociate while weak acids and bases will not fully ionize. Strong acids will produce more photons in solutions than weak acids.

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I like to remember that if it is an acid it will donate protons, it is a proton donator. If it is a base it will be a proton acceptor.

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Are only transition metals in the d block able to form ligand complexes?

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Yes, whenever you see that there are the same two molecules on the same side you will know it is cis, and if you see them on opposite sides it is trans.

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Specific shapes will tell you the amount of electronic density that is found. For example for Tetrahedral you have 4 regions of electron density regions, which means there will be 4 hybridization orbitals which is sp3.

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Whenever you see a single bond know that it is sigma. When you see a double or triple bond one will be sigma and the other two will be pi bonds. Sigma bonds are single covalent bonds.

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Will the hybridization orbitals always be equal to the number of electronic density regions? If yes, why?

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Does anyone know if we can turn in homework this week on molecular structures since we have the test 2 on it this week?

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I know that double and triple bonds are not considered double or triple regions of electron density, but why? Why do we not count them as such?

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Due to lone pair repulsion, the more lone pairs there are the more repulsion there will be.

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Dr. Lavelle mentioned in lecture that test 2 will not include hybridization.

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When you have 5 regions of electron density your electronic shape is Trigonal bipyramid, such as BrF3, but since in those regions two of those are lone pairs the molecular shape will be T shape. As for NH3, your regions of electronic density is 4 giving it an electronic shape of a tetrahedral, and s...

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In my discussion my TA said that it is sufficient to just write that the bond angles are less than 109.

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By just looking at a Lewis structure how can we distinguish the type of bond and dipole moment present?

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How does more surface area influence strength of bonds and boiling point?

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How does a molecules bond type relate to its boiling point? Which types of bonds will cause higher or lower boiling points?

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Due to Nitrogen’s half filled orbitals, it makes it more stable and more difficult to remove and electron as opposed to oxygen which has two paired electrons.

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If the electronegativity difference between the two elements is greater than or equal to 2.5 then it is a ionic bond, if the difference is equal to or below 1.5 it is a covalent bond. Basically the greater the difference in electronegativity the more pull on electrons one element will have over the ...

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Isoelectric refers to elements that have the same amount of electrons, but have very different chemical characteristics.

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Octet exceptions are the first 4 elements in the periodic table which are; H,He,Li, and Be, as they will never have a full octet. An exception to this octet guideline are all elements after Neon, so in the 3p block and on, these elements are allowed to have more than 8 electrons, they don’t have to ...

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The element with the lowest ionization energy will always be in the middle, but hydrogen will never be in the middle. Just look at your periodic table and remember that the ionization energy increases as you go across the periodic table (left to right)

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If asked for a Lewis structure for an element with multiple variations (resonance) you have to include the resonance structures and indicate that there is a hybridization of the the structure, which will be a a combination of the resonance structures. To be safe I would always include it.

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Can someone explain why in order to find the electron affinity, you need to subtract the energy of the neutral atom from the energy of the final. Thank you.

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When writing the electron configuration of an ion, it changes from that of its parent element because you are changing the number of electrons in the element. When writing the change configuration you have to look at the charge of the ion, if its a positive charge it means that electrons were remove...

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In the lecture Professor Lavelle states that obtaining a formal charge of 0 is much more important than following the octet rule.

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Resonance just means you can write a Lewis structure in different ways, you can write bonds in different ways, but it is still the same molecule.

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Covalent bonds can only be formed by nonmetals, and metals are more likely to form ionic bonds. Remember that metals often times become cations because it is easier for them to give up electrons. Non metals have high ionization energy.

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Since there was a question in the homework which asked to name the types of light/radiation from highest to lowest energy, I am assuming we will be tested on it and expected to memorize them, that would be my safest guess.

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It is measured in meters, it is a distance. You can give it in picometers, and nanometers as well.

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After increasing the frequency and the threshold of the electrons being met, in order to have more electrons being ejected you can then increase the intensity as it produces more photons at this energy, which increases photon, electron interactions. But remember that this will not change the amount ...

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When you increase the intensity of light you are only increasing the number of photons being emitted, this does not increase the energy that each photon emits. In order to have electrons be released from metal, the energy of each individual photon must be high enough to pass the energy threshold and...

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After you find the wavelength of the radiation, you then find the energy by using E=h*v, which is Plancks constant 6.626x10^-34J times frequency which is given. Hope this helps!

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I am having a hard time understanding the concept of different spin states in electrons, I never learned this in High school chem. Can anyone explain how we know if an electron is in a spin up or spin down state?

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What did Professor Lavelle mean when he said that an electron is in a particular state, not in a specific orbital? I am having a hard time understanding this concept.

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From what I recall Professor Lavelle saying is that each atom has unique electronic structures and energy levels, which is why they can only absorb or emit unique frequencies that are allowed by their unique structures.

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What I got from lecture was that the larger the mass the smaller the wavelength properties making it not detectable. So anything less that 10^-15m does not have detestable wavelength properties.

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For part b you are asked to find the energy emitted by 5 mg of Sodium atoms. You first have to find the number of moles in 5mg of Na, you then take this number and calculate the energy by multiplying the number of moles in 5mg of Na by Avogrado’s constant over 1 mole, you then multiple that by what ...

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Why does does the the model equation Ek=1/2Me-ve^2 not change when you increase intensity? How is this different from the wave model?

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In lecture we went over the photoelectric effect, and I understood that if an incoming photon does not have the energy needed to remove an electron, and electron won’t be ejected. My question is what is that threshold that the photon should hit? What energy level are we comparing it to and why?

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I believe this was because we are supposed to round up.

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Yes, the empirical formula is the ratio of elements, unlike the molecular formula which gives you the exact numbers of elements in a compound.

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