CHEMISTRY COMMUNITY

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Catalysts decrease the reaction rate by providing new reaction mechanisms.

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k is the rate constant for all orders. You can look at the second order equations to solve problems:)

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It tells you what formulas and units to use. Hope this helps:)

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A is the pre-exponential factor and it is a constant that relates the equation to the number of collisions and orientation. hope this helps:)

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Catalysts lower the activation energy for a reaction by providing a new mechanism. They speed up the reaction by decreasing the amount of time in the transition state. hope this helps:)

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They have higher k values and speed up the reaction even more. hope this helps:)

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It provides a new mechanism for the reaction that speeds it up. It is not used up in the reaction.

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Hi, the slow step should be given. You can assume that the step before the slow step is in equilibrium:)

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It acts the same on both the forward and reverse reactions:) there is an achieve question for week 10 on this that helps:)

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You can use the equation t(1/2)=0.693/k. :)

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The instantaneous rate decreases as the reaction proceeds--you can see this as the tangent line gets less steep as the time passes. hope this helps:)

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Hi, you can do the E of the Cathode minus the E of the Anode. Your V should always be positive. hope this helps

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Another tip that helps me is putting OH on the side where there is no O already and then putting H2O on the side that already has O (because that allows you to balance the H and O) hope this helps.

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I like to think of "red cat" where reduction takes place at the cathode. hope this helps.

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Also, with cell diagram notation, does the anode always have to be on the left and the cathode on the right? thanks

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It means that the order is not affected by concentration, but rather factors like temp and catalysts. hope this helps:)

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How do you know when to add Pt, and which side does it go on? thanks

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Hmmm, achieve seems to be working for me now...

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Noooo:( alright, thank you so much

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Is achieve down for anyone else??

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Yes, it should always be in K because when your temp is negative (in C) it can mess up your calculations. Hope this helps:)

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yes, they are all state functions:)

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Yes because the units for ΔH are kJ (the units should be the same in your calculations). hope this helps

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yes, it should always be in K (because K always gives positive values)

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Could someone explain why deltaG is 0 for number 13? thank you so much

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When gibbs free energy is negative, the system releases energy (is in a more stable state). This also means that energy is not needed for the reaction to occur and so it can favor the products.

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You can calculate it using the second law of thermodynamics which is delta S = q rev/ T. Hope this helps.

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When the temp increases, the random motion of particles (which is entropy) also increases. Gases have higher entropies because the particles can move in more possible positions. Hope this helps.

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A reaction is spontaneous when the reaction goes from a higher energy state to a lower energy state without any required energy, and it favors the products. Hope this helps.

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Can someone explain why deltaG is 0 for boiling points? I am referring to the bromine example from class. Thank you:)

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An isothermal reaction means that the temperature stays the same throughout the reaction. An example is during phase changes where the energy is being put into breaking bonds (for example going from solid to liquid) rather than increasing the temp of the system. This makes it possible for a solid an...

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When heat is going into something, q is +, when heat is being released from something, q is -. Keep in mind that the sign of q is relative to the system and surroundings, meaning it depends on if you are looking at the heat of the system or surroundings. Hope this helps.

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A couple equations that help are Cp=Cv+R and deltaU=nCvdeltaT. hope this helps

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We use an integral to calculate the infinite number of steps that increase the volume of a gas and do work. hope this helps

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Work is the energy transferred to or from an object from the application of force along a distance. For example, when a gas expands at a constant pressure, it does work on a piston because the volume increases (force along a distance) hope this helps:)

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I do not think we need to, but it is helpful. The equation we need is on the formula sheet:)

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pH determines how acidic/basic a solution is (it is the -log of the H+ ion concentration), and pKa is the -log of the Ka value

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Do we need to memorize the equation deltaU=nCvdeltaT for the midterm? I recall we needed it in the achieve hw. thanks

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I also used the equations ΔU=nCVΔT and CV = Cp-R, but I do not remember learning them in class, does anyone know which lecture these equations are in?

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How do you know when to use 8.314 J⋅mol−1⋅K−1 instead of 0.08206 L⋅atm⋅ mol−1⋅K? thank you

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pH = -log[H+]
pKa = -log[Ka]
(p represents the function -log)

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Only include gases and aqueous

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if Q < K, products are favored ad the reaction is shifted to the right.

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It means that the acid only releases one H+ ion.

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pH=-log[H+]
pOH=-log[OH-]
Kc=1x10-14=KaKb

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Put both values into your ice chart, and only one will work (will be positive) :)

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Ka is for acids
Kb is for bases
Kc is for concentrations
Hope this helps:)

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You have to multiply them:)

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Does anyone know why for week 1 #6 the reaction forms more products? thank you

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For week 1's achieve #4, does anyone know how to get the total pressure after you have found x? thank you

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It represents the product over reactant ratio and is used to calculate/represent the extent of chemical equilibrium.

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Yes, solids and solvents are not used in the equation because their changes in concentration are negligible.

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Yes, when you have to look at an equation in your work you should always balance it (or check to make sure it is).

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Yes, it speeds up both reactions causing them to reach equilibrium faster:)

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Are Kp and Kc the exact same when it comes to the equilibrium equation products over reactants?

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They are basically the same thing, H+ is attached to water in an aqueous solution to make H3O+, but we often only look at H+ because it affects the pH.

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They can all accept protons.

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Weaker acids have shorter bond lengths--they hold on to their hydrogen ions more tightly, so it is more difficult for them to release H+ ions, making them less acidic. hope this helps:)

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Strong acids: HCl (hydrochloric acid) HNO3 (nitric acid) H2SO4 (sulfuric acid) HBr (hydrobromic acid) HI (hydroiodic acid) HClO3 (chloric acid) HClO4 (perchloric acid) Strong bases: LiOH (lithium hydroxide) NaOH (sodium hydroxide) KOH (potassium hydroxide) Ca(OH)2 (calcium hydroxide) RbOH (rubidium ...

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Strong acids fully dissociate. It can be helpful to memorize them:)

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Does anyone know if the same applies to this year's chem 14a final--if we need to completely understand these concepts? thanks

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Could someone maybe explain what a coordination sphere is and why it is significant? thank you

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Does anyone know if we will need to be able to name coordination compounds on the final? thanks

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Question: does anyone know why we label them as lewis or bronsted rather than just saying that they donate/accept H+ or donate/accept lone pairs? thanks

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This might be a bad question, but do both strong acids and bases have conjugates? thanks

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Hi! Do any of you know what information about chelates we will need to know for the final? thank you:)

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With molecules with the formula H2C(C)xCH, could someone explain why molecules with an even number of C atoms have H atoms that lie on the same plane? thank you

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Could someone explain the thought process behind the 4 questions on achieve #11? I am having trouble understanding how to decide which hybrid orbitals to select. thank you

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I am a little confused on the visual 3d structure of pi bonds--how is there one unhybridized orbital for each pi bond atom above and below the atom? Also--how does the unhybridized orbital form the pi bond? thank you

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Does anyone know why we are working with transition metals with coordinate bonds and not other types of atoms? Thank you!

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Yes, a triple bond has two pi bonds and one sigma bond.

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Just curious--does anyone know why we have to label them sigma and pi bonds? Is there a particular reason they need specific names?

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Can a pi bond be formed by itself (without a sigma bond first)? Can just two pi bonds exist together?

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Can someone explain what orbitals are involved in sigma and pi bonding and why? thanks

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Hi, can someone explain why there is a sigma bond and a pi bond in a double bond? thanks

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For the question "Select which intermolecular forces of attraction are present between CH3CHO molecules," how did some of you go about deciding which forces of attraction exist? Do you need to draw out the molecule? thank you

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Thank you for this advice, I did not know that these chem classes would be so important for the mcat!

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Looking at problems like achieve #9, will we need to do average bond length calculations on our midterm? (if anyone has any predictions?)

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Can someone explain why structure B is favored over structure C? thanks

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For Achieve #4, for the question "Based on the bond lengths and bond character, which of the Lewis structures actually contribute substantially to the overall structure of the carbamate ion?" could someone explain why they all contribute to the overall structure? Does the molecule resonate...

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In achieve #4, could someone explain the difference between the terms "ample" and "overwhelmingly" and their applied definitions in the question choices?? Thanks:)

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A lone pair of electrons are valence electrons of an atom that are not paired with another atom--they are represented by two dots (but sometimes are not drawn to save space and be efficient)

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Could someone explain what the diagonal line in the periodic table is and what trends relate to it? thank you:)

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Hi, generally they both increase because when an atom is more attracted to electrons, it is attracted to the atoms with those electrons, thus reactivity increases. hope this explanation helps

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and could someone explain why ionic radii decrease across a period? thanks

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Can someone explain why atomic radii increase across a group? thank you:)

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Can someone give a brief explanation as to why atomic radii increase down a group? thank you:)

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Does anyone know what the highest energy level that an electron in the H atom could be excited to? I am just a little confused on how an electron can be excited to a level that isn't there. Or maybe there are levels that exist around atoms but electrons aren't there?? thank you

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You must multiply by avogrado's number to get your answer #2 in units per mole instead of per atom like in answer #1. Hope this helps:)

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Can someone explain what electron affinity is and how it is measured? thank you:)

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Does the s orbital hold up to 2 electrons? I thought that an electron with n=4 and l=0 could hold 20 electrons (2+8+8+2), but achieve says I am wrong. Can someone explain?

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For question 16, does anyone know if the sinusoidal wave answer choice where the starting and ending point are different would be a compatible answer choice? Does the fact that the graph starts and ends at the same point matter?

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Does anyone know why we cannot use the equation Wavelength=h/p for light? This was mentioned on 10/11. Thank you

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Hi! Does anyone know if this content will be on the midterm or if it was just something interesting he mentioned in lecture? Thank you.

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Just to double check, our midterm 1 is before the past few weeks of hw is due (Sunday), right?

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Is there a way we can obtain the workshop worksheets and answers if we were not able to attend the session?

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To clarify a little, LDFs happen between molecules. As electrons move in atoms' electron clouds, sometimes they arrange in a way where an atom in in a molecule has a slightly negative side (because the electrons grouped there) and that is attracted to a slightly positive side of another atom. These ...

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To add on, Planck's constant represents the relationship between the frequency of a photon to the energy it has. This constant can be derived experimentally by measuring a photon's frequency and measuring its energy. If you divide the energy by the frequency, you get the constant. (this is just the ...

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To add on, on order for an emitted electron to have kinetic energy, there has to be more energy than the work function given to the electron. If the energy put in is the same as the work function, the electron will still be released, but will not move once out of the atom.

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Wavelength (nm) is the length of a full wave while the frequency (s^-1) is the how often the wave occurs in a period of time (its speed). They are inversely proportional to each other.

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