CHEMISTRY COMMUNITY

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what even are elementary steps

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805307623 wrote:Activated Complex- collection of intermediate molecules that are created as a chemical reaction progresses
Transition state- intermediate of a chemical reaction that makes up the highest potential energy

When do we use these concepts in the material that we have learned and will be tested on?

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jisulee1C wrote:since the slow step is the rate determining step, changing the activation energy of an already fast step will not change the rate because it is not changing the rate of the slow step

how do you determine the fast and slow step?

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we're all on standby until he updates us

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AnnaYan_1l wrote:Catalysts reduce the activation energy between reactants to products, meaning it takes less energy to make the forward reaction occur

does this affect the reverse reaction too?

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Kayla Denton 1A wrote:Catalysts are present as reactants in the very beginning and products at the end. Intermediates, on the other hand, are not present in the initial reaction but are produced within one of the steps and then consumed within another step.

a catalyst is one of the reactants?

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Jiyoon_Hwang_2I wrote:For steady state, the first step of the reaction must be slower than the second step. On the other hand, for pre-equilibrium, the first step must be faster than the second step.

how do you know which step is the fast step and which is the slow step

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Alexis Webb 2B wrote:k' is the rate constant for the reverse reaction.

is this just the reciprocal of the forward reaction?

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they all have different relationships with time and therefore produce different graphs.

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the overall order is equal to the sum of all the orders of the reactants. The order of each reactant is the exponential value of the reactant

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Gillian Ward 1F wrote:Possibly, it is in the curriculum.

what is the third order?

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I personally recommend the online sapling learning problems. The review sessions are great but I've noticed the sapling learning problems are more in line with the test material and you can work at your own pace. Also the site provides very in depth explanations about each problem which I find very ...

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When would you use E=E°-(RT/nF)lnQ vs E=E°-(0.05916V/n)logQ ? Also, I understand that you can substitute RT/F for 0.025963 for the ln equation when its under standard condition - 25 degree celsius. Is this correct? Yes, also I use the log one when dealing with H+ or OH- concentration; however, both...

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if it is in acidic solution you use H+ to balance out the equation and if it is in basic solution you use OH-

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Alison Trinh 1E wrote:n represents the order of the reactant, which in turn gives insight into the mechanism of the reaction.

how do you know what the order is

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Samantha Silva 1F wrote:The number of moles.

moles of what?

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Vicki Liu 2L wrote:Reaction order is essentially the power to which a reactant concentration is raised in order to give an accurate relationship between it and the rate of the overall reaction.

how do you find this number

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You can look at the reactions graph. Which ever graph produces a straight line will give you the reaction order. For zero order the graph would be (A) v time and would give a straight line with a -slope. First order reaction would be ln(A) v time and would give a straight line with a -slope. Second...

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Because it gives the exact slope at a specific time rather than an average of slopes over a range of t values

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Eesha Chattopadhyay 2K wrote:Can we also use the ln(k2/k1)=-delta H standard/R[1/t1 -1/t2] to solve this problem or do we have to find the separate standard G to find the values of K?

the question says to use data in the appendix so I'd find the standard G to find K values

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WYacob_2C wrote:How can you derive ln(K1/K2)= -delta H/R (1/T1 - 1/T2) from the Van't Hoff equation given on the formula sheet: lnK=-delta H/RT + delta S/R ? Thank you in advance.

it honestly would probably be easier to just memorize it than try deriving it during the test

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kristi le 2F wrote:The vant hoff equation can be used to calculate K at different temperatures if stand enthalpy of real lion is known.

what is real lion

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kennedyp wrote:What's the equation needed to convert K back to Kc? I assumed you would just rearrange the Kc to K equation, but I wanted to ask just to be sure.

aren't those the same

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TarynD_1I wrote:I think we use Van't Hoff when trying to calculate how K is affected by a change in temperature

yes this is correct as we have a K1 and K2 and a T1 and T2

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they aren't ignored, the just get cancelled out when deriving the new equation

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Brian_Ho_2B wrote:Substances with a higher, positive standard reduction potentials are not able to reduce H+ to H2, while substances with lower, negative reduction potentials can reduce H+ to H2.

why would the substance with a higher reduction potential has less potential to reduce H+? Sounds counter intuitive

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DesireBrown1J wrote:Why is n moles of electrons transferred instead of the number of electrons transferred? How do we convert it into moles if they are electrons?

They are the same. The number of electrons is the moles of electrons.

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Kate Osborne 1H wrote:standard conditions are a specific ratio of products to reactants and if the ratio is not that then you have to use the nernst equation

are you referring to K? what else would a specific ratio be

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the reduction potential. Once you determine which half reaction is oxidized, you change the sign of this potential.

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the electromotive force is Ecell, the max potential when very little current is flowing. When there is no current flowing, that is when the difference is at its maximum. I thought electromotive force was the max potential of the cell before any current flow? How do you determine "little curren...

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charleejohnson1L wrote:The salt bridge keeps the two solutions neutral so the systems can exchange electrons. I hope this helps :)

it allows for the flow of ions as well

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805291863 wrote:Also, how is the n value determined here?

n value is determined by the moles of electrons in each of the balanced half rxn equations

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KeyaV1C wrote:I got -27 kJ/mol as my answer.

how did you get this??

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I keep getting -2.7 kJ as well. Can someone explain what we are doing wrong?

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if the reduction half of the rxn goes from In3+ to In2+, why does the answer key say that 2 electrons are added to In3+ to get to In2+. Why is it not 1 electron???

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What is the nerst equation?

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half reactions let us understand what is happening exactly to the molecule being reduced and same for the molecule being oxidized. Each reaction on their own has cell potential measured in volts; so, by looking at both measures, we can add them together to get the cell potential as a whole. But ove...

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half reactions let us understand what is happening exactly to the molecule being reduced and same for the molecule being oxidized. Each reaction on their own has energy potential measured in volts; so, by looking at both measures, we can add them together to get the energy potential as a whole. But ...

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So this redox reaction occurs within a single cell?

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what is the difference between Ecell and Eocell?

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n represents the number of electrons transferred in this equation!

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How are we supposed to know the oxidation number for each element in a compound?

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if the compound is oxidized, it will lose electrons. And if it is reduced, it will gain electrons. You can determine which process the compound undergoes by looking at its change in charge.

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it is the study of chemical processes that cause electrons to move, resulting in electricity that is generated by the movements of electrons from one element to another. This reaction is known as a redox reaction and is important because we will be doing many redox reaction problems in electrochemis...

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Ryan Lee 1E wrote:N_a is going to be Avogadro's number whereas lowercase n is going to be the number of moles.

When do we use Avogadro's number instead of moles?

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DarrenKim_3G wrote:residual entropy is the remaining entropy left in molecules at 0 K

what does that mean? and when will we use this?

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if there is both a change in volume and temperature you do two separate calculations for each using the proper C respectively and then add the two together

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this is the internal energy of the system. so w would be the work either done by or on the system and q would be the heat either absorbed or given off by the system. the changes are looked at in the perspective of the system

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yes, it is the same one

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do you have to explicitly state per mole or is that implied already

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so the surrounding is the universe?

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Lauren Tanaka 1A wrote:Negative entropy is possible and just means that there is an overall decrease in entropy for the given system.

what does decrease in entropy mean for the system though

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eduardomorales5 wrote:Negative entropy means there is a decrease in the disorder of the system or increase in the order of the system.

how is it both?

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Mitchell Koss 4G wrote:Closed is like a test tube with a cap on it, so solution can be heated or lose heat.
Isolated is behind thick walls like a bomb calorimeter or thermos so no outside interaction can occur.

how do we determine which one it is, or will it be stated?

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Nawal Dandachi 1G wrote:q would be positive if heat is being added to the system and negative if heat is being removed. w would be positive if work is done by the system and negative if work is done on the system.

what is an example of work being done on or to the system?

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ALegala_2I wrote:You use w=-PV when there is an expansion occurring at a constant external pressure. You use the other equation when there is a change in internal and external pressure for expansion work.

what is the other equation?

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how many types are there?

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Yes, the system vs. surrounding should not be something you have to memorize. As mentioned before, the system is simply the situation in question, such as a piston. Since the first law of thermodynamics states the conservation of energy, a change in energy of the system means a resultant change in ...

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We will discuss it more when we start talking about thermodynamics. For now, all we need to know is that there is a difference in the amount of work done depending on whether the gaseous system is under pressure or not. what is this difference? Is this just a concept we have to know or are their fo...

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MingdaH 3B wrote:No, you can touch it.

wait what this a serious response lol

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Outline 3 (Thermochemistry)

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Brian J Cheng 1I wrote:Depends on the information given and the setup of the question. For example: if multiple rxn equations are given with their respective enthalpy changes, then you might suspect Hess's Law. If bond energies are given, then you might use bond energies.

what exactly are bond energies?

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Why does enthalpy increase as temperature increases?

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if the equation uses the g variable then use grams. If it uses the m variable which is usually represented by n, use number of moles.

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it measures heat of a system with CV (the volume is fixed so pressure is not constant)

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well,heat capacity is an extensive property because it depends on the amount of substance. If we divide the heat capacity by the amount of substance, it becomes an intensive property.

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the sign of enthalpy indicates if the reaction is endothermic (positive) or exothermic (negative)

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in an exothermic reaction if temp is decreased the rxn will move forward as it is a "product" (is released)

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you leave out any molecule that is a pure liquid or solid. If H20 is in a gas phase, then it is included

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pka and pkb are added together to get 14; so, if you know one, you can subtract it from 14 to get the other

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volume and pressure are inversely related. it's easy to answer those questions if you memorize that

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because the pressure is decreased and in order to minimize this change, the reaction reaction move towards the side with more moles so there is more pressure

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One of the UAs said that the amount of sig figs in the problem is the amount of sig figs you place after the decimal for pH

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correct that is what that means. forward rxn favors the product

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just the material from weeks one and two!

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because the change in x is so small, the original molarity of the molecule being changed by x is a suffice approximation.

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it goes to the side with less moles.

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Kimberly Koo 2I wrote:R is the universal gas constant, which is 0.082 L.atm/mol.K

there are different R constants for different units though

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pure liquids and solids are not involved in the ice box so H20 wouldn't be involved in liquid form. However, it is when it is in gas form like the examples in class.

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that is strange. I thought that K and Kc were the same. The only thing I can think of is if K were calculated in Pressure and than converted to Kc but I didn't do the math to test that. I also don't know why it would be calculated differently.

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Wendy Perez 1E wrote:Adding to this conversation, what does amphiprotic mean again?

can accept or donate a proton

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the moles represent the amount of X that will change. If the molecules go into the eq the change is -, and if the molecules come out of the eq the change is +

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The UA's said the material would cover up to this friday's class material so I would focus of the first two weeks of information. The lecture videos that Lavelle posted cover a lot of the information and have great practice problems!

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You should calculate Q so you know which direction the reaction is moving and then you can identify if the products or reactants are favored to determine if x is positive or negative for each molecule

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When do we know when to use which R constant?

What are the two R constants and when are they used?

Is the unit for gas measured in atm pressure or bars?

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To solve for Q we have to be given the values of each product and reactant, correct?

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This principle tries to minimize the effect of change by shifting the direction of the reaction in order to maintain equilibrium

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Yes, if the reaction is shifted to the left that means that the are more moles on the left side of the reaction which are the reactants. While if the reaction is shifted to the right that means there are more moles on the right side of the reaction which are the products. if there are more moles on...

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Q doesn't have to be strictly not at equilibrium. It can be at any point in the reaction including equilibrium, K.

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have we gone over this in class in an example equation?

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do you omit pure solids and liquids while solving for K too?

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the volume is already included in the concentration as it is moles over volume

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Are the assignments on sapling learning mandatory? And if so, when are they due?

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correct it is just a unit

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yes it will be temporarily shifted

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K is the general term for equilibrium constant. Kp is for reaction involving gases and Kc is for reactions involving aqueous.

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Why d we have to put P in front of the molecules? for example= (P O2) + (P H4)

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partial pressure is used because the reaction only involves gases

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If, in the presence of water, a salt gains an H+ (becoming an acid) and produces OH- ions, the solution will be basic. If, in the presence of water, a salt loses an H+ (becoming a base) and produces H+ ions, the solution will be basic. <- you mean acidic??** ex: C2H3O2 (-) (aq) + H2O (l) ---> HC2H3...

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a weak base will have a lower pH than a strong base

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