CHEMISTRY COMMUNITY

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On slide 5, we are told to calculate the partial pressure in bar so we use lnk=deltaG/-RT I understood what we were doing when we got k to equal 10. The next step was setting k to equal the concentrations of product over the concentration of reactants giving us 10=2x/x^2. How do we get x to equal 0....

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Can someone explain the difference between rates and rate constants

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Will the answers be posted for the worksheets and packets that we would've went over during the review session?

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would it be the same as long as it is standard conditions? at standard temperature?

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how do we know when we should use products-reactants vs delta g= delta h - t delta s

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How can we differentiate a catalyst and an intermediate in the reaction if they both cancel out and don't end up in the overall reaction?

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Can someone break down the arrhenius equation for me?
I was trying to do section 7D of the kinetics hw and I'm confused on the different k values

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just making sure for test two, in regards to outline four, we need to know Focus 5G3, 4, and 5J3 right

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I also had trouble with this one, I read on another chemistry community question that when the ecell is negative we have to flip the cell around

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I figured out what I did wrong if anyone else is also stuck:

to balance for acidic solutions:
12e- + 12H+ + P4 --> 4PH3
3(8H2O + P4 --> 4H2PO2- + 8H+ +4e-)

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You can relate E to Gnot using Gnot = -nFE. From there, relate Gnot to K using Gnot = -RT lnK. In this case, the reaction given makes K equal to Ka I solved up until K but didn't know how to get to Ka. In the solutions manual they took the square root of K to solve for Ka. Do you know why this is t...

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In this question, it told us that a 1.0M NiSO4 (aq) solution was electrolyzed by using inert electrodes then asks for the cathode and anode reaction. I wrote the reaction for Ni2+ + 2e- --> Ni from the NiSO4 given in the equation but didn't know if that was the cathode or anode. Since this is saying...

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When we make a cell diagram for cd(s) + 2Ni(OH)3 (s) --> Cd(OH)2 (s) + 2Ni(OH)s (s) at first I was confused on why the cell diagram would look like Cd|Cd(OH)2|KOH||Ni(OH)3|Ni(OH)2|Ni because I didn't know why we added the KOH but I was informed we needed it because since when we were balancing, we a...

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When we write the cell diagram for the following reaction
2NO3- (aq) + 8H+(aq) + 6Hg(l) --> 3Hg2 2+ (aq) + 2NO(g) + 4H2O(l)

how come the diagram does not include a solid on the anode side?
Hg(l)|Hg2 2+ (aq)||No3-(aq)| H+(aq)|NO(g)|Pt(s)

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I learned that for basic solutions we can balance like a acidic solution and once we get our final result we would add the same number of hydroxides to the side with h+ to balance and create water then cancel out the waters on the other side. I didn't have trouble with this strategy but when I got t...

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Since you are given the k value and the partial pressures to find Q, you would use deltaG=-RTlnk + RTlnQ and this should give you the answers in joules

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In the notes, we said that we could use le chatelier's principle in order to see how concentration affects cell potential. When the increase of a reactant was greater than 1.0m, then e cell> standard cell potential and when the increase of a product was greater than 1.0m, then e cell < standard cell...

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We are given a list of metals and asked to order them starting with the most strongly reducing metal. I looked up the standard values in the appendix and this list was from most negative to most positive. Since these values correlate to the reduction potentials, why does a more negative value parall...

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For this one, I did get to the same step as the solutions manual than lnQ= 14.8 however I don't understand how they isolated Q to equal 10^6 because I got 2.6x10^6. Did anyone get the same answer or did I isolate the variable wrong

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For cells that have enot=0, how do we know which concentration goes on top and which goes on the bottom for the reaction quotient?

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You would write the half-reaction without Pt(s), since it simply serves as a solid electrode for the cell diagram. Because a reduction reaction is occurring in the anode, there is a gain of electrons added to O2(g) as it also reacts with water, H2O(l) to produce hydroxide, OH-(aq). So the anode hal...

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Julie_Reyes1B wrote:Because pH>pKa, the acid will mostly deprotonate. Since it deprotonates it will become the conjugate base, ChH3COO-. The conjugate base will have a net charge of -1.

so was this question asking the charge of the conjugate base?

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we are asked to calculate the equilibrium constants for the equation using lnk=nE/.02569. I don't understand why n in this case would be 2e- because then I don't believe the charges are balanced, can someone explain this to me

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Once we determine that the reaction is spontaneous, we have to write a cell diagram for the reaction. In part a why is H+ included in this cell? I thought it was just used to balance the equation

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It asks for which process with delta H and delta G be expected to be most similar? I narrowed it down to either a or b during the test but then I got confused on the difference between them. The only thing I noticed was that option a was all in the solid state whereas option b had many different pha...

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What I did was I found Ka and used the pH given to find the concentration of H+. Since the equation for Ka is [H+][A-]/[HA], you can find the ratio of conjugate base to acid by dividing Ka by the concentration of H+. But how would you know if it stays as a salt in the stomach or becomes something e...

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For this question, it was asking what the net charge for acetic acid is when at ph 6 and pka 4.75. I was confused because I thought acids don't have charges. I wrote that the acid is neutral because when is dissociates wouldn't it become the conjugate base instead?

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I read on another post to look for the option that had the greatest number of moles, I was trying to do that on the test but i got similar numbers for many of the options which leads me to conclude I just calculated wrong. Could someone walk me through how they picked the correct answer

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Can someone explain how we write the cell diagrams for this problem? I thought Au+ would be on both the anode and cathode side because each half reaction has that, instead they have Au(s) on both sides

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For this part we are given the cell:
Pt(s)|O2(g)|H+(aq)|| OH-(aq)|O2(g)|Pt(s)

How are we supposed to write the half reaction for the anode?
In the solutions manual e=-.83

Why would it be negative if we are talking about a galvanic cell?

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For galvanic cells it says we have to have a positive potential difference therefore we have to identify it as anode and cathode in the way that would make the cell potential positive. When would we do this instead of identifying the half reactions and determining if it is spontaneous through the si...

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Are there solutions to the multiple choice portion of the midterm? I feel as those are more of the ones I struggled with so I would like to see how to solve those ones. Do we just have to go to office hours if we want to know the reasoning behind the answers?

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How is the reaction gibbs free energy (calculated using delta g= -rtlnk = rtlnQ) different from the gibbs free energy we calculated last week?
And can someone explain why it would form products when positive and reactants when negative? Is it also spontaneous only if it is positive?

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We are given the following reaction:
Cl2 (g) --> HClO (aq) + Cl2 (aq)

how come the half reaction with Cl2 is written as
Cl2 (g) + 2e- --> 2Cl-(aq)? if the reaction has Cl2 on both sides of the original equation

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I believe it is all dependent on gibbs free energy because we need delta s and delta h to know if the reaction will be spontaneous or not. I would just make sure you know how to manipulate the variables and come to the conclusion of what needs to happen for the reaction to be spontaneous or non spon...

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i think we just have to know that in a perfect crystalline substance there is no entropy. This can be found using the residual entropy equation: deltaS=kblnw and because it is already perfect the equation would then be delta s= kbln 1 which would be zero. This tells us that in a perfect crystalline ...

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What are the different types of entropy such as positional entropy and can someone explain when each occurs

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What is the difference between heat, heat capacity, and specific heat capacity? They all seem so similar to me and I get confused

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I know that having a negative delta g tells us that the reaction is spontaneous. When we are looking at delta s the total change in entropy being positive would also tell us the reaction would be spontaneous. Is this because a large delta s is being subtracted from delta h making delta g more negati...

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How come a negative value of gibbs free energy is more stable compared to a positive value?

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Th problem: 2SO2 (g) + O2 (g) --> 2SO3 (g) at 25C and 1 atm (with piston and constant pressure). initially .030 mol So2 and .030 mol O2 are present in a cylinder. He then adds a catalyst to initiate the reaction. In part C it tells us the creation goes to completion and the pressure at the reaction ...

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I found this endorsed answer on chemistry community: "The kekule structure of benzene suggests alternating single and double bonds, whereas the resonance structure contains six bonds that are between a single and double bond. The resonance structure is more stable, as all six bonds between the ...

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I am also confused on this because I thought because resonance had a higher enthalpy, more heat was absorbed making it a higher energy state and therefore less stable? Someone please explain

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Benzene is more stable and less reactive than would be predicted from its Kekulé structures. Use the data in Table 4E.3 to calculate the lowering in molar energy when resonance is allowed between the Kekulé structures of benzene. When we calculate the molar energy without resonance, we get 2880 kJ,...

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"For a certain reaction at constant pressure, ΔH=-15kj and 22kj of expansion work is done on the system by compressing it into a smaller volume. What is ΔU?" I understand that ΔU=ΔH+w is the general equation. Here we know H is -15 I am confused because if it is expanding, I know an expansi...

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When we add or subtract, I know we are supposed to use the one with the least number of places after the decimal. But when we have two numbers without decimal points such as 524+340 would it be two sig figs because of 340 or would it be 864 because it still doesn't have an places after the decimal p...

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It depends on the volumes given. That could be possible, but I think it means that, in comparison to an irreversible reaction, both reactions can reach the same final volume. However, the reversible reaction occurs slowly, that's why the equations are different. More work is done in this instance a...

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For reversible reactions the equation for work is w=-nrtln(v2/v1)
When it says that it can expand reversibly to the same final volume, does that just mean volume two is just double volume one?

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yes! this is because it is a state property

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When it is being compressed and volume is decreasing then work done on the gas/system is positive and gas done by the system is positive. When there is an expansion there is negative work done on the gas and positive work done by the gas.

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Steam causes burns more than water because the change of phase from liquid water to water vapor requires more energy

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why is the enthalpy negative when bonds are formed rather than when they are broken?

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how do we calculate the heat necessary to raise the temperature of water

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"piston confines 0.250 mol He to 1.50L at 25C [...] the gas is able to expand through additional 1.20L against constant pressure of 1atm." The answer had 3 sig figs. I read the sig fig worksheet on Dr. Lavelle's website but I am still confused. What part of the question counts for sig figs...

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In problem 4A7b it asks what percentage of heat is used to raise the temperature of water. We are also told to specific heat and molar capacities. I wanted to know what the equation was to solve this question

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"In an experiment, 0.020 mol No2 was introduced into a flask with volume 1.00L and the reaction 2NO2(g) <---> N2O4(g) was allowed to come to equilibrium at 298k A) using the information in table 5E.2, calculate the EQ concentrations of the two gases" from the table 5E.2, the k value for th...

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You would use the number that is less than your initial concentration you were given in the original problem.

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They are pure substances; solids do not change concentration and in lecture I believe Dr. Lavelle said that the liquids act as solvent so the concentration is not really changed.

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You can use the approximation when your K value is smaller than 10^-3 so you can save time not doing the quadratic equation. This is because a value that small in comparison to the initial values given will not affect your x value by much. After solving for x, you can do the % depronated. This is ca...

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I did not take Dr. Lavelle's class last quarter; however, I plan on making sure I know how to do the problems given in outline 1 and 2. My TA suggested just to get as many practice problems done as possible because that is the best way to study 14B material. Last quarter for 14A I did read the textb...

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If you increase N2, the increase in reactants would shift it toward the products meaning it would make more product. If you were to make more products, you need both the reactants to make it, H2 would also have to decrease.

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The principle is used to predict how how the system will react to stress. It will change to reduce this given stress. It would be important to know how temperature, pressure/volume, increase in reactants/products, decrease in reactant/products that affect the equation. It could shift left or right d...

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They would not because we only take into account the gases. We take into account their molar concentrations.

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Adding an inert gas to the container at constant volume would mean that pressure would increase but the equilibrium would not shift because it is not directly affecting the concentration of reactants and products. If it was the other case where addition of a gas changed the volume at constant pressu...

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Nathan Rothschild_2D wrote:Kw is the equilibrium constant for water and at 25 C is 10^(-14), but if the equation doesn't specify the temperature, can we assume that the reaction is taking place at 25 C?

I believe so, if it was at a different temperature, that temperature would have to be specified.

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They are the same value, just keep in mind that this value changes at different given temperatures. The one we use most often is 1.0 x10-14 at 25C.

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I Know the first test is going to cover chemical equilibrium and acids and bases. Will we have to know how to find the pH of aqueous solutions (topic 6D)?

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The question asks to determine if the statement is true or false and explain why. In part c it states "If one starts with higher pressure of reactant, the equilibrium constant will be larger." I thought this was true because if there is higher pressure of reactant it will shift toward the ...

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