CHEMISTRY COMMUNITY

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you would substitute the values given using the Arrehunsius equation where the catalyzed reaction is on the numerator and the uncatalized is on the demoniamtor. make sure to convert kJ to J and also dont forget the negative sign in the numerator when calculating the ratio. the value you use for R is...

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the reason why is because the workMAX is when current approaches zero, since it is the initial reaction before the reaction approaches equilibrium. as the reaction progresses the work output decreases and so does the potential difference (battery is dying down as the reaction approaches equilibrium)

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the more positive the number is the more disordered it is. entropy of gas > entropy of liquid > entropy of solid

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enthalpy is in reference to heat lost or gained (H) and entropy is in reference to disorder (S). the relationship between the two is S = H/T

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these mean the that the products formed are under standard conditions (1 ATM, 25 degrees, etc) and that the reactants are in their standard form. So for CO2, the reactants would be C(graphite) and O2 since these are the standard forms of carbon and oxygen. so under these assumptions, is when standar...

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yes it looks like you were correct! I also like to check if my answers are correct by testing it with the other experimental trials to avoid mistakes!

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yes they can show up! the overall rate law is determined by the slowest elementary step, and if the catalyst is part of the reactants, then yes it is part of the rate law. remember that catalysts usually appear in the reactants side FIRST, so there is a possibility that it could show up in the rate ...

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kinetics controls the reaction when the products of the faster reaction predominated the solution. thermodynamics controls the reaction when the product is most thermodynamically stables. you can tell which one dominates depending on the reaction. usually at low temperatures kinetic control predomin...

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the way I balance redox reactions under basic conditions is that first I balance the electrons. Then I add the OH- ions to the side that is more positive in order to balance the charges on each side of the reaction. Then i add H2O to balance the Os (H2O is neutral so it doesn’t affect the overall ch...

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stoichiometric coefficient of the reactant affect the rate order. for example if the reaction is 2A—> B then the rate = k[A]^2 which means that the reaction is second order

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under acidic conditions means that when you balance redox reactions, you would use H+ ions. for under basic conditions you would use OH- ions to balance the reactions. Additionally this means that the pH of the solution is below 7. We can use the information to determine whether the solution is neut...

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hi constant volume is when the volume is being kept constant, which is usually done when gases are being INSERTED into the piston. constant pressure is when pressure is being kept constant, which is usually done by EXPANSION. Cp > Cv since work is being done by the gases during expansion.

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elementary steps are the step reactions that occur to form the overall reaction. In the kinetics units, elementary steps are when you need another element to produces a desired product in the overall reaction. We did an example in class involving NO2 and CO, where the reaction with NO3 was the eleme...

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hi I believe the order of reaction depends on the number of reactant. the order of the reaction are like the exponents of the rate law. for example if the rate = k[A] then the order is 1.

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hi the difference between average rate and instantaneous rate is that for average rate you are calculating the slope between two different points on the graph. For instantaneous you are calculating the slope of the graph at a single point (tangent line). You can think of instantanous rate as the ave...

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hi they are all the same! just be careful when looking what values are given. If the question provides concentrations of elements where the reaction is not at equilibrium, then use the equations with Q, but if the reaction is at equilibrium, then use the equation with K.

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I believe for this one you are comparing the reduction potential for each elements and then comparing it to the reduction potential of water. When the reduction potential of the metal is smaller than the water, then the metal is the reducing agent and the water is being reduced. when the reduction p...

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hi! to find oxidation numbers, there are certain elements that you have to just remember. hydrogen is always +1 and oxygen is -2. However be careful since elements when they are alone have an oxidation number of zero. So O2 would have an oxidation number of 0.

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yes usually H20 is on the other side (for half reactions)! However there are times where the overall reaction will cause H20, OH-, H+ to cancel, so just be careful about the generalization

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if Q is less than K then the reaction will move forward. Since Q = [P]/[R] if Q<K then that means that there are more reactants and therefore the reaction will move forward to create more products. if Q = K then that means the reaction reached equilibrium

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hi you would use ΔS∘rxn=ΣnS∘(products)−ΣnS∘(reactants) to find enthalpy and ΔG∘rxn=ΣnG∘(products)−ΣnG∘(reactants) to find free energy I think in the problem, it gives a link to a table with all the values. plug the values in the equation and you should get the answers! you can also use ΔG = ΔH - TΔS...

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Hi the significance of the salt bridges is to keep the electrons in motion. So the anions in the salt bridge flow toward the anode (ex. Cl-) and cations in the salt bridge flow toward the cathode(ex. Na+). The movement of these ions keeps each half-cell electrically neutral. The electrons from Cl- a...

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hi the first thing to look for balancing the redox reactions is figure out how many electrons are gained or lost by different elements. you could then write the electrons into the equation. the you would need to balance the reaction until the electrons cancel out. a trick that I liked which also Lav...

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hi the reason why we convert free energy into joules is because in the tables usually entropy is given in J/(mol·K). So when using the equation deltaG = delataH - TdeltaS, the units have to be constant, so you have to convert free energy to joules before solving for kelvins.

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The way salt bridges balance out the ions between the two galvanic cells is it keeps the electrons in motion. So the anions in the salt bridge flow toward the anode (ex. Cl-) and cations in the salt bridge flow toward the cathode(ex. Na+). The movement of these ions completes keeps each half-cell el...

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chemical reaction produce electric current (battery) and electric current causes chemical reaction (charging phone) This usually happened during electron transfer in chemical reactions

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micro states is the positions that molecules can take up and the greater volume the greater number of micro states. note that microtates all have the same energy states. micro states can also be called as arrangement or distribution

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you would first calculate the change in entropy under constant volume and then change in entropy under constant pressure. Also for change in volume, I believe that you need to multiply the entropy by the number of moles because the initial value that you calculated was the entropy for 1 mole. Then a...

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the difference between Q and K is that Q is the ratio of products to reactants at ANY time during the reaction whereas K is the ratio of products to reactants at EQUILIBRIUM

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hi the gas constant that you use is dependent on the units given and units you need, so depending on what units need to cancel, you use that gas constant

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hi I think it is because the C-H bonds are not technically broken/formed, and really the only thing that is being broken and formed are the C-C bonds. personally, I find it difficult to see what bonds are actually being broken and formed, so when doing these problems, I just assume that ALL bonds in...

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hi I believe for a base it is the same thing as an acid. so it would be final concentration of [OH-] divided by the initial concentration of the base to get the percent protonation.

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lower pka means stronger acid. lower pkb means stronger base. since pka + pkb = 14, a small pka means a high pkb. using this calculations, we can also determine that high pkb means a stronger acid and a higher pka means a stronger base.

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hi I believe that if the table gives you Kb when you need Ka, then you would do Kw/Kb to get Ka, which you can then use to calculate the pka. then all you need to do is compare the pka values to rank the acidity. hope that helps!

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hi I believe that when you have a reaction that involved a salt being disolved, you can look at the equilibrium constant to determine the solubility. Large constant means high solubility because many of the reactants were converted into products. Small constant means low solubility because very few ...

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extensive properties means that the value of something is DEPENDENT on the AMOUNT of a substance. for example heat capacity is extensive since it requires more heat to increase 500g of lead by 1 degree than it does to increase 1g of lead by 1 degree. intensive property means that value is NOT depend...

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yes you can but also be careful if you are given specific heat capacity which is per grams or molar heat capacity which is per moles. As long as all the units cancel to give you joules, then it should be fine

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for this problem you basically would “modify” the step reactions so that when you add them together, molecules would cancel so that you end up with the final equation. for example, since the final reaction you want 3Cl2, you would multiply the second reaction by 3 (which means also multiply deltaH b...

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under constant pressure, work is being done through expansion. in Lavelle’s lecture, when a calorimeter is under constant pressure and temperature is added, the volume increases and thus work is being done to move molecules out of this “new” space. so in equations Cp > Cv since under constant pressu...

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delta u is the change in internal energy. energy can be lost or gained through two forms: heat and work. so to calculate delta U you would add heat released/absorbed (which is enthalpy) and work done. this gives you the equation: deltaU = deltaH - P*deltaV

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as people above said q=nC∆T refers to molar heat capacity and q=gC∆T refers to specific heat capacity. Based on the information you are given and also what you are asked for, you would use each equation.

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yes it would because increasing the temperature for reactions shifts the reaction equilibrium (shifts it right or left) shifting the reaction would affect the value of the pH

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I would also know the relative values of the enthalpies based on the type of bonds. single bonds have smaller enthalpy values that double bonds. And molecules with resonance have an enthalpy value between them.

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the important standard states to remember is that the halogens are diatomic molecules and so are oxygen and nitrogen. Additionally carbon’s standard state is graphite (a solid). Usually you would have to remember these. I think you can also make a best guess based on how they appear in most reactions.

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we can think of the relationship in terms of the equation PV = nRT. If temperature increases and pressure is constant, volume must increase. When the volume increases, the gas must move the particles in that extra space out of its way, which means that the gas is performing work (losing energy). If ...

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hi believe enthalpy includes energy as well because sometimes systems lose energy from work. for example when enthalpy is also nCp(delta temperature). here the value of Cp is impacted by work of the gas being released (it's pushing molecules out of its way).

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enthalpy is the change in heat from a system. a positive enthalpy means that energy was put into the system (ie. to break bonds, endothermic) a negative enthalpy means that energy was released (ie. bonds made, exothermic)

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if you multiply ka and the kb, you’ll find that it equals kw which is a constant of water that is 10^-14.

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yes because the pka times the pkb is pkw which is 10^-14. Using this we can derive the formula ph + pOH = 14

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you dont have to use the quadratic formula if the ka/kb value is smaller than 10^3 because its so small its almost negligible.

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I believe temperature affects the constant. For example if you increase the temperature, K increases, causing the reaction to shift right. however I believe that you will not be given a change in temperature and asked to find the constant (at least not as of now in class).

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Hi! I believe the reason we did this is because Cl2 appears on both the reactant and product side when we add up the equations. because of this, Cl2 “cancels” out. Even if we included it when calculating K, they would cancel (unaffecting the actual value of K) since the numerator and the denominator...

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It depends on the reaction itself! so if you check the ratios periodically, equilibrium is reached once the ratios start to remain constant.

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The rates of the forward reaction and the reverse reaction is the same only if the system is at equilibrium. This is be cause at equilibrium the concentration of R and P dont change at equilibrium.

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Depending on the value of Q in relationship to the value of K, you can predict the direction of the reaction. If Q < K that means the concentration of products is smaller than the concentration of products at equilibrium. Since more products are needed for Q to reach K, the FORWARD reaction is favor...

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you would use the names, so use flouro.

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protonated means that the acid will remain in the neutral form of HA. but if the acid is ionized, then the acid will be in a charged form of H+ and A-.

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you can look at where they are in the periodic table. The further apart they are, then the more ionic character the molecule has. note that ionic bonds are between a metal cation and a nonmetal anion, so you can see that those are usually far apart from each on the periodic table.

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usually if the salt contains a weak base as its cation (ex. NH4+) then the salt is acidic, while if the salt has a conjugate base of weak acid(ex.CH3COO-), then the salt is basic. Also small highly charged metal cations act as acids to decrease the pH.

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yes this is correct. CH2FCOOH, CH2ClCOOH, CH2BrCOOH, and CH2ICOOH are actually are all weak acids which is indicated by COOH which is a carboxyl group. I think the professor was talking about how when comparing the relative strength of weak acids, you need to also consider the ability of an anion to...

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and oxo acid is when the O and H are directly bonded to each other. So in HClO2, the H and O are bonded to each other and it is considered an oxoacid

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hi! know that double bonds (pi + sigma bond) do not have a rotational ability and are quite rigid. Single bonds (sigma bonds) have the ability to rotate. I remember that Professor Lavelle used his hands and markers to demonstrate this in lecture!

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hi! I believe that answer to that is yes sadly. however using techniques like just dropping the “ine” and adding “oro” (chlorine is chloro) hopefully makes it easier

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hi! remember the order of the compounds of the coordination compounds is that the metal should come at the end. also after the metal, remember to also write the oxidation state in Roman numerals in parenthesis. also within the coordination sphere, chlorine is referred to as chloro similar to how flu...

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coordination numbers is the number of bonds that the ligands from with the metal center ion. so the coordination number is dependent on the number of ligands and how many bonds each ligand can form with the metal center. in the example you gave, there are six ligands (3 CO and 3 Cl) each form only o...

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hi! I believe chelating ligands are ligands that form a cage or a ring around the center metal ion, where polydentate ligands don’t necessary need to be able to form a cage or ring around the center ligand. hope that helps!

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hi I dont believe that you can’t really determine the coordination compound based on the coordination number. Because the coordination number is the number of bonds that the ligands make to the center atom, the coordination number is dependent on the coordination compound - not the other way around

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yes! because of resonance, bonds have partial double bond character and since we know that pi bonds exist within double bonds, the pi bonds are delocalized in order to accommodate for the partial double bond character.

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hi yes usually metal complexes occur with a transition metal because it can multiple oxidation states. You put the roman numeral if there is a oxidation state number of the metal element, and there usually almost is so yes always include the roman numeral if necessary.

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As far as my understanding coordinate covalent bonds are more common in lewis acids and bases because they are molecules that electron deficient(acid) and electron rich(base). Coordinate covalent bonds that occur in the metal complexes occur when the ligand donates the two electrons to the metal cen...

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hybridization helps explain how atoms form bonds. For example in class we learned about CH4. looking at the atomic orbitals of CH4, you can see that you have 2 electrons in 2s which symbolizes a lone pair, and then 1 electron in the 2px and 2py orbitals which means that C can only form 2 bonds in th...

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Hi hybridization refers to when the orbitals are mixed and blended. This would be orbitals like 2sp^2. Unhybridization refers to the atomic oribitals such as 2s and 2p^2. The reason why you have hybridization is because the arrangement of electrons is more favorable because there is less overall ene...

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Hi! I dont think the presence of lone pairs affect bond length, but it does affect bond strength. The lone pairs cause electron electron repulsion, which weakens a bond. hope that helps!

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Hi! in an ionic compound when the size of the anion increases that means it is more polarizable because there are more electrons. more polarizability indicates covalent character in ionic compounds, and higher covalent character means less soluble. so basically, the larger the anion, the less solubl...

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low ionization energy is basically when the atom requires less energy to lose an electron. This would mean that cations would have low ionization energy, so removing an electron from Na to from Na+ requires less energy that removing an electron from Mg. Ionization energy follows the same trend as el...

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hi I would know the formula for the ones that professor Lavelle talked about in class. I also heard that you can ask the ta’s present at the exam, to clarify the formula. for the shapes, I would definitely memorize all the ones that he went over in class. this would be for the linear and bent shapes...

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Hi I had gone to one of Professor Lavelle’s discussion sessions and a similar question was asked about CH3Cl, and he said that the bond angle for H-C-H is slightly less 109.5 and H-C-Cl is slightly larger because of the electron repulsion. So the workshop is correct and I think the book just didnt g...

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hi! elements in period 3 and after that are in the p block can have the expanded octets!

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Hi I was confused on why CHI3 has a higher melting point than CHF3. This is from hw #3F.5c

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hi! so I think M2+ means that an electrons were removed, and because s orbital have a higher energy than d orbitals, the electrons from the s orbital would be removed first. So the ground state configurations do not have s orbital ions.

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hi you would but the + inside, next to the element that has that formal charge

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hi it only has 10 valence electrons, so yes 3d is considered valence. I think 18 valence electron would be for Kr or Xe. 18 is like how many electrons would completely fill the valence shell. hope that helps

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Hi Mn has 7 valence electrons in total. you can count that by starting from potassium and then counting up until you reach MN. Since in the problem, its asking for Mn4+, this means that the atom lost 4 electrons to give it a positive charge. 7 electrons minus 4 electrons gives you 3 valence electron...

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Hi! I thought that cations lose electrons from p orbital BEFORE d. The energy in d orbital isin fact lower than p orbitals like the person above said, but that’s why they are less likely to leave. since p orbitals have more energy, they leave the cations first. just like how the electron configurati...

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Hi! I believe that all atoms require a complete octets besides the first 4 elements. Boron is also tricky, because it can be stable with only 3 bonds. Usually for a molecule to be stable, the atoms need a complete octet. Even with resonance, each atom should have an octet.

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Hi I wouldn’t say you need to know all of them but defiantly memorize the basics like the trigonal planar, tetrahedral, etc. No the lewis structures don’t have to be drawn to be the same as the VSPER model

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Hi! we don’t have to draw these structures on the midterm, but we ill be needed to identify structures, so I would be familiar with radicals and also using formal charge to find the best structure

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Hi! a valence shell is composed of all the orbitals that make up a period. so for Mn, the 3d orbital is included in its valence shell. lewis structures show bonding between elements. bonding occurs between the outermost orbitals of a valence shell in the s and p orbitals. thus, you don’t count the e...

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Hi I would say that usually for the most part, the elements further down would be larger since it has more orbitals. like an element with a 3s orbital is definately smaller than an element with a 6s orbital

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Hi! according to a TA it is not going to cumulative but obviously the final is going to be, so make sure you still understand the topics from week 1-3 for that

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hi regarding trends, as you go down a period the effective nuclear charge increases because there more electrons are effected by the protons and are pulled toward the nucleus

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I would be careful with that reasoning. Ionic bonds are different from covalent bonds in other ways such as how ionic bonds are between a metal and a nonmetal, while covalent bonds are between nonmetals and nonmetals or metalloids.

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Ru2+ has one more electron than Ru3+. So there should be total of 6 electrons in the orbitals. Although you expect Ru2+ to be [Kr] 4d^4, 5s^2, the reason it is [Kr] 4d^5, 5s^1 is because the atom is most stable when the d orbital is either half full or completely full. So one electron from the s orb...

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you would do it the second way because this way you have the most oribitals with lower energy in the beginning and higher energy at the end (4f has lower energy than 6p). it helps to remember by always making sure that the “n” values go from smallest to largest in electron configuration

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hi! usually charges are placed on the upper right hand corner of lewis structures. but also make sure that the addiontional electrons due to the charge are part of the lewis structures as well

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hi! I believe that you can use double bonds when you are trying to create that octet or when you realize that the formal charges when you use single bonds is not 0 and therefore unstable.

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hi a localized electron I believe is one where it belongs only to a single bond and doesn’t “travel” between multiple elements. usually localized electrons are in molecules that do not have resonance

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hi!
I was wondering if we could tell the difference between ionic bonds and covalent bonds based on the structure of lewis sturctures and if yes how?

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hi can someone explain to me how we know which element we put in the center for the lewis structures. im still kinda confused about that

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hi
I was wondering if someone could explain how we use the formal charge to change the way we draw the lewis structures

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