CHEMISTRY COMMUNITY

VPatankar_2L

A pseudo first-order reaction is one that is not normally first order but can be changed to a first-order reaction by significantly increasing or decreasing the concentration of one of the reactions. By doing so, you would be measuring the effect that the reactant whose concentration you are not cha...

VPatankar_2L

You can tell the orders based on the graphs: for zero-order the graph of [A] vs time would be linear, for first-order the graph of lnA vs time would be linear, and for second-order the graph of 1/[A] vs time would be linear. You can also determine the order based on a data table by using experiment ...

VPatankar_2L

For the pseudo rate law, you would write the rate law in terms of the reactant that is in excess. Thus, you would substitute k' for k[reactant that is maintained at its original concentration]. For example in the reaction A + B --> C, and B's concentration were increased so that it would be in exces...

VPatankar_2L

You can use the coefficients of reactants in an elementary step to determine the orders of each reactant fr the rate law. For the nonelementary step, you can't determine the rate law without experimental data. The combination of elementary steps can help you derive the overall reaction and the overa...

VPatankar_2L

The rate will generally correspond to the slower reaction because that will govern the rate of the overall reaction. In this case, the rate of the slow reaction is rate = k[NO][Br2] which matches the answer.

VPatankar_2L

Thee order can also tell you which graph [A] vs time, ln[A] vs time, or 1/[A] vs time will show a straight line.

VPatankar_2L

I think you can use the equation ln (kr2/kr1) = (Ea/R)(1/T1 - 1/T2) and plug in the value for k1 at 25 degrees C as well as the Ea, R and the calculated values of temperature in Kelvin. This should get you the correct answer.

VPatankar_2L

You shouldn't use stoichiometric coefficients to find the order of a reaction for overall reactions. This is the case because it has not been experimentally determined that the reaction is in second order with respect to A. You can use them to write the forward and reverse reaction rates for element...

VPatankar_2L

The integrated rate law for the zero order reaction is [A] = - k t + [A]0. When t=t1/2, we can substitute this value into the equation to get [A] at t1/2 = -k(t1/2) + [A]o. So t1/2 = [A]o / 2 k. The integrated rate law for first order reaction is ln [A] = -k t + ln [A]o. When t = t1/2 we can substit...

VPatankar_2L

I think you are forgetting to square the concentration of C. When you input the values for A, B, and C for k[A][B]^2[C]^2, I think you calculated (2.85 x 10^12 L^4/mol^4 s)(0.00301 mol/L)(0.001 mol/L)^2(0.00115 mol/L) which would get you 9865.275 L/mol s. Since the reaction is second order with resp...

VPatankar_2L

Since one Faraday is 96485 C/mol, it can be multiplied by n (moles) in the equation delta G = -nFE to just get kJ. What are the units for E and how do we get to Joules from coulombs? The units for E are Volts, and one Volt = 1 J/C. So, when you multiply n (moles) by F (C/mol) and E ( V = J/C) you g...

VPatankar_2L

A cell reaction with a positive cell potential has a strong tendency to take place and will result in more products at equilibrium. As a result, K will be larger than 1 when E*cell > 0. When a cell has negative cell potential, the reaction is less likely to take place thus generating fewer products ...

VPatankar_2L

You should use the following half-reactions:
oxidation: Sn --> Sn2+ + 2e-
reduction: 2H+ + 2e- --> H2
This will help you calculate E*. then you can combine the two to find the net which would be Sn + 2H+ --> Sn2+ + H2 writing the expression for Q should give you Q = [H2][Sn2+]/[H2]^2

VPatankar_2L

Since one Faraday is 96485 C/mol, it can be multiplied by n (moles) in the equation delta G = -nFE to just get kJ.

VPatankar_2L

For maximum work calculations, the anode is in the reactants while the cathode is in the products. For example with question 6N.3 part a, Pt(s)|H2(g, 1.0 bar)|HCl(aq, 0.075 mol/L)||HCl(aq, 1.0 mol/L)|H2(g, 1.0 bar)|Pt(s), the oxidation reaction is H2 --> 2H+ + 2e- while the reduction reaction is 2H+...

VPatankar_2L

Platinum should be used when there is no metal present to conduct electrons from the anode to the cathode. You would include platinum when a solid metal isn't present to allow for the transfer of electrons.

VPatankar_2L

Also, unlike in Hess' law where you could multiply the enthalpy values by the same coefficient that you multiplied the entire reaction by, you can't use the same strategy with cell potential. Standard reduction potential gives the voltage difference between two standard electrodes which is always th...

VPatankar_2L

I think charge is still being transferred when you have maximum cell potential and maximum work. The relationship between E and work is E = -w/charge where charge = moles of e- transferred x F = nF. As a result, wmax = -nFE which suggests that in order for a maximum work value to result, there shoul...

VPatankar_2L

For an acidic solution, if there are more Oxygen atoms in the reactions you would add H3O+ to supply more H+. For a basic solution, if there are more Oxygen atoms in the reactants you would add H2O to supply more H+.

VPatankar_2L

The formal charge is a charge on a molecule that is present when the shared electrons are equally divided between atoms in each bond. The oxidation numbers are not always equal to the actual charge on the molecules, they are used as a way to keep track of the number of electrons an atom has.

VPatankar_2L

The reaction of the permanganate ion with Fe2+ in water is written as: 8H+ + MnO4- + 5Fe2+ --> Mn2+ + 5Fe3+ + 4H2O This reaction can show that MnO4- is the oxidizing agent because it is reduced to Mn2+ and Fe2+ is the oxidizing agent because it is oxidized to Fe3+. This can be seen in the half-react...

VPatankar_2L

Delta S is constant in the Vant Hoff equation because the change in entropy of the system at equilibrium is constant. Delta S doesn't increase because it has reached its maximum.

VPatankar_2L

You can generally only use lnK = (-delta H/RT) + (delta S/T) when the reaction is at equilibrium because you are setting Q = K.

VPatankar_2L

H2S(aq) + Cl2(g) --> S(s) + Cl-(aq)
In this reaction, Cl2 gains electrons to form Cl- thus Cl2 is being reduced. An oxidizing agent is the electron acceptor in a reaction, and in this case, Cl2 gains electrons while H2S loses electrons.

VPatankar_2L

Delta H only = q at constant pressure, so if the pressure is not constant you won't be able to calculate a value for Delta H

VPatankar_2L

The reaction enthalpy is the heat released or absorbed for the reaction; it is the difference in enthalpy for the products and reactants. The enthalpy of formation for a mol of substance in its standard state is the change in enthalpy that occurs when that substance is formed from its elements. The ...

VPatankar_2L

Yes, if you decrease the concentration of NO, the concentration of H2O will increase because the reaction will shift to the right to generate more products. If you increase the concentration of NO, the concentration of H2O will decrease as the reaction will shift toward the left to generate more rea...

VPatankar_2L

Constant pressure situations could also be referred to as isobaric, which would lead you to use the equation w = -PdeltaV. however, if the external pressure for a system is zero even though a value greater then zero is provided for the internal pressure, the work done would be zero.

VPatankar_2L

Heat capacity is a state function because its value doesn't depend on the way by which the temperature was changed or the path taken to add or subtract heat. The heat capacity is determined by the overall change in these two factors.

VPatankar_2L

The values given indicate what the heat capacity of an ideal gas could be at constant volume and constant pressure. the main concept to know here is that the change in internal energy = (3/2)Rdelta T. You can find the heat capacity by dividing delta U by delta T. You can use the "How Do We Know...

VPatankar_2L

Since diluted aqueous solutions have similar heat capacities as water, you can assume that the heat capacity of the calorimeter is the same as that of the solution. This would allow the qreaction to equal -qcalorimeter.

VPatankar_2L

I don't believe that there is a maximum heat capacity for a substance. The heat capacity given for that particular substance is the amount of heat energy necessary to increase the temperature of that substance by one unit per mass. This suggests that there is a set value for the heat capacity for a ...

VPatankar_2L

I don't believe that there is a maximum heat capacity for a substance. The heat capacity given for that particular substance is the amount of heat energy necessary to increase the temperature of that substance by one unit per mass. This suggests that there is a set value for the heat capacity for a ...

VPatankar_2L

A reversible process can occur in either direction; it can be reverted back to its original position through very small changes made to the surroundings.

VPatankar_2L

The formula for heat can be either q=nCT where n stands for the number of moles, or it can be q=mCT where m stands for the mass in grams. The formula you use will depend on whether the specific heat capacity (C) is given as J/gK where you would use q=mCT or if it is given as J/molK where you would u...

VPatankar_2L

A compound is in its purest form when it is in its most stable form. An example of this is O2 which has an enthalpy of formation of zero because it is the most stable form of oxygen, whereas O3 would have an enthalpy of formation that was not equal to zero. Generally, gases are in their most stable ...

VPatankar_2L

Mass, volume, and density are also state functions. As state property is not dependent on the path taken to obtain that state, it is only dependent on its current state.

VPatankar_2L

A reversible process is one that can return to its original state by making very small changes to the system by means of its surroundings. Reversible processes can occur in either direction.

VPatankar_2L

Dr. Lavelle was saying that if you look at the heating curve of water, you will notice a transition between the phase changes of water. It starts off as solid ice and as it is heated, the temperature of the solid rises to form water. The transition between ice and water is called the melting point a...

VPatankar_2L

Generally, if you see smaller molecules on the reactants side forming a larger molecule on the products side, it is endothermic. If you see a molecule dissociating into smaller molecules, it is exothermic.

VPatankar_2L

Exothermic reactions have a negative overall enthalpy because energy is released when bonds are formed. Thus the products require less chemical potential energy than reactants, to hold atoms together. For endothermic reactions, the overall enthalpy of the reaction is positive because energy is requi...

VPatankar_2L

The -x was ignored because the value would have been so small that 0.1-x would be rounded to 0.1. If K is less than 10^-3, you generally ignore the -x and use the initial concentration without explicitly factoring in the change.

VPatankar_2L

You can use M1V1 = M2V2 where M1 is the concentration of the original solution, M2 is 0.178 mol/L from part i, V2 is 500 mL, and V1 is 5 mL. You are using 5mL for V1 because that is the volume of the original solution that is used to dilute it to 500 mL.

VPatankar_2L

You could use the pKa to find the pKb by subtracting pKa value from 14. The lower the pKb value, the stronger the base.

VPatankar_2L

When you are writing out your ICE table, you want to find the concentration of reactants and products at equilibrium. For your initial concentration, you would calculate 0.4 mol/3 L H2 to find the initial concentration of H2 which is 0.133 mol/L. For the change in concentration, you would multiply 0...

VPatankar_2L

Yes I think you should always convert from Pa to atm or bar before you continue with calculations.

VPatankar_2L

The partial pressure refers to the pressure of a gas that could be calculated if it were alone in a container of the same volume and at the same temperature as the original mixture.

VPatankar_2L

When writing out your equilibrium constant, you wouldn't consider liquids and solids present in the reaction since they are pure substances and don't change over the course of the reaction. So when you write out your ICE box, you would only include gases and aqueous products and reactions.

VPatankar_2L

A change in pressure is brought about by a change in volume. A change in pressure can cause the reaction to shift to the left or to the right based on the number of moles of products and reactants. But this shift occurs to restore the value of the equilibrium constant.

VPatankar_2L

1. First, calculate the concentration of all gasses by dividing the amount in mols (this is given) by the volume (5L) 2. Set up your ICE box (as shown below) y writing down the initial concentration for all gases 3. Write out the equilibrium constant expression 4. calculate the value of x which repr...

VPatankar_2L

Hi! Energy is actually required to break bonds which means that a certain amount of energy must be provided to the reaction in order for the dissociation of X2 to occur. As you can see in this image (https://i.stack.imgur.com/jm5uO.png) bound atoms have low potential energy, and energy is required f...

VPatankar_2L

What does it mean when dipoles "cancel out?" Dipoles could cancel out if the are facing the same direction and if the atoms surrounding the central atom are all the same. This would mean that the electronegativity difference between the central atom and each of the bound atoms is the same...

VPatankar_2L

If the question asks "how many atoms on the structure would form a hydrogen bond?" you would just count the number of atoms that would have hydrogen bonding sites. But if it asks for the number of hydrogen bonding sites, you would count each available lone pair where bonding could occur.

VPatankar_2L

Cations that are small and have a high charge have large polarizing power. Anions that are large and have small charge have high polarizability.

VPatankar_2L

The intensity, or the number of electrons emitted from the metal, can be acknowledged when the frequency of the incident light is at or above the threshold frequency. If the threshold frequency is not reached, no electrons will be ejected no matter how high the intensity of the light is.

VPatankar_2L

You can compare the bond length of binary acids whose central atom varies down a group to determine which acid is stronger or weaker.

VPatankar_2L

The acid on the reactants side of the equation will have a proton that it will lose on the products side. This is how you can identify the Bronsted acid on the reactants side, and the opposite is true for the Bronsted base. Once you have found the Bronsted acid and base, you should remember that the...

VPatankar_2L

Make sure you have the correct decimal places for your molarity. 13.6 mg --> 0.0136 g
moles NaOH = (0.0136 g)/(40 g/mol) = 3.4 * 10^-4 mol
Molarity = (3.4 * 10^-4 mol)/(0.350 L) = 9.7143 *10^-4 mol/L
pOH = -log [9.7143 *10^-4 mol/L] = 3.01

VPatankar_2L

The greater the electronegativity of A in A-H for binary acids, across a period, the stronger the acid. The stronger the bond between A and H in A-H down a group, the weaker the acid. For oxoacids, the greater the number of oxygen atoms bound to the central atom, the stronger the acid. Oxoacids can ...

VPatankar_2L

Also, if the structure contains trigonal planar or linear arrangement, the atoms involved will be in the same plane.

VPatankar_2L

If the central transition metal is bound to four ions or molecules, it is considered either square planar or tetrahedral. Generally, you don't assume that transition metals have lone pairs, which is why the shapes of coordination compounds aren't as extensive.

VPatankar_2L

Anions that have the greatest polarizability are those that are large and less electronegative. Cations that have greater polarization power are those that are smaller and have a high charge.

VPatankar_2L

Hydrogen bonds occur between a Hydrogen atom that is covalently bonded to a more electronegative atom (F, N, O) and another electronegative atom that has lone pairs. An ion-dipole bond is an electrostatic interaction between an ion and a molecule that has a dipole.

VPatankar_2L

Larger molecules will have stronger London Dispersion Forces, which means that their boiling point will be high.

VPatankar_2L

Generally, you can look at the terminal toms to determine whether a structure will be polar or polar. With linear, trigonal planar, and tetrahedral structures, if the terminal atoms are the same the molecules will be nonpolar. But if the terminal atoms are different, the molecules will be polar. Reg...

VPatankar_2L

S character is directly proportional to the bond angle, so as the s character of a hybrid orbital increases the bond angle increases as well. In VSEPR, electrons are arranged to experience minimum repulsion. A high s character would increase the electron density across the central atom, so the bond ...

VPatankar_2L

I think that if you draw a Lewis Structure for the molecule, you will see that the atom that forms a double or triple bond with the central atom is contributing more electrons than the atom that is forming a single bond with the central atom.

VPatankar_2L

Polarity plays a part in determining which structure has a higher boiling point. AsF3 has the higher boiling point because it is a polar molecule and thus has dipole-dipole interactions, while AsF5 is a nonpolar molecule with London dispersion forces. London dispersion forces are weaker than dipole-...

VPatankar_2L

In terms of resonance Lewis Structure, electrons can be delocalized if they are free to move throughout the plane. This means that a double bond between Oxygen and Nitrogen, for example in the structure NO3, can be moved between any of the Oxygens while the remaining two form a single bond with Nitr...

VPatankar_2L

Oxygen can form double, single, or triple bonds depending on the atom it is bonding with. Oxygen can form a triple bond with Carbon since the total number of valence electrons is 10 which means that there are 5 pairs of electrons. The only way that you can form five pairs of electrons for a CO Lewis...

VPatankar_2L

I think you can also call it V shaped, although that sounds a little informal.

VPatankar_2L

I think it has to do with the fact that Chlorine's atomic radius is larger than that of Oxygen, so Oxygen's outermost electrons are held more tightly to the nucleus than Chlorine's outermost electrons. Also, the change in electronegativity is greater as you move up or down a group, than if you move ...

VPatankar_2L

If you are referring to ionic bonds then you just draw both atoms separately with their complete octet and place them next to each other, without bonds. The anion will pull electrons away from the cation. If you are talking about resonance structures, the atom that is either double bonded or triple ...

VPatankar_2L

I think for the first question, the answer is that the CN bond in H3CNH2 is longer than the CN bond in HCN because Carbon and Nitrogen share a triple bond in HCN while they only share a single bond in H3CNH2. Single bonds are longer than triple bonds because less electrons are being shared. For part...

VPatankar_2L

If the central atom is in row one and row two, with the exception of the incomplete octet elements, you should calculate the number of valence electrons of the structure and then divide by two to find the number of electron pairs. When you add all of the atoms around the central atom and account for...

VPatankar_2L

Also since Oxygen is more electronegative that Chlorine, it can carry the -1 charge.

VPatankar_2L

The energy gaps between the energy levels of the Balmer series are much smaller than the gaps for the Lyman series, so that's why the frequency produced is also smaller.

VPatankar_2L

I think the answer key is saying that all three are possible resonance structures since Chlorine is in the third row of the period table and has an expanded octet. Thus, in the first diagram chlorine can have eight electrons surrounding in, in the second diagram Chlorine can have 10 electron, and in...

VPatankar_2L

For this question, you have to remember the equation: E photon - work function = Kinetic Energy (of electron). In this situation, the E=hv equation applies to the photon and finding the energy of the photon. But to find the energy of the emitted electron, you need to use KE=(1/2)m(v)^2.

VPatankar_2L

Another thing you could do is calculate the total number of valence electrons for each molecule. If the total number is an odd number, the specie is a radical.

VPatankar_2L

If the question asks you to draw two resonance structures for Sulfur Dioxide, I think you should do both. But if it just asks for the Lewis structure, draw the one with the lowest formal charge.

VPatankar_2L

Lone pairs are pairs of electrons in the valence shell that are not shared with another atom through bonding. The lone pairs in a lewis structure are the pairs of electrons that are drawn as dots around the atom. For example, in NH3, N has one lone pair of electrons because it shares six with the th...

VPatankar_2L

You should convert the value of electron volts to Joules, and then write the equation of E=hv as E=(hc)/(wavelength). Then you can rewrite this equation as wavelength = (hc)/(E) and solve.

VPatankar_2L

I think there are some calculations you can do to tell which arrangement is the most stable. So, I think he might have us draw the most stable configuration.

VPatankar_2L

The length of the bonds is in part based on the distance between two atoms. Atoms that form double bonds with one another have a stinger attraction between them which means they are pulled closer together than if they were connected by a single bond. Thus, the distance between them is smaller which ...

VPatankar_2L

Yes, I think that if a proton and neutron had the same wavelength, they would have the same velocity. You can use De Broigle's to determine that wavelength = h/p which is the same as: wavelength = h/mv. v=h/(m*wavelength) and the mass of a proton and neutron are the same. If the wavelength is also t...

VPatankar_2L

The Lyman series is a spectrum series that produces ultraviolet emission lines from any energy level greater than or equal to 2 (n>=2) to energy level of one (n=1). The Balmer series produces emission lines from any energy level greater than or equal to 3 (n>=3) to energy level of two (n = 2). The a...

VPatankar_2L

You can convert the kJ to J by multiplying the energy by 10^3 joules. And the formula for kinetic energy is KE = (1/2)(mv^2) which can be used to solve this problem.

VPatankar_2L

Yes it's mostly used to find the indeterminancy in the position or the momentum. But you can use the value you calculated for the indeterminancy of the momentum to solve for the indeterminancy of the velocity of that particle.

VPatankar_2L

Yes, to get the wavelength of the electron you can't use c = 3 * 10^8 because it is the speed of light, thus the speed of a photon. The question has specified the velocity of the electron, so you have to use this velocity in De Broglie's equation.

VPatankar_2L

Energy in the situations that discuss light is considered as J/photon. If the energy is provided in eV (electron Volts), you will have to convert it to J/photon. The conversion factor is about 1 eV = 1.6 *10^-19 J/photon.

VPatankar_2L

You use Rydberg's equation when the question talks about an electron transitioning from one energy level to another. Generally, you will use it to sole for the final or the initial energy level, based on the information that is provided. Sometimes, you will also be asked to calculate the frequency o...

VPatankar_2L

You should use the equation, wavelength = (plank's constant)/(mass x velocity). You can convert the mass of the baseball into grams and then just plug in the rest of the information.

VPatankar_2L

Constructive interference refers to waves that are in phase. This means that you can add them to give rise to a larger wave. Destructive interference refers to waves that are out of phase, which means that you can subtract the waves' peaks. If both waves are at their highest peak at a given moment, ...

VPatankar_2L

Yes, both equations will essentially give you the same result. Dr. Lavelle suggested using the H-atom equation because it really helps you see whats going on during the transitions, and how the energy is affected. This will allow you to understand the fact that energy is emitted (and thus lost) when...

VPatankar_2L

My TA said to write each calculation answer with at least four decimal places after the decimal point so that when you do further calculations, you have the most precise value from before. But the final answer should be written with the correct number of significant figures.

VPatankar_2L

Make sure you bring a scientific calculator. Graphing calculators aren't allowed.

VPatankar_2L

I think in general, ionic bonds are stronger than covalent bonds. But covalent bonds are stronger than ionic bonds in water.

VPatankar_2L

The glucose and other sugars aren't relevant because there are no chloride ions present in glucose.

VPatankar_2L

Generally if you're given a molecular formula, you will be able to reduce the number of moles of each element by a certain factor. If you're given an empirical formula, you can't divide by a number to reduce the umber of moles of the element in the formula.

Search found 104 matches