CHEMISTRY COMMUNITY

Victoria Zheng--2F

Increasing the mass of the cathode will not change the E cell because solids are not taken into account when calculating K or Q for a chemical reaction, which means when you apply the Nernst equation to calculate the Ecell, the mass of the cathode and anode are not taken into account, so they do not...

Victoria Zheng--2F

A catalyst is not used up in the reaction, which means that it will appear first on the reactant side of one step of the reaction and then appear again as a product in another step of the reaction. However, the catalysts will not appear in the overall reaction.

Victoria Zheng--2F

The Arrhenius equation can be used for any reaction order because it is concerned with the rate constant and activation energy of the reaction instead of reaction orders. The Arrhenius equation basically shows how the temperature and adding catalyst changes the rate of the reaction, which is changin...

Victoria Zheng--2F

The rate-determining step is the slowest step in the chemical reaction because the reaction can not proceed any faster than the slowest step in a chemical reaction. In order for the overall chemical reaction to complete, the slowest step has to be completed, which makes it the rate-determining step.

Victoria Zheng--2F

The unit of K for a zero-order reaction is M/s, which is the same as the unit of rate. The unit of K for a first-order reaction is 1/s. The unit of K for a second-order1/M reaction is 1/M*s. The unit of rate is always M/s

Victoria Zheng--2F

A compound is a catalyst if it is not used up in the reaction, so the compound will reappear in the steps on the product side of the reaction. However, catalysts are not present in the overall chemical reaction.

Victoria Zheng--2F

I don't really know how to approach homework problem 6O.3. The question reads that Aqueous solutions of (a) Mn21; (b) Al31; (c) Ni21; (d) Au31 with concentrations of 1.0 mol·L21 are electrolyzed at pH 5 7. For each solution, determine whether the metal ion or water will be reduced at the cathode.

Victoria Zheng--2F

When the enzyme/catalyst is saturated, meaning that adding more reactants can no longer speed up the rate of the reaction because the enzymes/catalyst are all occupied with substrates, then the reaction rate is independent of the concentration of the reactants.

Victoria Zheng--2F

Since the unit of rate is M/s, if the reaction is zero-order, the unit of k is the same as the unit of rate. If the reaction is first order, then the reactant will have the unit M and the unit for k would be 1/s since the unit of rate is always M/s. If the reaction is second order, the reactant will...

Victoria Zheng--2F

When there is no solid in the anode or cathode that can act as an electrode, which means that there is only gas and aqueous solutions present, inert electrodes will be used.

Victoria Zheng--2F

A zero-order reaction means that the rate of the reaction does not depend on the concentration of the reactant.

Victoria Zheng--2F

Hello. Homework 6L.9 reads (a) Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride. (b) Write the balanced equation for the cell reaction and devise a galvanic cell to study the reaction (write its cell diagram). I am not sure...

Victoria Zheng--2F

Hello. When we balance the hydrogens in redox reactions in acidic environments, should we use H+ or H3O+? Would using H3O+ change the stoichiometric coefficients? The book uses H+, but should I use H3O+ instead?

Victoria Zheng--2F

H2O and H+ are used to balance reactions in an acidic environment, where H2O is used to balance the oxygens and H+ is used to balance the hydrogens.

Victoria Zheng--2F

Hello. Homework 6L.7 reads that Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions:
(a) AgBr(s) ∆ Ag1(aq) 1 Br2(aq), a solubility equilibrium.
I am not sure how should I approach part a here?

Victoria Zheng--2F

The order of the cell diagram is that the anode should be on the left of the cell diagram while the cathode would be on the right of the diagram.

Victoria Zheng--2F

Hello. For the Homework problem 6L.1, how can I find the moles of the electrons transferred in the reaction, which is n for the equation deltaG=-nFEcell?

Victoria Zheng--2F

Hello. I am unsure about how to balance the redox reaction. I am also unsure about what is being reduced in this reaction.

Victoria Zheng--2F

For Homework 6K.3 Part d, I am not sure how to balance the redox reaction. What is being oxidized in this reaction?

Victoria Zheng--2F

Part d basically combines all the species from the two half-reactions to form a complete reaction. The first step is to cancel out the electrons for both half-reactions by either multiplying one of the half-reaction or cancel out if they have the same number of electrons. Next step is to cancel out ...

Victoria Zheng--2F

When balancing redox reactions the safe method is to first find all the oxidation states of each species and then decide what is being reduced and oxidized, which will minimize errors.

Victoria Zheng--2F

Hello. What method should I use to solve homework question 4I.1, should I be using q/T for temperature of 800K and q/T for temperature of 200K and subtract the the delta S for 800K from the delta S of 200K? What is the reasoning behind this method? Or should I use other methods?

Victoria Zheng--2F

For the Third Law of Thermodynamics, at the absolute temperature of 0K for a perfect structure, there will only be one possible position, which means that the degeneracy is 1, and since the entropy is taking the natural log of degeneracy, natural log of 1 is zero, so the entropy of a perfect structu...

Victoria Zheng--2F

Because when you decrease the pressure, the volume increases, which means that the molar concentrations of the reactants and products decrease. Since the molar concentrations of gases and aqueous solutions are inversely related to volume, increasing the volume decreases the molar concentration of th...

Victoria Zheng--2F

Adding more solids to the reaction does not cause the equilibrium to shift because the solid is not taken into consideration when we are calculating K.

Victoria Zheng--2F

A reaction will be spontaneous if the change in Gibbs Free energy is a negative value. A reaction will not be spontaneous if the change in Gibbs Free energy is a positive value.

Victoria Zheng--2F

Standard enthalpy of formation is often used to calculate the standard enthalpy change of a reaction. enthalpy is often associated with the internal energy of a system.

Victoria Zheng--2F

Hello. I understand how to calculate the entropy change when the volume of the system changes, but how would I calculate the entropy change when pressure changes? Is it the same equation for volume just with modifications?

Victoria Zheng--2F

The third law of thermodynamics basically states that a perfect object will reach an entropy of zero when it reaches the temperature of 0K because, at that temperature, the atoms will stop moving, which provides a reference point for measuring the entropy of any substance at any temperature.

Victoria Zheng--2F

The 6.01 kJ/mol value is the heat of fusion for water going from ice to water, and the 40.7kJ/mol value is the heat of vaporization going from water to water vapor.

Victoria Zheng--2F

Hello. I don't quite understand what is the meaning of there is no expansion work done when the pressure is constant?

Victoria Zheng--2F

Hello. I don't quite understand the difference when the pressure of the system is constant and when the system is equilibrium, what does it mean by taking infinitesimal small steps to change the volume? Why are we using the derivative and integral to calculate the sum of all the small steps? Thank y...

Victoria Zheng--2F

A state function is a property that does not depend on the path taken to reach value. Enthalpy is a state function because enthalpy is the amount of heat absorbed or released, which is calculated using the final value minus the initial value, but enthalpy does not depend on the steps and path taken ...

Victoria Zheng--2F

Negative work does not really mean that it is less than positive work. The negative sign indicates that work is being done in the opposite direction, and the numerical value indicates the magnitude or amount of work done.

Victoria Zheng--2F

qv can not equal delta H because qv is constant volume, but the pressure of the system changes as the temperature increases(more random motion by gas particles), and the definition of enthalpy states that enthalpy is the amount of heat absorbed or released at constant pressure, so since the pressure...

Victoria Zheng--2F

Hello. I don't really know how to approach the problem 4D.9. The question states that: The enthalpy of formation of trinitrotoluene (TNT) is 267 kJ?mol21, and the density of TNT is 1.65 g?cm23. In princi- ple, it could be used as a rocket fuel, with the gases resulting from its decomposition streami...

Victoria Zheng--2F

For this question, the first step is to find the concentration of both ammonium carbamate and CO2 by finding the molarity of the two molecules. The concentration of ammonium carbamate is 1.28M, and the concentration of CO2 is 3.95*10^-4M. Then, set up an ICE table with initial concentrations 1.28, 0...

Victoria Zheng--2F

partial pressures are the pressures of each individual gas in a mixture of gases, and the total pressure is the sum of all the partial pressures of each individual gases in the mixture.

Victoria Zheng--2F

Hello! In the lecture on Friday, Dr. Lavelle talked about buffer solutions, but I am unclear about how buffer solutions work and how to make a buffer solution, can someone please clarify how buffer solutions work? Thank you!

Victoria Zheng--2F

For the salts in topic 6D, their acidity and basicity depend on whether cations and anions affect the pH of the solution. If the cations are in group I and group II, then they generally do not affect the pH of the solution. If parts of the salt are the conjugate acid of a weak base, then it would ma...

Victoria Zheng--2F

What do you mean by converting 0.025 moles per 250 milliliters? For part (a), since the concentration of HCl is already given, and 1 mole of HCl yields 1 mole of H3O+, the pH of the solution can be found through taking the -log of the concentration, which is -log[0.025], which gives you the pH value...

Victoria Zheng--2F

Yes, the K in the second column is the K calculated with partial pressures of the molecules.

Victoria Zheng--2F

For this problem part a, first write the chemical equations for the weak acid, then set up the ICE table and use the concentration of H3O+ to find the x and solve for the equilibrium concentrations for each compound, then calculate the Ka and pKa. For part b, the process is the same, but instead of ...

Victoria Zheng--2F

I think in this case, aluminum forms a coordination compound with water, and Cl3 acts as a spectator ion in the equation, so the molecule will not appear in this net equation.

Victoria Zheng--2F

I am kind of confused on how to solve the homework 6B.11 part B. The problem reads: A student added solid Na2O to a volumetric flask of volume 200.0mL, which was then filled with water, resulting in 200.0mL of NaOH solution. Then 5.00mL of the solution was transferred to another volumetric flask and...

Victoria Zheng--2F

since the equilibrium constant Kc is very small, x would be a very small number and subtracting a very small x from 0.114 moles will essentially give you 0.114 moles, so in the denominator, you can just put 0.114 moles^2 and solve the equation, which would give you an approximation. I think your ans...

Victoria Zheng--2F

In the first row, the concentration of H3O+ is given, so you can calculate pH by taking the negative log of the concentration of H3O+. Then, you can calculate pOH by using the equation pH+pOH=14. Then, you can calculate the concentration of OH- by calculating 10^-pOH. In the second row, the concentr...

Victoria Zheng--2F

Since the equilibrium constant K stays the same for the same reaction under the same condition, if the initial concentration for reactants is higher, meaning having more reactants, then since the ratio of reactants and products stays the same (K), there will be a higher concentration of products at ...

Victoria Zheng--2F

Do the partial pressures of all the gases in a reaction always have to add up to 1atm?

Victoria Zheng--2F

The answer is A for this question because the equilibrium constant is giving a ratio of the concentrations of products and reactants at equilibrium, which gives the relative concentrations of products and reactants at equilibrium.

Victoria Zheng--2F

mmol means millimole, so the given amounts should be converted to moles before calculating the reaction quotient.

Victoria Zheng--2F

The answer is true because the equilibrium constant K, stays the same in this case for this reaction, so if the reaction starts with a higher concentration of reactants, which means more reactants, the reaction will produce a higher concentration of products at the end, which means more product.

Victoria Zheng--2F

b) can be mono or bi dentate because of the three oxygens bonded to the central carbon, depending on the position of the oxygens, two of them will be closer together thus possible for bonding to the same metal, which makes it bidentate. The third oxygen thus is monodentate because it consists of onl...

Victoria Zheng--2F

Yes, it does mean there are two possible sites of hydrogen bonding with oxygen having two lone pairs Hydrogen bonding can only happen when hydrogen is bonded to highly electronegative atoms such as NOF. The possibility of hydrogen bonding with hydrogen bonded to something else depends on the electro...

Victoria Zheng--2F

When CO2 reacts with water, they form the carbonic acid H2CO3
When SO3 reacts with water, they form the sulfuric acid H2SO4

Victoria Zheng--2F

NH4 charge is +1
H2O charge is 0
NH3 charge is 0
CN charge is -1
OH charge is -1
NO2 charge is -1
SCN charge is -1
SO4 charge is -2
C2O4 charge is -2
CO3 charge is -2
PO4 charge is -3

Victoria Zheng--2F

A higher pOH value means the solution is more acidic, while a lower pOH value means the solution is more basic.

Victoria Zheng--2F

The best way to differentiate between mono, bi, and polydentate is to draw the Lewis structure of the ligand. Lone pairs can help you decide how many binding sites the ligand has, but the distance between the lone pairs is also very important in deciding mono, bi, and polydentate. If the binding sit...

Victoria Zheng--2F

In part b) there is a proton transfer from NH4 to I-, forming NH3 and HI, which makes this reaction a Bronsted reaction, and the proton donor, which in this case is NH4+ will be bronsted acid and I- will be the bronsted base. In part c) there is no proton transfer between CH3COOH and NH3, so it is n...

Victoria Zheng--2F

A double bond does not count as a polydentate because the ligand is still bonding with the metal at one binding site; polydentate ligands have multiple binding sites that can bind the metal.

Victoria Zheng--2F

A chelate is a complex form containing a ligand that forms a ring of atoms that includes the central metal atom. It involves a polydentate ligand and a single transition metal forming a coordination compound with the ligand binding to the central metal atom at multiple sites.

Victoria Zheng--2F

Polydentate refers to ligands binding the transition metal at multiple sites. It does not have to do with the naming of the ligands but the number of binding sites the ligands have.

Victoria Zheng--2F

How do we know how many coordination bonds can a transition metal form? What determines the number of coordination bonds it can form?

Victoria Zheng--2F

It would still be considered as a polar molecule because the dipole moment of hydrogen might not be strong enough to cancel the dipole moment of chlorine and the arrangement of hydrogen and chlorine atoms in a square planar also affects the polarity of the molecule.

Victoria Zheng--2F

A trigonal bipyramidal shape molecule does have bond angles of 90, 120, and 180.

Victoria Zheng--2F

pi bond is not two bonds, pi bond is one bond with the orbitals overlapping side by side.

Victoria Zheng--2F

Cis- and Trans- molecules are isomers, which means they have the same molecular formula, but the arrangement of the atoms in the molecule is different. Cis isomers are polar, and trans isomers are nonpolar, but cis isomers are isomers with functional groups on the same side, while trans isomers are ...

Victoria Zheng--2F

I think that in this case, since AsF3 is a polar molecule and AsF5 is a nonpolar molecule, the dipole-dipole attraction between AsF3 molecules are greater than the London Dispersion forces between AsF5 molecules, thus it is harder to break the bonds of AsF3 molecules, so the boiling point is higher.

Victoria Zheng--2F

The shape of the molecule is Octahedral because there are 6 electron-dense regions surrounding the central atom (4 bonds and 2 lone pairs). Square Planar is the molecular geometry for molecules with the octahedral molecular shape and has 2 lone pairs around the central atom.

Victoria Zheng--2F

The Molecular Shape for d is Trigonal Bipyramidal, and the molecular geometry is Sawhorse.
The Molecular Shape for f is Octahedral, and the molecular geometry is Square Pyramidal.

Victoria Zheng--2F

Lone pairs prefer to be on an equatorial position because the angle would be the greatest between the lone pairs and the bonding pairs, thus making the lone pairs farthest away from the bonding pairs and make the electron repulsion lower. Two lone pairs can be in an equatorial position as long as th...

Victoria Zheng--2F

To determine if the molecule is polar or nonpolar, you would draw the dipole moments for the molecule to see if they cancel out. If the dipole moments cancel out, then the molecule is nonpolar. If the dipole moments do not cancel out, then the molecule is polar.

Victoria Zheng--2F

CN- does have a triple bond. If CN- has a double bond, then there would not be enough valence electrons to fulfill the octet on both carbon and nitrogen because there are only 10 electrons in total, and for a double bond, 12 electrons are needed.

Victoria Zheng--2F

n=4, l=1 means it is the 4p subshell, and the p subshell have three orbitals that can contain 6 electrons in total.

Victoria Zheng--2F

A highly polarizable anion means that the anion generally has a large size and more electrons. Due to the large size and more electrons, the nucleus will exert less force to pull the valence electrons, which makes them easily distorted and make the electron cloud of the anion be easily pulled toward...

Victoria Zheng--2F

Can someone please explain the concept of dipole moments? I don't quite understand it. Thank you.

Victoria Zheng--2F

Neutrons and protons do have wave-like properties, and all particles do exhibit wave-like properties, but we can only detect these waves if the object traveling has a small mass. Particles with a large mass generally have wavelengths that are too short to be detected.

Victoria Zheng--2F

Formal charge indicate stability by indicating if each of the element contains a charge in the bond. Bonds are more stable if more elements in the bond have a zero formal charge. In addition, if elements in the bond have a nonzero formal charge, then the bond would be more stable if elements with hi...

Victoria Zheng--2F

Matt Sanruk 4F wrote:Also how would you identify if a species is a radical or not?

You can identify species as radicals by drawing their Lewis structure and see if there are any unpaired valence electrons. For example, CH3 is radical because there is one unpaired valence electron when you draw the Lewis structure.

Victoria Zheng--2F

I think that since elements in period 3 have electrons that occupy the n=3 principal energy level, that means these elements can have electrons in s, p, and d subshell, so they can expand their octet and fill the d orbital too even if they don't have any electrons in the d orbital.

Victoria Zheng--2F

Since 4s is the outermost shell for the element Nickel, the electrons will be removed from the 4s shell first, so Ni 2+ will have an electron configuration of [Ar] 3d^8.

Victoria Zheng--2F

Bonds can have both ionic and covalent character because electrons are not shared equally between the elements. Even though the electrons are shared, which gives them a covalent character, some elements will have greater electronegativity, which allows them to pull the electrons closer to them, maki...

Victoria Zheng--2F

when do you know to turn into a double bond instead of leaving the electrons on the other side of the element when drawing a lewis structure? You would turn into a double bond when the total number of electrons you drew for the elements exceeds the total number of electrons of the compound you have...

Victoria Zheng--2F

Homework Question 1F.19 asks why are s-block metals typically more reactive than p-block metals? I don't really know the answer to this question. Is it because s-block metals have lower ionization energy?

Victoria Zheng--2F

Does the Octet Rule apply to Boron (B), or is Boron a special exception that only needs 6 valence electrons?

Victoria Zheng--2F

I think s and p orbitals both do have electron density because electrons are found on s and p orbitals. However, there is no nodal plane (where there is no electron found, which is 0 electron density) in the s orbital.

Victoria Zheng--2F

When we put dots to represent valence electrons for elements, is there any rule on where (start putting dots on the left side, right side, etc.) to start drawing the dots?

Victoria Zheng--2F

I don't quite know where the g orbital fits in the periodic table and what do we need to know about the g orbital?

Victoria Zheng--2F

The question says that the bowling ball of mass 8.00kg is rolled down a bowling alley lane at 5.00+/- 5.0m/s. I don't know if the change in the velocity of the bowling ball is 10m/s or 5m/s?

Victoria Zheng--2F

Hello. The process of solving this problem is that first identify the n value to find the shell. The next step is to identify the l value to find the subshell, l=0 is the s-orbital, l=1 is the p orbital, l=2 is the d orbital, and l=3 is the f orbital. Then, identify if there is an ml value present; ...

Victoria Zheng--2F

I need a little help in understanding what the magnetic quantum number, ml indicates. What is the orientation of the orbitals?

Victoria Zheng--2F

Hello. I think for this question the information about baseball must weight between 5.00 and 5.25oz is just an extra piece of information that allows you to check if the baseball's weight is within the correct range of weight. I hope this helps.

Victoria Zheng--2F

Homework Question 1B.9: A lamp rated at 32W (1W=1J/s) emits violet light of wavelength 470nm. How many photons of violet light can the lamp generate in 2.0s? How many moles of photons are emitted in that time interval? I don't know how to approach this problem. Should I start with calculating the en...

Victoria Zheng--2F

1A.3 asks which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning (a) speed of radiation decreases (b) the wavelength of radiation decreases (c) the extent of change in the electrical field at a given point decreases (d) energy of the radiatio...

Victoria Zheng--2F

To use the change in energy method to solve this question, you would first calculate the frequency of the light using its wavelength, which involves the equation c=λv. This would give you the change in energy of the transition from the initial energy level to the final energy level. The next step is...

Victoria Zheng--2F

I think the question is giving you the number of wavelengths emitted instead of the actual wavelengths emitted by the photons. In other words, the number given to you is the number of photons (1,614,098) emitted with a specific wavelength. I hope this is helpful.

Victoria Zheng--2F

The photoelectric effect is an experiment that discovered light has the properties of particles. The equation of calculating the energy of a photon E=hv comes from this experiment. The electrons will only be ejected when the energy is greater than or equal to the threshold energy (work function), an...

Victoria Zheng--2F

Hello. I think you might have accidentally input the wrong power of 10 in the calculator. To do this question, you would use the equation E=hv(energy= to Planck's constant*frequency), so when you plug in the numbers into the equation, you would have E=(6.626*10^-34)*(3.00*10^15), which will give you...

Victoria Zheng--2F

To find the limiting reagent for this question, you would first write a balanced equation, and then convert the reactants from grams to moles by using their molar mass, and then you compare the molar ratio between the two reactants. If they have a 1:1 ratio, then that means the number of moles for b...

Victoria Zheng--2F

In M9, the question reads that Copper(II) Nitrate reacts with Sodium Hydroxide to produce a precipitate of light blue Copper Hydroxide and asked to write a net ionic equation. I have a balanced equation, but sodium and nitrate are left out in the answer key. My question is that for net ionic equatio...

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