CHEMISTRY COMMUNITY

Tessa House 3A

As others said, because the order of c is zero, it does not influence the rate. Therefore, you shouldn't include it in your rate law. Anything with a zero order does not influence the rate, and changing its concentration will not influence the rate of the reaction. You may have also included it some...

Tessa House 3A

If you're asking how to determine the oxidation number, start with the known oxidation numbers. Oxygen's oxidation number is always 2-, so for Cl2O7, the oxygens contribute 14- to the charge of the molecule. Each Cl must be 7+. For ClO2-, the oxygens contribute 4- charge to the molecule, so Cl must ...

Tessa House 3A

To start, it helps to know that the anode is on the left side and the cathode is on the right side of the diagram. This means on the left side, oxidation is occurring. Using this, you can determine which species are products and reactants. If both species are products or both are reactants, you may ...

Tessa House 3A

I am not entirely sure, but I believe we would be given standard reduction potentials for problems like this. I do not think we would have to come up with it on our own. Otherwise, we could not determine the cell potential to determine how to form the galvanic cell. The table with reduction potentia...

Tessa House 3A

One way to remember is that milli- is 10^3 (one thousand), so there are 1000 mmol in 1 mol. Divide the number of mmol by 1000 to get the number of moles.

Tessa House 3A

The order of a reaction tells you how much the concentration of a reactant affects the rate of a reaction. In a zero-order reaction, the concentration of reactants has no influence on the rate. In a first-order reaction, the concentration of reactants has a higher influence, as does a second-order r...

Tessa House 3A

Something being spontaneous means that the delta G is negative, meaning the final free energy is lower than the initial free energy. This does not specify the path taken between the final and initial state, which may have a high activation energy. Although the reaction may be spontaneous, the path b...

Tessa House 3A

Because k is positive but first and zero-order reactions have a negative slope when graphed using their equations, the slope is negative k for these two. However, for second-order reactions, the slope is positive so it is just k. I hope this helps!

Tessa House 3A

I don't think that a molecule can be oxidized and reduced at the same time because oxidation is when a molecule loses electrons and reduction is gaining electrons, so they cannot happen at the same time. However, a molecule can be a reducing agent (causing something else to be reduced) and oxidized ...

Tessa House 3A

I think that the transition metals are usually good conductors. The elements on the right-hand side of the periodic table aren't good conductors. So for example, I don't think that I2(s) would be a good conductor and you would need to use Pt(s). I hope this helps!

Tessa House 3A

E naught cell is the cell potential at standard conditions, as the person above said. E cell is the cell potential not under standard conditions, which means that it also depends on the temperature and concentration of reactants and products. E naught cell and E cell can have different signs dependi...

Tessa House 3A

Electrolytic cells are nonspontaneous and have negative standard cell potentials so they must be driven by another spontaneous process. I think they appear similar to Galvanic cells, but must be driven by another process because they are not spontaneous, unlike Galvanic cells. This source drives the...

Tessa House 3A

I think that no matter how many electrons are transferred or how many times the reaction occurs, E naught does not change. It is an intensive property, so the value is not affected by the number of times the reaction occurs. This is why you do not need to multiply it by any value.

Tessa House 3A

Another way to think about it is that in a concentration cell, at standard conditions there will be equal concentrations of the same species. This means neither one of the sides of the half reaction will tend to act as an oxidizing or reducing agent because they have the same potential. This means t...

Tessa House 3A

I think that some elements tend to always have the same oxidation numbers. Oxygen is usually 2- and group 1 metals (in this case K) are usually 1+. The only element that does not have a certain oxidation number is Cl, so you can determine this oxidation number based on the other two. There are some ...

Tessa House 3A

If work is done on a system, the value is positive (think of an increase in internal energy). If a system does work, the value of w is negative (think of a decrease in internal energy). I hope this helps!

Tessa House 3A

The size of the molecule does affect the entropy because larger molecules will have more degeneracy. Molecules with larger masses also have higher entropies. You are correct that the entropy of gases, liquids, and solids have different entropies because the entropy of a gas is significantly higher t...

Tessa House 3A

The system that is at a higher temperature will release heat, so the sign of q is negative. The system at the lower temperature will absorb this heat and will have a positive sign for q. I hope this helps!

Tessa House 3A

I believe that you would find free energies of formation from a table that gave standard Gibbs free energies of formation. You wouldn't calculate it yourself. Compounds with positive free energies of formation have a delta G value that is positive, meaning this reaction is not spontaneous. The react...

Tessa House 3A

I think that STP is at 0 degrees Celsius. You may have heard 25 degrees Celsius when talking about things in their standard state because 25 is often the temperature given in tables referring to standard states. This is different than STP.

Tessa House 3A

Like the people above said, I believe you are correct. Positive work means work is being done on a system (think of an increase in internal energy so it is positive). When work is negative it means the system is doing work (a decrease in internal energy so it is negative). I hope this helps!

Tessa House 3A

You use standard Gibbs free energy when the reaction is occurring at standard state. If not, you can use the standard Gibbs free energy to calculate the Gibbs free energy under conditions not at standard state. This value would be different than delta G naught.

Tessa House 3A

I think that's correct! One way to remember if the reaction is spontaneous in the forward direction is if K is large, the products are more stable and the forward reaction is spontaneous under standard conditions. The opposite is true for when it is not spontaneous. I hope this helps!

Tessa House 3A

Work done in a reversible expansion occurs when the pressure of the inside and outside are similar and the pressure on the outside is slowly decreased in very small increments, slowly causing the gas to expand. This does more work than an irreversible pathway in which there is a sudden expansion of ...

Tessa House 3A

I think that it is sometimes useful to know that qp=delta H under conditions of constant pressure in certain equations. We wouldn't necessarily use the equation itself to solve anything, but often it is useful to know that the heat released or absorbed is equal to the change in enthalpy. This is bec...

Tessa House 3A

One way to think about this problem is that the heat required to melt the ice plus the heat required to raise the temperature of the ice (to the final temperature) is equal to the heat released to cool the water (a negative value). Therefore, calculate the heat required to melt that specific mass of...

Tessa House 3A

Entropy is a measure of disorder, so it can come from thermal entropy and entropy that comes from the different positions an atom can be in. Residual entropy is purely the entropy that results from these different positions. This means that it is the entropy present when atoms are at T= 0K, because ...

Tessa House 3A

If you are talking about reversible or irreversible expansion, irreversible expansion occurs when a gas expands against a constant pressure. This is more rapid and is not reversible. Reversible expansion of a gas occurs when there are very small changes in external pressure that results in very smal...

Tessa House 3A

When pressure is constant, it is not implied that volume is also constant. Often, when pressure is constant, volume changes to keep the pressure constant. Therefore, if volume increases, it may be to prevent the pressure from increasing if there was no change in volume. A constant pressure does not ...

Tessa House 3A

The number of particles refers to the number of CO molecules, not the number of atoms in CO. This is because the number of atoms is taken into account by determining the possible positions C and O can be oriented in, which is 2. Then, by raising that to the power of the number of CO molecules, degen...

Tessa House 3A

To start, I would convert pH to concentration of H+ and set up an ICE table, putting in this known equilibrium concentration of H+. You also can solve for the concentration of the conjugate base (if working with a weak acid) and x, because they are the same as the concentration of H+. I think that y...

Tessa House 3A

We know that pKa=-log(Ka) because p represents the negative log of something. This means that -pKa=log(Ka) and 10^-pKa=Ka. This is how you can solve for the equation to convert pKa to Ka if you don't remember how to. I think it is important to know how to get from pKa to Ka because often Ka values a...

Tessa House 3A

I think that in this case, Cl- is the conjugate base of a strong acid, HCl, so it would not affect the pH of the solution. CH3NH3+ would act as an acid by donating a hydrogen ion to water. The equation for this would be CH3NH3+ (aq) + H2O (l) <--> CH3NH2 (aq) + H3O+ (aq). CH3NH3+ has a positive char...

Tessa House 3A

I think that the equation given in the textbook for this problem is incorrect and it should actually be 2HD(g) ⇌ H2(g) + D2(g). This can also be found on the Solution Manual Errors. You are correct that if there were fewer moles of gas in the products and the pressure was increased due to compressio...

Tessa House 3A

Another way to think about this is using Le Chatelier's principle. If the reaction is endothermic, it uses heat. Therefore, if you increase the temperature, the equilibrium will shift in the forward direction (towards the products) to try to absorb some of this heat. This is to reduce the change tha...

Tessa House 3A

Percentage protonated is used for calculations involving a base and percent ionization is for an acid. This is because a base gains a hydrogen ion, so it is protonated. Percent protonated is the percent of molecules that are protonated over the original concentration of the base. For an acid, it los...

Tessa House 3A

A stronger base will have a large Kb value because this means the products are more highly favored in the reaction and the concentration of OH- will be higher (a product). Therefore, higher Kb values imply a stronger base. Because pKb=-log(Kb), as Kb increases, pKb decreases. On the graph of -log(x)...

Tessa House 3A

I think you should check to make sure it follows the 5% rule even if you have an equilibrium constant equal to or less than 10^-4 because I believe sometimes the approximation may not be entirely accurate even if K is small. I do think there was a problem in which K was around 10^-4, but the approxi...

Tessa House 3A

Yes, it is important to consider that you are using the Kw for water at 37 degrees because it is a different value than the Kw for water at 25 degrees. Because the solution is neutral, the concentration of hydronium and hydroxide are equal. We also know that the equation for Kw is the product of the...

Tessa House 3A

I don't think that equation would be given, but you can figure it out based on how Al3+ acts as an acid. Al3+ forms coordinate covalent bonds with six water molecules. One of these water molecules bonded with Al reacts with a water molecule in the solution, transferring a hydrogen ion, and forming h...

Tessa House 3A

I agree with the person above. I think of it like when Q<K, in the equilibrium expression the numbers in the denominator, or reactants, are greater because the value of Q is smaller than K. Therefore, there is a higher concentration of reactants and products will be formed, favoring the forward reac...

Tessa House 3A

I believe the reason that Kc changes when you change the temperature of an equation is that more reactant forms product or vice versa without any more reactant being added in the first place. Therefore, the ratio between the two will permanently change because the reactants will form more products, ...

Tessa House 3A

I think that you are correct in that immediately there will be a significant increase in the amount of reactant, but as the reaction proceeds, it is used up to form product. However, I think there is still more reactant than before because if it all went to form product, the concentration of product...

Tessa House 3A

Hi, I am not sure about this but based on how I believe you would calculate pH from pKa or pKa from pH, you might need the concentration of some of the reactants or products at equilibrium or an initial concentration so that you can solve for equilibrium concentration. If you were given pKa, you cou...

Tessa House 3A

Because -log(Ka)=pKa, you can rearrange this to get 10^-pKa=Ka. Plug in the pKa and you can get the Ka. You can always just rearrange the original equation to solve for Ka. I hope this helps!

Tessa House 3A

An inert gas is just a noble gas, or a gas that will not react. You want to add an inert gas so that it will not affect equilibrium in any way by reacting with reactants or products. Otherwise, it would have an effect on the equilibrium. If the gas is an inert gas, it would not affect equilibrium.

Tessa House 3A

I think that saying "the equilibrium lies to the left," for example, would mean that when the reaction is at equilibrium, there is a greater concentration of reactants than products. Saying "the equilibrium shifts to the left" would mean that the reaction was not at equilibrium a...

Tessa House 3A

You wouldn't be given partial pressures for aqueous solutions because you only use partial pressures for gases. If you did have a reaction with both aqueous substances and gases and you were given the partial pressures of the gases, you would use the ideal gas law to convert partial pressure to conc...

Tessa House 3A

You are correct. I also agree with the above posts. The way I view it is during an endothermic reaction, heat is on the reactants side of the equation since endothermic reactions take in heat. Therefore, decreasing heat is like decreasing the amount of reactants, so the equilibrium would shift left ...

Tessa House 3A

I think that you are correct that reactants will have a negative sign for the C part of the ICE box while products will have a positive sign. This is because when you start with a certain amount of reactant and no products, it goes to form some amount of products. Therefore, you are decreasing the c...

Tessa House 3A

Nitrogen in NH3 has four regions of electron density. Three of them are single bonds with hydrogen and one is a lone pair. You can tell this based on the lewis structure he drew. Therefore, there should be four hybrid orbitals. To get four hybrid orbitals, you need one s orbital and three p orbitals...

Tessa House 3A

Boron only needs to have 6 valence electrons, so B(OH)3 has boron with three single bonds to oxygen (which are each bonded to a hydrogen). This means that there is room for a lewis base to come in and donate two electrons to boron, giving it 8 valence electrons and another bond. Because B(OH)3 accep...

Tessa House 3A

Hi, If both the cation and anion of a salt come from a strong acid and strong base, this salt is neutral because the conjugate base/acid of the strong acid/base are both weak. This means they will not act as an acid or base in water. However, when the cation or anion of a salt comes from a weak acid...

Tessa House 3A

I believe that in part b, ClO- is a weak base in water and gains a hydrogen ion to form HClO, so it is important to include Cl in the equation because it is part of the reaction. For part c, Cl- is just the anion in the salt and is not involved in the reaction. In this case, C5H5NH+ is a weak acid a...

Tessa House 3A

Amphoteric molecules can act as both acids and bases, so to begin I generally check to see if the molecule contains hydrogen or not. If there is no hydrogen in the molecule, it cannot release a proton (acting as an acid) and is not amphoteric. If the molecule does have hydrogen in it and has a negat...

Tessa House 3A

For this question, I thought that an sp^3 hybridization would have a lower s-character than a sp^2 orbital because there are more p orbitals in the hybridization, and therefore more p-character and less s-character. The bond angles are greater with sp^2 hybridization (120 degrees) than with sp^3 (10...

Tessa House 3A

Like everyone said, Cl- would be the ligand you are probably thinking about. It has 8 electrons and therefore 4 lone pairs. To add on, only one of these lone pairs can form the coordinate covalent bond at a time to a transition metal as he has discussed before.

Tessa House 3A

Both tetrahedral and square planar have four bonds, so they are common for complexes with a coordination number of 4. Trigonal bipyramidal geometries have 5 bonds. Seesaw is not correct because although the coordination number is 4, it is not common for coordination complexes with 4 bonds to form th...

Tessa House 3A

If the ligand is a polydentate, it can form a chelate. I think you can tell that something is a polydentate based on partly its size and also if there are multiple lone pairs available to form a coordinate covalent bond with the transition metal. The ligand has to be large enough to bind more than o...

Tessa House 3A

Hi, The example of oxygen transport is one example of coordination complexes in biological systems. The transition metal in this case is iron, which is bound to multiple different ligands. The first four bonds are from a polydentate, specifically a tetradentate, which means that this same ligand bin...

Tessa House 3A

Yes, another way to think of this question is that there are 5 regions of electron density, so without the lone pairs, it would be trigonal bipyramidal. The lone pairs are placed on the equatorial positions, meaning you end up with a linear molecule with three lone pairs. The bond angle is 180 degre...

Tessa House 3A

Chelating ligands bind cations tighter because they have multiple bonds and form a ring. This can be important for different reasons, but in the example given in class, it was important to prevent DNA replication. I think the importance of it depends on the situation, but chelating ligands hold on t...

Tessa House 3A

Ligands are molecules that are electron pair donors, or lewis bases. Often, they form a coordinate covalent bond with a transition metal. Therefore, you would expect to see a ligand when you have a transition metal and an electron donor (the ligand) that can bond to it, forming a coordinate covalent...

Tessa House 3A

Transitions metals can have multiple different oxidation numbers depending on what they bond with, so you must determine the oxidation number based on what the transition metal is bonded to. If the overall compound has a neutral charge, then find a way to balance out the charges using the central at...

Tessa House 3A

The center atom itself is not the ligand, so if a center atom had a lone pair, it wouldn't be a ligand. The ligand is what attaches to the central ion and forms the coordinate covalent bond. The ligand is what donates the electrons to the central atom.

Tessa House 3A

Hi,
Isoelectronic means having the same number of electrons. For example, a cation may have the same number of electrons and be isoelectronic to another element because it has lost electrons.

Tessa House 3A

A high electronegativity means that an atom is likely to gain electrons, which is generally true of elements on the top right of the periodic table. You can determine the difference in electronegativity by looking at where the elements fall on the periodic table. Elements on the bottom left of the p...

Tessa House 3A

Hi,
Yes, ions do have LDF forces because they still have electrons that are polarizable. Everything has LDF forces because they are due to instantaneous dipoles that form due to the distribution of electrons.

Tessa House 3A

The l quantum number is the orbital angular momentum quantum number, which tells you which subshell the electron is in. l=0 means the s subshell and l=1 is the p subshell. This is how you would determine if the electron is in the 3s or 3p subshell.

Tessa House 3A

The electron configuration for Cu is [Ar]3d10 4s1, because having a full d subshell is more stable than having an almost full d subshell. Therefore, the 4s subshell is halfway filled (4s1) and the d subshell is filled for Cu. When Cu loses an electron, it loses an electron from the 4s subshell first...

Tessa House 3A

When two atoms are covalently bonded, this bond will be polar if there is a difference in electronegativity. Sometimes, the dipoles formed due to polar bonds cancel out in a molecule, such as in CH4. However, sometimes the dipoles do not cancel out and the overall molecule will be polar. To determin...

Tessa House 3A

Hi, If you have two molecules that each have the same number of formal charges that are not zero, I believe the more electronegative atoms tend to pull the electrons more and the negative formal charge should be put on the more electronegative atom. Therefore, you should choose the structure in whic...

Tessa House 3A

Hi,
In resonance structures, electrons are delocalized, which makes them more stable. The electrons are also distributed more evenly, which means that the energy of the overall molecule is lower and it is more stable. Therefore, resonance structures are more stable than if there was no resonance.

Tessa House 3A

4s is lower in energy than 3d until the 3d subshell starts to be filled, when 4s becomes higher in energy due to shielding. This is why 3d is written before 4s in the electron configuration after it begins to be filled. This is also why electrons are lost from the 4s subshell before the 3d subshell....

Tessa House 3A

Covalent bonds can have some ionic character if the electrons are not shared equally. In a polar covalent bond, there is some ionic character because one atom is pulling the electrons stronger than the other. A higher ionic character occurs when the atoms have a larger difference in electronegativit...

Tessa House 3A

Because electrons are constantly moving around in an atom, there can be a temporary partial charge at a certain area in the atom. If one side of an atom in a molecule has a temporary partial positive charge, an atom next to this may have a temporary induced dipole. The electrons in that atom may tem...

Tessa House 3A

I do not think that an expanded octet necessarily makes a molecule unstable because the d orbitals can be involved in bonding, but it does not mean that the molecule is unstable. In some cases, the expanded octet allows for more atoms to have a zero formal charge, which makes the molecule more stabl...

Tessa House 3A

Usually, you try to make the formal charges of the atoms zero. If this is not the case, as in this problem, you should give the most electronegative atoms the negative formal charges because they tend to attract electrons most. Oxygen is the most electronegative, so it would have a negative formal c...

Tessa House 3A

To identify if an element has an octet or not, count the number of lone pairs and electrons in the bonds formed. Every single bond has two electrons and each double bond has four because every line represents two electrons. Add the number of electrons in the bonds to the number of electrons in the l...

Tessa House 3A

Many elements will have an octet, meaning they have 8 valence electrons when they bond. However, there are some exceptions. Because the first elements on the periodic table only have a 1s subshell, they do not need 8 electrons to fill their outermost shell. However, elements like F have a 2s and 2p ...

Tessa House 3A

Na is larger than Cl because they have the same number of shells, but Cl has more protons and a higher nuclear charge, which makes it smaller. Na+ has lost its outermost electron and has therefore decreased in size. Cl- has gained an electron and increased in size. Because Na+ lost the electron in i...

Tessa House 3A

Increasing the intensity of the light does not increase the energy per photon, as each photon's energy is determined by frequency and wavelength. This way of looking at the problem takes in the particle properties of light because you are finding the energy of each individual photon. However, increa...

Tessa House 3A

Because the energy difference between the shells gets a lot closer together at the higher shells, the 4s subshell actually has lower energy than the 3d subshell before 3d begins to be filled. Electrons will fill the subshell with the lower energy first, so they begin to fill the 4s subshell after th...

Tessa House 3A

The 4th quantum number tells the spin of the electron. If the electron is spin up, the 4th quantum number is +1/2 and it is -1/2 if the electron is spin down. I think you will know if the electron is spin up or spin down based on what you are told. The 4th quantum number is also the one not determin...

Tessa House 3A

Hi, Your steps look correct and when I plugged in those values into my calculator, I got the first answer choice if you round to one significant figure. Are you sure you calculated it correctly? To be sure, make sure you divided h by both of the values in the denominator by putting parenthesis aroun...

Tessa House 3A

It is good to understand overall how you derive it but likely knowing the equations will allow you to understand where you get it from. You can use E=pc and E=hc/wavelength, canceling out c, and solving for wavelength to derive the equation. If you have the equation sheet, likely it will not be too ...

Tessa House 3A

I believe that when talking about the photoelectric experiment or light, increasing the intensity does increase the overall energy of all the photons combined because it increases the number of photons. However, increasing the intensity of light does not increase the energy of each individual photon...

Tessa House 3A

Since they give you the radius and say the uncertainty in position is 1% of this value, you can find uncertainty in position first. Convert 0.05 nm to m because these units are needed for later calculations. Then take 1% of this value by multiplying it by 0.01 to find the uncertainty in position. Fr...

Tessa House 3A

In class, we were testing to see if the correct model of an atom is one where the electrons are confined to the nucleus. Therefore, the uncertainty in their position could only be equal to the diameter of the nucleus, because they could not leave the nucleus. This means delta x is equal to the diame...

Tessa House 3A

First, you would need to calculate the energy at the two energy levels using that equation. After that, you could find delta E by doing Efinal - Einitial. This value would end up positive or negative, which is determined by whether the electron is emitting energy or absorbing it.

Tessa House 3A

Heisenberg's uncertainty principle deals with moving objects because it involves momentum. In order for there to be momentum, there must be velocity because the formula for momentum is p=mv. A stationary object would not work because it has a velocity of zero. Heisenberg's uncertainty principle rela...

Tessa House 3A

When talking about the photoelectric effect, the work function and threshold energy are essentially the same thing. The work function is the minimum energy required to remove an electron from a substance. The threshold energy is also the minimum energy required to remove an electron. The work functi...

Tessa House 3A

In this question, you are asked to find the kinetic energy of the electron first in order to solve for the energy of incoming light, found using the energy required to remove the electron as well (found using the work function). To calculate the kinetic energy, use the mass of the electron and its v...

Tessa House 3A

The unit mmol is a millimole, which is 10^-3 mol. You can figure this out because m stands for milli, which is 10^-3 of something.

Tessa House 3A

When the peak of one wave interacts with the trough of another, the waves basically cancel out, so the resulting wave is smaller. This is because they are out of phase. When the waves are in phase and the peak interacts with a peak, or a trough interacts with a trough, the resulting wave is larger b...

Tessa House 3A

This is the work function, which tells you the energy required to remove one electron from the metal. It can be given in problems in J or kJ, but in the case it is given in kJ/mol for a metal, you might need to calculate the energy required to remove one electron rather than one mole to solve other ...

Tessa House 3A

Hi, I think that generally molecules refer to covalently bonded atoms and formula units refer to atoms bonded with an ionic bond. This is because an ionic bond does not form a molecule. Therefore, it is called a formula unit. This problem is asking for the moles to be calculated, as well as molecule...

Tessa House 3A

Hi, I do not think that theoretical yield will ever equal actual yield because there are many ways that actual yield may turn out to be less than theoretical yield. Actual yield may be less than theoretical yield because of side reactions, impurities, sticking to the side of the beaker, and other re...

Tessa House 3A

If a hydrocarbon is being combusted, the chemical equation with be the hydrocarbon + O2 forms CO2 + H2O. Butane is a hydrocarbon so this equation will apply and all you have to do is balance it. If there is also nitrogen or another element in the molecule being combusted, other products may form.

Tessa House 3A

To start, find out which reactant is the limiting reactant. Once you know this, convert grams or moles of limiting reactant to grams of the excess reactant by using the mole ratio of the reactants found in the balanced chemical equation and the molar mass of the excess reactant. Do this to find out ...

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