CHEMISTRY COMMUNITY

Ashley Ko 3I

Hi! Pt(s) is necessary because I2 is not a metal (even though it is a solid, it cannot act as a conductor). Thus, an inert conductor, such as Pt(s), has to be added. Hope this helps!

Ashley Ko 3I

Hi! I am not completely sure, but I think either one would be okay since both are inert conductors. However, I think Pt(s) is used more commonly. Hope this helps!

Ashley Ko 3I

Hi! I don't believe that catalysts cause a similar pattern. Catalysts only affect the rate of the reaction. Since the addition of a catalyst would not affect the equilibrium position of the reaction, neither reactants nor products would be favored by the addition/absence of a catalyst. Hope this hel...

Ashley Ko 3I

What should be excluded from cell diagrams? Is H2O the only species that should be excluded?

Ashley Ko 3I

Hi! I agree with the above post. Pt(s) is used for example when the anode or cathode is aqueous (no metal to act as the conductor). Hope this helps!

Ashley Ko 3I

Does adding a catalyst increase or decrease the rate constant? Does increasing the temperature always increase the rate constant? Why does temperature and catalysts increase/decrease the rate constant?

Ashley Ko 3I

When determining the molecularity of an elementary step, can we look at stoichiometric coefficients? For example, if the reactants are 2A + B, would the molecularity be trimolecular? Thank you in advance!

Ashley Ko 3I

Hi! In Friday's lecture, Professor Lavelle mentioned the following equation: k = k'/([B0]^M*[C0]^L). What are the values of M and L? Do we assume we already obtained those values from experiments?

Ashley Ko 3I

Hi! The chemical equation given in the textbook is wrong. The chemical equation should be the following: Cl2(g) ---> ClOH(aq) + Cl-(aq) (see Professor Lavelle's solution manual errors on his class website). Hope this helps!

Ashley Ko 3I

Hi! The chemical equation in the textbook is wrong (see Professor Lavelle's solution manual errors on his class website). The chemical equation should be the following: Cl2(g) --> ClOH(aq) + Cl-(aq). In this case, Cl is being reduced and oxidized (Cl2 is both the reducing and oxidizing agent). Hope ...

Ashley Ko 3I

Hi! To find the number of moles of electrons transferred (or the number of electrons transferred), I think it is helpful to write the half-reactions and then balance them. If the number of electrons in each half-reaction is different, you have to multiply the half-reactions by some constant so that ...

Ashley Ko 3I

Hi! Your steps seem correct. Maybe check that you are using the correct value for Fe? There are multiple reduction half-reactions listed with Fe in it. Make sure to use the standard potential value corresponding with the following reduction half-reaction for Fe: Fe^2+(aq) + 2e- ---> Fe(s). Another m...

Ashley Ko 3I

Update: I figured out what I was doing wrong but if anyone has any tips for balancing redox reactions, I would greatly appreciate it!

Ashley Ko 3I

Hi! I got the same answer as you. Maybe check how you entered the chemical equation into Sapling? You have to use the various tools they give you. For example, for exponents and subscripts make sure to use the tools with an X and a box (the box is either in the exponent or subscript position). Also,...

Ashley Ko 3I

Hi! Could you post the original question? I had different chemical equations.

Ashley Ko 3I

Hi everyone!

Can someone help explain how to balance the equation for N2H4 + ClO3^- --> NO + Cl^-? I have tried several times but keep on getting the wrong answer. Thank you for everyone's responses in advance!

Ashley Ko 3I

Hi! I believe a greater mass results in a higher molar entropy because of the following: a greater mass means a greater number of subatomic particles, which means a greater number of microstates since each subatomic particle can occupy different positions. A greater number of microstates means a gre...

Ashley Ko 3I

Hi! I believe there are two types of entropy: residual entropy (positional entropy) and thermal entropy. When determining which compound has the greater entropy, the phase of the compounds is more important than the complexity of the compounds. For instance, gases will always have greater entropy th...

Ashley Ko 3I

Hi! I'm not completely sure since I am confused about the exact situations surrounding equilibrium myself but maybe someone else could confirm the following: A phase change indicates equilibrium between two phases. I believe that although we can assume that delta G is equal to 0 during a phase chang...

Ashley Ko 3I

Hi! The reason a positive entropy change means a spontaneous reaction is because an increase in entropy means a decrease in the Gibbs free energy as seen in the following equation: delta G = delta H - T*delta S. I believe a negative delta G (regardless if it is standard Gibbs free energy or not) ind...

Ashley Ko 3I

Hi! Hopefully, the following can answer a few of your questions . . . - The internal energy of a closed system can be changed in two ways: heating/cooling and compression/expansion. - The volume can be changed in closed systems; thus, the work can be calculated for closed systems if there is compres...

Ashley Ko 3I

Hi everyone! Is the end result of expansion/compression pressure equilibrium between the system and its surroundings. For example, does a system with a pressure of 2 atm keep increasing in volume until its pressure is equal to its surroundings, which has a constant pressure of 1 atm (constant extern...

Ashley Ko 3I

Hi everyone! I am a little confused about what isobaric actually refers to. I know that isobaric means constant pressure; however, is the pressure its referring to the pressure of the system/reaction, external pressure, or both?

Ashley Ko 3I

Hi! So, the heat of vaporization is typically the amount of heat it takes to vaporize one gram of a substance (units is usually in J/g for example). However, for this question, they ask for kJ/mol. Thus, you have to convert the joules to kilojoules and grams to moles in your calculation.

Ashley Ko 3I

Hi! So, to isolate K, you would first divide delta G r by -RT, resulting in the following: (delta G r /(-RT)) = ln(K). Then, you would make each side the exponent of e to get rid of the natural log (e to the power of a natural log leaves you with the input(s) of the natural log for example e^(ln(2))...

Ashley Ko 3I

Hi! I believe the only mistake I saw was the value you used for the gas constant. Since the units used in the equation include L, atm, and K, the gas constant value you should use is 0.0821 L*atm/(mol*K). Hope this helps!

Ashley Ko 3I

Hi! I believe that heat capacity has to always be a positive value since it represents the amount of heat required (adding heat so endothermic and a positive value) to raise the temperature of the compound by 1 temperature unit (typically either K or C). The same reasoning applies to specific heat c...

Ashley Ko 3I

Hi! I agree with many of the posts above! During a phase change from liquid to vapor, heat is being used to break the attractive forces/bonds between the liquid molecules (because heat is being used to break the attractive forces/bonds, the temperature doesn't change during a phase change). Water sp...

Ashley Ko 3I

Hi! I believe that for this question, you would use q (heat gained) = -q (heat lost). The water with the higher temperature would represent -q (heat lost) and the water with the lower temperature would represent q (heat gained). First, you would need to convert the volumes to mass using the density ...

Ashley Ko 3I

Hi! I believe that for this question, you would essentially use the following equation: q (heat gained) = -q (heat lost). However, you would also need to add the amount of heat it takes for the phase change from solid (ice cube) to liquid (water) to the q (heat gained) side. So, the overall equation...

Ashley Ko 3I

Hi! For this question you use the following equation: delta G = delta H - T*delta S. You first set delta G equal to 0 because at boiling point the compound is at equilibrium, specifically between the liquid and vapor phase. Then, you solve for T by substituting delta G and the values given in the qu...

Ashley Ko 3I

Hi! I believe an ideal gas is a gas whose molecules are not attracted to one another (no intermolecular forces between molecules) and any collisions between the molecules are completely elastic, meaning no energy is lost. Gases under STP conditions tend to be referred to as ideal gases (STP means &q...

Ashley Ko 3I

Hi! For this question, you would use Hess's law and manipulate the chemical equations in order to get 2M + 3Cl2 = 2MCl3. As for manipulating the chemical equations, you want to try to manipulate them in a way such that when you combine the chemical equations together you get 2M + 3Cl2 = 2MCl3 (if tw...

Ashley Ko 3I

Does this mean that the salt and the water are both neutral solutions (pH=7)? I don't think this is necessarily true since the salt can be acidic, basic, or neutral depending on its ions or, in other words, the strength of the acid and base that formed the salt. For instance, a neutralization react...

Ashley Ko 3I

Hi! I believe for this question you would just use q (heat gained) = -q (heat lost) except add the q or heat it takes for the phase change from solid (ice cube) to liquid on the q side. In other words, you would use q (heat for phase change) + q (heat gained) = -q (heat lost). For the phase change, ...

Ashley Ko 3I

Hi! This question involves several heat calculations. The first calculation involves using q = m*C*delta T to calculate how much heat it takes to increase the temperature of the ice cube from -10 degrees celsius to 0 degrees celsius (melting point of water). The second calculation involves using q =...

Ashley Ko 3I

Hi! I agree with the above post! Energy can be transferred between a system and its surroundings if, for example, heat is absorbed or lost by a system. A real-life example would be a cooling pack. The cooling pack (the system) feels cold because it is absorbing heat from its surroundings (your hand)...

Ashley Ko 3I

Hi! For this question, you first need to convert the volume of the water to mass (this step is simple since the volume to mass ratio of water is 1:1). Then, you would use the equation q (heat gained) = -q (heat lost), where q = m*C*delta T. In this case, q (heat gained) would represent the heat ener...

Ashley Ko 3I

Hi everyone! I was wondering if anyone knew whether or not the 5% rule that we use to check whether or not an assumption is valid applies to partial pressures as well. For example, can we assume that x is small enough to approximate when x is less than 5% of the initial partial pressure? Or do we ju...

Ashley Ko 3I

Hi! I believe that since H3PO4 is a basic salt, this means that it tends to attract H+ ions from the water because bases tend to be proton acceptors. Also, by looking at the ions that H3PO4 dissociates into, PO4^3- is the ion that makes the salt basic (it is a basic anion) and would attract H+ proto...

Ashley Ko 3I

Hi! I believe that for acids, it's typically acid + water yields conjugate base + hydronium ion, and for bases, it's typically base + water yields conjugate acid + hydroxide ion. Hope this helps!

Ashley Ko 3I

Hi! I believe that Professor Lavelle said that if the value of Ka/Kb is less than 10^-4, then it is safe to assume that the value of x is small enough to approximate. However, to check if your approximation is valid, divide x by the initial concentration and then multiply by 100%. If x is less than ...

Ashley Ko 3I

Hi! I'm not completely sure, but I think it would be safe to assume that [H3O+] = [OH-] in the absence of other information (like the presence of acids/bases or the pH or pOH) and even if the Kw is not equal to 10^-14 as a result of a change in temperature (the value of the hydronium/hydroxide conce...

Ashley Ko 3I

Hi! By using the quadratic equation, x = -b +/- rad(b^2-4ac)/2a, you can solve for x, which represents the concentration of the ions resulting from the dissociation of the acid or base. Then, you can find the percent ionization by dividing x by the initial concentration of the acid or base (given in...

Ashley Ko 3I

Hi! You use Kc or Kp mainly based on the values given in the question. For instance, Kc is used when concentrations are given and Kp is used when partial pressures are given. However, Kp only applies to gases. Kc applies to both aqueous solutions and gases. You can also convert between concentration...

Ashley Ko 3I

Hi! A negative delta H means the reaction is exothermic and heat is a product (this is because heat is released). A positive delta H means the reaction is endothermic and heat is a reactant (this is because heat is required for the reaction to proceed forward). When the temperature is increased, thi...

Ashley Ko 3I

Hi! I believe you use an ICE box (or RICE box) when dealing with weak acids/bases or when trying to find the equilibrium concentrations after a concentration change. "R" stands for the reaction, "I" stands for initial concentration, "C" stands for change, and "E&qu...

Ashley Ko 3I

Hi! I was wondering what you could tell about the concentrations of the reactants and products based on the value of K? For example, when K = 1, does that mean the concentration of the reactants = the concentration of the products? Or is this only true if both the number of reactants and products an...

Ashley Ko 3I

I'm not completely sure, but last quarter, I believe it was 50 posts total by the end of the quarter. I would just post at least 5 times by the end of each week just to be safe (plus posting consistently helps keep you on track for 50 posts total by the end of the quarter). Hope this helps!

Ashley Ko 3I

Hi! I agree with the post above! If the pressure is doubled by halving the volume, then the concentration of the gases would increase. This can be seen through the concentration equation: concentration = n/V (n = moles of gas, V = volume). There is an inverse relationship between volume and concentr...

Ashley Ko 3I

Hi! I believe you can determine the H+ concentration from Ka and then use this H+ concentration to find the pH. For instance, given that Ka = [H+][A-]/[HA], you can solve for the H+ concentration by substituting Ka and the acid concentration, which are given in the question, into the equation. Then,...

Ashley Ko 3I

I believe Le Chatlier's principle does apply to temperature changes. For example, if a reaction is exothermic (heat is a product), then a temperature increase would cause the reaction to shift left. If a reaction is endothermic (heat is a reactant), then a temperature increase would cause the reacti...

Ashley Ko 3I

Hi! I believe K refers to equilibrium constants calculated with partial pressures while Kc refers to equilibrium constants calculated with concentrations. If all the species in a reaction are gases (since pure substances are not involved in the calculations they can be disregarded), then calculate K...

Ashley Ko 3I

Hi! I believe you are correct. Since pure substances (solids and liquids) are not used to calculate reaction quotients/equilibrium constants, the only species left is a gas; thus, the partial pressure equilibrium constant would be calculated. Hope this helps!

Ashley Ko 3I

Hi! When a reaction favors the reactants, this means the reaction will proceed in a manner to form more reactants (in other words favoring the reverse reaction). When a reaction favors the products, this means that the reaction will proceed in a manner to form more products (in other words favoring ...

Ashley Ko 3I

Hi! I agree with the above post, but I think the first value you mentioned (0.8205...) is the one typically used since it cancels out the units in the ideal gas law equation. Hope this helps!

Ashley Ko 3I

Hi! I believe follow-up questions/posts to your own posts also count towards the 5 posts per week. Hope this helps!

Ashley Ko 3I

The HCN is not split into ions at the beginning because HCN is a weak acid (dissociation of weak acids is not significant enough). Hope this helps!

Ashley Ko 3I

The weaker the acid, the stronger its conjugate base is. Hope this helps!

Ashley Ko 3I

Hi! I think carbonato and sulfito generally act as monodentates (in rare cases, however, they may act as bidentates). I believe the only polydentates you really need to know are oxalato (a bidentate), EDTA (a hexadentate), and en (a bidentate). Hope this helps!

Ashley Ko 3I

Hi! I believe in the textbook it mentions under Lewis structures how for oxoacids, meaning acids that contain O, the hydrogen bonds to the O; thus, the halogen (Cl, Br, I) would also bond to O, making O the central atom. Hope this helps!

Ashley Ko 3I

No, while seesaw has 5 regions of high electron density, trigonal pyramidal only has 4 regions of high electron density. Hope this helps!

Ashley Ko 3I

Hi! A substance can act as a Bronsted acid and Bronsted base if it has BOTH of the following: a H proton that it can donate (like an acid) and a negative charge so it can accept a H proton (like a base). Hope this helps!

Ashley Ko 3I

Hi! I agree with the above post. I also think it's important to keep in mind the denticity of the ligands in the coordination complex. For example, if one of the ligands is bidentate, then it could form 2 coordinate covalent bonds with the central atom (it would count as 2 instead of 1 towards the c...

Ashley Ko 3I

Hi! I agree with Khoa in that HBr is a stronger acid than HCl because it is easier to remove the H proton from HBr than from HCl. I would say in terms of periodic trends, the smaller the atomic radius or the greater the electronegativity, the weaker the acid since the H proton will be harder to remo...

Ashley Ko 3I

Cobalt is 3+ because [Co(NH3)3Cl3] is neutral, NH3 is a neutral ligand, and Cl is an anionic ligand with a 1- charge (since there are three Cl, their overall charge contribution is 3-). Thus, the cobalt is 3+ so it can cancel out the charge contribution of the Cl. Hope this helps!

Ashley Ko 3I

Hi! I believe that the coordination number only refers to the central atom, Fe, since Fe bonds with each CO in the coordination complex. Hope this helps!

Ashley Ko 3I

Hi! So both CH3(-) and CH2(2-) have four regions of electron density, and since the repulsion between two lone-pairs are greater than that between two bonding atoms or a bonding atom and a lone pair, CH2(2-) would have a smaller bond angle (it has two lone pairs while CH3(-) only has one lone pair) ...

Ashley Ko 3I

Hi! If a molecule has lone pairs, this does not always mean it is polar. For instance, a molecule with lone pairs is only polar if the lone pairs cause the atoms surrounding the central atom to become asymmetrically arranged. As a result, the dipole moments would not cancel out. However, if you are ...

Ashley Ko 3I

Hi! I personally like to review by reading the textbook. I find the examples helpful and reading solidifies my understanding of the content. However, I think it’s important to also make sure to watch all the lectures at least once and complete all the homework assigned.

Ashley Ko 3I

Hi! I agree with the above post that every molecule that has a T-shape will be polar. Out of the four molecular shapes with 5 electron domains/density regions, two will always be polar: T-shape and see-saw. This is because the lone pairs of each cause an asymmetrical arrangement (dipole moments won’...

Ashley Ko 3I

Hi! I agree with the above posts about electronegativity and dipole moments! I think it’s also helpful to look at the molecular shape and the types of atoms surrounding the central atom. For example, if all the atoms surrounding the central element are the same, then the molecule is most likely nonp...

Ashley Ko 3I

I believe the molecular shape would be linear. Hope this helps!

Ashley Ko 3I

Hi! Yes, I believe that a more stable geometry involves minimizing the amount of electron-electron repulsions. Hope this helps!

Ashley Ko 3I

Hi! I believe you don't need to know how to calculate bond angles. You just need to memorize the general bond angles and be able to determine based on the molecular shape how the bond angle changes. For example, lone pairs decrease the bond angle so for a molecule like H2O, which has 2 lone pairs, t...

Ashley Ko 3I

Hi! I agree with the above two posts. The molecular shape should be square planar since there are 6 electron domains (2 of which are lone pairs and the other 4 are bond domains). Hope this helps!

Ashley Ko 3I

Hi! I believe axial atoms are those that line on the vertical axis/plane of the molecule and equatorial atoms are those that line on the horizontal axis/plane. Hope this helps!

Ashley Ko 3I

Hi! So intermolecular means BETWEEN MOLECULES and intramolecular means WITHIN A MOLECULE. For instance, intermolecular forces occur between molecules (hydrogen bonding can occur between two H2O molecules). In contrast, covalent bonding occurs between two atoms in a molecule and is an example of an i...

Ashley Ko 3I

Hi! To my understanding, hydrogen bonding occurs between a hydrogen atom of one molecule and one of three electronegative elements in another molecule (F, O, or N --> I memorize these elements as like fun or fon). The hydrogen atom of the first molecule must also be bonded to one of the three electr...

Ashley Ko 3I

Hi! I guess an easier way of memorizing how to calculate formal charge is the following: Formal charge = # of valence electrons of the atom - number of electrons in lone pairs (electrons surrounding the atom) - number of bonds (so a single bond is equal to one and a double bond is equal to 2 etc.) T...

Ashley Ko 3I

Hi! With dipole-dipole interactions, they occur between two polar molecules or molecules with dipole moments (a positively charged end and a negatively charged end). In contrast, with ion-dipole interactions, one of the two interacting entities is an ion while the other is a polar molecule. Hope thi...

Ashley Ko 3I

Hi! You could write out the electron configuration for each ground-state atom and see what orbital the outermost electron occupies (for atoms that are in the d-block, electrons would be removed from the s-subshell before the d-subshell since the s-subshell becomes of higher energy level once the d-s...

Ashley Ko 3I

I agree with the above post. No, the order does not matter. I believe this is because the orbitals kind of fill up randomly since the energy of each orbital is about the same. Hope this helps!

Ashley Ko 3I

Hi! So the greater the polarizing power of a cation, the greater the covalent character in a bond because there would be a greater shared region between the cation and anion. As for the silver halide example, as the size of the anion increased, so did the covalent character. This is because an incre...

Ashley Ko 3I

Yes, if ml is specified but not ms, then there are two electrons possible with the same ml quantum number. This is because ml refers to a specific orbital and orbitals can only have a maximum of two electrons. Hope this helps!

Ashley Ko 3I

Hi! Elements with an energy state of n = 3 or greater can have expanded octets. The important point is that for n = 3 or greater energy states, there are d-subshells available, allowing elements to have more than 8 electrons. Hope this helps!

Ashley Ko 3I

Hi! So, I believe that for elements with energy levels/states equal to or greater than n = 3, there is a general rule that expanded octets can have a maximum of 12 electrons. Hope this helps!

Ashley Ko 3I

Hi! So, the quantum number, ml, refers to a specific orbital. It is related to l in that the range of ml is -l to +l. For example, if l = 2, then the ml can be -2, -1, 0. +1, or +2 (this makes sense since l = 2 refers to the d-subshell, which has 5 orbitals). As for electron spin, every orbital has ...

Ashley Ko 3I

Hi! I would try what the above response said and also take out the commas. Hope this helps!

Ashley Ko 3I

I think it would be helpful to use a periodic table to help you determine the number of electrons. For instance, memorize where the s, p, d, and f blocks are. In general though, I believe the main things you need to know are the following: n refers to the energy state, l refers to the subshell (if l...

Ashley Ko 3I

The quantum number, l, refers to the various subshells. For instance, when l = 0, it is referring to the s-subshell. In this case, since l = 1, it is referring to the p-subshell (5p). As a result, the number of electrons that can be in n = 5, l = 1 should be 6. Hope this helps! Also, by specifying t...

Ashley Ko 3I

Hi! So, I believe salts typically consist of a metal and a nonmetal. However, salts can also be made up of in general a cation and an anion (ionic bond). I think that (NH4)SO4 is considered a salt because the chemical bonds in (NH4)SO4 are considered ionic (NH4 is a cation with a charge of 1+ and SO...

Ashley Ko 3I

The quantum number, l, basically represents the different possible subshells, such as s, p, d, and f. The maximum value for l is n-1. For example, when n=3, the maximum value for l is 2 (this makes sense because the n=3 energy level has 3 possible subshells - 3s, 3p, and 3d). There are also some gen...

Ashley Ko 3I

Hi! If given mass percent composition, then you should convert the percentages to grams and then calculate the mol of each element to find the empirical/molecular formulas. However, if given the mass of each element (not percent mass composition), you can convert directly to mol and then find the em...

Ashley Ko 3I

If the problem indicates that the kinetic energy of the electron is 0, then the energy you are finding would be the threshold energy or work function. In other words, you are finding threshold energy if you are just calculating the minimum energy required to eject the electron (no excess energy). Ho...

Ashley Ko 3I

Hi! So, I believe it is written as h/(4pi) because it is more accurate to do so. If you divide h by 4pi, you get a really long, complicated number and would have to round to write it as a constant. As a result, calculations would be less accurate. Hope this helps!

Ashley Ko 3I

Hi! I believe you made a mistake when converting the grams of H2O to grams of H. I think you may have forgotten to apply molar ratios (multiply by 2 after converting H2O to moles). You should get 0.060 g for H. For every 1 mol of H2O, there is 2 mol of H. For the empirical formula, I got C2H6O. Also...

Ashley Ko 3I

Hi! I think that all you need to know is that in both atomic and molecular spectroscopy, each element/molecule produces unique absorption/emission lines. Hope this helps!

Ashley Ko 3I

The answer is no because the wavelength of large everyday objects, such as the electric car, is so small that it is immeasurable or unnoticeable. As a result, we say that they do not have wave-like properties because they follow the classic model. Hope this helps!

Ashley Ko 3I

Hi! I believe in one of Professor Lavelle's lectures, he mentions how the energy of the photon emitted is equal to but opposite in sign to delta E. The energy emitted by the electron (negative because reference level is 0) cancels out the energy of the emitted photon (positive). Hope this helps!

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