CHEMISTRY COMMUNITY

Melody Haratian 2J

How is E naught related to K? Does a positive E naught mean K>1 and a negative E naught means K<1?
Thanks!

Melody Haratian 2J

Why can’t you have intermediates in rate laws?

Melody Haratian 2J

Hi guys! Can someone explain some of the differences between method of initial rates and the integrated rate law? I know how to use both but am confused on which situations I should use each method in.

Melody Haratian 2J

Can someone explain the difference between catalysts and intermediates and how they look in a chemical reaction and how they affect it?

Melody Haratian 2J

Hi guys!
How is the rate constant affected by temperature?

Melody Haratian 2J

When do you have to use an inert electrode like Pt while constructing the cell diagram?

Melody Haratian 2J

Hi guys!
What’s the general outline for writing the shorthand notation of a galvanic cell? I always get a bit confused whenever I’m writing it.
Thanks!

Melody Haratian 2J

Hello, for the zero order [X] vs t graph, the rate is constant and not affected by concentration. The rate = k, and since the rate of change of [X] is constant and never changes, it will show as a straight line plot verses time. The plot is decreasing since the reactants decrease as they become prod...

Melody Haratian 2J

Hello! for this question, for the first order reactant ( being A) you only multiply the amount of the concentration being altered once to the initial rate. So for the first problem, you multiply .5 and the initial rate once. For the second order reactant ( B) you multiply the the amount of concentra...

Melody Haratian 2J

Does anyone know under what conditions E naught will typically equal zero?

Melody Haratian 2J

Hi everyone! Does anyone know how to determine k for a second order and third order reaction. The question is:
For each reaction order, identify the proper units for the rate constant, k. Not all of the choices will be used.
Answer choices: M/s, 1/s, M²/s, 1/(M²*s), 1/(M*s)

Melody Haratian 2J

Can someone explain why the anode typically loses mass while the cathode typically gains mass?

Melody Haratian 2J

Hello! Can someone explain why there is no change in E for this problem? The problem is: Consider the generic redox reaction shown. X(s)+Y+(aq)↽−−⇀X+(aq)+Y(s) If the coefficients in the redox reaction are doubled, how will the given quantities be affected for a voltaic cell under nonstandard conditi...

Melody Haratian 2J

Since we are at standard conditions, the potential of the reaction will be 0 V. Therefore, the E∘ for the reaction will be 0 V.

Melody Haratian 2J

What factors make a compound a stronger reducing agent?

Melody Haratian 2J

Hi guys! I'm having a hard time finding the answer to #5 on the sapling HW for week 7/8. The question is: Identify the oxidizing and reducing agents in the skeletal (unbalanced) reaction. Then, balance the reaction, including the phase (solid, liquid, etc.) of each species. The reaction takes place ...

Melody Haratian 2J

Hi everyone!
Can someone explain the function of a salt bridge in a galvanic cell? I get a little confused about it sometimes.
Thanks!

Melody Haratian 2J

Hi guys!
I’m taking chem 14 BL next quarter. I’m a little nervous going into it. How was the class for anyone who took it this quarter?
Thanks!

Melody Haratian 2J

What are some factors that increase residual entropy?

Melody Haratian 2J

How do you convert from delta H to q?

Melody Haratian 2J

Can someone explain the difference between a regular calorimeter and a bomb calorimeter?

Melody Haratian 2J

Hi guys, For 4F.9 I was wondering why the answer key has ln(15.00atm/.5 atm) instead of ln(.5 atm/15.00 atm). I thought that the final pressure had to be in the numerator and the initial pressure in the denominator. The full question is: Calculate the change in entropy when the pressure of 1.50molNe...

Melody Haratian 2J

Hi guys!
Can someone explain the difference between delta U and delta H?
Thanks

Melody Haratian 2J

Hello!
Can someone explain how to find the ΔS of a system vs the ΔS of the surroundings? What different methods do you have to use to solve for the two of them.

Melody Haratian 2J

Hey everyone! Can someone explain what residual entropy is and how to determine what compounds have residual entropy? The problem I'm having trouble with is #1 on the sapling HW, which is written below: On the basis of the structures of each of the molecules, predict which compounds would be most li...

Melody Haratian 2J

Hey guys, does anyone know how to find ΔH in this problem? The problem is #10 from sapling Wk 5/6: The small bags of silica gel you often see in a new shoe box are placed there to control humidity. Despite its name, silica gel is a solid. It is a chemically inert, highly porous, amorphous form of Si...

Melody Haratian 2J

Hello!
Delta G naught also always stays the same since the reactants and products are at standard temperature and pressure. On the other hand, Delta G can change as a reaction proceeds.

Melody Haratian 2J

For finding the change in temperature, you usually don't need to convert since the change in temperature in Kelvin and Celsius will be equal.

Melody Haratian 2J

When performing calculations for thermodynamics, when do you use R = 8.314 J·K-1·mol-1 vs R= 8.206 x 10-2 L·atm·K-1·mol-1. I'm a little confused on which types of equations I should use the different Rs in,
Thanks!

Melody Haratian 2J

Hi guys, I'm having trouble knowing what formulas to use to calculate this problem. The problem is #17 on the week 3/4 sapling, which is written below: An 80.0 g sample of a gas was heated from 25 ∘C to 225 ∘C. During this process, 346 J of work was done by the system and its internal energy increas...

Melody Haratian 2J

Can someone give examples of open systems, closed systems, and isolated systems?
I’m having a little bit of trouble identifying between them

Melody Haratian 2J

Hi guys, I'm having a lot of trouble getting started with problem #10 from the week 3/4 sapling. Can someone help me out? The problem is: An ice cube with a mass of 53.6 g at 0.0 ∘C is added to a glass containing 413 g of water at 45.0 ∘C . Determine the final temperature of the system at equilibriu...

Melody Haratian 2J

Why do we need to specify if the the specific heat capacity of a gas is at constant pressure or at constant volume?

Melody Haratian 2J

Hi guys! In lecture Lavelle discussed that heat capacity is an extensive property and that specific heat capacity is an intensive property.
Can someone explain the difference between an extensive and intensive property?

Melody Haratian 2J

When should you write the equilibrium constant as Kc and when should you write the equilibrium constant as Kp?

Melody Haratian 2J

What factors affect, or change, the equilibrium constant K?

Melody Haratian 2J

Which of the three methods being Hess’s law, bond enthalpies, and standard enthalpies of formation, is the most accurate and which is the least accurate?

Melody Haratian 2J

Can someone explain the differences between the standard enthalpy of formation and the standard reaction enthalpy?
Thanks!

Melody Haratian 2J

Hi guys! I was checking my answers for 5J.5 d and I don’t understand why the answer should be no change. It says that there are the same number of moles of gas on both sides of the equation but I see different number of moles on the sides of the equation. The problem is: State whether the reactants ...

Melody Haratian 2J

For acid/base equilibrium, do we only have to use ice tables to find the concentrations of the acid/base at equilibrium if the acid or base is weak? Why do we not use ICE tables if the acid or base is strong?
Thanks!

Melody Haratian 2J

When you’re finding equilibrium concentrations for an acid, do you always have to use Ka as its equilibrium quotient?

Melody Haratian 2J

Hi guys,
I’m having some trouble going through #5 on the acids/base sapling homework. The problem is:
The K_b for an amine is 1.118 * 10^-5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.757? Assume that all OH^- came from the reaction of B with H₂O.

Melody Haratian 2J

If water was a liquid participating in a reaction but not the main solvent, would it still be included in the equilibrium equation for the equilibrium constant?

Melody Haratian 2J

Hi guys! When you’re calculating for equilibrium concentrations using ICE tables, when can you ignore the value of X in the denominator?

Melody Haratian 2J

When you add together two equilibrium equations, what happens to the equilibrium constants of the two equations?

Melody Haratian 2J

Can someone explain what happens when Q> K and Q< K?
I’m having a bit of trouble understanding the concept.
Thanks!

Melody Haratian 2J

Hi guys, I’m having trouble on the final part of #10 in the sapling homework. Can someone guide me through it? The problem is: The reaction N 2 O 4 <—> 2NO 2 is allowed to reach equilibrium in a chloroform solution at 25C. The equilibrium concentrations are 0.373 mol/L N 2 O 4 and 2.04 mol/L NO 2 . ...

Melody Haratian 2J

For endothermic reactions, how does K change when you add heat. How does K change when you add heat to exothermic reactions? Also, why does K change instead of Q when you add heat to the reaction.

Melody Haratian 2J

Hi guys! I’m having a lot of trouble getting started with the chemical equilibrium sapling HW, problem #4. The problem is: At a certain temperature, the given reaction has an equilibrium constant of K p = 329. PCl 3 + Cl 2 <—> PCl 5 PCl 5 is placed in a sealed container at an initial pressure of .07...

Melody Haratian 2J

Does changing pressure only cause a change in the reaction when the volume ( thus the concentration) is being changed?

Melody Haratian 2J

For the quick way shown in lecture #3, why does the reaction shift right when the volume decreases and there are more moles of gas on the left?

Melody Haratian 2J

If the value of K is in between 10^-3 and 10³ does equilibrium not sit towards the right or left? Where would we define equilibrium as going towards?

Melody Haratian 2J

Why doesn’t the value of K change when you change the concentration of the reactants or products?
Why does only temperature change K?

Melody Haratian 2J

Hi guys!
Do you use Q when you are unsure if the reactants/products are at equilibrium? Do you also use Q if the problem doesn’t explicitly state if the reactants and products have reached equilibrium?
Thanks!

Melody Haratian 2J

Hi guys!
I’ve been a little confused on this but for acids, are stronger acids more or less stable? Would electron withdrawing in an acid make it stable or not?
Thanks!

Melody Haratian 2J

Why is CH₂Cl₂ polar?
Can’t the C-Cl dipole bonds be opposite of each other and cancel each other out after having drawn the Lewis structure?

Melody Haratian 2J

Hi guys! While I was doing the homework I noticed some of the transition metals had different names than their chemical formula, like iron ( which was ferrate when written as part of the chemical formula of a coordination compound). Are there any specific metals we should know that will have differe...

Melody Haratian 2J

Hi guys!
Does anyone know what we should specifically know about acid rain? Do we have to understand the chemical formulas for different nonmetal oxides that react with H2O to produce acid rain?

Melody Haratian 2J

Since metal oxides ( with metals being from groups one and two) typically produce two moles of OH- for every oxygen atom they have in their chemical formula, would they be typically stronger than metal hydroxides?

Melody Haratian 2J

I was doing the sapling homework and was confused on why HCN is a weak acid instead of being a weak base. Since the nitrogen of HCN has a lone pair, I thought it would be a weak base since it can accept a proton from water. Can someone explain why it is a weak acid instead?
Thanks!

Melody Haratian 2J

For molecules with lone pairs of electrons on the central atoms, are they typically polar or nonpolar?
Is there a way to use the shape of molecules with lone pairs on the central atom to determine the polarity of the molecule?
Thanks!

Melody Haratian 2J

What ligands we should be familiar with or that we should memorize/ know the chemical formula for?
Thanks!

Melody Haratian 2J

Hi guys! I’ve been having trouble understanding this part of question 18 from the Week 7/8 homework. The question is “ A general formula for molecules of this type is H 2 C(C) x CH 2 , where x is a whole number.” Select the correct statement about the relationship of x to the orientations of the hyd...

Melody Haratian 2J

Hi guys!
Why do lone pairs of electrons on molecules occupy more space than bonded electrons?

Melody Haratian 2J

Hi guys!
I was doing the sapling HW for week 9 and got stuck on #5. What does the “en” in [Cd(en)Br₂] mean? Also, how would you find the coordination number for this molecule?
Thanks

Melody Haratian 2J

Hi guys!
For a molecule, if it had a single electron unbounded instead of a lone pair of electrons being unbounded, how big of an effect would that have on the molecule’s bond angles.

Melody Haratian 2J

Hello!
I don’t think those assignments are worth extra credit. I did them a while back, and they’re just to help you with the basics and getting used to using Sapling.

Melody Haratian 2J

Hi guys!
I was going over lecture #23 and had something I was a little confused on.
For the molecule Benzene (C₆H₆)
where is the electron for the un-hybridized p-orbital located? Also, is it delocalized?
Thanks!

Melody Haratian 2J

Hi guys!
I’m still a bit confused on this but can someone explain what makes a delocalized pi bond and what makes it different from a regular pi bond?

Melody Haratian 2J

Hi guys! I was doing the sapling Homework for week 7/8 and had trouble on number 17. The question is draw the three possible structures of C3H4 and the follow up question to it is to select the choice that contains all of the bond angles that are represented in the structures of C3H4. I was able to ...

Melody Haratian 2J

Can someone explain why CH₂Cl₂ is a polar molecule based on its molecular shape?

Melody Haratian 2J

Do ion-ion interactions have LDF forces?

Melody Haratian 2J

Hi guys!
I’m having a lot of trouble understanding why SO2 is a Lewis acid. Sapling says that it’s a molecule with a polar double bond but how does that help it accept more electrons?
Thanks!

Melody Haratian 2J

Hello! The stronger the intermolecular forces between the molecules, the higher the melting and boiling points will be. Vapor pressure refers to the amount of vapor released when a liquid turns into a gas. The more vapor released, the higher the vapor pressure. Weaker intermolecular forces have a hi...

Melody Haratian 2J

Hello! Cu is part of the exceptions in electron configuration. So its configuration for a neutral atom of Cu is [Ar]3d 10 4s 1 , because it prefers a full d shell. When Cu loses an electron, it will lose its outermost electron. In this case, its outer most electron is in the 4s shell ( since 4s 1 is...

Melody Haratian 2J

Hi! It’s possible for there to be an unpaired electron in a Lewis structure. When it happens the molecule is called a radical, because one of its electrons are unpaired and it’s highly reactive. An unpaired electron in a Lewis structure happens when there is an odd number of valence electrons when y...

Melody Haratian 2J

If there are many LDF interactions, can they become stronger than a dipole-dipole interaction?

Melody Haratian 2J

Hi guys!
Can someone let me know the order of intermolecular interactions from weakest to strongest?
I get them confused a lot of times.
Thanks!

Melody Haratian 2J

Hi guys! So covalent bonds are polar when the electrons are shared unequally and they’re nonpolar when the electrons are shared equally. Usually, how close do the atoms have to be in electronegativity for a bond to be considered nonpolar.
Also, are C-H bonds considered nonpolar?
Thanks!

Melody Haratian 2J

Hi guys! I’ve seen a couple of homework problems on oxidation numbers. Can someone explain what the oxidation number is and how you find it.
Thanks!

Melody Haratian 2J

Hi guys!
For a hydrogen atom, if you were to excite the electron so that it would go from 2s to 2p, would the energy of the electron change?
Thanks!

Melody Haratian 2J

Hi everyone!
Can someone explain why resonance structures are usually more stable? I’ve been having some trouble understanding this.
Thanks!

Melody Haratian 2J

Hi guys!
Do we need to know m_s to specify an orbital or do we only need to use the first three quantum numbers to specify the orbital?
Thanks!!

Melody Haratian 2J

Ion ion interactions are stronger because ions are fully charged. An example is NaCl, Na has a full +1 charge, and Cl has a full -1 charge. Ions are fully charged because the cation loses its electrons, and the anion gains electrons. These large and opposite charge values create a big attraction. T...

Melody Haratian 2J

Hello! For a radical, if an atom has an unpaired valence electron (or 7 electrons instead of 8) then it is a radical. You can tell if the valence electron is unpaired if one of its electrons is alone. So if an atom has or is sharing ( through covalent bonds) 6 electrons and has one additional unpair...

Melody Haratian 2J

Ion ion interactions are stronger because ions are fully charged. An example is NaCl, Na has a full +1 charge and Cl has a full -1 charge. Ions are fully charged because the cation loses its electrons and the anion gains electrons. These large and opposite charge values create a big attraction. The ...

Melody Haratian 2J

Hi guys! I was working on some formal charge problems and had a quick question. When calculating formal charge, would an molecule with a charge of +2 be more stable if all of that charge was on one atom of the molecule, or would it be more stable if the charge was separated on two atoms, each with a...

Melody Haratian 2J

I was watching Dr.Lavelle’s lecture from last Friday. What does polarizable mean and what does it mean for something to be highly polarizable?
Thank you!

Melody Haratian 2J

Hi guys! For problem 2B.part (c) I was wondering how you would know the order of the atoms when drawing the Lewis structure of the molecule. There’s a lot of different atoms in this molecule, and I’m a little confused on how to order them. Here’s the problem: “ Draw the complete Lewis structure of t...

Melody Haratian 2J

Hi everyone! For question 2B.5 part b from the textbook, which is “ Draw the Lewis structure of (b) hypobromite ion BrO-“ I was wondering why the structure doesn’t have a double bond instead of the single bond it’s shown to have in the answer key.

Melody Haratian 2J

Does the atomic radius increase when you go from 2s to 2p?

Melody Haratian 2J

I was working on the homework and some electron configurations had electrons in the f state. Do we have to know how to write electron configurations using the f- orbitals?

Melody Haratian 2J

Hi guys!
I was watching lecture #14 and I noticed that nitrogen was used as the central atom. I thought oxygen was an exception in ionization energies, so it would have a lower ionization energy than nitrogen due to its electron-electron repulsions. Why is nitrogen used as the central atom?

Melody Haratian 2J

Hello! Oxygen will also have a lower first ionization energy than fluorine because of fluorine’s higher atomic number. Because fluorine has a higher atomic number, it has more protons, thus a higher effective nuclear charge. This positive nuclear charge will attract electrons more, and result in a h...

Melody Haratian 2J

Hello! When there are zero electrons occupying the 3d orbitals, 4s will have a lower energy than 3d. This means that 4s will go after 2p when writing electron configurations. However, when electrons begin to fill the 3d orbitals, then 4s will have the higher energy than 3d. Therefore, 4s will be wri...

Melody Haratian 2J

Hello! The second ionization energy is higher than the first one because it becomes harder to remove a second electron from an atom after you have already removed the first one. You will need more energy to remove a second electron, thus resulting in a higher second ionization energy. Atoms do not w...

Melody Haratian 2J

Hi guys! I have a couple of questions about ionization energies. Would there be any other exceptions that we have to know other than oxygen for ionization energy trends? Are there any other exceptions due to electron repulsions for the typical ionization energy trend?
Thanks

Melody Haratian 2J

Hi!! Happy Halloween!!
My family and I dressed up and are watching some Halloween themed movies together. We also ordered food tonight and bought some candy!

Melody Haratian 2J

Hi everyone!
The atomic radii increases down a group and decreases across a period. I was wondering, which one has a greater effect on the atomic radii? Does going down a group increase the atomic radii more than going across a period would decrease the atomic radii?
Thanks!

Melody Haratian 2J

Hi everyone!
Just to clarify, is the 4s higher than energy than the 3d orbital? It’s energy was mentioned in lecture a couple of times, but I’m a little confused.
Thanks

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