CHEMISTRY COMMUNITY

J Medina 2I

Yes, if given all other information, the Arrhenius equation can be used to find the activation energy, Ea. I think exponential could be referring to when both sides are raised to the power of e which cancels the ln on the left and then raises the right side to the power of e.

J Medina 2I

I think it depends on your individual TA

J Medina 2I

What units is Kr in a first order, 2nd order, and 0 order reaction?

J Medina 2I

What is ln [A] in the Arrhenius equation, ln kr = ln A - (Ea/RT)

J Medina 2I

Why is the anode considered the product and the cathode considered the reactant?

J Medina 2I

In the Nernst Equation, E = Eo -(RT/nF)ln Q , for Q specifically, do we put the anode concentration at the top or the bottom? And why?

J Medina 2I

I'm confused on the following question and was wondering if someone could provide a mental walkthrough of how they got the answer. (The answer is given by the textbook: (a) Second order in NO, first order in O2 ) "When the NO concentration is doubled, the rate of the reaction 2NO (g) + O2 (g) -...

J Medina 2I

n is the number of electrons transferred which cannot be determined until your redox half-reactions are balanced. These half-reactions should have the same number of electrons transferred on opposite sides.

J Medina 2I

With reaction profiles to get delta H you have to subtract the end of the graph (products) by the beginning of the graph (reactants). So you have to remember that EXOTHERMIC reactions release energy into their surroundings meaning there is a loss of energy from the system ( meaning delta H = - ). So...

J Medina 2I

When Galvanic cells are brought up it helps me to immediately think of batteries to help me remember that Galvanic cells convert chemical energy into electrical energy.

J Medina 2I

If a concentration cell has the same concentration on the anode and cathode then the reaction is at equilibrium and there is no net transfer of electrons in either direction. If this happens in a battery it means that the battery is dead.

J Medina 2I

n is the number of electrons transferred and can be seen in the half reactions when balanced. Since your redox half reactions are balanced, the number of electrons given off should be the same for both half-reactions.

J Medina 2I

Q is the the concentration of the products divided by the concentration of the reactants. It is used in the Nernst equation as a replacement for K when a reaction is not at equilibrium.

J Medina 2I

Will we usually be told if the redox reaction we're asked to balance is either acidic or basic?

J Medina 2I

Maybe you meant that when pKa = 10^-7 that the pH = 7, which would be true.

J Medina 2I

They're the same thing just different names

J Medina 2I

No, the test will only cover material from page 2 of Outline 4: Thermodynamics and all of Outline 5: Electrochemistry.

J Medina 2I

I think half reactions do not give the state of the reactants and products, like (aq), (s), or (g).

J Medina 2I

H+ is used for balancing hydrogen atoms in acidic solutions and OH- is used to balance hydrogen in basic solutions. H2O is used to balance oxygen for both types of reactions.

J Medina 2I

What are basic conditions?

J Medina 2I

Conventionally it is shown flowing left from right where the left is the anion (anode) and the right is the cation (cathode).

J Medina 2I

Eesha Sohail 1D wrote:If the direction is reversed, does G become positive? And what is this reverse case named, if the normal is a battery?

I think batteries are Galvanic cells and happen when G is negative. When G is positive the reaction becomes nonspontaneous and is called an electrolytic cell.

J Medina 2I

The Nernst Equation relates cell potential to the concentration of what is being reduced and oxidized in their aqueous solutions.

J Medina 2I

STP means Standard Temperature and Pressure which is 273 K and 1 atm.

J Medina 2I

Pressure inside a vacuum is zero so when using the equation w = - P ex * delta V, the work done by a system is also equal to zero.

J Medina 2I

What are some examples of monatomic gases where we will have to calculate enthalpy with Cv,m as 3/2 R? Will most calculations for with Cv,m use the values associated with Linear molecules (5/2 R) and Nonlinear molecules (3 R)?

J Medina 2I

PranaviKolla2B wrote:Can someone explain what it means when the reaction shifts one way or another?

A reaction shifts left when reactants are being produced at a higher rate than products and a reaction that shifts right means that products are being formed at a higher rate than the reactants.

J Medina 2I

So does irreversible just refer to anything that is not at constant temperature, or is there a more specific definition?

J Medina 2I

If you exclude the x and want to double check afterwards to see if the approximation is accurate, then you can calculate the protonation percentage, or deprotonation percentage depending on the question, and if it is below 5% then the approximation is correct.

J Medina 2I

I think so, Lavelle mentioned that everything on the first page of the Thermodynamics Outline, which I think is also the first two rows of problems.

J Medina 2I

I would guess that you take the square root of the Kw value given since we are dealing with water.

J Medina 2I

An example of an extensive property is Heat Capacity because it tells you the amount of heat required to raise the temperature of an object by 1 degree celsius but it does not tell you how much of that object is present, so the information provided is not useful for other calculations.

J Medina 2I

For this problem you would not be able to find the heat capacity of Kr gas because the final volume is not given to us, but I am also confused on determining which equation to use for this.

J Medina 2I

You could probably check by including the -x and then using the Quadratic Formula and then comparing this value to the value you got when you ignored the -x.

J Medina 2I

If more pressure is exerted, then the reaction will shift to the side with less moles. I like to think of the reaction as being squeezed and to adapt, the reaction overflows onto the side that is less cramped up because there is more space there.

J Medina 2I

If you are calculating the change in enthalpy of a substance and that substance changes phases then it is important to add the energy required by the phase change in order to get an accurate calculation for ΔH.

J Medina 2I

For the methods discussed in lecture on Friday, we will need to be given multiple ΔH's so that we can add or subtract them to find out the value of the ΔH we don't know.

J Medina 2I

The standard state is the substance's phase (solid, liquid,gas) at 25 degrees Celsius and at 1 atm of pressure.

J Medina 2I

A change in volume will also directly affect the pressure of a system. A decrease in volume will lead to a higher pressure and an increase in volume will lead to lower pressure. Thinking of the equation PV=nRT is helpful since it shows how pressure and volume are inversely proportional.

J Medina 2I

I know we don't include H2O (l) in caluclations for Kb and Ka but why is that?

J Medina 2I

If you have trouble deciding whether a reaction is endothermic or exothermic based on direction of heat flow, I find it helpful to think of the melting of ice as an example. Ice melting into liquid water is an ENDOTHERMIC reaction. The ice's surrounding has to be warm in order for liquid water to be...

J Medina 2I

I think he just mentioned how the information we are learning will be helpful if we take Chem 14Bl where we will be doing titrations, but no I don't think we'll be tested on them.

J Medina 2I

When making a buffer, you want to choose weak acids or weak bases since strong acids or bases will make the solution's pH too extreme. The reason for this is that weak acids and bases do not fully dissociate.

J Medina 2I

Sometimes certain problems will make it easier to calculate pH, and if the pOH is being asked then you can take the pH (-log(H3O+)) and subtract that value from 14 (since pH + pOH + 14).

J Medina 2I

Does it have to do with using significant figures? Like when we round our answer to a significant figure, the difference in our answer that a -X would have provided does not even make a difference in our final rounded answer?

J Medina 2I

If you're looking at a graph, an endothermic reaction will be drawn so that the ending of the graph is higher than the beginning. This means that the products of the reaction will have greater energy than the reactants. And for an exothermic reaction graph, the ending of the graph will be lower than...

J Medina 2I

Is there a different way we should approach a problem where we have to calculate the equilibrium constant if the given chemical reaction is heterogeneous and not homogeneous.

J Medina 2I

The units cancel out (concentration/concentration), making K unitless.

J Medina 2I

005384106 wrote:In what instances would the state of a molecule be important? (gaseous, aqueous, solid, or liquid)

Solids and liquids are excluded from calculating K. But, a gaseous reaction indicated using Kp and an aqueous reaction indicates using Kc.

J Medina 2I

I don't think K can equal 0. If K were to equal 0, then that means there would be no product, meaning a reaction isn't taking place.

J Medina 2I

You could calculate Q and if it matches K, then the reaction is at equilibrium.

J Medina 2I

Why is part d neutral?

d) KBR

And is asking whether an aqueous solution of this will have a pH < 7 , pH > 7, or be neutral

J Medina 2I

What kind of things in a problem suggest that we use DeBroglie's equation?

J Medina 2I

Does this work the other way around too? If we were given a H3O+ concentration of 1.56 x 10^-4 where there are 3 sig figs, would we have to write the pH as 3.807 or as 3.81 ?

J Medina 2I

What does it mean for pH to be negative?

J Medina 2I

When writing the formula for a coordination compound containing a ligand that can be abbreviated, such as sodium bisoxalato(diaqaua)ferrate(III) containing oxalato, are we able to also write the abbreviation in the formula. For example can this coordination compound be written as: Na[Fe(OH2)2(ox)2] ...

J Medina 2I

Lewis bases are positively charged. Lewis acids are negatively charged and usually have a lone pair.

J Medina 2I

Most solutions are in this range. Remember that pH is logarithmic so a pH of 15 would have a concentration of ions 10x greater than a solution with a pH of 14, which is not common.

J Medina 2I

Neutral ligands have the same name except for a few. Water turns to "aqua," ammonia turns to "ammine," and CO turns to "carbonyl." Ligands that are anions end with o.

J Medina 2I

I don't think we have been told of any exceptions in lecture so I think it's safe to assume that we wouldn't be asked any questions where knowledge of an exception would be needed to answer the question.

J Medina 2I

However many ligands are attached to the central atom is what determines the coordination number. You can determine this by looking inside the brackets.

J Medina 2I

I think it's safest to label each bond individually with a "σ" on top of one line and a "π" on top of the other line.

J Medina 2I

If a lone pair is present in a molecule, then it will affect the bond angles of the surrounding atoms since the repulsion force lone pairs is greater than bonded atoms.

J Medina 2I

Patricia Cardenas wrote:Does anyone have advice on how to start drawing lewis structures/resonance structures?

The first step would be to identify the least electronegative atom because this one will typically be the central atom.

J Medina 2I

Yea if the formula is AX2E then the angles are similar to a trigonal planar molecule (<120) but if the formula is AX2E2 then the bond angles are similar to a tetrahedral molecule (<109.5)

J Medina 2I

I think Lavelle mentioned in lecture that cisplatin not only stops cell division of cancer cells but stops division for all cells

J Medina 2I

Square planar has 6 electron dense regions but two of those are lone pairs, making the formula AX4E2 whereas tetrahedral only has 4 electron dense regions, all of which are bonds to another atom, making the formula AX4. The two lone pairs in a square planar molecule repulse the 4 bonds to form a squ...

J Medina 2I

Lone pairs take up more space making the rest of the bonds move away in order to lower repulsion.

J Medina 2I

If you're talking about the rules stated in the textbook, Rule 2 is telling us that multiple bonds (double bonds, triple bonds) count as only a single region of high electron density. The same way a single bond is counted as one. And the same way a lone pair counts as one. Adding up all the electron...

J Medina 2I

Lone pairs and bonds need to be placed where they will cause the least amount of repulsion. Considering lone-pairs have a stronger amount of repulsion than bonds do, their placement is prioritized in terms of where it will cause the least amount of repulsion. In the see-saw example shown in class th...

J Medina 2I

Xenon has d-orbitals, allowing it to store more electrons in its valence shell than atoms without any d-orbitals, like those that are at or come before 4s^2 .

J Medina 2I

Lone pairs have the strongest repulsion strength because lone pairs are less restrained than a bonding pair would be so it takes up more space making the rest of the atoms move away to lower the repulsion acting upon them.

J Medina 2I

Hydrogen bonds are the strongest intermolecular force

J Medina 2I

Atomic radius increases going left across and down groups of the periodic table. Having higher atomic numbers means having more protons that pull the electrons closer to the nucleus, decreasing the atomic radius as you move right across the periodic table.

J Medina 2I

A coordinate covalent bond is when one atom is responsible for giving off a lone pair that contributes to making the bond with another atom without the second atom having to sacrifice one of their own electrons to create the bond.

J Medina 2I

I think the question would specify if you had to use a specific notation.

J Medina 2I

This is why rod-shaped molecules will generally have higher melting points. A lot more dipole interactions have to be broken.

J Medina 2I

Hydrogen and Helium fill up a duplet (2 valence electrons). Other exceptions include atoms in the d-block since they have 5 orbitals allowing them to hold more than 8 outer electrons.

J Medina 2I

It's easy to think of it as any valence electrons that aren't touching (being shared by) any other atoms in the lewis structure

J Medina 2I

Electronegativity decreases down a column because the atom gets larger and the electron gets farther away from the pull of the positively charged nucleus. Ionization is related to this since this weaker pull allows less energy to be needed to remove an electron from an atom.

J Medina 2I

I think you can assume you're able to write the shorthand notation unless told directly by the question to write the entire configuration out.

J Medina 2I

Bond length does have effects. Shorter bonds (such as triple bonds) will require more energy to break apart because the shared electrons are closer to the positively charged nuclei and thus have a stronger pull on these electrons.

J Medina 2I

In a Lewis structure they're the two dots on the sides.

J Medina 2I

Atom ionization energy levels generally follow a trend of decreasing as you move left across and down the periodic table.

J Medina 2I

I think in lecture Lavelle mentioned that H, He, Li, and Be are exceptions to the octet rule.

J Medina 2I

These numbers are the length of each bond. The double bonds are shorter because there is a stronger pull there which makes it tighter.

J Medina 2I

The biggest difference is their shape and their ability to hold e-. The s-orbital can only hold 2 e-. The p-orbital can only only 6 e-. The d-orbital can only hold 10 e-. The f-block can hold 14 e-. In the ground state of an atom, the electrons must fill up all spots in lower energy levels before m...

J Medina 2I

A black body is a material that absorbs all radiation. No object is a true black body, it is more of an idea in the same way frictionless surfaces are used in physics problems.

J Medina 2I

Orbitals are probability density functions and nodal planes are where there is a 0 percent likelihood of finding an electron.

J Medina 2I

Wavelengths are measured in meters since it is a distance. It is common to see them measured in nanometers which is 1x10^-9 of a meter.

J Medina 2I

s^-1

refers to cycles per second

J Medina 2I

I found it helpful to read the chapters covered in lecture and going through all the example problems given. I also write question marks in my notes during lecture to remind myself what seemed confusing at the time so I can study it later.

J Medina 2I

It's Planck's Constant. If you multiply it with frequency (v) you get the energy of the photon.

J Medina 2I

If we use the rounded version of the atomic mass (let's say to the hundredths) and correctly use significant figures, would our answer be wrong if the answer we get is right according to the rounded calculations we made?

J Medina 2I

Shorter wavelengths imply higher frequency (v), means more crowded bumps and higher energy for removing electrons

J Medina 2I

I think you can use the Mass of electron given in the constants sheet and plug that into the 1/2mv^2 equation which will give you the kinetic energy of the electron. Then you use c=(lambda)v to get the wavelength.

J Medina 2I

It's also important to remember that the Angstrom is not an SI unit

J Medina 2I

I think it'd be a good idea to leave an answer in scientific notation if the answer in normal form would be an ambiguous number of significant figures. For example if you want to show 1000 with 3 significant figures just write 1.00 x 10^3

J Medina 2I

No the rules are different. For adding and subtracting when dealing with decimals you can only include the decimal value that was closest to the decimal. For example if we had to add 522.7 + 49.44 = 572.14, we would have to round down so that the answer is 572.1 But for multiply or dividing you can ...

J Medina 2I

Yes, you would assume that your sample is 100 g, but to convert to moles, you actually have to divide by the molar mass of each element as found on the periodic table (so 12.01 g/mol for C). You don't need to divide 63.15 by 100 because if you assume the sample is 100 g, then 63.15% of 100 would ju...

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