CHEMISTRY COMMUNITY

Anna O 2C

When we are balancing redox reactions, will we have to be able to tell off the question if it's in an acidic or basic solution or will we have to be able to figure it out off the reaction itself? If so, how do we do that?

Anna O 2C

When we are adding up bond enthalpies or enthalpies of formation for specific reactions to get the overall reaction enthalpy, do we need to change the signs of the values we will be given in a table for bond enthalpies or enthalpies of formation? Or can we just have all the bonds in absolute value a...

Anna O 2C

Rate of consumption is just more specific than rate law because it determines whether the rate is positive or negative.

Anna O 2C

one way to think of integrals is by looking at a graph. If you have a normal equation, say y=2x, the slope of that equation is 2, so the derivative of that equation is 2 because no matter what x you put in, the slope there will always be 2! For integrals, you're basically given the slope of x at any...

Anna O 2C

Yes because the rate of a reaction will be determined by the step that takes the longest and has the greatest impact on the overall length of the reaction.

Anna O 2C

Kinetics and thermodynamics can both have a say in whether a reaction will proceed. When ΔG<0, the reaction will occur spontaneously and will be thermodynamically favorable, but not always kinetically favorable as seen in the case of diamonds and graphite which would have to overcome kinetic barrier...

Anna O 2C

Spontaneity is just the ability for a reaction to proceed forward or backwards without added energy required to carry it through. This is determined by Gibbs free energy not the rates of reaction.

Anna O 2C

A way that I think about the slow vs fast rates is with cooking. The entire length of the cooking session will be determined by the step that takes the longest and has the biggest overall effect on the time duration (example would be the baking in the oven compared to measuring the ingredients which...

Anna O 2C

^Pt is added to the side of a cell diagram that doesn't have a metal conductor such as when one half reaction is composed only of aqueous solutions.

Anna O 2C

E will not change since it is intensive however depending on the direction of the equation you might change its sign.

Anna O 2C

The amount of OH- or H+ is based off of whether it is a basic or an acidic reaction.

Anna O 2C

To answer your question I think the Cl- is being oxidized in the HClO- it is gaining an electron in one of the compounds.

Anna O 2C

You had OH- when dealing with bases because they are going to result in the addition of more bases as they accept hydrogens.

Anna O 2C

A negative delta H means that the heat transfer is negative and thus the system is losing heat.

Anna O 2C

It is a shallower slope because it is a slower process to reaching the next phase change whereas for low heat capacity, it takes less energy and heat and thus has a steep slope because it reaches the next phase easier.

Anna O 2C

Heat lost by the metal should be a negative value while the water receiving the heat should have a positive value.

Anna O 2C

To add on, often times Dr. Lavelle might also ask questions that require you to "recreate" the shape of the graph and the changes occurring at each phase.

Anna O 2C

Can someone explain why heat transfer is ΔU at constant volume and interpreted as ΔH at constant pressure?

Anna O 2C

Since we are stopping before Gibbs Free Energy for the midterm, how far into the Thermodynamics outline do we have to know?

Anna O 2C

Kc is the value of Q taken only at equilibrium while Q is the same ratio but taken at anytime during the reaction, not specifically at equilibrium.

Anna O 2C

Generally I would recommend using only pressures and concentrations because that is what practice problems in the textbook use.

Anna O 2C

To add on, make sure you show up early because his fill up very quickly.

Anna O 2C

Often times if they don't say it outright, you can infer through whether they are referring to the concentrations of acids or bases in a solution.

Anna O 2C

To add on, make sure to always verify at the end that your approximation was less than 5% otherwise the approximation won't hold and you need to use the formula for finding roots.

Anna O 2C

They simply correspond with different values, but distinguishing between them is essential in order to use the correct R constant value.

Anna O 2C

Condensation releases heat and is exothermic because molecules are going from the gas phase to the liquid phase by making bonds. Creating bonds will release excess energy as the two molecules move to a lower energy level so that energy will be released back into the surroundings in the form of heat.

Anna O 2C

The slope corresponds with the coinciding heat capacity of that specific liquid. The higher the heat capacity, the more heat is require to raise its temperature so it will take longer for the temperature to rise thus leasing to a smaller slope and less steep curve.

Anna O 2C

To add on to what's above, the best way to prepare for all these sections in my experience is to follow along with the practice problems that show the steps and then self test yourself on more ! Good luck!

Anna O 2C

Enthalpy is usually represented in kJ/mol, and many questions will present measurements in either J or smaller quantities, so it's always important to check to make sure you do any necessary conversions ! :)

Anna O 2C

Energy is being used to elevate energy within the system, not raise the temperature which is why they can be different phases but same constant temperature.

Anna O 2C

Steam is at a higher energy level than boiling water is so even though they are existing at the same temperature, the extra energy and thus burning ability is transferred to a burn victim when the steam condenses and lowers temperature after contact with skin.

Anna O 2C

Work is dependent on its transition from its final to initial stage so it cannot be considered a state functions in the way enthalpy can.

Anna O 2C

Isolated systems have to be closed but they also don't allow the passage of heat or energy with their s.urroundings

Anna O 2C

Whether or not it is on the test, deriving it is simple because you only have to take the negative log of the concentrations to get the respective pH and pOH. It is important in general to remember the relationships like those such as Kw because they will come in handy on the midterm and final as we...

Anna O 2C

The reactants are favored because in a closed vessel with solids and gases, the increase in pressure isn't going to affect the solid, it will only affect the gases. Because of this, increased pressure will cause the reaction to move towards the side with less moles of gas and thus less partial press...

Anna O 2C

I've seen videos where ice can be frozen to 0°C and remain in liquid form, but when you shake it, it immediately turns into slushy and freezes over. Does this have to do with the water graph we looked at today where there is a solid chunk of time/transition between solid and liquid? Where even thoug...

Anna O 2C

As stated above, condensation is exothermic. When you look at it from a molecular standpoint, the molecules are transitioning from the gas phase to the liquid phase. Individual atoms are thus coming together and bonding with each other, a process that release excess heat as the bonded molecule is mo...

Anna O 2C

Q is calculated in the same way as K, only it can be taken at anytime during the reaction instead of K which is exclusively valued at the time of equilibrium. Because Q is the same ratio as K, you can utilize its value in relation to K to determine where the reaction lies in its accordance to the gi...

Anna O 2C

Kc will remain constant throughout the whole reaction as long as the temperature remains constant. When the concentrations change, the reaction will simply respond by producing more or less of either reactant or product to filter the introduced additives into the equilibrium. For example, if you add...

Anna O 2C

To add on, if only moles or concentrations are given for one side, it is generally safe to assume that these will be the only initial values given and that your x value will be taken away from these given values. This is because in your resulting equation, the x needs to have a reference point to an...

Anna O 2C

Generally, I think we focus on using concentrations. However, 5I.23 in the 7th edition textbook version uses mole values for the ICE tables instead of concentration.

Anna O 2C

Posting on Chemistry Community can take on many forms. You can ask a question about lecture, discussion, textbook problems, homework, and even administrative questions such as study groups. In addition, you can answer people's questions or add onto an existing discussion. Any substantial post will c...

Anna O 2C

Could you explain what problem you are referring to? Writing out the problem would be easiest.

Anna O 2C

Adding on, Kp is used for gases in the reaction, ignoring solids and liquids. When a reaction includes aqueous solutions, you can't use Kp because liquids can't have pressure, just concentrations.

Anna O 2C

Adding on, K is referring to the concentrations held to the specific power and ratio as stated in the balanced equilibrium equation given in the problem. Knowing the concentrations won't do you any good if they aren't held to the correct power within the fraction for K.

Anna O 2C

I don't know what question you're referring to but for sp3 must be 4 regions of electron density. You might be missing a lone pair or if it's a coordination bond there might be a hydrogen attached that isn't shown.

Anna O 2C

Adding to the last reply, they can expand into their d orbitals because at row 3 the 3s and 3p also include 3d even though it's in the 4th row.

Anna O 2C

The surface area is larger for the rod shaped molecules so there will be more surface area for the two to interact upon, resulting in tighter and stronger bonds.

Anna O 2C

Also a good point to know is that the water and sulfuric acid mix to create h2so4

Anna O 2C

Is the coordination number determined by the number of atoms attached to a central atom, the number of bonds (including double and triple) or the number of regions of electron density?

Anna O 2C

The hybridization will be sp2 because the s orbital can only form 1 bond and the 2 p orbitals must be combined with the s orbital to allow for 3 bonds to be made by the central atom. This results in the hybridization with 1 s orbital and 2 p orbitals, so sp2.

Anna O 2C

Yes, because the s orbital can only form one bond and the p orbital can form 3 bonds but the center atom in a tetrahedral shaped molecule forms 4 bonds so the s and 3 p orbitals must combine, resulting in an sp3 hybridized orbital.

Anna O 2C

Generally, this can be solved by creating a Lewis structure of the molecule. Once you make this, you can see which atoms have lone pairs available for bonding or which atoms in a compound are able to add another bond even if they have a full octet already as in the case of phosphorus which can have ...

Anna O 2C

I don't believe you will have to memorize the names of all the polyatomic ions, but at this point in the course you should know the names of several of the molecules that we use regularly such as cyanide and carbonate. Other than that, the final is highly unlikely to have a section dedicated to just...

Anna O 2C

I'm looking for examples of polar molecules with an octahedral shape and I'm struggling to find any. Is there an exception saying that octahedral shapes are usually nonpolar or are there any good example of octahedral structures that are polar? Thanks!

Anna O 2C

Adding on to the reply above me, the lone pairs distort the attached atoms more than normal bonding pairs do because when they aren't engaged in a bond, electrons move more freely and this causes them to be more repulsive. Because of this, the lone pairs take up more room than atoms do and thus pus...

Anna O 2C

Polarity depends on symmetry of the molecule. Sometimes lone pairs can cancel out, such as in the case of AX4E2, which is square planar. Since the lone pairs are directly opposite each other, the repulsion caused by them cancel out, and thus the atoms remain in a symmetrical position. Adding onto t...

Anna O 2C

Pi bonds result because you can't have 2 sigma bonds in a double bond. Sigma bonds are the shortest and connect the two atoms most directly. Any other bond that occurs will have to arch around the existing bond to reach the other atom and thus become a pi bond. Every bond formed after the initial si...

Anna O 2C

If a structure has multiple bonds then the total molecule will have bonds the average length of all the present bonds. A molecule that has resonance has multiple possible bond placements in a Lewis structure, but this simply translates to having bonds that are averaged out over the different bond le...

Anna O 2C

Another hint in figuring out whether a molecule is going to be polar is its geometry. If the same atom is spaced around the central atom such as CH4 then the electronegativities around the central atom will be equal in magnitude and symmetrical and thus be nonpolar; for shapes with multiple atoms, t...

Anna O 2C

Adding on^^ For the Molecular shape, you know that Sb is the central atom. From there, we have 2 Chlorines and 2 Oxygens attached to it. Since there aren't any lone pairs on the central atom we know that there are only 4 regions of electron density giving us AX4 which corresponds with a tetrahedral ...

Anna O 2C

The sigma bond is going to the shortest and closest bond. When you form extra bonds, those electrons can't invade the bond space already occupied by the sigma bond so they have to arch over in order to reach the other atom. Kind of like if you're hugging someone and then another third person joins t...

Anna O 2C

The course page for this unit says we need to know how to distinguish sigma and pi bonds by their shapes, properties, and component orbitals. Just remember that the double bond isn't really "=" but one of the bonds will have to arch over the other. I remember this because pies are round an...

Anna O 2C

It won't really matter in the 3D version because even though 4 atoms might seem like they are next to each other on paper, they will actually all be an equal distance from the atoms next to each other in the tetrahedral shape. As long as you know it's a tetrahedral shape, that implies that they are ...

Anna O 2C

Lone pairs have more repulsive energy than electrons engaged in a bond between two atoms because they aren't being "tied down" by the positive energy of two atoms. Thus they have more "push" per say and can repel nearby atoms more than bonded electrons can. When this happens, the...

Anna O 2C

Lone pairs affect the shape of a molecule because electrons have negative and repulsive energy. They are constantly being tugged at and pushing each other away. When they are sitting as a lone pair, they have more freedom to buzz about near their home base atom. When the electrons are engaged in a b...

Anna O 2C

Test questions, unless given experimental data to permit exact bond angles, will generally accept "less than 109.5" because, without an experiment, one can't really know the extent to which the lone pairs can alter the position of the bonded atoms because there isn't a calculation to tell ...

Anna O 2C

The regions of high e- density will determine the shape but lone pairs have more repulsion energy than electrons in bonds so the lone pairs will alter the bond angles. VSEPR models only take into account where the atoms are, not where the lone pairs are, but the lone pairs need to be considered beca...

Anna O 2C

I would recommend drawing the structure with the implied "3Dness" (the dashes and the solid black triangles) since that is the only way you can correctly label it a tetrahedral. If you draw it in the 2D version, the bond angles won't be displayed properly because that would imply that the ...

Anna O 2C

When there is a difference in electronegativity, one atom is going to have more of a pull on that electron that the other, meaning the electrons will spend more of their time near that atom, so the negativity will be largely on that side of the molecule. That side of the molecule thus has a partial ...

Anna O 2C

The dashed lines means that there is an attraction between those two dipole moments. For example, if you draw multiple H2O molecules the dashed lines will be connecting oxygen and hydrogen atoms on the two different molecules because one has a positive and one has a negative dipole so they are attra...

Anna O 2C

I'm pretty sure a molecule is going to be linear as long as there aren't any lone pairs on the central atom. When the molecule is linear, there aren't any lone pairs taking up space and pushing the other attached atoms away, thus bending the molecular shape. I think this only applies to chains of at...

Anna O 2C

Nitrogen would be the central atom because the central atom should be the one that is least electronegative because it is more likely to share electrons. Central atoms should be chosen based on their electronegativity, not ionization energy. Hope this helps!

Anna O 2C

This is also because Helium is a noble gas. Since it also has very few orbitals and energy shells in the ground state, the electrons experience little to no shielding and thus require extreme amounts of energy to remove electrons.

Anna O 2C

ml is the magnetic quantum number. This just tells you which orbital the electron is in. For example, an electron in chromium could either be in the -2, -1, 0, 1, or 2 orbital. ms is spin magnetic quantum number. This tells you whether the electron has up spin or down spin (the two electrons in an ...

Anna O 2C

I'm struggling to clarify how to utilize ml and ms for quantum numbers. I understand that n is the period of the element, and that l is for the orbital the valence electrons, but I'm not sure on the concept behind the ml and ms as well as the numbers when an element is in the d-block. Say for exampl...

Anna O 2C

^^ To add on, Hydrogen is willing to give away its one electron to become more stable and Aluminum wants electrons in order to get closer to the noble gas configuration and more stability, so Aluminum will take 3 Hydrogens that each provide 1 electron.

Anna O 2C

Yep! Ag sits one electron away from having a full d orbital so the second electron from the 5s orbital instead occupies the d orbital to bring it to a full and therefore more stable state. Therefore the 4d becomes 4d10 and the 5s becomes 5s1.

Anna O 2C

Removing the second electron generally requires more energy because of the proton's net positive charge. When the first electron is removed, the positive pull of the protons gains more power over the fewer electrons still left in orbital. Thus, more energy is then required from an outside source to ...

Anna O 2C

^^ And after that you can compare the separate molecules and their charges. For example, SO42- will have 4×6=24 O electrons (4 O and each one has 6 e-) and then S will have 6 e-, for a combined total of 30 e-. Then, since the molecule SO42- has a charge of -2, that means there are 2 extra electrons ...

Anna O 2C

Today we defined a chemical bond, discussed ionic bonds and how they differ between main group and p-block elements, covalent bonds, the octet rule, and basic Lewis structures as well as the Lewis structures of polyatomic species.

Anna O 2C

Also, the negativity will be concentrated on one side of the molecule/bond where one atom has a high electronegativity than the other. When this happens, even though both atoms are sharing the electron and thus attached to each other, the electron is more likely to be found closer to the atom with h...

Anna O 2C

Using the noble gases in the configuration allows us to only mention the most relevant electrons on the atom. When it comes to bonds and equations, the valence electrons are generally the only ones interacting directly with other atoms to it is both cumbersome and repetitive to mention all the lower...

Anna O 2C

Why is it that, for the Lyman and Balmer Series, the lines are super close and then there is a huge space in between and then more close sets of lines? I feel like as the energy level goes up, it should take almost exponentially higher energy from light to eject an electron.

Anna O 2C

^ Similarly to what was mentioned above, using the noble gases is fine just as we learned in lecture unless the question particularly requests for the full length version of such a configuration.

Anna O 2C

While you won't have to remember the equations for the test, it'll be important to remember the SI units for these formulas such as whether a formula requires meters or kilometers and converting accordingly.

Anna O 2C

I agree with the erasable pens. They come in 5 packs on amazon and most have pretty durable erasers. Just make sure the pens you get don't smear when you erase! The low quality pens will leave marks on your paper so test them out beforehand.

Anna O 2C

So electrons in higher energy states contain higher potential energy, while electrons in lower energy states contain lower potential energy? Does this mean that electrons in higher energy states are more unstable than electrons in lower energy states? So isn't that why it's easier for electrons to ...

Anna O 2C

I know that an electron requires energy from light in order to be excited and pushed up to the next energy level, and that an electron will give off energy when it returns back to ground state in the form of photons, but I don't understand where the energy is kept while an electron is buzzing around...

Anna O 2C

Thank you for this advice! I want to become a physician's assistant, so while I don't have to take the MCAT, PA school requires chemistry knowledge and math. Which math series did you take since I know that students going to medical school are required to take a full year of math? Thanks!

Anna O 2C

The safest way to prevent incorrect rounding early on is to use the entirety of the number given on the periodic table. With other pieces of data, rounding is more difficult to fully avoid, but avoiding rounding with Periodic elements will produce the most accurate answer possible, and then it can b...

Anna O 2C

The more steps you show, the easier it is for a TA to trace your steps backwards say you make a mistake. Often times if you make an error early on in a calculation such as in adding molar masses, but do the steps correctly (albeit with an incorrect value), you can still receive partial credit becaus...

Anna O 2C

The stoichiometric coefficients indeed are pertaining to moles of CH4. One mole of CH4 has 6.022x10^23 molecules of CH4, one mole of C, and 4 moles of H. A mole simply refers to the number of objects in a sample, and thus simplifies large quantities of atoms/molecules, just as it's easier to say a d...

Anna O 2C

I have found that Dr. Lavelle is very effective at reviewing all necessary fundamentals needed for that lesson at the beginning of lecture. I took Honors Chemistry sophomore year and I am also a freshman this year. For me at least, the best way I've found to really get through the material is to wat...

Anna O 2C

For two photons to combine their energy to eject one electron, they would 1) need to hit the electron at the same time in order for both energies to add up to enough for an ejection which is extremely rare, and 2) like Dr. Lavelle said I think that the premise for our entry level quantum mechanics i...

Anna O 2C

Like mentioned above, if the question asks for specific units, use those. Otherwise, often times it comes down to the practicality and simplicity of an answer. If an answer in wavelength comes out to be 4.60×10^-9 meters, it is more efficient to simply say 4.60 nanometers. Often times formulas requi...

Anna O 2C

Light intensity has to do with the amount of photons in a light sample. This is especially important when considering threshold energy in quantum mechanics. Intensity doesn't affect the amount of electrons ejected from a sample if the individual photons in the sample don't have a high enough frequen...

Anna O 2C

I have found that in general the best way for me is to take handwritten notes. I have several different colored pens that I utilize during class, and I switch between the different shades whenever we transition from lecture to explicit equations or from PowerPoint to hand drawn graphs/models. The co...

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