CHEMISTRY COMMUNITY

Sabrina Galvan 3J

Enthalpy only depends on the final and initial states, meaning it is not dependent on the path it takes to get there. Heat is not calculated the same way.

Sabrina Galvan 3J

I was also having this issue, because I was converting the molarity from units of mmol/L to mol/L. However, when I just inputted the exact values sapling gave me, the answer was finally correct. Hope this helps.

Sabrina Galvan 3J

The "Great British Bake Off" is one of my favorites! Its perfect for background noise when doing homework, and for watching with full attention. I love to bake, and just watching one episodes gives me so many new baking tips! For movies, its generally the last one I watched LOL, but "...

Sabrina Galvan 3J

Even though I've only had it once, its a vegan korean salad from a restaurant in San Luis Obispo. I've tried to recreate it so many times, but its never them same :'(. More generally though, its spicy pad thai or anything with noodles!

Sabrina Galvan 3J

Hi! I agree with the statements above, but am I also correct in saying that the cell with the more positive E° is always the cathode unless energy is introduced into the system as in an electrolytic cell? In the case of an electrolytic cell, do the electrons flow in the opposite direction than they...

Sabrina Galvan 3J

Yup! and noting further differences between them, standard values have a fixed value during the duration of a reaction, but the value of nonstandard values do change as a reaction proceeds.

Sabrina Galvan 3J

The addition of electrons first comes from the basis that the charges of the reactants and the products are equal to one another. For oxidation, the electrons will be placed on the side of the products, and for reduction, the electrons will be placed on the side of the reactants. When combining the ...

Sabrina Galvan 3J

As a first year, I'm really looking forward to walking on campus for the first time since being admitted as a student. Even though I've toured the campus a few times, I imagine that the feeling of walking through campus will be significantly different :)

Sabrina Galvan 3J

I recently finished Circe by Madeline Miller and I loved it! She portrays Circe in an empathetic light, as the book goes through many classic greek myths in her perspective. If it weren't for school and other responsibilities, I would've read it in an entire day!

Sabrina Galvan 3J

In addition to going over textbook problems, I find redoing Sapling problems extremely useful as well! The explanations help refresh concepts or procedures that I may have forgotten over the quarter, also they're a nice preface to the textbook problems because some questions are very similar.

Sabrina Galvan 3J

I always found ceviche to be an interesting dish! It's essentially letting raw shrimp marinate in an acidic base (oxymoron haha) mainly composed of lemon or lime juice. The citric acid causes the proteins in the shrimp to go through denaturation, changing its physical and chemical properties so that...

Sabrina Galvan 3J

Could someone explanation the equation conceptually?

Sabrina Galvan 3J

You can use this if it says "there's no heat gained/lost", thermal equilibrium, or if the system is isothermal. This is because when qsurr = -qsys, that means qsurr + qsys = 0 and that there's no net heat transfer. Since there's no net heat transfer, there isn't a change in temperature. h...

Sabrina Galvan 3J

The salt bridge helps the cells maintain a neutral charge as electrons move from one-half cell to another! This helps the reaction continue without disruption or repulsion from the negative charge of the electrons.

Sabrina Galvan 3J

Work of compressions is negative for the surroundings, but work of compression is positive for the system, because the system isn't applying any force. Instead, the surroundings are creating the pressure through compressions, making work negative.

Sabrina Galvan 3J

Would an isolated system could as a adiabatic.

Sabrina Galvan 3J

LeanneBagood_2F wrote:can someone remind me what residual entropy is please?

Residual entropy is the entropy that remains present when a system has reached 0 Kelvins, and the entropy itself comes from the different positions molecules and atoms can have within a substance.

Sabrina Galvan 3J

They are calculated similar to one another, and one can be used to convert to the other using the PV = nRT formula.

Sabrina Galvan 3J

When they are both positive, the reaction will be non spontaneous at low temperatures, and spontaneous at high temperatures.
This affect is seen in the equation deltaG = deltaH - TdeltaS

Sabrina Galvan 3J

The usage of kelvin or celsius will depend on the other units of the other values in the equation. You would want them all to match, so only use kelvin, if the other values also include kelvin units and vice versa for celsius.

Sabrina Galvan 3J

Sean Wang 1F wrote:Yes, the equation Cp=Cv+R can be used to convert between Cp and Cv.

Could someone explain this equation in greater detail? How does adding Cv to the gas constant create Cp?

Sabrina Galvan 3J

This is correct since we know that if Q<K, the reaction will favor the products and therefore occur spontaneously since that is the way it moves toward. When Q is greater than K, the reaction will favor the reactants and therefore need the energy to move in the forward direction. I totally agree wi...

Sabrina Galvan 3J

They cannot be negative because the value specifies the amount of heat that can be taken in per mass of a substance, therefore making it an endothermic calculation. If it were negative, this would imply an exothermic process, which does not match the definition of heat capacities.

Sabrina Galvan 3J

Typically, the equation is q(surroundings) = -q(system), if the system is exothermic. In this scenario, the calorimeter is acting as the surroundings, and the reaction as the system. Therefore the previous equation becomes, q(calorimeter) = -q(reaction), and they are set equal to one another, becaus...

Sabrina Galvan 3J

Entropy comes from the idea that energy and matter tend to disperse in a disorder manner, therefore a substance will have greater entropy if it is capable of greater disorder. This disorder can be thought of as dispersion, and when comparing solids, liquids, and gases, gases have a greater degree of...

Sabrina Galvan 3J

When comparing two different systems, the system that absorbs energy will carry a positive q value, while the system that releases energy will carry a negative q value. In terms of temperature, the system that has the lower initial temperature will absorb heat because it will increase in temperature...

Sabrina Galvan 3J

As others have stated, drawing the lewis structures of both the reactants and products is the best way to determine which bonds are broken and which bonds are formed in a reaction. For example, if the reactant side has four C-H bonds and the product side has three C-H bonds, then it can be determine...

Sabrina Galvan 3J

The given ΔH of 358.8 kj tells us that 4 moles of CS2 are formed given that much heat is absorbed. Because the problems tells us that 389 kj of heat were absorbed, we can expect our final answer of moles of CS2 to be more than four. To solve, we use stoichiometry to find the total amount of moles of...

Sabrina Galvan 3J

For the heat gained by the ice, there must be a phase transition where energy is put into the system until it becomes liquid water. That is why the problem gives you the standard enthalpy of fusion, allowing you to calculate and accommodate for the energy put into the system that changed the ice in...

Sabrina Galvan 3J

Yes! Because we are looking for the final temperature of the system, we need to set each system's heat equal to one another. Therefore, we need to find the amount of joules needed to melt the ice as a part of ice's supplied heat, so yes we would need to multiply the amount of moles of ice by the ΔHf...

Sabrina Galvan 3J

Catherine Bubser 2C wrote:We would treat these as the same state, correct?

Yes

Sabrina Galvan 3J

Almost! Because bonds between atoms occur at their lowest energy states, the breaking of a bond requires an in put of energy, making it positive, as you stated. However, I think you meant when bonds are formed enthalpy is negative, again because bonded atoms preferred to be at their lowest energy st...

Sabrina Galvan 3J

As others have stated, because H2SO4 is a polyprotic acid, it will deprotonate twice. The first time it will dissociate completely, hence why the concentrations of 0.15 are used again for the second deprotonation. Because HSO4- is now a weak acid, the change in its initial concentration and its equi...

Sabrina Galvan 3J

Yes! The reason why partial pressure is dependent on moles is seen through the relationship of moles and pressure in the equation PV=nRT, where one can see that when the amount of moles increases (n), then pressure too increases (P), and the same relationship can be said when moles decrease as well,...

Sabrina Galvan 3J

arisawaters2D wrote:Thank you! So just to clarify the second deprotonation will always have a smaller K value than the first?

Yes! This is because it is more difficult for a molecule to ionize into H+ ions even further, and therefore it has to become less acidic.

Sabrina Galvan 3J

On the Acid and Base Equilibria outline, the last bullet point states "Calculate the pH in these industrial, environmental, and biological examples: Carbon dioxide reacts with water to form carbonic acid, which makes carbonated drinks acidic, acidic rain, rivers, and lakes in the environment, a...

Sabrina Galvan 3J

But I thought that If [H30+]<10^-7 that means that the solution is basic not neutral because the pH would be above 7 and if the pH is above 7 then it is basic? This is almost correct, as someone previously stated, when specially calculating the pH first using the [H3O+], values below 10^-7 result i...

Sabrina Galvan 3J

What is the formula for finding the percentage of deprotonation?

Sabrina Galvan 3J

For clarification, the reason why temperature increases when the state of water stays the same is because the energy added to water is causing particles to move faster, so the change in temperature is a reflection of the increase in kinetic energy? Yes that is true. Temperature will continue to inc...

Sabrina Galvan 3J

As the state of a substance progresses from a solid, to a liquid, and to a gas their intermolecular forces become less stable, and less strong, For gases and liquids, there aren't any intermolecular attractions between gas molecules, while there will be attractions between the molecules in a liquid ...

Sabrina Galvan 3J

They are both used for the same phase of a substance when it goes from a liquid to a vapor/gas.

Sabrina Galvan 3J

Because only the initial pressure for PCl5 is given, it is assumed that the reactants do not yet have an initial pressure, meaning the reaction has to go in the reverse direction. Because it is going in the reverse, PCl5 will decrease in pressure because it is being converted into PCl3 and Cl2, whic...

Sabrina Galvan 3J

From what I know to be true, the lower the pH the stronger the acid, and the closer the pH of an acid is to about seven, the weaker it is. However, after doing the sapling homework, acids that are classified as weak (#1 weak monoprotic acid and #3 lactic acid as examples) once solved, have extremely...

Sabrina Galvan 3J

In Dr. Lavelle's first lecture on acid and base equilibria, he gave us a worked example: what are the molarities of H30+ and OH- 0.0030 M Ba(OH)2, where Ba(OH)2 <-> Ba+ + 2OH-? He then went on to state that because the base is a strong base, it completely dissociates in water. That much I understoo...

Sabrina Galvan 3J

Adding onto what has been said above, autoprotolysis is an automatic process and occurs in molecules that are amphiprotic. Dr. Lavelle actually first mentions this in Monday's lecture, 1/11.

Sabrina Galvan 3J

A salt will be basic if it contains the conjugate base of a weak acid A salt will be acidic if it contains the conjugate acid of a weak base. To add onto this, a salt will be neutral when it contains the cation of a strong base, and an anion of a strong acid. For example, KCl is a neutral acid beca...

Sabrina Galvan 3J

The reaction quotient is used to calculate the ratio of products to reactants at any point during its reaction, and its most important purpose is how it compares to K, the fixed ratio of products and reactants at equilibrium. If Q = K, then the reaction is at equilibrium, however if it does not equa...

Sabrina Galvan 3J

I is the initial concentration, C, is the change, and E is the equilibrium concentration. For example, in A -> B + C, with initial concentration of A being 0.25M and C at equilibrium being 0.15 A B C I 0.25 0 0 C -x +x +x E 0.25-x x x Then you know x = 0.15 and can use it to find K. Just to add ont...

Sabrina Galvan 3J

To answer the first part of your question, we would use them if we're given the initial concentrations and the Kc/p of a reaction, and we are asked to find the the concentrations at equilibrium.

Sabrina Galvan 3J

Yup! They are both calculated the same way, and Q is used as a way to compare the state of the system and whether what direction the reaction is going relative to the value of K.

Sabrina Galvan 3J

Partial pressures are mainly used when the products and reactants are both gases. Therefore, if a problem gives you their concentrations, you would use PV=nRT, and manipulate the equation to give you P=(n/V)RT, where n/V is equal to the concentration. After calculating their pressures, you would the...

Sabrina Galvan 3J

H2PO4- is also another great example of an amphoteric molecule.
For a molecule to be amphoteric, it has to be able to donate an H+ ion (a Brønsted-Lowry acid), and it needs to be able to accept an H+(a Brønsted-Lowry base), so it must also carry a negative charge.

Sabrina Galvan 3J

Yes, however the strength of the conjugate base will be very weak.
The formula for this will be
HA + H20 -> conjugate base + H3O+

Sabrina Galvan 3J

SF4 has a total of 34 valence electrons to share, seven electrons per fluorine and six electrons per sulfur. Added together, this creates a total of 34 electrons, and after drawing the lewis structures and placing the needed electrons around the fluorines, you are left with a single lone pair that h...

Sabrina Galvan 3J

In addition to what has been mentioned above, lone pairs that take part in resonance structures are not included in the electron densities that make up an atom's hybridization, because they are delocalized electrons.

Sabrina Galvan 3J

In Dr. Lavelle's Final announcement, he states, "Final covers all material (approximately weighted to the amount of time covered in the syllabus). Quantum was the biggest section. Questions will come from the textbook homework listed in the syllabus." Does this mean that all of the questio...

Sabrina Galvan 3J

chinmayeec 3L wrote:I'm not sure if your answer key is different, but 180 degrees is correct and that's what the answer key says.

I copied this from the answer key: (d) The structure of N2O is linear with a bond angle of 180 degrees. AX2

Hope that helps!

Huh my answer key must be different, thank you so much!

Sabrina Galvan 3J

My lewis structure for N2O is O as the central atom, and is double bonded to N on the left and right, with two lone pairs on each nitrogen. Therefore the shape is linear, but I am confused on the bond angle. Because it's linear, I assumed the bond angle would be 180 degrees, but upon checking the an...

Sabrina Galvan 3J

Ag can take on the oxidation states of +1, +2. & +3 because it is a transition metal. Therefore to determines its oxidation state within this question lies on the overall charge of the molecule, which is -1. Cl has an oxidation state of -1, and because there are two Cl, it contributes to a total...

Sabrina Galvan 3J

The coordination number of five is only applicable to Fe. CO would not have coordination numbers because it is not the central atom, but they do play a role in determine the coordination number for Fe since they are the surrounding atoms of Fe.

Sabrina Galvan 3J

Water is amphoteric! Water can take on the form H3O+ or OH- depending on the other molecule it is reacting with in an aqueous environment.
Water acts as a base with reacting with an acid.
HCl + H20 -> H30+ + Cl-
And acts as an acid when reacting with a base
H2O +NH−2 -> OH− +NH3

Sabrina Galvan 3J

In some molecules, the presence of a lone pair causes the molecule to lose its symmetry, therefore its dipoles would not cancel out causing it to be a polar molecule. But as many have mentioned, lone pairs are not determinedly a factor of polar molecules. It is best to look at how the lone pairs are...

Sabrina Galvan 3J

Yes, in addition, to having the lowest formal charges, negative formal charges must also be on the most electronegative atom within the compound.

Sabrina Galvan 3J

Yes! Because Br is larger, it has a weaker bond to H, allowing it to dissociate more easily and completely, as all strong acids are assumed to completely dissociate within a solution.

Sabrina Galvan 3J

Yes! Lone pairs repulsion is the most has the greatest repulsion strength. However there is still repulsion among long bonding pairs, and bonding-bonding pairs, with their strength decreasing in that order.

Sabrina Galvan 3J

The resonance structures that will contribute the most are the ones with the smallest magnitudes of charges, with the negative charge being on the most electronegative atom. This makes the most stable resonance structure.

Sabrina Galvan 3J

Finding the overall charge of the molecule can be found through adding all of the formal charges of the atoms within the molecule.

Sabrina Galvan 3J

It's polarity is due to the difference in electronegativites between nitrogen and oxygen, but also because its molecular shape. Due to a lone pair on Nitrogen, the central atom, it causes the shape to be trigonal planar, therefore the dipole moments between nitrogen and oxygen do not cancel out, cau...

Sabrina Galvan 3J

Lone pairs have a greater repulsion in comparison to boned pairs. These lone pairs therefore force the bonded pairs close to one another, as the lone pairs take up a greater space due to the repulsion.

Sabrina Galvan 3J

Lewis acids are electron acceptors and lewis bases are electron donators. Because F- has a negative charge, it can donate an electron to the neutral atom BF3. Additionally, BF3 is electron deficient, giving it another reason why it can accept electrons, further making it a lewis acid.

Sabrina Galvan 3J

In addition, if a charge of zero is not possible, then a stable resonance structure would also have the smallest magnitude of charges, specifically, the smallest negative charge would be on the most electronegative atom.

Sabrina Galvan 3J

Electronegativity decreases as atomic radius increases because the distance between the nuclei and the valence electrons increases, so the atoms ability attract electrons decreases.

Sabrina Galvan 3J

Another way to determine whether multi-element molecules have dipole moments or not is by drawing out the dipoles between the elements of the molecule, specifically between atoms that are bonded with other atoms. Atoms within the molecule that do not have dipole moments that cancel out are an overal...

Sabrina Galvan 3J

The more bonds there are, the less lone pairs the atoms will have (i.e. two atoms joined with a triple bond have less lone pairs than two atoms joined in a single bond because more electrons are involved in the bond). Thus, molecules with single bonds have more free electrons, which repel each othe...

Sabrina Galvan 3J

Because molecules prefer to be in a lowest state of energy, an input of energy is required to break bonds as it makes them unstable and undesirable for the molecules to be bonded. This needed increase in energy relates to a higher boiling point, which will provide said energy.

Sabrina Galvan 3J

Hydrogen bonding occurs with molecules of O, F, & N. This is due to their electronegativities which will cause a partial negative charge that will allow hydrogen bonding to occur with a partial positive charge from the H in the water molecule. Molecule C is the only one that represents the corre...

Sabrina Galvan 3J

This is a good question. I know it's best to get formal charges of 0 to make it most stable. But how do we know when to stop manipulating the Lewis Structure? How do we know when we are close enough to the most stable form? We know we're close to the most stable form when the most electronegative i...

Sabrina Galvan 3J

For an hydrogen bond to form, a hydrogen atom has to be bonded to a strongly electronegative atom of one molecule, and another strongly electronegative atom of another molecule. N-H bonds are polar, as nitrogen is an electronegative atom. So the H in that bond is slightly positive and will create a ...

Sabrina Galvan 3J

To draw a Lewis strucutre with the lowest formal charge, the first step is have the central atom be the one with the lowest ionization energy, then when calculating the formal charges, the negative charges should be on the most electronegative atoms. It should also have the fewest and smallest magni...

Sabrina Galvan 3J

Yes, and it will always be the product of the wavelength and frequency.

Sabrina Galvan 3J

It's the most electronegative because of its orbital 2P which optimally would contain six electrons. Because Fluorine only has five, it's attraction is due to being so close to its most stable configuration, making it the most electronegative.

Sabrina Galvan 3J

Catherine Bubser 2C wrote:If asked to compare an element that is in the group to the left of the noble gas, would that element have a higher electronegativity then?

in comparison to noble gases I believe the answer would be yes since those elements do not have a full octet like the noble gases do.

Sabrina Galvan 3J

Because Oxygen has a lower ionization energy where it requires less energy to be removed an electron than nitrogen and fluroine to add onto why it requires less energy, oxygen has a lower amount of protons in comparison to nitrogen and fluorine, therefore oxygen has a larger radius in comparison as...

Sabrina Galvan 3J

Hydrogen bonding occurs when an H atom is bonded to a more electronegative atom, N, O, or F. The higher electronegativity of these atoms pulls on Hydrogen's only electron closer to themselves. This causes the more electronegative atoms to have a partial negative charge and the hydrogen atoms to have...

Sabrina Galvan 3J

Empirical numbers have to contain whole numbers since you can't have a fraction of an atom. Therefore, if you get nonwhole numbers in your conversation to the empirical formula, multiple the ratios by whole numbers until your product is close to the nearest whole number!

Sabrina Galvan 3J

Energy is released when an electron is added to an atom and is absorbed when an atom releases an electron. Atoms want to be their most stable, accounting for why there are anions and cations. When electrons are added, the atom is stabilized, hence the release of energy, and releasing an electron req...

Sabrina Galvan 3J

In order of smallest to largest ionic radius, it goes cation, normal, and anion.

Sabrina Galvan 3J

Hey guys, thank you for these tips but I am still really stuck on this question. I did: (6.26x10^-34) / (6.31 x 10^23) (442.4) to find the wavelength. My units gave me my answer in m like the question asks for, but I still keep getting it wrong. I'm not sure what else to do... Because plank's const...

Sabrina Galvan 3J

Wait so the wave needs to be able to connect to itself at the end? Do you want identical starts/finishes basically? I'm still a bit confused. Not exactly identical starts and finishes. For a wave to be compatible, and for how the images are displayed for this question, the waves have to go through ...

Sabrina Galvan 3J

The answer to this solution actually requires three sigfigs, signified by the dot at the end of 100. pm. Therefore the answer is 3960 m/s

Sabrina Galvan 3J

Emilie_Paltrinieri_1K wrote:So what was the new equation that they found after doing the experiment of the photoelectric effect?

They found that the energy of a photon is proportional to planks constant and frequency
Ephoton=(h)(v)

Sabrina Galvan 3J

How many photons with a wavelength of 793 nm are needed to melt 445 g of ice? The enthalpy of fusion of water can be found in this table. What formulas are needed to solve this and why? Im stuck. Thanks The energy of a photon can be found by using the equation (h)(c)/lambda, and this equation is th...

Sabrina Galvan 3J

Hi! So I'm pretty sure I have the same problem as you for #9 (metal objects inside a microwave oven). This is how I approached the problem. We're looking for wavelength without frequency, so I rearranged these two equations: c=λv and v=E/h. First, I rearranged the first equation to be in terms of f...

Sabrina Galvan 3J

You always want to covert any units into the SI base units before beginning the problem. The only time you'd convert SI units into different units is if the problems asks for it in your final answer!

Sabrina Galvan 3J

Everyone in this thread is mentioning Avogadro's number, but as I look through my notes, I can't seem to find anything about it. Does anyone know which lecture talked about this? It most likely is from one of the first lectures we had on fundamentals, but the textbook explains Avogadro's number on ...

Sabrina Galvan 3J

Wait so we have to solve for the product of each reactant in order to determine which one is the limiting reactant? Is there not a shorter way? No not really. The limiting reactant determines how much product can be made, therefore one has to convert the moles of reactant to the moles of product to...

Sabrina Galvan 3J

While it may be difficult to know which states all of the compounds may exist in, there are diatomic elements that would be best to know. These diatomic elements are O2, F2, I2, H2, N2, and Cl2 which cannot exist as a singular atom, and are therefore a compound of two of itself that must also exist ...

Sabrina Galvan 3J

Question: In a combustion reaction, how do we find the amount of oxygen? In every combustion reaction, O2 is a necessary reactant, and CO2 is an absolute product. Therefore, the first steps in solving the amount of oxygen in a reaction is to ensure the reagent and product are present, and then bala...

Sabrina Galvan 3J

Hi, so just to double check my understanding, when calculating molar mass of compounds, we ignore the coefficient in front of the compound (ie. if there is a two, we don't multiply molar mass by two) because the coefficient simply represents the molar ratio of reactants/products, at least when we a...

Sabrina Galvan 3J

Some elements of the periodic table have 4 sig figs as their molar mass and others have far more. When calculating the molar mass of a compound, how many sig figs should there be or number be rounded to? For molar masses, typically the most sig figs that should be accounted for in the compound is f...

Search found 100 matches