CHEMISTRY COMMUNITY

AniP_2D

Would the reversibility/irreversibility of a system be given explicitly in a problem, or would that be something that we have to figure out for ourselves? If so, how would we determine if a system was reversible or not? This information will most likely be given. It may be possible that two work va...

AniP_2D

Would the reversibility/irreversibility of a system be given explicitly in a problem, or would that be something that we have to figure out for ourselves? If so, how would we determine if a system was reversible or not? This information will most likely be given. It may be possible that two work va...

AniP_2D

When calculating deltaG using the products minus reactants method, you would have to take into account the stoichiometric coefficients.

AniP_2D

These equations are all on the formula sheet so there isn't really a need to memorize them.

AniP_2D

The two equation would be deltaG(standard)=-RTlnK and deltaG(reaction)=deltaG(standard)+RTlnQ, which as mentioned, can be found on the formula sheet.

AniP_2D

For deltaH and deltaG to be very similar, the change in entropy has to be minimal, so you would look to see which reaction has the least change in entropy, which would be A since the phase remains a solid throughout the reaction.

AniP_2D

For an irreversible expansion, use w=-P(deltaX). For a reversible expansion (isothermal), use w=-nRT(ln deltaV2/deltaV1). Would the reversibility/irreversibility of a system be given explicitly in a problem, or would that be something that we have to figure out for ourselves? If so, how would we de...

AniP_2D

I believe you would first find the final temperature of the system and then using that you would find the change in enthalpy of the hot and cold water. Then using the enthalpy, you would find the entropy of each and then combine the two entropies to find the total entropy.

AniP_2D

I also keep getting 107, so there probably is an error.

AniP_2D

You have to first balance the oxygens in the equation O3->O2 by adding one water to the right side. Then, the balance the hydrogens, you have to add 2 H+ to the left side. In order to balance the charge then, you have to add 2 e- to the left side. The question tells us that the reaction occurs in a...

AniP_2D

I believe the answer key in the book is incorrect.

AniP_2D

You would first use deltaG(naught)=-RTlnk and then you would use deltaG(reaction)=deltaG(naught)+RTlnQ. Since the question is asking for the deltaG(reaction), you would have to use these 2 equations.

AniP_2D

Since we want an answer with Joules and moles, we would use the R constant 8.314 J.K^-1.mol^-1.

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Those actually are actual molecules, you can find them at the bottom of page A10.

AniP_2D

Its also important to note that you add H+ when the solution is acidic and OH- when the solution is basic.

AniP_2D

Will we typically be given the information of whether a solution is acidic or basic when trying to balance redox reactions or will we have to figure it out on our own?

AniP_2D

Appendix 2B in the back of the book has a list of all the E naught values.

AniP_2D

If I'm not mistaken, I believe you add Pt when there is no other metal. Since Hg is a metal, you would not need to add Pt.

AniP_2D

Oxidation is when electrons are lost, so electrons will be on the right hand side (products) of the reaction, while reduction will be on the left hand side (reactants), since reduction is when electrons are gained.

AniP_2D

I believe you can, but just to be safe I would use the sign of G to determine the answer for that.

AniP_2D

In an isolated system, no heat can be transferred and the volume remains constant, but in a closed system, heat can be transferred and the volume also remains constant.

AniP_2D

Also, it is important to remember that under reversible expansions more work is always done than in irreversible expansions.

AniP_2D

No, spectator ions such as Cl, are not included.

AniP_2D

From information I gained from the book, discussion, and videos, I also believe that when talking about constant pressure, you use Cp, but when talking about constant volume, you use Cv.

AniP_2D

Extensive properties depend on the amount given to you, while intensive properties don't. Since the specific amount is not given to you for heat capacity, it is an extensive property however, since you are given the amount for specific heat capacity, it is an intensive property.

AniP_2D

I agree and believe its best to leave it in J/C unless told otherwise. Also, for heat capacity, the units are J/C, but for specific heat capacity, it should be J/g*C.

AniP_2D

You would use this equation when you are asked to find deltaU at a constant volume.

AniP_2D

I think they initially converted the 100C and 20C to kelvin, which would result in 373K and 293K, and then they took the difference, which results in 80K.

AniP_2D

A quick way of determining which R value to use is to look at the units given to you. The units you would need to cancel out should correspond with that of the R value you use.

AniP_2D

For part b it asks to find the change in entropy for the vaporization of 50g of ethanol at 351.5K. So the way I went about solving this problem was to first calculate the change in entropy of the phase change since ethanol is still in the liquid phase and has not reached the boiling point. Then I ad...

AniP_2D

The path taken to reach the end of state functions does not matter, however since the path taken does matter for heat and work, they are not considered state functions.

AniP_2D

In order to cancel out, the molecules must be on opposite sides. This may require you to reverse a reaction and change the enthalpy of the reaction in order to make canceling them out possible.

AniP_2D

For this problem you would use Hess's Law. You would reverse C2H6 since you need to use the enthalpy for its production rather than its decomposition so the -1560 would turn into +1560. Then you would double the enthalpy for H2 since the coefficient in front of H2 is 2, giving you -572. Then you wou...

AniP_2D

If I'm not mistaken, Cv is used under constant volume while Cp is used under constant pressure.

AniP_2D

The equation you use for internal energy is deltaU=q+w.

AniP_2D

The conjugate seesaw simply states that the stronger the acid, the weaker its conjugate base and the stronger a base, the weaker its conjugate acid.

AniP_2D

Solids and liquids are not included in the equation for the K constant, only gases and aqueous solutions.

AniP_2D

If the pressure is increased, the system shifts to the side with less moles, and if the pressure is decreased, the system shifts to the side with more moles.

AniP_2D

No there are no specific values that you need to memorize. A helpful thing to know however, for the test is how to go from Ka to Kb and how to find the pH and pOH given the values of Ka or Kb.

AniP_2D

For part B, you do not take C into account since it is a solid so technically the left side would have 1 mol and the right side would have 2 mols, hence the reason why the system would shift to the left. For D, the amount of moles on both sides equals 2, so since the amount of moles are equal, there...

AniP_2D

When K<10^-3, you are allowed to approximate and the 5% rule is just a means of confirming that your approximation is valid.

AniP_2D

Adding on to this, does the Le Chatelier's Principle only apply for the partial pressures or do I need to know how to apply it for concentrations? Le Chatelier's Principle is applied to both concentrations and partial pressures, however I believe that you would apply the principle to concentrations...

AniP_2D

According to the ideal gas law, PV=nRT, pressure and volume are inversely proportional.

AniP_2D

The reason why CO2 would decrease when CO decreases is because, according to Le Chatelier's principle, the system will shift to the left of the reaction in order to provide a balance, meaning that CO2 will decrease in order to contribute to this balance.

AniP_2D

Le Chatelier's principle is significant because we can use it to predict what may happen to a substance when changes in things like temperature and concentration are inflicted. I think it applies to all reversible reaction.

AniP_2D

Since water is a liquid, it is omitted from the equilibrium constant, giving the denominator in this specific equilibrium constant a value of 1.

AniP_2D

Equilibrium composition means the stating the concentration for each products and reactant in the chemical equation.

AniP_2D

Depending if there is an initial amount of products or reactants, the one with no amount will increase and the other will decrease. To determine how many values of X increase or decrease, you must see if the reactant and products have a coefficient in the balanced equation.

AniP_2D

If you know the molar concentration, then you should technically be able to figure out the volume.

AniP_2D

An example of when to use this function is if you are given pressure and need to find concentration. You can also use it to find the pressure if you are given concentration.

AniP_2D

They used this version of the Lewis structure due to formal charge.

AniP_2D

Yes I think that should be it. An easy way to check if your hybridization is correct is that the exponents of the s, p, and d orbitals should add up to the amount of electron clouds. So sp^2 has an electron density of 3 since 2+1=3.

AniP_2D

Yes they do. You would count the lone pairs as an additional bonding site. So for example, a molecule with 2 shared pairs (2 sigma bonds) and one lone pair would have an electron density equal to 3. This would lead the molecule to have a hybridization of sp^2.

AniP_2D

Both are correct but I think the preferred way is to right it beginning with d.

AniP_2D

I think the oxidation number should always be included in Roman numerals after the transition metal because since the metal can have different oxidation numbers, it is important to specify the oxidation number.

AniP_2D

When drawing a molecule, you would go about drawing the bonds as you normally would and just label the sigma bonds and pi bonds.
1 bond= 1 sigma, 0 pi
2 bonds=1 sigma, 1 pi
3 bonds= 1 sigma, 2 pi

AniP_2D

If a molecule has dipole moments that do not cancel, then it is polar. If the dipole moments do cancel, then it is non-polar. One general rule to know is that molecules with a tetrahedral shape generally are non-polar unless the the outer atoms are not identical. Also while linear shaped molecules a...

AniP_2D

To determine the hybridization you would look at the electron density of a molecule.

AniP_2D

A linear shaped molecule has no lone pairs at the central atom, while a bent shaped molecule does have one or two lone pairs at the central atom.

AniP_2D

They are considered universal because every molecule, polar or non-polar, has London Dispersion Forces. However, it is important to know that London Dispersion Forces are the most prominent intermolecular force in non-polar molecules.

AniP_2D

Anytime a C atom bonds with an H atom (C2H2, CH6, C10H5, etc.), know that it is always non-polar and that there are no dipole moments.

AniP_2D

Hydrogen bonds can only be formed when H bonds with F, O, or N.

AniP_2D

Another tip is that if the atoms around the central atom are not the same (ex. CH3F), then the molecule is very likely to be polar.

AniP_2D

A hydrogen bond is a type of dipole-dipole interaction found amongst polar molecules. It is very strong, meaning that molecules that have hydrogen bonds have a high boiling point. Hydrogen bonds can only occur when an H atom bonds with either a F, O, or N atom.

AniP_2D

What is the difference between a dipole-dipole force versus a dipole-induced dipole force?

AniP_2D

C, N, O, F, and Ne are the main elements that must follow the octet rule. There are elements like hydrogen that only need two and those like boron that need 6. Also any element past phosphorus can hold more than 8 electrons.

AniP_2D

Yes, elements Phosphorus and onward can hold more than 8 electrons in their shell and thus can exceed the octet rule.

AniP_2D

Yes, when drawing a lewis structure, the optimal structure will have a central atom with formal charge 0. It would be ideal for all of the atoms to have a formal charge of 0, but since this is not always possible your main concern should be to make the central atom have a formal charge of 0.

AniP_2D

Al can not have an expanded octet because only elements Phosphorus and onward can have more than 8 electrons. However, Al is one the exceptions to the octet rule in the case that it can have less than 8 electrons.

AniP_2D

The less electronegative a compound is, the more ionic it will be. When looking at the periodic table, you can confirm that Cl is more electronegative than Br, meaning that SiCl is more electronegative. With this information, you can determine that SiBr is more ionic than SiCl.

AniP_2D

You would use m(l) to determine the number of orbitals. For example, if you were given n=2 and l=1, the m(l) would be -1,0,1 which tells you that there are 3 orbitals.

AniP_2D

Any element past Phosphorus (including P) are an exception to the octet rule and can hold more than 8 electrons.

AniP_2D

The least electronegative atom is the central atom when drawing Lewis structures.

AniP_2D

In the scenario you just described, it would be best to have 3 formal charges of 0 and one +1. When trying to draw the most stable lewis structure, you want the formal charge of the atoms to be as close to 0 as possible.

AniP_2D

For now, I don't think we're expected to know the formulas.

AniP_2D

Cu is one of two exceptions when it comes to electron configurations (the other is Cr), so its electron configuration is [Ar]3d^10 4s^1. So when you subtract an electron due to the positive charge in part a, you would end up with the electron configuration [Ar]3d^10 since you subtracted the electron...

AniP_2D

Usually with different resonance structures, there are different formal charges. A formal charge of 0 means that the molecule is most stable so you want to draw the resonance structure that will give you a formal charge of 0, making it the most stable.

AniP_2D

You would have to write out all 5 values instead of just saying 5.

AniP_2D

To determine the number of orbitals you would look at ml from l.

AniP_2D

There needs to be a double bond between Si and the two oxygens because the double bonds allow for the octet rule to be satisfied for Si. If you were to use single bonds, Si would only have 4 electrons when 8 are needed.

AniP_2D

The subshell notation is basically the n-value and and the subshell that corresponds to l. If l=0, s is the subshell, l=1 then p, l=2 then d, and l=3 f So for (a) the subshell notation would be 5d and for (b) it would be 1s For orbitals you would just look and see how many possible ml values the cer...

AniP_2D

(a) a is 3 orbitals because the possible outcomes for ml are -1, 0, 1 (b) b is only 1 orbital because the value of ml is already given to you. Since only 1 value of ml is given (ml=-2), there is only 1 orbital (c) for n=2, the possible l values are 0 and 1. The possible ml values for l=0 are ml=0 an...

AniP_2D

Can someone please explain the concept of a spin state? I am having trouble understanding what a spin state is and what it means in regards to the orbital. Thank you.

AniP_2D

n is the principal quantum number and it tells you what shell the electron is in l is the angular momentum quantum number and it describes shape. l=0,1,2,...n-1 Depending on what your l is you can determine whether your electron is in the s, p, d, or f orbital ml is the magnetic quantum number and i...

AniP_2D

You would use Energy=(Planck's constant)*(frequency) to find the energy of the photon. If you do not have the value of frequency, you would use speed of light=(wavelength)*(frequency) to find frequency and then plug it into the equation for energy.

AniP_2D

Kelvin Chung 1C wrote:Do we need to know the SI unit equivalents for each term, like the joule?

I am not sure if you need to know them, but for the quantum section it would extremely helpful to know that a J is equal to kg*m^2*s^-2

AniP_2D

If the molecular formula can no longer be simplified, then it is viewed as both the molecular and empirical formula.

AniP_2D

You would use the amount of moles of the limiting reactant to find the amount of moles used of the excess reactant using the stoichiometric coefficients of the balanced chemical equation. Once you find out how many moles of the excess have been used, you can then subtract that amount from the amount...

AniP_2D

It is a typo as the correct answer is 150 pm.

AniP_2D

h represents Planck's constant, which is 6.626*10^-34 J*s

AniP_2D

Usually what I do when I'm adding/subtracting or multiplying/dividing, and the result is too long of a number to write down fully, is to just round the answer to 2 digits more than the amount of sig figs needed and then when I reach the final answer I will then round to the amount of sig figs needed.

AniP_2D

Yes, you should and if you are presented with values that have a different amount of sig figs, remember to use the same amount of sig figs as the value that has the least amount of sig figs for your final answer.

AniP_2D

When you are trying to determine the amount of sig figs to use when carrying out tasks such as addition/subtraction or multiplication/division, the rule is to use the same amount of sig figs as the number with the least amount of sig figs presented in the problem.

AniP_2D

Usually when you are given a decimal that is .5 or higher, you would round up to the next whole number.

AniP_2D

There are a few rules that one must take into consideration when dealing with significant figures. 1. Any number that is not zero is considered significant. 2. Zeros are only considered significant if they are between two significant figures (any non-zero number). 3. Also, zeros that are placed afte...

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