CHEMISTRY COMMUNITY

rita_debbaneh2G

As far as I know, if you're not multiplying by anything or reversing the reactions, just add the values together. If you reverse a reaction, add the opposite value of the reaction enthalpy. If you multiply by a coefficient, multiply the reaction enthalpy with the same coefficient.

rita_debbaneh2G

Notice that in this reaction, two compounds are combining to form a new one. When you form bonds, you release energy. Hence, it's exothermic.

rita_debbaneh2G

Can someone explain with examples?

rita_debbaneh2G

How do you use the quadratic equation to solve for percent ionization?

rita_debbaneh2G

Why is the pH for strong acids just the negative log of the molar concentration of the acids?

rita_debbaneh2G

For example, many of the problems in 6D basically require an understanding of whether the compound used is acidic or basic. How can we tell this just by looking at the compound

rita_debbaneh2G

Find the initial concentration of the weak acid or base in each of the following aqueous solutions: (a) a solution of HClO with pH 4.60; (b) a solution of hydrazine, NH2NH2, with pH 10.20. Can somebody explain how they set up the problem for these? I know that you compute 10^-pH for the concentratio...

rita_debbaneh2G

In example 6a2, when we're calculating the OH- concentration from Ba(OH)2, the chemical equation is only Ba(OH)2 dissociating. In other words, we don't put in H20, it's just Ba(OH)2(s) --> Ba2+(aq) + OH2-(aq). But when I work out the answer for self test 6a3a (which is right underneath), I get the a...

rita_debbaneh2G

The value of Kw for water at body temperature (37 degrees C) is 2.1 x 10^-14. (a) What is the molar concentration of H3O+ ions at 37 degrees C? (b) What is the molar concentration of OH2- in neutral water at 37 degrees C? Can someone explain how to do this? Also, for part b, does "neutral water...

rita_debbaneh2G

I just rechecked the question as well. It does say 6*10^-5 molar concentration for HI. This means that the concentration of H3O+ will be 6*10^-5 molar as HI is a strong acid and completely dissociates. Using the equation for Kw = [H30+][OH-] and knowing that Kw at 25 degrees Celsius is 1*10^-14, we...

rita_debbaneh2G

We know that HI is a strong acid and will fully dissociate as an aqueous solution (HI(aq) + H2O -> H3O+(aq) + I-(aq)). Since you know the molar concentration for HI, you can calculate how many moles (and therefore concentration) of H3O+ will be produced. This should be 6.0 x 10 ^-3 M because there'...

rita_debbaneh2G

Estimate the concentrations of (a) H3O+ and (b) OH- at 25 degrees C in 6.0 x 10 ^-3 M HI(aq).

Can someone explain how to do this?

rita_debbaneh2G

I remember going to a workshop hosted by Justin in which we did a problem where we used the Ideal gas law to calculate either the pressure or concentration of a reactant. When I was doing Problems from 5I, I thought I could use this same method, but instead, I had to take the moles and simply divide...

rita_debbaneh2G

Basically the title. There was a little portion in 5G that said to use the net ionic equations when calculating K for compounds that dissolve completely. However, pretty much all the problems in the book and modules don't do this. When should I be expected to use this method

rita_debbaneh2G

For reference, I'm having trouble with part b: In an experiment, 2.0 mmol Cl2(g) was sealed into a reaction vessel of volume 2.0 L and heated to 1000. K to study its dissociation into Cl atoms. Use the information in Table 5G.2 to calculate the equilibrium composition of the mixture. (b) If 2.0 mmol...

rita_debbaneh2G

For example, let's say the reactants are an aqueous solution and a solid and the products are a gas and an aqueous solution?

rita_debbaneh2G

Dr. Lavelle said something along the lines of this in the lecture today. Can someone explain why this is the case?

rita_debbaneh2G

pH is the concentration of H+ ions while pOH is the concentration of OH- ions. Kb signifies the dissociation constant of a base with increasing the stronger the base is (because strong bases dissociate completely). Alternatively, pKb is the log of the constant. The greater this value, the weaker the...

rita_debbaneh2G

A Bronsted acid is a hydrogen ion (proton) donor while a Lewis acid is an electron acceptor. A Bronsted base is a hydrogen ion (proton) acceptor while a Lewis base is an electron donor.

rita_debbaneh2G

A buffer is a solution that resists pH change when an acidic or basic compound is added. It's composed of a conjugate acid and conjugate base that are present in equilibrium, and they neutralize acids and bases in the form of hydronium and hydroxide ions.

rita_debbaneh2G

A proton is accelerated in a cyclotron to a very high speed that is known to within 3.0 x 10 2 km/s. What is the minimum uncertainty in its position? this is an example question in the 1B section but because the work isn't displayed, I'm not sure where I'm going wrong with it. The answer is .11 pm. ...

rita_debbaneh2G

A reaction vessel contains 5.77 g of white phosphorus and 5.77 g of oxygen. The first reaction to take place is the formation of phosphorus(III) oxide, P4O6: P4(s) 1 3 O2(g) S P4O6(s). If enough oxygen is present, the oxygen can react further with this oxide to produce phosphorus(V) oxide, P4O10: P4...

rita_debbaneh2G

When they say the sample is transferred to a flask or container of X volume, your second volume for your calculation is only X. You don't need to add the original sample volume. So basically, don't add anything to the 125 ml. Hope this helps!

rita_debbaneh2G

A good way to remember the differences between these two is interpreting them as # + tooth. For example, monodentates are "one toothed." Therefore, they only bind to one ligand. Similarly, polydentates are "many toothed." They can bind to more than one ligand.

rita_debbaneh2G

-ate is used at the end of the compound's name when its net charge is negative. Otherwise, or when it's neutrally or positively charged, you don't have any suffix.

rita_debbaneh2G

A coordination compound is a compound with one or multiple metal centers that bind to ligands. Complex ions have metal ions at their centers and are surrounded by other molecules or ions. Coordination compounds differ from complex ions because of their lack of charge. Coordination compounds have no ...

rita_debbaneh2G

En is the abbreviation for the coordination compound ethylenediamine. It's a bidentate ligand which means that its nitrogens donate their lone pairs when it acts as a donor.

rita_debbaneh2G

What's the difference between electron and molecular geometry? How do you find the former?

rita_debbaneh2G

There's one central atom (A), two interactions occurring on account of the bonding with two hydrogen atoms (B₂), and two lone pairs on the central atom (E₂). Upon examining the molecule with the geometry of AB2E2, the descriptor is bent.

rita_debbaneh2G

Localized electrons act like they normally do. For example, lone pairs that are localized remain close to their respective atom. However, delocalized atoms appear in different locations among different forms of a molecule.

rita_debbaneh2G

In a nutshell, you're taking the atomic orbitals you already have and mixing them to make new orbitals. And much like how mixing different chemical compounds can lead to new properties, creating new orbitals leads to new molecular geometries and bonding characteristics. One easy way to determine the...

rita_debbaneh2G

Equatorial atoms are those which bond with non ring atoms and form angles that are small compared to the plane of the ring. Axial atoms are those which bond with non-ring atoms and form angles that reach up to 90 degrees. Also, equatorial are an a horizantal axis (think equator) and axial are on a v...

rita_debbaneh2G

In order to count sigma bounds, you do have to count the single bonds. So, in a way, single bonds are sigma bonds. However, it's also important to note that sigma bonds also occur in double and triple bonds.

rita_debbaneh2G

Periodic trends show that moving from left to right on the periodic table increases electronegativity. As a result, oxygen is more electronegative than nitrogen: there will be a disproportionate sharing of electrons among the oxygen atoms in the molecule making nitrogen slightly positive and the oxy...

rita_debbaneh2G

The ion related trends are as follows. When you move from top to bottom of the periodic table, the ionic radius decreases, the ionization energy decreases, and electronegativity decreases. Moving from left to right shows that ionic radius increases, ionization energy increases, and electronegativity...

rita_debbaneh2G

Elements within the same group share the number of valence electrons in common which is vital to their characterizing considering its the valence electrons that participate in the reactions. This explains similarities in chemical properties.

rita_debbaneh2G

Metallic character is greatest in the lowest left corner of the periodic table because of the increased shielding that occurs and the minimal effective nuclear charge that results from this. As a result, it's very easy for these elements to lose atoms.

rita_debbaneh2G

Can someone explain why this occurs?

rita_debbaneh2G

How do you best distinguish which Lewis structures are the best via formal charge and bond length? I'm struggling to pick the right structures. For reference, this is the one about the perchlorate ion.

rita_debbaneh2G

Can someone explain how they did the phosphite ion resonance structure? I was able to draw all the other resonance structures but I'm stuck on this one.

rita_debbaneh2G

Mikayla Kwok 3L wrote:4s does have a lower energy than 3d when no electrons are in the 3d subshell, but once the 4s and 3d subshells are occupied (which happens after Z=20), 3d has the lower energy.

Sorry is it ok if you explain why? I just want to understand it conceptually. Thanks :))

rita_debbaneh2G

I was watching the first lecture of Week 4 and Dr. Lavelle, at one point, said that the 3d orbital is a higher energy level than the 4s orbital. But then he said multi electron atoms with Z=20 and onward have 4s as the higher energy level orbital. Why is this the case?

rita_debbaneh2G

Can someone explain this in depth? When would this be present in an atom, if at all?

rita_debbaneh2G

This part of the question reads How many orbitals can have the following quantum
numbers in an atom: (c) n = 2. Can someone explain how they got the answer to this one?

rita_debbaneh2G

The effective nuclear charge is the net positive charge experienced by an electron in a polyelectronic atom. The periodic trend for determining weakest to strongest e.n.c is as follows: it increases as you move from left to right on the periodic table and decreases as you move from top to bottom. So...

rita_debbaneh2G

You'll probably be given what you're looking for in the form of, say, atoms. You can use the equation N=nNa to calculate for whatever you need to find with N=atoms/molecules/etc of whatever, n= moles of whatever, and Na= Avogrado's constant.

rita_debbaneh2G

Hey! I wouldn't worry about that. We never got a list of any specific compounds or polyatomic ions that we should have down for the course. I don't think we'll be tested on knowing the formulas of random substances we're given on problems.

rita_debbaneh2G

I think you have it down right: in general, I use other values in my calculations to determine sig figs. And I remember that one of the sig fig rules on the 14A website said that integers aren't counted for sig figs. So I wouldn't really worry about this issue. Use wavelength/frequency instead.

rita_debbaneh2G

Hello. It's important to know constants like Avogrado's and Planck's that are used often in calculations. And by "know," I mean being familiar with their uses considering we get a sheet of constants to use on our tests. In addition, I'd say that familiarity with that chart of SI to metric ...

rita_debbaneh2G

I think this was mentioned casually in an earlier lecture or module video. But if I were you, I wouldn't do anything with sig figs (as in rounding the numbers) until you have finished all computations. If you're worried about what to write (because sometimes your number has seven numbers after the d...

rita_debbaneh2G

When it comes to zeroes and decimals, all zeroes after a decimal point are significant. For example: 17.00. Also, when there are zeroes before a decimal point, they can be significant as long as they're "trailing" or the last kind of number in the value. For example: 170.00

rita_debbaneh2G

The only numbers that count for sig figs in scientific notations are those of the value being multiplied with the 10^n. In other words: no.

rita_debbaneh2G

The most common way I see conversions presented when looking at conversion charts is essentially x•10^y. I think for the sake of leaving things uncomplicated, this would probably be the best way to go. Also, it keeps sig figs consistent.

rita_debbaneh2G

Dimensional analysis is the process by which you convert one unit to another. For example, it can be something as simple as converting from meters to centimeters, in which you're increasing within a specific unit of length, or converting from degrees Celsius to Kelvin, in which you're converting fro...

rita_debbaneh2G

Hydrogen bonding is when a hydrogen atom bonded to a much more electronegative atom (essentially F, O, or N) forms an attraction to an H atom bonded to another such electronegative atom. The ability for these H atoms to form an attraction to other H atoms relies on polarity resulting from bonding wi...

rita_debbaneh2G

In my AP Chemistry class, we were required to memorize the strong acids and bases and a list of polyionic compounds. While nothing has been explicitly said, I think it would be a good idea to just because of the prevalence of certain compounds in practice problems.

rita_debbaneh2G

mmol means millimole. If you want to convert it to moles, just multiply the amount of mmol by 10^-3. Also, think of it this way: don't let the fact that the base unit is a mol. Just remember the King Henry Died By Drinking Chocolate Milk acronym and use it to multiply or divide by 10^n when necessary.

rita_debbaneh2G

When it comes to zeroes and the decimal place, just remember this. If there IS a decimal place, trailing zeroes are sig figs. This is regardless of if they are before or after the decimal place. If there is NO decimal place, trailing zeroes are not sig figs. So at the end of the day, it depends on t...

rita_debbaneh2G

hello! I think this is the kind of situation in which you wont' necessarily be asked to define them on the test, but it's imperative to have a grasp on them. Much of the Fundamentals and related questions rely on these principles. I think it would be a good rule of thumb to memorize the constants li...

rita_debbaneh2G

I was reviewing Fundamental E and came across this question in the textbook that asked "Why do chemists typically not measure out very precise, predetermined masses when making up solutions?" I'm just wondering if anyone knows the answer to this since I'd like to understand this topic more...

rita_debbaneh2G

A photon is essentially a small subatomic particle of light that carries energy. They're found in wavelengths of light as packets of energy.

rita_debbaneh2G

A photon is the smallest particle of light possible. Meanwhile, a quantum is the smallest possible particle at the subatomic level. I don't think they're interchangeable because the former carries a measure of energy while the latter is a measure of energy. However, they are very much related.

rita_debbaneh2G

There is an inverse relationship with wavelength and frequency. When the wavelength is longer, the frequency is weaker because during a segment of time, the wave will hit a certain point less times than if the wavelength were shorter. On the other hand, when the wavelength is shorter, the frequency ...

rita_debbaneh2G

I think it's a good idea to just have down them down in the order of, let's say, ascending or descending frequencies or wavelengths. In other words, don't necessarily memorize the specific numbers, but be aware of what on the photoelectric spectrum has a higher/lower frequency or wavelength with res...

rita_debbaneh2G

I think energy in the context of light and wavelengths would be bundles of photons that travel in the light waves. Energy has to do with the frequency of the wavelength. It's characterized by the equation E= hcλ. On the other hand, intensity is defined as the power of light going through a unit area...

rita_debbaneh2G

One good rule of thumb is to remember the equation N=n(Na) with N being the amount of something (let's say molecules, atoms, etc.), n being the moles of that something, and Na being Avogadro's constant. If a question gives you a number of molecules or atoms or so forth and asks for the number of mol...

rita_debbaneh2G

This depends on the operation. When adding or subtracting, look for the value with the least amount of numbers in the decimal place. Your answer will have that same number of digits after the decimal point. For example, if you're subtracting 17.923-6.6, your answer will be 11.3. Note the single valu...

rita_debbaneh2G

I remember Dr. Lavelle saying to make sure that the coefficients in the chemical reaction are all whole numbers in one of the modules. While I'm not sure if you'll get points taken off, I'd just multiply them all out to be on the safe side. It also makes any conversions or calculations easier simply...

rita_debbaneh2G

I don't think there's a strict order to it. I personally just make a list of the number of each element on each side of the equation. If they're not equal, then I add numbers as necessary.

rita_debbaneh2G

You might be mixing up the fact that you're moving the decimal point to the left to change 291.7 into scientific notation. The first thing to keep in mind is that the mantissa must be greater than one but less than ten. For this specific case, it'll be 2.917. Now, if you were to put the exponent as ...

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