CHEMISTRY COMMUNITY

Chris Tai 1B

Here are some of the important ones - deltaT = change in temperature deltaS = change in entropy deltaH = change in enthalpy deltaU = change in internal energy deltaV = change in volume deltaP = change in pressure W = work The other W = degeneracy, which helps you find entropy Csp = specific heat cap...

Chris Tai 1B

A calorimeter was calibrated with an electric heater, which supplied 22.5 kJ of energy as heat to the calorimeter and increased the temperature of the calorimeter and its water bath from 22.45 8C to 23.97 8C. What is the heat capacity of the calorimeter? The equation q = nCdeltaT seems especially re...

Chris Tai 1B

(a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its temperature from 20.0 8C to the boiling point of water, 100.0 8C. (b) What percentage of the heat is used to raise the temperature of the water? Could someone help me walk through...

Chris Tai 1B

Air in a bicycle pump is compressed by pushing in the handle. The inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm. (c) What is the change in internal energy of the system? How do we approach part c with the information given? I thought since heat was...

Chris Tai 1B

If we want to apply Hess's law to this situation, we're typically given the change in enthalpy (deltaH) for both of the reactions independently. For the reaction N2(g) +O2(g) -> 2NO(g), deltaH = 180kJ For the reaction 2NO(g) + O2(g) -> 2NO2 (g), delta H = -112 kJ So, using the logic above to combine...

Chris Tai 1B

To build off of this, in thermochemistry the state property of enthalpy is often used, where we care most about the change in enthalpy (deltaH). Through this state property, we can determine whether a reaction is exothermic (deltaH is negative and releases heat) or endothermic (deltaH is positive an...

Chris Tai 1B

The best way to determine whether an acid or base is weak is to memorize all the strong acids and bases and see if that acid is strong. If it's not strong, it's a weak acid or base. The strong acids are HBr, HClO4, H2SO4, HNO3, HCl, and HI. SImilar logic can be applied to the bases. The strong bases...

Chris Tai 1B

Standard reaction enthalpy (deltaH) is the enthalpy of the reaction that occurs when all the reactants and products are in their standard state at 1 atmosphere. Standard enthalpy of formation (deltaHf) is the standard reaction enthalpy (deltaH) for the formation of one mole of a substance from its e...

Chris Tai 1B

It depends on the question. If the question wants you to use deltaH to find something like temperature, deltaS (change in entropy), or deltaG (change in gibbs free energy), then it'll most likely be given to you or easily derivable. However, if the question wants you to find deltaH itself, then you'...

Chris Tai 1B

The best way to know which acids are weak are to know which acids are strong. Everything that isn't a strong acid is essentially a weak acid. The strong acids are HBr, HClO4, H2SO4, HNO3, HCl, and HI. SImilar logic can be applied to the bases. The strong bases are all the hydroxides and the ones tha...

Chris Tai 1B

The kPa, which is kilopascals, has to be converted to atmospheres. Since 1 kPa = 0.00987 atm, the book is just dividing by 100 as a shortcut to complete this conversion.

Chris Tai 1B

In table 5G.2, there are values for both K and Kc. In what instance would we use K, and in what instance would we use Kc instead?

Chris Tai 1B

Dissociation of a diatomic molecule, X2(g) <-> 2 X(g) occurs at 500 K. The equilibrium state of the reaction is shown in 1 and the equilibrium state in the same container after a change has occurred is shown in 2. Which of the following changes will produce the composition shown? (a) Increasing the ...

Chris Tai 1B

In part d of this question, the equation produced is actually 2HD(g)⇌H2(g)+D2(g) instead of 2HD(g)+H2(g)⇌D2(g), which makes sense since the equation is now balanced. I'm not entirely sure how all the inert gas/noble gas stuff affects the way that the reactants/products shift in the event of higher p...

Chris Tai 1B

When the concentrations of H30+ and OH- are the same in a given water, they are quite small and equivalent at 10^-7 M each. This leads to a pH of 7, since -log(10^-7) is 7. The reason there exist these concentrations of H30+ and OH- is because due to chance, water may as an amphiprotic compound form...

Chris Tai 1B

(a) 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 F2 was placed into the reaction vessel ins...

Chris Tai 1B

Use the information in Table 5G.2 to determine the value of K at 300 K for the reaction 2 BrCl(g) + 1 H2(g) <-> Br2(g) + 2 HCl(g).

Is there a way to determine the value of K given this table? If so, how?

Chris Tai 1B

NH3 is more complicated since it can act as both an acid and a base, just like water. If it donates a proton, it becomes NH2-, and if it accepts a proton, it becomes NH4+. So, NH3 is technically amphiprotic, meaning it's hard to determine if it'll always be a base (it depends on the solution it's in).

Chris Tai 1B

A porphyrin ring is one that completely surrounds an atom (like a transition metal) and often forms coordinate covalent bonds with it. For instance, in the heme complex, the iron metal atom is surrounded by a porphyrin ring, where four different nitrogen atoms form coordinate covalent bonds with it....

Chris Tai 1B

I think it would also be good to know why en is bidentate and why edta is hexadentate. For ethylenediamine (en), the two amine groups on the ends of the molecule can both function as ligands, which means en can create a chelating ligand ring around a transition metal, and is bidentate because it att...

Chris Tai 1B

Decide which acid in each of the following pairs is the stronger and explain why: (a) HF or HCl; (b) HClO or HClO2; (c) HBrO2 or HClO2; (d) HClO4 or H3PO4; (e) HNO3 or HNO2; (f) H2CO3 or H2GeO3.

Could someone provide brief justifications for which acid is stronger in each example?

Chris Tai 1B

A careless laboratory technician wants to prepare 200.0 mL of a 0.025 m HCl(aq) solution but uses a volumetric flask of volume 250.0 mL by mistake. (a) What would the pH of the desired solution have been? (b) What will be the actual pH of the solution as prepared? For part a, I started by multiplyin...

Chris Tai 1B

The molar concentration of HCl in hydrochloric acid is reduced to 12% of its initial value by dilution. What is the difference in the pH values of the two solutions?

What equations would I use to set up this problem?

Chris Tai 1B

State whether the following oxides are acidic, basic, or amphoteric: (a) BaO; (b) SO3; (c) As2O3; (d) Bi2O3.

Why is b acidic? Doesn't the molecule have to have a H+ to donate in order for it to be acidic?
Could someone also provide a examples of c and d reacting in an amphoteric manner?

Chris Tai 1B

Why doesn't the number of bonds affect which hybrid orbital is formed? For instance, in ethylene c2h4, why is the double bond in between the carbons just two sp^2 hybrid orbitals instead of two individual sp^3 orbitals (since there are four bonds formed by carbon in total)?

Chris Tai 1B

Consider the bonding in H2C=CHCHO. (a) Draw the most important Lewis structure. Include all nonzero formal charges. (b) Identify the composition of the bonds and the hybridization of each lone pair—for example, by writing sigma(H1s,C2sp^2 ). for part b, why is the sigma bond sigma(C2sp,O2p^2) while ...

Chris Tai 1B

How do you determine whether the hybridization of the valence electrons has a 2 compared to 3 in front of it? For instance, why is the bond between the carbon and hydrogen sigma(H1s^2, C2sp^2) instead of sigma(H1s^2, C3sp^2)? Could someone give me an example of an atom that forms 3sp^2 or 3sp^3 hybr...

Chris Tai 1B

Because the third isomer in this drawing has the chlorines on opposite sides of the "benzene" ring, those chlorine bonds are indeed polar as they are connected to a single carbon, but the molecule as a whole is not polar because the dipole moments created by those two opposite chlorine can...

Chris Tai 1B

Be careful when determining whether a molecule is polar or nonpolar - it matters if the dipole moments cancel or not. The bonds within a molecule may be polar, but the molecule as a whole may be nonpolar if those polar dipole moments cancel. For instance, in CCl4, the dipole moments all cancel since...

Chris Tai 1B

Even if the molecule is "bent" or "angular" the molecule as a whole should be found in a single plane. This is true for those "bent" shaped molecules, but also for molecules that are trigonal "planar" and square "planar" (the name suggests that they ...

Chris Tai 1B

The reason there must be some hybridization in the orbitals is that it best fits the VSEPR model. If the valence electrons were only that of the p orbitals attached to carbon, then in the methane example the hydrogens would be attached to carbon at 90 degree angles from each other, which clearly vio...

Chris Tai 1B

Before solving any part of this problem, you should try and create a lewis dot structure like the one shown above; then you can look at each of the individual carbons to determine the bond angles. For instance, because the first CH2 carbon is sigma bonded to two hydrogens and double bonded to anothe...

Chris Tai 1B

The reason octahedral shapes need to have an extra two valence d electrons is because the p suborbitals can only hold up to three valence electrons in such a given orbital, so atoms like Xe and P must go into the d orbital regions (which mix with the preexisting s and p orbitals) to gain more valenc...

Chris Tai 1B

One way to differentiate two molecules, assuming we don't know their shape, is to differentiate each through their name. For instance, two molecules have the same molecular formula, C5H12. However, one is called pentane where as the other is called 2, 2 dimethylpropane. Pentane is a rod shaped molec...

Chris Tai 1B

One way to differentiate two molecules, assuming we don't know their shape, is to differentiate each through their name. For instance, two molecules have the same molecular formula, C5H12. However, one is called pentane where as the other is called 2, 2 dimethylpropane. Pentane is a rod shaped molec...

Chris Tai 1B

Those all look correct!
You can also think about shapes with more than two electron pairs, such as
AX2E3 linear, 180, or
AX3E3 t shaped, 90, or
AXE4 linear, 180 and so on

Chris Tai 1B

Which of the following molecules are likely to form hydrogen bonds: (a) PH3; (b) HBr; (c) C2H4; (d) HNO2? Turns out only d would form hydrogen bonds with other molecules, is there a reason that HBr doesn't? I know hydrogen bonds are usually formed when the hydrogen is attached to a N O or F, but are...

Chris Tai 1B

Identify the types of attractive intermolecular interactions that might arise between molecules of each of the following substances: (a) NH2OH; (b) CBr4; (c) H2SeO4; (d) SO2. Can someone walk me through parts B and C? Why wouldn't part b have dipole-dipole interactions (isn't Br way more electronega...

Chris Tai 1B

The London force is widely considered universal because any molecule or atom that has electrons or an electron cloud will inevitably have moments where one side of the molecule is more negative than the other due to random electron movements in the cloud. This in turn causes the opposite side to be ...

Chris Tai 1B

Are Molybdenum and Silver also exceptions to filling the 5s shell just like Chromium and Copper are? So would the electron configuration for Mo be [Kr] 4d^5 5s^1 and for Ag be [Kr] 4d^10 5s^1?

Chris Tai 1B

What is the difference between a Lewis acid and a Lewis base? What are some examples of Lewis acids and Lewis bases?

Chris Tai 1B

What was the photoelectric experiment originally designed to do?

Chris Tai 1B

To build off this, intensity in the wave model is described as the amplitude of the waves. However, it photons are treated like packets of light, then increasing the amplitude of the "waves" will merely increase the number of same-energy level photon packets. The energy of the photons, tha...

Chris Tai 1B

What is the difference between Polarisability and Polarizing Power?

Chris Tai 1B

For instance, an atom like Phosphorus can hold more electrons than just the octet that it gets, since it would fill up its 3p shell, next moving onto the 3d and the 4s shells. Phosphorus can do this because it is in the 3rd period of the table. This is much more difficult for atoms that are in a low...

Chris Tai 1B

I would really recommend trying to do as many of the homework problems as you can, so that when you come across a concept or a problem that you're not sure to how to solve, you can either ask here on Chemistry Community or go back and read the textbook so that you solidify that base of knowledge for...

Chris Tai 1B

The question is a bit tricky because it also doesn't give the work function in terms of joules, which is what you need to plug into the equation E(photon) = E(work function)+E(kinetic energy of e-). Rather, it's given in electronvolts: 2.93 electron volts. There are 1.60218x10^-19 J in 1 eV, so we c...

Chris Tai 1B

This speed is always the speed of light, which is about 3x10^8 m/s. The equation that we can use to find either wavelength or frequency of electromagnetic radiation is (wavelength)(frequency) = (speed of light).

Chris Tai 1B

Here's what you know: there are 2.4x10^21 photons, and the wavelength of each photon is 633 nm. Convert wavelength to meters - 633x10^-9 m. Find frequency using (wavelength, 633x10^-9)(frequency) = (speed of light, 3x10^8) to get frequency v = 4.739x10^14 You can find the energy per photon to be E =...

Chris Tai 1B

Typically in calculations, it should be alright to use 3.00x10^8 in place for the speed of light. This definitely depends on how precise you want your result to be.

Chris Tai 1B

Having multiple resonance structures gives us more of an explanation for experimented observations, such as the different bond lengths between atoms in a given molecule. For instance, if a single bond in the molecule is 1 A and a double bond is 2 A but the molecule has several different resonance st...

Chris Tai 1B

If the shell is 5s (due to the n=5 and l=0 values) then visually there cannot be any other orientations of the s orbitals. S orbitals are symmetric, as opposed to p d and f orbitals, which means they really only have one orientation. Because the value of ml reveals which orientation the orbital is i...

Chris Tai 1B

Here's some reasoning for why the numbers of unpaired electrons exist as they do: Ga: [Ar] 3d10 4s2 4p1 - 1 unpaired electron, because there's only one electron in the px subshell Ge: [Ar] 3d10 4s2 4p2 - 2 unpaired electrons, because there's one electron in the px subshell and one in the py subshell...

Chris Tai 1B

One such exception is the ionization energy for oxygen. Because atoms tend to prefer to have either full or half full shells, oxygen will prefer to have 3 electrons in the p orbital instead of having only one pair and two unpaired electrons. Conversely, Nitrogen is somewhat content with its half ful...

Chris Tai 1B

You can also think of this in terms of valence electrons. The 4s shells will contain electrons that are more likely to be lost, thus ionizing a particular atom. Since it's more probable for a 4s electron to be given up by an atom than a 3d electron, the 3d shell should come first in the sequence. Th...

Chris Tai 1B

Since d orbitals are present in a plane rather than along a line like p orbitals, we can use something like dxy to represent a d orbital that is in the xy plane. However, the lobes of the orbital aren't along the x and y axes, but rather in between the axes. Hence, the dxz and the dyz orbitals also ...

Chris Tai 1B

Which of the following subshells CANNOT exist in an atom:
(a) 2d
(b) 4d
(c) 4g
(d) 6f
Why is 6f able to exist in an atom? I'm a bit confused since the f-block of the periodic table ends at 4f and 5f

Chris Tai 1B

I also used delta v = 10, which got me a solution of delta x >= 6.6 x 10^-37. I think the answer key may be incorrect here since the change in velocity could vary from 0 m/s to 10 m/s, which has a clear difference of 10-0 = 10

Chris Tai 1B

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km/s. (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50 3 1016 Hz. How much energy is required to...

Chris Tai 1B

In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. Which equation(s) would I use to solve this problem? I'm still a bit confu...

Chris Tai 1B

Quanta or quantum in Latin is "how much", indicating that it's more of an amount of something that lacks units. For instance, in the context of photons, these quanta can simply be "packets" as Max Planck suggested of energy. The effect of these packets can be observed by analyzin...

Chris Tai 1B

For an example of converting 50nm to Angstroms: A good way to think about it is what was said before; you could also first convert nm to m and then convert that to Angstroms (easiest to conceptualize in my head). So, 50nm = 50 x 10^-9 m Since every Angstrom is 10^-10 m, we divide 50 x 10^-9 m / 10^-...

Chris Tai 1B

Solving for the other phosphorus oxide, using a similar method: First find the percentage of oxygen present in the oxide; since 56.34% of the compound is phosphorus, 43.66% of the compound must be oxygen. If we pretend that we have 100g of this substance, then we know that 56.34 g would be phosphoru...

Chris Tai 1B

In the spectrum of atomic hydrogen, several lines are generally classified together as belonging to a series (for example, Balmer series or Lyman series, as shown in Fig. 1A.10). What is common to the lines within a series that makes grouping them together logical? Could someone help me understand w...

Chris Tai 1B

G.25 Practitioners of the branch of alternative medicine known as homeopathy claim that very dilute solutions of substances can have an effect. Is the claim plausible? To explore this question, suppose that you prepare a solution of a supposedly active substance, X, with a molar concentration of 0.1...

Chris Tai 1B

I would start by using the equation for molarity and go from there: Molarity = number of mols/volume for part a, we can find the numbers of mols of Na2CO3 by taking 2.111 grams and dividing it by the molar mass of Na2CO3, which is about 106. Hence, we get 2.111/106 = 0.01992 mol Na2CO3. To find the ...

Chris Tai 1B

I find it easiest to first convert the micromoles to moles (for me it's personal preference) so get 1.44x10^-6 moles of glucose. Then you can use the equation Molarity = mols/Volume to find the volume needed, and input the values you've found. Hence, 1.44x10^-6 moles / 1.25x10^-3 mol/L = V = 0.00115...

Chris Tai 1B

When you're trying to find the volume needed to get moles of Na+, it's best to use the equation Molarity = moles/Volume. You know that the number of moles of Na2CO3 in the given amount of grams is 2.111g/106gmol^1 = 0.01992. You can then calculate the molarity of Na2CO3 within the given 250 mL solut...

Chris Tai 1B

A student prepared a solution of sodium carbonate by adding 2.111 g of the solid to a 250.0-mL volumetric flask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transfer into a flask to obtain (a) 2.15 mmol Na+; (b) 4.98 mmol ...

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