CHEMISTRY COMMUNITY

Ryan Chang 1C

There are other forms of these equations that may be helpful to memorize because they don't appear on the formula sheet.

One example is ln(k1/k2) = Ea/R[(1/T2)-(1/T1)]

Ryan Chang 1C

We do not need to know how to, since the integrated rate laws will be provided on the formula sheet. However, according to my TA, it may be useful to memorize other helpful forms of these laws that do not appear on the formula sheet.

Ryan Chang 1C

It is a way of note that you are finding/using a different k value. I've also seen different k values expressed in other terms such as k2, where the original k value is expressed as k1.

Ryan Chang 1C

Rates are generally never expressed as negative, even when referring to reactants.

Ryan Chang 1C

How do we decide which experiments to use to determine the rates with respect to A and B? thank you! First, you have to realize that C is zero order reactant. Now that C is independent and doesn't affect the other concentrations, to find the order of A, compare experiments 2 and 4 because the conce...

Ryan Chang 1C

A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction (c) With no overpotential at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis? The solution manual uses the E^o ...

Ryan Chang 1C

We add inert electrodes such Pt(s), C(s), etc. when there is no other metal present in the cathode or anode, or when both the oxidizing and reducing species are in the same solution.

Ryan Chang 1C

Yes a strongly reducing metal is the same as a strong reducing agent, and a strongly oxidizing metal is the same as a strong oxidizing agent.

Ryan Chang 1C

You can convert torr to atm by dividing the torr values by 760. The units will then cancel out as you solve the equation.

Ryan Chang 1C

A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction (c) With no overpotential at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis? The solution manual uses the E^o v...

Ryan Chang 1C

The total charge of Hg2+ is 4+. Since there are two electrons depicted in the reactants, the total charge of the reactants is 2+. This balances with the products, which has a total charge of 2+ as well since the charge on Hg2 as a whole is 2+.

Ryan Chang 1C

It's the number of electrons that are reduced/oxidized in the reaction.

Ryan Chang 1C

An inert electrode only needs to be added when there is no metal present. The cathode and anode are independent of this, meaning that the cathode can have an inert electrode while the anode doesn't, or vice versa. In this case, the anode has a metal present, which is Hg(l), since mercury is a metal ...

Ryan Chang 1C

An inert electrode must be added when there is no metal in the cathode or anode. In this case, H2(g), H+(aq), Cl-(aq), Cl2(g), aren't metals, so an inert electrode such as Platinum must be added to both sides. I believe Dr. Lavelle mentioned that the order within the cathode and anode don't matter, ...

Ryan Chang 1C

The charge on both sides of the reaction need to be balanced, so add electrons to whichever side has a higher charge.

Ryan Chang 1C

I saw elsewhere that this is just an error in the solution manual. The number of moles of electrons should be 1.

Ryan Chang 1C

Calculate Ecell for each of the following concentration cells: (b) Pt(s)|H2(g, 1 bar)|H1(aq, pH 5 4.0)||H1(aq, pH 5 3.0)|H2(g, 1 bar)|Pt(s) When I wrote the half reactions, I got (2H+) + (2e-) -> H2 and H2 -> (2H+) + (2e-) I would assume that n=2 based on the half reactions, but the answer key says ...

Ryan Chang 1C

In cell diagrams, is it possible for platinum to only be on one side?

Ryan Chang 1C

Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: (a) AgBr(s) -> Ag+(aq) + Br-(aq), a solubility equilibrium In the half reaction for the anode, the answer key gives the following reaction: AgBr(s) + e- -> Ag(s) + Br-(aq) Why doesn't...

Ryan Chang 1C

Write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations:
(d) Au+(aq) -> Au(s) + Au3+(aq)

How do you know what the cathode and anode is?

Ryan Chang 1C

Just found a section in the textbook that says that the only polyprotic acid that we would need to calculate the concentrations for the second deprotonation is sulfuric acid. Why do we need to do the same for H3PO4?

Ryan Chang 1C

What values do you use to calculate if the percent at the end is less than 5.

Ryan Chang 1C

The equilibrium constant K always remains constant, so any change in the values of the reactants has to be accounted for by another change. A) H2 decreases to account for the increase in CO2. This is because the value of the products (numerator) has to remain constant. B) CO2 will decrease to accoun...

Ryan Chang 1C

How do you know if you can ignore the second ionization when calculating the pH of polyprotic acids?

Ryan Chang 1C

Why does the value of R has to be altered depending on if the problem gives constant volume or constant pressure?

Ryan Chang 1C

(a) Using Trouton’s rule, estimate the boiling point of dimethyl ether, CH3OCH3, given that H(vap) = 21.51 kJ/mol. (b) Using standard reference sources available in your library or on the Internet, find the actual boiling point of dimethyl ether and compare this value with the value obtained by usin...

Ryan Chang 1C

The greater the degeneracy, the more disorder a system has, therefore resulting in a great value of entropy.

Ryan Chang 1C

Adding on to the comment above, an increased value of microstates results in more disorder is a system, therefore increasing the value of entropy.

Ryan Chang 1C

Although exothermic and endothermic are two different reactions, in terms of calculating entropy, you don't have to worry about whether the reaction is exothermic or endothermic. The change in temperature will always be calculated as T(final) - T(initial).

Ryan Chang 1C

4A.19 A piece of copper of mass 20.0 g at 100.0 8C is placed in a vessel of negligible heat capacity but containing 50.7 g of water at 22.0 8C. Calculate the final temperature of the water. Assume that no energy is lost to the surroundings. Are there any special rules for sig figs for calculations r...

Ryan Chang 1C

This past week we also went over 4E.3

Ryan Chang 1C

Why do solids and gases have a lower heat capacity than water?

Ryan Chang 1C

I google the enthalpies of formation because not all of them are given in the textbook. I'm sure if a test like this ever appear on an exam Prof. Lavelle would provide us with a table of enthalpies of formation.

Ryan Chang 1C

Prof. Lavelle provided us with 3 different methods. Using bond enthalpies was the second method he gave us. If the bond enthalpies aren't provided, the third method can be used, which is subtracting standard enthalpies of formation for the reactants from the standard enthalpies of formation for the ...

Ryan Chang 1C

Why is the enthalpy of vaporization greater than the enthalpy of fusion.

Ryan Chang 1C

Will NH4F produce and acidic or basic solution?

Ryan Chang 1C

In order to determine whether the solutions of the salts will be acidic, neutral, or basic, you must consider the cation and the anion of the salt. First check if the anion to see if it's acidic, neutral, or basic (Table 6D.2 gives a list of acidic, neutral, and basic anions). If the anion is acidic...

Ryan Chang 1C

Hemoglobin (Hb) molecules in blood carry O2 molecules from the lungs, where the concentration of oxygen is high, to the tissues where it is low (see the Interlude following Focus 5). In the tissues the equilibrium H3O+(aq) + HbO2- (aq) : HHb(aq) + H2O(l) + O2(aq) releases oxygen. When muscles work h...

Ryan Chang 1C

Why do we typically disregard the second deprotonation of polyprotic acids?

Ryan Chang 1C

Does expanding the volume affect the equilibrium?

Ryan Chang 1C

Could someone explain ATP hydrolysis and its connection to the class?

Ryan Chang 1C

The value of Kw changes when heat is added to the system. Since the autoprotolysis of water is an endothermic reaction, adding heat will increase the value of Kw because the reaction will favor the formation of products more. In other words, the equilibrium will shift to the right.

Ryan Chang 1C

It doesn't matter how you solve for pressure, however the most simple way is to just divide nRT by volume assuming that the problem gives you values for n, r, and t.

Ryan Chang 1C

How do we determine if K, Cl2, of F2, is thermodynamically more stable in problem 5I.13?

Ryan Chang 1C

I couldn't find a Table 5E.2 either so I would assume that it's a typo. Question 5.39 appears to be referring to Table 5G.2 anyways so I would just use that.

Ryan Chang 1C

Psi is another unit of pressure.

Ryan Chang 1C

The K value for this reaction is 160. Since HI (2.21x10^-3 M) is the product and H2 (unknown) and I2 (1.46x10^-3 M) are the reactants, the expression will look like this:

160 = (2.21x10^-3)^2 / (H2)(1.46x10^-3)

Solving for H2 gives you 2.1x10^-5 M.

Ryan Chang 1C

You forgot that solids are not factored into the expression, so As should be removed.

Ryan Chang 1C

The partial pressures will be different. In this case, the partial pressure in the second container will be higher. Keeping in mind that K = products/reactants, since K must remain a constant, the partial pressure of the product O2 must be higher to match the higher partial pressure of the reactant ...

Ryan Chang 1C

(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...

Ryan Chang 1C

You can attempt to visualize the molecule, but your safest bet is drawing the lewis structure every time. For example, you can infer that CH4 has a coordination number of 4 since the 4 hydrogens are attached to the central atom Carbon.

Ryan Chang 1C

Ferrate is used when iron appears in an anionic complex. This is because when iron appears in an anionic complex, we take its latin name ferrum and replace -um with -ate.

Ryan Chang 1C

You can also look at bond lengths and the resulting anion stability between molecules to determine which acids are stronger.

Ryan Chang 1C

Just wanted to bring up that the sig fig rules for ph/pOH calculations are different than the rules for normal sig figs. If you are given 3 sig figs in a question, your final answer doesn't necessarily have 3 sig figs, but rather has 3 decimal places. Here is an example: 0.012 M of H3O+ = -log(0.012...

Ryan Chang 1C

You are using the correct formula to find the concentration of OH, which is [M]=10^-POH. Plugging in the numbers you get: 10^-14.176 = 6.668 x 10^-15 M, which is the correct answer.

Ryan Chang 1C

What are the rules for naming acids?

Ryan Chang 1C

Another way to look at it is that acidic oxides are oxides that reacts with water to form a solution of a Bronsted acid. SO3 is an example of an acidic oxide because when it reacts with water, it forms H2SO4. SO3 + H20 --> H2SO4. Since H2SO4 is an acid, SO3 is an acidic oxide.

Ryan Chang 1C

SO3 is basic, not acidic. Acidic oxides are oxides that reacts with water to form a solution of a Bronsted acid. SO3 is an example of an acidic oxide because when it reacts with water, it forms H2SO4. SO3 + H20 --> H2SO4. Since H2SO4 is an acid, SO3 is an acidic oxide. It is also useful to not that ...

Ryan Chang 1C

Are we expected to know how to name acids? For example, in question 6A.7, the problem asks us to name the acid:

6A.7 Below are molecular models of two oxoacids. Write the name of each acid and then draw the model of its conjugate base. (I don't have the molecules shown)

Ryan Chang 1C

In each of the following salts, either the cation or the anion is a weak acid or a weak base in water. Write the chemical equation for the proton transfer reaction of this cation or anion with water: (a) NaC 6 H 5 O; (b) KClO; (c) C 5 H 5 NHCl; (d) NH 4 Br. How do you determine whether the cation or...

Ryan Chang 1C

Ferrum refers to the latin name for iron and then the compound has an overall negative charge so you add ate to make it ferrate Cooper is right in this context. Although ferrate is known as the polyatomic ion [FeO4]2-, in this context, ferrate refers to the metal in the coordination compound molecu...

Ryan Chang 1C

Lavelle has a chart of all the names on his website. You can find it by clicking on "Naming Coordination Compounds" link. You should definitely memorize all of the names on his chart.

Ryan Chang 1C

Correct me if I'm wrong but I believe HN(CH2CH2NH2)2 is tridentate because the central atom would be nitrogen, which is attached to a hydrogen and 2 CH2CH2NH2 molecules.

Ryan Chang 1C

All of the compounds that you listed can be polydentates:

HN(CH2CH2NH2)2 is tridentate, CO3^2- is mono or bidentate, and oxalate is bidentate.

Ryan Chang 1C

You don't need to know them, but I believe Lavelle gives us full credit if we use those names. On Lavelle's website, you can find a list of ligand names that Lavelle accepts.

Ryan Chang 1C

We are expected to know the shape of the molecule but not the exact bond angles. However, when there are lone pairs surrounding the central atom, we are expected to know that the bond angles are slightly less compared to central atoms with no lone pairs.

Ryan Chang 1C

For SO2Cl2, the solutions say that there are two possible dot structures. One of them has a double bond and 2 lone pairs attached to the oxygen, while the other has a single bond and 3 lone pairs attached to the oxygen. I understand how the reasoning behind both dot structures, but does Dr. Lavelle ...

Ryan Chang 1C

The molecules in both c and d both have a bent shape because the central atom formula is AX2E, or in other words the central atom is connected to two bonds and has one lone pair. When this bent shape occurs, the bond angles are slightly less than 120 degrees because there are 3 concentrations of ele...

Ryan Chang 1C

Could someone explain the shape and bond angles of C2H4? I don't understand why it's trigonal planar.

Also, I don't understand the answer for the shape and bond angles of N2H4. If someone could explain that as well that would be great!

Ryan Chang 1C

Could someone explain the shape and bond angles of (CH3)2Be? I don't understand why the shape is tetrahedral about carbon atoms.

Ryan Chang 1C

They all describe the same types of intermolecular forces.

Ryan Chang 1C

Vapor pressure is correctly defined in the post above. Knowing what vapor pressure is can help you solve problems like 3F.19 part (b) Explain why the vapor pressure of diethyl ether (C2H5OC2H5) is greater than that of water. Since water has hydrogen bonds and C2H5OC2H5 does not, the molecules are he...

Ryan Chang 1C

Also keep in mind that ion-ion interactions are much stronger than other interactions between ions and molecules.

Ryan Chang 1C

Explain the difference in the boiling points of AsF3 (63 degrees C) and AsF5 (-53 degrees C).

I'm trying to understand this problem. Why does AsF3 have a higher boiling point? I thought that more electrons means a higher boiling point.

Ryan Chang 1C

Identify the types of attractive intermolecular interactions that might arise between molecules of each of the following sub- stances: (a) NH2OH; (b) CBr4; (c) H2SeO4; (d) SO2. I understand a, b, and d but why does H2SeO4 have dipole-dipole interactions? I don't understand why it is a polar molecule.

Ryan Chang 1C

What's the difference between london dispersion and van der waals forces?

Ryan Chang 1C

Another way to put it is that polarizing power increases among cations from left to right and bottom to top, while polarizability increases from right to left and top to bottom.

Ryan Chang 1C

Recall that ionic bonds form between molecules with a high difference in electronegativity, usually those with a electronegativity difference greater than 2. BaBr2 is the only molecule that primarily forms ionic bonds because the difference in electronegativity between Ba and Br is greater than 2. O...

Ryan Chang 1C

Polarizing power increases from left to right, from bottom to top on a periodic table.

Ryan Chang 1C

Up to how many electrons can be held in the valence shell of capable elements?

Ryan Chang 1C

The 3d orbital has a slightly lower energy level than the 4s orbital, which is why 3d comes before 4s. The 3d orbital is filled up with electrons first, then the 4s orbital, then the 4p orbital.

Ryan Chang 1C

What does he mean when he writes x, y, and z during electron configuration? Is that necessary? x, y, and z represent the different orbital orientations. Some orbitals may be lined up along x axis, others along the y axis, and others along the z axis. The reason why you write x, y, or z is to specif...

Ryan Chang 1C

The principle quantum number (n) is the number before the letter in the given orbital. To find the angular momentum quantum number (l) you use to following: s; l=0 p; l=1 d; l=2 f; l=3 For part a, n=6 since the orbital is 6p, and l=1, since it is a p orbital. For part b, n=3 since the orbital is 3d,...

Ryan Chang 1C

D-orbitals have a slightly lower energy level than s-orbitals in the same period, therefore d-orbitals are filled with electrons first before s-orbitals. For example, the 3d orbital would be filled with electrons before the 4s orbital.

Ryan Chang 1C

If you remember in class, Cu is an exception for telling the electron configuration from the periodic table. From reading the periodic table, we would expect the configuration to be [Ar]3d^9 4s^2, BUT through experiments, scientists have found that the e- configuration is actually [Ar]3d^10 4s^1 be...

Ryan Chang 1C

Give the ground-state electron configuration expected for each of the following ions: (a) Cu 1+ ; (b) Bi 3+ ; (c) Ga 3+ ; (d) Tl 3+ For part A, I thought that the answer was [Ar]3d^84s^2 but the solution manual says that the answer is [Ar]3d^10. Why are the electrons from the 4s orbital put into the...

Ryan Chang 1C

Also the Balmer series deals with visible light while the Lyman series deals with ultraviolet light.

Ryan Chang 1C

After converting the values, plugging in each value would look like this:

(6.626x10^-34 kg ms^2 s^-1)/(1.675x10^-27kg x 100x10^-12m) = 3.96x10^3m/s

Ryan Chang 1C

All you have to do is draw a square with the length equal to the diameter of the actual atom. The area would represent the potential space the electron could be.

Ryan Chang 1C

The uncertainty value would be 0.2pm because the position could be at 2.34 to 2.36.

Ryan Chang 1C

Yes, the original velocity of the ejected electron is used to solve this question. The first step is to find the energy of the photon, which can be calculated by adding the kinetic energy of the ejected electron to the energy required to remove the electron from the metal surface. Recall that kineti...

Ryan Chang 1C

Adding on the the post above, wavelength is equal to the speed of light divided by frequency.

Ryan Chang 1C

I would definitely be familiar with those series and I wouldn't be surprised if we need to know them for future tests.

Ryan Chang 1C

I've been using 3.00x10^8 m/s for module and homework problems and have been just fine.

Ryan Chang 1C

You can find the list of homework problems in the syllabus. I would just go through each section and see which ones apply to what Lavelle has lectured on so far.

Ryan Chang 1C

I believe since we use the equation c = w*f, then 3e8= 98.6e6x. to solve for x (wavelength) then divide by the frequency. I got 3.05 meters. Are c and w*f constant values in the equation you used? C is a constant value which is the speed of light. Lavelle introduced it in lectures as 3.00x10^8 m/s ...

Ryan Chang 1C

I would assume not, but this may be something good to double check with Lavelle or a TA. I do remember this question from the homework though.

Ryan Chang 1C

In response to Lauren, I believe that chemical equations will already show that oxygen by itself is diatomic, as well as the other diatomic molecules. Also, an easy way to remember the diatomic molecules is: Have (hydrogen) No (nitrogen) Fear (fluorine) Of (oxygen) Ice (iodine) Cold (chlorine) Beer ...

Ryan Chang 1C

You only need to use the molar mass of one reactant to find the product, so you can keep the molar masses of the products separated. First, convert the grams given of a particular reactant to moles. Then, use the molar ratio of the balanced equation to determine how much of a particular product is c...

Ryan Chang 1C

Is there a specific order atoms have to be in? For example, in glucose, how do we know that carbon comes first, then hydrogen, then oxygen.

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