CHEMISTRY COMMUNITY

Maggie Bui 1H

It is not methylene because methylene refers to a group in the middle of the carbon chain (-CH2-). The CH3 attached to one of the carbons in the double bond is a substituent by the rule that is discussed in this section, and is therefore called a methyl group. There is no "ethyl" in the na...

Maggie Bui 1H

Before we think about lowering numbers, we should find the longest chain first. Because the structure's longest chain would include 4 carbons, we use "but".

Maggie Bui 1H

"Iso" doesn't count as a prefix; it's part of the name. The prefixes that indicate number of a certain substituent (i.e. dimethyl, the "di") do not count in alphabetical naming, but prefixes that are part of a name (like isopropyl's "iso" or "neo") do.

Maggie Bui 1H

When we name a compound, there's no special designation for double or triple bonds. You just have to put the number carbon where the substituent is attached and name the substituent. Keep in mind though that you want to minimize the number of the carbon the substituent is attached to. For example, i...

Maggie Bui 1H

Rate laws don't have intermediates in them because intermediates are produced in one reaction and used up in (one of) the following reaction(s). And yes, you should solve for the intermediate to replace it if it shows up in the rate of formation for a product of the overall reaction.

Maggie Bui 1H

We've learned how to balance chemical reactions and write out chemical formulas, and know the reaction takes place in an acidified solution, so I think we should be expected to know how to balance the half-reactions. However, I think we'd have to be given the reduction potentials for each half react...

Maggie Bui 1H

We don't always necessarily want a positive cell potential: if we want a spontaneous reaction, we would need a positive cell potential, but that's not what we're looking for here. The first reaction is oxidized because we need to reverse that reaction to calculate Ka. The reaction that is associated...

Maggie Bui 1H

To be an electrode, it's not enough that something is solid; it also needs to conduct electricity, as electrons are transferred via electrode.

Maggie Bui 1H

To balance out the oxygen in a basic redox reaction, you'd add H2O, not OH-. To balance hydrogen, you'd add H2O and OH-. Which ever side needs hydrogen, add H2O to that side and add a corresponding amount of OH- on the other side. Notice that if you add H2O on one side and OH- on the other, you'll h...

Maggie Bui 1H

H2O and H+ are used to balance out the numbers of oxygen and hydrogen atoms in the reaction. The first step of writing out the reduction half-reaction is to write down the reactant and product involved with what's being reduced. Balance any atoms that aren't hydrogen or oxygen first. {Cr_2O_7}^{2-}\...

Maggie Bui 1H

Cadmium ions are removed because they react with the sulfide ions that dissociate from sodium sulfide, and precipitate as CdS.

Maggie Bui 1H

The solutions manual uses the positive reduction value for the anode, but notice that this positive reduction potential is being subtracted from the reduction potential of the cathode. We learned to reverse the sign of the reduction potential of the anode and then add the two half-reaction potential...

Maggie Bui 1H

Though it doesn't explicitly reverse the reduction potential, the solutions manual does essentially the same thing. Instead of reversing the reduction potential and then adding the two half-reaction potentials to get the standard cell potential, it just subtracts the reduction potential of the anode...

Maggie Bui 1H

Though I'm not sure when you'd choose which as an electrode, graphite functions as an inert electrode much as platinum does.

Maggie Bui 1H

Keep in mind that these constants are a result of aggregating different constants used in the Nernst equation. Both values are calculated assuming the reaction takes place at 25 degrees Celsius (298 Kelvin), and using the value of the gas constant, 8.314 Joules over moles times Kelvin and Faraday's ...

Maggie Bui 1H

The first step should being figuring out what's oxidized and what's reduced. The straightforward way is to go through each reactant and its corresponding product and see how each element in it changes oxidation states, but since we know that transition metals commonly change oxidation states, I thin...

Maggie Bui 1H

I'm not sure how you're calculating the charge, but first, it's good to start with any transition metals if you see any because they typically change charge in redox equations. You can find the oxidation number of chromium (Cr) by looking at oxygen. Oxygen's common oxidation state is 2-. There's 7 o...

Maggie Bui 1H

Electrolysis is not technically a rechargeable battery because the reaction has to be able to go the opposite direction to be a battery. Electrolysis describes using an electric current to "push" a reaction in a direction opposite of the favorable direction, which is what happens each time...

Maggie Bui 1H

The only gas in the equation is the oxygen gas; for every 4 moles of aluminum that react, 3 moles of oxygen react, so for one mole of aluminum, 3/4 of a mole of oxygen will react. The sign on the moles is negative because you are using up 3/4 of a mole of oxygen (as opposed to gaining 3/4ths of a mo...

Maggie Bui 1H

As you said, mathematically, this makes sense; if you calculate the entropy change with some q value at 20 degrees Celsius and the same q value at 30 degrees Celsius, the entropy change of the 2nd calculation is smaller than that of the first. Rather than the temperature change though, I think it's ...

Maggie Bui 1H

Hm, I think you have them mixed up? Heat released is negative and heat absorbed is positive. This all goes back to the concept of a system and the surroundings. The system is what we're focusing on while the surroundings are everything else. We think of change in energy from the perspective of the s...

Maggie Bui 1H

First, I would write down what you're given in variables, ex. Pressure (P) =2.00atm. Then, relate the given with what you're looking for. In part a, you're looking for "work...done in the compression". Recall that work is force over a distance and pressure is force over an area. Page 22 in...

Maggie Bui 1H

Usually we subtract a final quantity from an initial quantity to calculate a change, but in this case, we should be thinking about what is affecting the system and how it is affecting it. Whether to add or subtract a quantity depends on its sign, which is determined by how the system is affected by ...

Maggie Bui 1H

It's not so much that O2 is an exception as it is that the standard enthalpy of formation of an element in its most stable form is 0 (this definition is found on page 294 of the book). I think this makes more sense if you think about the "reaction" you'd need to form these elements. You co...

Maggie Bui 1H

In this specific problem, the answer book probably says to ignore the second ionization because it is too small take into account. I don't think there's a specific cutoff of when to omit the second ionization, but I think if it doesn't contribute to changing the significant figures of the answer, it...

Maggie Bui 1H

The chloride ion (Cl-) doesn't affect pH because pH is a measure of how acidic (or basic) something is based on its hydronium ion concentration (H3O+). We aren't looking at charge, so the charge of the chloride ion wouldn't affect the pH of the solution, and if we're talking about hydrochloric acid ...

Maggie Bui 1H

Even if there's a solid in the reaction, you can still calculate the Q and K using just the concentrations of the reactants and or products in gas phase.

Maggie Bui 1H

Simply put, hybridized orbitals mesh together different unhybridized orbitals to better account for experimental observations. For example, the book gives the example of carbon: we know from experience with Lewis structures that carbon usually forms 4 bonds, but according to its electron configurati...

Maggie Bui 1H

Also, just a note: trigonal pyramidal is shape based on that of tetrahedral. However, while tetrahedral has four bonds attached to the central atom, trigonal pyramidal has three bonds and one lone pair attached to the central atom. Due to lone pair repulsion, the bond angle of trigonal pyramidal is ...

Maggie Bui 1H

Hi Ariana,

Electrons are removed from orbitals with the most energy first, so electrons from the 3p orbital will be removed before electrons from the 3s orbital.

Maggie Bui 1H

In this part of the exercise, I believe they mean the 5th group within the transition metals, which would refer to what's actually the 7th group transition metals (manganese, technetium, etc.).

Maggie Bui 1H

Hi Matt, I don't have an answer for all the specific examples you suggested, but in general, I believe irregularities in atomic radius are due to electron-electron repulsion and effective nuclear charge: electron-electron repulsion may cause electrons to spread out and effective nuclear charge affec...

Maggie Bui 1H

The high energy electron may already be releasing all of its energy - the smaller n is, the more energy it takes to move between the two energy levels (it'd take more energy to move from n =2 to n =1 than to go from n=4 to n=3). Therefore, if there were a high energy electron on one of the higher le...

Maggie Bui 1H

A general approach I typically use is writing down given information and thinking about what I know about the quantities given. The problem gives us the wavelengths of light and mentions a lithium photomultiplier is used; I singled out these tidbits of the problem because they deal directly with the...

Maggie Bui 1H

It's not so much when the word "neutralize" is used, but if you're given the mass of only one reactant, I think it's safe to assume that the other reactant is present in excess. Therefore, it wouldn't affect the amount of product produced, so you can proceed with calculations using your gi...

CHEMISTRY COMMUNITY

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