CHEMISTRY COMMUNITY

Catherine Daye 1L

An elementary step is one that occurs within a reaction to produce the final products shown in the final balanced equation. It is not typically show in the final equation and includes intermediates.

Catherine Daye 1L

In a cell diagram, the anode is on the left side, and the cathode is on the right.

Catherine Daye 1L

You use Kp for gases if you use partial pressure for gases. You can also change pressure to concentration using PV=nRT and in that case, you would use Kc since you’re now using concentrations.

Catherine Daye 1L

That is when a reaction rate only depends on k. So, if you’re given a table of different concentrations and k’s, you would see that a change in concentration doesn’t change k.

Catherine Daye 1L

Delta S total is the change in entropy in the system and surrounds. You should just add the change in entropy of the system and change in entropy of the surroundings.

Catherine Daye 1L

The cell potential does not depend on the mass of an electrode.

Catherine Daye 1L

A concentration cell has the same anode and cathode but the concentrations on either side are different, so in a cell diagram you’d indicate that.

Catherine Daye 1L

Intermediated are not in the overall rate law expression because they get created and used up during the reaction.

Catherine Daye 1L

You need to write out the half reactions first. When you combine the half reactions, n is the number of electrons on either side of the equation (they cancel each other out).

Catherine Daye 1L

The intermediate is never in the rate law expression because intermediates get used up in the intermediate steps. The rate law only includes substances present in the end of the reaction.

Catherine Daye 1L

The n value is the number of electrons in a reaction.

Catherine Daye 1L

Activation energy is the minimum amount of energy required to induce a reaction. On a diagram, it is the distance between the energy of the reactants and peak of the “hump”.

Catherine Daye 1L

Electrolysis is when a non-spontaneous reaction is driven by a current.

Catherine Daye 1L

Yes, the anode is written on the left side and it is the one being oxidized. An easy way to remember this is “an ox” (anode oxidized) and “red cat” (cathode reduced).

Catherine Daye 1L

The reducing agent causes reduction of other species, and the oxidizing agent causes oxidation of other species. So the reducing agent is oxidized by the oxidizing agent while the oxidizing agent is reduced by the reducing agent.

Catherine Daye 1L

A porous disc doesn’t the same thing as a salt bridge. They both ensure electron flow throughout the system.

Catherine Daye 1L

The salt bridge allows for the flow of electrons.

Catherine Daye 1L

An oxidizing agent is what is being reduced and a reducing agent is what is being oxidized.

Catherine Daye 1L

Oxidizing agents are what’s being reduced and reducing agents are what’s being oxidized.

Catherine Daye 1L

Salt bridges allow for electron flow between beakers.

Catherine Daye 1L

Intensive properties don't depend on the amount of a substance, while extensive properties do. For example, density is intensive but mass is extensive.

Catherine Daye 1L

Spontaneous reactions are described as having a negative Gibbs free energy.

Catherine Daye 1L

Yes, the definition is adiabatic is when heat doesn't transfer.

Catherine Daye 1L

Yes, this equation can be used at any time as long as these states remain constant.

Catherine Daye 1L

You have to think about how Ka=[A][H+]/[CB] (CB being conjugate base). By rearranging the equation, you can get Ka/[H+] = [A]/[CB], which is a ratio.

Catherine Daye 1L

Yes, we should assume this unless the question states otherwise.

Catherine Daye 1L

Yes, it will but just the basics since he only went over it a little bit.

Catherine Daye 1L

When it’s smaller than 10^-3

Catherine Daye 1L

You need to memorize the strong acids (there are only a few) and strong bases are elements in the first 2 columns and OH

Catherine Daye 1L

One thing you could do is look at the individual topic files he posts on his website. There’s a list of things you should know for each section and I use it like a checklist :)

Catherine Daye 1L

Yes, they are on his website under math assistance!

Catherine Daye 1L

Yes, the best way is to memorize the strong acids and bases (there aren’t too many). In general, a strong acids start with H and strong bases end with OH. Everything else you can assume is weak

Catherine Daye 1L

Yes, because the energy from the temperature is used to break/create bonds between molecules for their phase change.

Catherine Daye 1L

It’s everything up to and including thermodynamics. There are review sessions posted on his website.

Catherine Daye 1L

When heat is lost (exothermic) there is a negative sign since q indicates heat gained. So when -q=q one thing loses heat and the other thing gains (+q) that heat lost.

Catherine Daye 1L

K1 is when an acid/base dissociates for the first time. K2 is when the resulting conjugate base/acid from the previous reaction dissociates a second time.

Catherine Daye 1L

Temperature remains constant during a phase change because the energy that would increase temperature is instead being used to break bonds for a phase change.

Catherine Daye 1L

This is because the numerator of Q needs to increase to reach equilibrium (K value), and the concentration of products is the numerator.

Catherine Daye 1L

A higher pKa means a weaker acid since pKa is -log [acid]

Catherine Daye 1L

Steam causes more severe burns because it has more heat energy since there is a phase change from liquid to gas.

Catherine Daye 1L

To calculate pOH, you use the concentration of a base. Alternatively, you calculate the pH using the concentration of an acid. The question may also include a Ka or Kb value. The Ka indicates the equilibrium constant of an acid (uses concentration of hydronium ions), and the Kb indicates the equilib...

Catherine Daye 1L

You can omit the x term when the K value is less than 10^-3.

Catherine Daye 1L

You have to memorize the strong acids and bases. If the compound is not one of the memorized acids/bases, we assume they’re weak. In general, strong acids start with H and strong bases end with OH. Aside from that, there are a few obscure ones you should memorize.

Catherine Daye 1L

Acids make solutions that have a pH from 1-7, stronger acids making lower pH values than weak acids. pH doesn’t depend on concentration, but the strength of the acid/base.

Catherine Daye 1L

Yes, we have to memorize strong acids and bases. The common rule is that strong acids start with H and strong bases end with OH. Then there are a few other obscure strong acids and bases you should memorize.

Catherine Daye 1L

K is used for when the reaction is at equilibrium, while Q is used for when the reaction is not. A reaction at equilibrium moves at a different rate than when it’s not at equilibrium. Therefore, they’re different numbers that you can compare to determine which direction the reaction favors.

Catherine Daye 1L

The equilibrium constant K is the ratio of reactants to products, and ratios don’t have units.

Catherine Daye 1L

Q is calculated the same way as K, so you only include gases and aqueous solutions.

Catherine Daye 1L

The reaction quotient is the rate of the equation when it’s not at equilibrium. This is important because you use it to determine which “direction” the reaction favors (towards products or reactants) by comparing it to the equilibrium constant K.

Catherine Daye 1L

You use Kp for gases because it indicates partial pressure, since gases don’t really have a “concentration”. Kc is for concentrations of solids, liquids, and aqueous solutions.

Catherine Daye 1L

You should start by writing out the chemical equation of the salt in water. If the product has H+/H3O+, then the solution is acidic. If the product has OH-. then the solution is basic.

Catherine Daye 1L

Yes, but Dr. Lavelle said this is a chem 14b (I think) topic so we don't need to know this.

Catherine Daye 1L

pH shows the concentration of hydronium ions in the solution. Weak acids result in a low concentration of hydronium ions because the hydrogen doesn't dissociate easily, therefore resulting in a less acidic solution (pH closer to 7).

Catherine Daye 1L

An oxoacid is an acid with oxygen in the compound. It is important to note that metallic oxides are strong acids.

Catherine Daye 1L

pH indicates the concentration of hydronium, while pOH indicates the concentration of hydroxide. You can think of them as the extent of acidity and basicity (respectively).

Catherine Daye 1L

Yes, because all molecules have electrons, and LDFs occur when electron clouds are more dense in one direction.

Catherine Daye 1L

You can use either on the test, although Lavelle focuses on the older version in lecture.

Catherine Daye 1L

Ka is the dissociation constant and it shows how easily acids dissociate ([H+][anion]/[H-A]). The higher the Ka, the stronger the acid. PKa = -log[Ka]. The higher the PKa, the weaker the acid.

Catherine Daye 1L

Chelating compounds create a ring when they create bonds, and polydentate compounds have multiple ligands. Compounds can be both chelating and polydentate, like CO3^-2

Catherine Daye 1L

A molecule has a linear shape if it is bonded to 2 atoms and has no lone pairs, or bonded to 2 atoms and has 3 lone pairs.

Catherine Daye 1L

A Bronsted acid is distinguished by starting with H, and a Bronsted base usually ends with OH.

Catherine Daye 1L

Ferrate is the name for [FeO4]^-2. Ferrous is for the cation Fe^2+ or iron(II).

Catherine Daye 1L

You look at the regions of electron density. Count the number of bonds and lone electron pairs around the central atom. That shows you the VSEPR formula (AXE), and you can determine the molecular shape.

Catherine Daye 1L

An oxidation number is the number of electrons lost or gained when making a chemical bond. If it is a negative number, the atom will gain electrons. If it is a positive number, the atom will lose electrons.

Catherine Daye 1L

A bent molecule has one or two lone pairs, while a linear molecule has three lone pairs or none.

Catherine Daye 1L

The general rule is to put the atomic symbol in alphabetical order.

Catherine Daye 1L

When labeling, one of the bonds is a pi bond, and the other is a sigma bond. Similarly, in a triple bond, one is a sigma bond, and the other two are pi bonds.

Catherine Daye 1L

Because fluorine has a higher electronegativity than chlorine, its bond with hydrogen is stronger. Therefore, HCl dissociates more easily, making it a stronger acid due to its complete ionization.

Catherine Daye 1L

Electron pairs are still important in the shape of the molecule, as they interact with the electron clouds of the atoms bonded to the central atom. Hybrid orbitals depend on the molecular shape, therefore, electron pairs are included in hybridization.

Catherine Daye 1L

I think you can just write what the textbook requires, which is <109.5. But you should write exact numbers for 90, 180, 120 degree angles.

Catherine Daye 1L

You can kind of think polarity as "unevenness" because electrons are unevenly distributed. Therefore, you can look at how symmetrical a lewis structure is to determine it's polarity. If it is completely symmetrical, then it is most likely nonpolar. If it is not, then it is polar with a sid...

Catherine Daye 1L

Sigma bonds are in single bonds, double bonds, and triple bonds; it's kind of like the first bond. Pi bonds are in double bonds and triple bonds; it's kind of like the subsequent bonds to pi bonds. Single bonds have one sigma bond, double bonds have one sigma bond and one pi bond, and triple bonds h...

Catherine Daye 1L

I've been reviewing the midterm and looking at concepts I didn't fully understand. I'm also doing problems in the textbook since some of the questions may be on the final.

Catherine Daye 1L

The 4s orbital is lower in energy. However, when it is full, it becomes higher in energy than 3d. This explains why we write electron configurations like 3d^2 4s^2 4p^6.

Catherine Daye 1L

Hydrogen bonds are weaker than ionic and covalent bonds, but hydrogen bonds are the strongest of the intermolecular forces.

Catherine Daye 1L

A dipole-dipole force is between molecules that are always polar. An induced dipole-induced dipole force is between molecules that have instantaneous dipole moments; the electrons move around, making the molecule temporarily polar.

Catherine Daye 1L

I think this is because they are very electronegative. Especially because they have small radii, it has strong bonds with hydrogen, which has the smallest radius of all the elements.

Catherine Daye 1L

Sigma bonds are in all bonds, and pi bonds are in double and triple bonds. Single bonds have one sigma bond, double bonds have a sigma and a pi bond, and triple bonds have a sigma and two pi bonds.

Catherine Daye 1L

Bond length is the distance between the two nuclei of the elements. The electron clouds influence bond lengths by making the elements farther/closer from each other with electron-electron repulsion.

Catherine Daye 1L

Although they are both important, formal charge is slightly more important. Not all lewis structures will be symmetrical.

Catherine Daye 1L

This doesn't really answer the question, but it's interesting to note that this also demonstrates how some ionic bonds demonstrate a more covalent character than others. If one bond has a really high electronegativity difference, it demonstrates less covalent character than one that has an electrone...

Catherine Daye 1L

Yes, because even though isoelectronic ions have the same number of electrons, they still have differing numbers of protons. When there are more protons in the nucleus, there is a stronger pull. Therefore, isoelectronic ions have the same electron-electron repulsion but different pulls from the nucl...

Catherine Daye 1L

No, they don't because they have all 8 valence electrons. These trends are based on the fact that elements tend to want to have a full valence shell. For example, ionization energy is the amount of energy it takes to remove an electron. Group 1 has low ionization energy because they want to lose the...

Catherine Daye 1L

The d orbital is lower in energy than the s orbital, so when you write the electron configuration you always write the d orbital first. For example, ... 3d^10 4s^2 4p^6, ... 4d^10 5s^2 etc.

Catherine Daye 1L

He might also ask questions that require you to differentiate the three different principles we learned. Ex. what principle explains the electron configuration 1s^2 2s^2 2p^6 for carbon? why can't 1s^2 2s^2 2p^3 (nitrogen) have paired electrons?

Catherine Daye 1L

I think the best way to study is to do practice problems. You learn how to solve a bunch of different problems on the same topic and won't be blindsided if a problem is worded weirdly.

Catherine Daye 1L

Yes, there are a few exceptions to the octet rule. This includes molecules with an odd number of electrons (ex. nitrogen), molecules with atoms that have more than 8 electrons (ex. sulfur), and molecules with atoms that have less than 8 electrons (ex. boron).

Catherine Daye 1L

Anions are larger because they add another electron, creating more electron-electron repulsion between the valence shell electrons and the electrons in the shell below it (increasing distance between the shells). Cations are smaller because they remove an electron, decreasing the amount of electron-...

Catherine Daye 1L

Yes, exactly! Also, note that elements in ionic compounds give and take electrons from each other, while elements in covalent compounds share electrons.

Catherine Daye 1L

A good trick is to write down a mini chart under the equation where you write down the elements and the number of moles for the reactant side and product side. Ie Reactants --> C 3, O 1, H4 Products --> C 1, O 2, H 2. This might help you keep track of your numbers without making your work too messy.

Catherine Daye 1L

The question is saying the bowling ball is moving at 5+5 m/s (10 m/s) or 5-5 m/s (0 m/s). That's why you multiply the mass by 10 m/s.

Catherine Daye 1L

This is because oxygen has one electron pair in the outer shell, while nitrogen has none. The electron pair contains electron-electron repulsion, making it easier to remove the most loosely bound electron, meaning it has low ionization energy.

Catherine Daye 1L

Actual yield is less than theoretical due to almost unavoidable mistakes, for example, slight inaccuracies in measuring out reactants or some of the product sticking to the side of the beaker when measuring. Theoretical yield is the largest possible yield in a reaction, as it assumes there are no mi...

Catherine Daye 1L

First, write down the molar masses of each element in the compound. Then find the molar mass of the compound by adding the atomic masses of the elements (making sure to account for the additional atoms ex. O2 is 32 g/mol). Finally, find the mass percent for each element using the equation [(molar ma...

Catherine Daye 1L

The radius is only measured when the element is in its ground state!

Catherine Daye 1L

I think that equation applies only to electromagnetic waves!

Catherine Daye 1L

I don't think so, but it should be helpful to know that electronegativity increases the closer it is to fluorine since it's the element with the highest electronegativity.

Catherine Daye 1L

Ionic bonds are stronger than covalent bonds because elements give/take electrons, whereas elements with covalent bonds share electrons.

Catherine Daye 1L

You use the Rydberg equation to calculate the wavelength of light released when an electron jumps down to lower energy levels.

Catherine Daye 1L

I think it's supposed to be in alphabetical order (ex. hydrogen, carbon, chlorine, oxygen). After taking chem for a while and getting used to seeing a bunch of different compounds, putting them in order will become automatic. :)

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