CHEMISTRY COMMUNITY

Isabella Dal Porto 1H

You take the value that you solved for when approximating and then divide it by the initial concentration given. If it is less than 5% after you multiply it, then the approximation is valid. If is is greater than 5%, then the approximation is not valid and you have to keep the -x and use the quadrat...

Isabella Dal Porto 1H

Wait for your TA to email you first.

Isabella Dal Porto 1H

I have not received any email yet.

Isabella Dal Porto 1H

I’m wondering if our TAs want us to email the homework this week for credit.

Isabella Dal Porto 1H

Most likely it will be online, but it’s best that we wait for Lavelle.

Isabella Dal Porto 1H

I believe that it is [anode]/[cathode].

Isabella Dal Porto 1H

I add H₂O and OH^- on the right side for reduction and then balance both sides by adding H₂O to the other side. For oxidation, add H₂O and OH^- on the left and balance the number of H by adding H₂O on the right. That's assuming you need to add any oxygens or hydrogens.

Isabella Dal Porto 1H

Commas are for when it's the same state (ex. Fe²⁺ _(aq), Fe³⁺ _(aq)), and vertical lines separate different states like g or aq.

Isabella Dal Porto 1H

For galvanic cells, spontaneous redox reactions convert the chemical energy to an electric energy. For electrolytic cells, non-spontaneous redox reactions convert the electric energy to a chemical energy.

Isabella Dal Porto 1H

You add Pt typically to the cell diagram when there are no other metals present.

Isabella Dal Porto 1H

My TA said to use the notation below as a guide.
solid|gas|aq||aq|gas|solid

Isabella Dal Porto 1H

I would just familiarize yourself with the two questions on it from the textbook. If he actually tests us on it, then it will most likely resemble those.

Isabella Dal Porto 1H

If it is on the outline or talked about during lecture, then it probably will be on the final.

Isabella Dal Porto 1H

I am pretty sure you can write it either way as long as you follow the conventions for writing out a cell diagram.

Isabella Dal Porto 1H

Electrochemical series is just the table that lists all the standard electrode potentials for different chemical species.

Isabella Dal Porto 1H

He might slightly adjust the overall grades at the end of the quarter, but he won't curve the tests individually.

Isabella Dal Porto 1H

You have to compare the metal's standard reduction potential to that of H₂. Metals above H₂ on the activity series dissolve in acids, while metals below H₂ do not dissolve in acids. I believe nitric acid is an exception for metals below H₂.

Isabella Dal Porto 1H

Electrochemical series is the table that lists all the standard electrode potentials (reduction potential or oxidation potential) of different chemical species.

Isabella Dal Porto 1H

You definitely need E values for both the cathode and the anode. Those half-reactions are given in appendix 2B of the textbook.

Isabella Dal Porto 1H

My TA also said that if the problem mentions alkali you use OH-.

Isabella Dal Porto 1H

Aside from delta G, a reaction is spontaneous if delta H is negative and delta S is positive.

Isabella Dal Porto 1H

Yes, delta E and delta U are both used to represent internal energy.

Isabella Dal Porto 1H

Both chemical formulas represent the same compound regardless of the order they are written in.

Isabella Dal Porto 1H

Oxidation is when a reactant loses electrons during the reaction whereas reduction occurs when it gains electrons during the reaction.

Isabella Dal Porto 1H

Yeah he usually doesn't curve the midterm even if the average is low.

Isabella Dal Porto 1H

I got -138.18 kJ like the solution manual. You probably have a small calculation error. Are all the signs correct and did you multiply each one by the correct number of moles?

Isabella Dal Porto 1H

There is the pizza rolls midterm review handout.

Isabella Dal Porto 1H

When there is a phase change, temperature remains constant for a period of time because all the heat added is being used to break bonds.

Isabella Dal Porto 1H

It doesn't greatly affect the final answer, but you might as well use 273.15.

Isabella Dal Porto 1H

Pizza rolls are the key words for the midterm review session worksheet that was today.

Isabella Dal Porto 1H

Work=-P $\Delta$ V

Isabella Dal Porto 1H

Compression will have positive work on the gas whereas expansion will have negative work on the gas.

Isabella Dal Porto 1H

Breaking the bonds that are holding the solid together requires energy. Thus, delta H is positive since the reaction is endothermic (needs energy/energy absorbed).

Isabella Dal Porto 1H

Many gases are just diatomic molecules or a combination of different elements. This doesn't affect the number of moles. Thus, you only need to consider the coefficient to get the number of moles.

Isabella Dal Porto 1H

Energy is neither created nor destroyed. That is why it is known as conservation of energy.

Isabella Dal Porto 1H

Catalysts speed up the rate of a reaction, but they do not affect the amount of reactants or products at all.

Isabella Dal Porto 1H

If eq is shifted right, then products will be favored. If eq is shifted left, then reactants will be favored.

Isabella Dal Porto 1H

Endothermic and exothermic mean heat is either being released or absorbed at a constant pressure. Endergonic and exergonic refer to changes in free energy. For endergonic reactions, energy is needed to drive the reaction in the forward direction. For exergonic reactions, energy is released in the fo...

Isabella Dal Porto 1H

My TA in 14A usually gave me points for following the right steps even though the final calculations were wrong.

Isabella Dal Porto 1H

I would also recommend going to the workshops since those problems are more complex than the ones covered in step-up sessions.

Isabella Dal Porto 1H

Midterms and finals are cumulative, but the tests aren't.

Isabella Dal Porto 1H

Basically, the equilibrium constant for an overall reaction is the product of the equilibrium constants for its component reactions. Thus, you would combine the reactions H_{2}+Cl_{2}\rightleftharpoons 2HCl and 2BrCl\rightleftharpoons Br_{2}+Cl_{2} and then cancel the Cl on both sides since it appea...

Isabella Dal Porto 1H

You need to know how to calculate the pH of a weak acid and its salt, which makes a buffer. The example Lavelle used in Friday lecture was nitrous acid and potassium nitrite.

Isabella Dal Porto 1H

The activity of a pure solid or liquid is equal to 1 so it doesn't affect the value of the equilibrium constant.

Isabella Dal Porto 1H

You can also answer questions from the new topics we'll cover during Wednesday lecture if your discussion follows it.

Isabella Dal Porto 1H

This equation will most likely show up on the test. It is used for finding the equilibrium pressure of a gas.

Isabella Dal Porto 1H

It is chemical equilibrium up to acid and base equilibria. The outlines for all the topics are on Lavelle's website.

Isabella Dal Porto 1H

It is helpful to know since the autoprotolysis constant of water, Kw, is used to calculate hydronium and hydroxide concentration. That helps us determine if the solution is more acidic or basic.

Isabella Dal Porto 1H

I would memorize the strong acids and bases because it is really helpful.

Isabella Dal Porto 1H

A buffer is defined as a chemical substance that helps maintain a relatively constant pH in a solution, even in the face of addition of acids or bases. The only thing I remember Lavelle mentioning in class was about how adding equal amounts of sodium acetate and acetic acid makes a buffer solution. ...

Isabella Dal Porto 1H

Pa is for acid and Pb is for bases. Ka is the dissociation constant for acids and Kb is the dissociation constant for bases.

Isabella Dal Porto 1H

Final grades have to be in for fall quarter.

Isabella Dal Porto 1H

I believe it is 24 month access, and the chem textbook is the same all throughout for the 14 series.

Isabella Dal Porto 1H

Mg(OH)2 is a strong base since strong bases are oxides and hydroxides that bond to group 1 and 2 elements.

Isabella Dal Porto 1H

Most likely he will discuss it during lecture tomorrow.

Isabella Dal Porto 1H

It is known that when naming an ionic compound, the cation is always first before the anion. For instance, in NaCl sodium is the cation and chlorine is the anion.

Isabella Dal Porto 1H

I also find it helpful to skip questions that initially cause confusion. When I return to them later on, I always have a clearer mind and feel less stressed given that I know I have completed the easier problems I am more confident about.

Isabella Dal Porto 1H

Yes. It is in reference to hydrogen.

Isabella Dal Porto 1H

Yes, that is why it is a Lewis base.

Isabella Dal Porto 1H

Bond order is defined as the number of chemical bonds between a pair of atoms, and it indicates the stability of a bond.

Isabella Dal Porto 1H

The hydrogen-chlorine bond in HCl is very weak and it completely dissociates in water. This qualifies HCl as a strong acid. On the other hand, the bonding in HF is relatively strong. Thus, it only partially dissociates in water and makes it a weak acid.

Isabella Dal Porto 1H

I also like to draw two arrows pointing towards one another (down a group, across a period) and label whether or not it's increasing or decreasing.

Isabella Dal Porto 1H

I believe section 9C since it has to do with coordination compounds.

Isabella Dal Porto 1H

Also are we going to finish with acid and base structures?

Isabella Dal Porto 1H

So the test will cover topics from section 2D in the textbook to what we've learned now?

Isabella Dal Porto 1H

Carbon dioxide is considered non-polar because of the symmetry of its bonding. The EN difference between C and O is 1.0, and it makes the bonds polar. Since the two polar bonds are at 180 degrees to each other, the dipoles cancel out.

Isabella Dal Porto 1H

I am pretty sure that it is sufficient to know the strengths relative to each other. Otherwise, I would ask Lavelle or your TA.

Isabella Dal Porto 1H

I believe Lavelle said in class that we are not expected to predict the exact angle. I am pretty sure that saying "less than 109.5 degrees" is fine.

Isabella Dal Porto 1H

If atoms in a molecule are symmetrical, then the charges are balanced by each other and the molecule is considered nonpolar. If a molecule is asymmetrical, it is polar.

Isabella Dal Porto 1H

Dipole moments occur when there is a separation of charge between two ions in an ionic bond or between atoms in a covalent bond. It occurs due to differences in electronegativity. Thus, the dipole moment will be larger if the difference in electronegativity is greater.

Isabella Dal Porto 1H

Since double and triple bonds have more electrons, they have stronger attractive forces on the nuclei of the bonding atoms. These atoms are pulled closer together, and it creates shorter bond lengths.

Isabella Dal Porto 1H

I believe the test is during your discussion section starting the 19th of November.

Isabella Dal Porto 1H

Forming bonds release energy and breaking bonds require energy.

Isabella Dal Porto 1H

Non-polar molecules are attracted through London dispersion attractions while polar molecules can be attracted through both London dispersion attractions and stronger dipole-dipole attractions.

Isabella Dal Porto 1H

Provided that the transition is from a high energy level to the ground state level, n=1 is the final state while n=3 is the initial state.

Isabella Dal Porto 1H

Calculating the formal charge allows you to find the most stable structure. Thus, just follow the equation FC = # Valence electrons - (# Lone pair electrons + # Shared electrons/2).

Isabella Dal Porto 1H

Resonance is helpful in determining which lewis structure to use. By calculating each formal charge, you can find the most stable one.

Isabella Dal Porto 1H

Row 3 and below can have more than 8 electrons. Since the electron configuration of Co^3+is [Ar] 3d^4 4s^2, it has 6 valence electrons.

Isabella Dal Porto 1H

Lavelle has stated on his website that the midterm covers the material up to the end of focus 2D.

Isabella Dal Porto 1H

The value he gave us for C-C bond lengths in class were experimentally observed so I would just ask your TA.

Isabella Dal Porto 1H

Basically when a neutral atom gains some electrons, an energy change occurs. This energy change is called the electron affinity.

Isabella Dal Porto 1H

I am not sure if they have any, but you could try making a same-day appointment at the test bank and seeing if there are any old exams you could review.

Isabella Dal Porto 1H

Also, I believe whether or not the ion is positive or negative affects the distance for the ionic radius. Thus, a cation would have a smaller ionic radius while an anion would have a larger ionic radius.

Isabella Dal Porto 1H

Hydrogen and Beryllium are also exceptions to the octet rule because they often form incomplete octets (less than 8 valence electrons). Overall, I would just focus on P, S, Cl since they are the most common elements that make stable compounds with expanded octets.

Isabella Dal Porto 1H

Is the Hamiltonian likely to be used a lot in this course? Is there an example problem that demonstrates when you would use or solve for?

Isabella Dal Porto 1H

So does the midterm cover the fundamentals up until the quantum world or will it include chemical bonds also?

Isabella Dal Porto 1H

Hund's Rule states that electrons in the same subshell occupy different orbitals with a parallel spin because of the fact that there is less electron repulsion and the lowest amount of energy.

Isabella Dal Porto 1H

Lavelle stated that the only ones that are important for Chem 14A are the s-block, the p-block, and the 1st row of the d-block.

Isabella Dal Porto 1H

The Schrodinger equation is basically used to describe an electron in an atom by calculating the electron's wave function. https://www.chemicool.com/definition/sc ... ation.html is pretty helpful in describing what it is and when it's applied.

Isabella Dal Porto 1H

The link that Lavelle posted on his website for sig figs states the rule. If the last digit is 5 and no number follows it , then you have to round to the nearest even number. Thus, if you need three sig figs and you have 0.4565, you have to round to the closest even number which is 6. Thus, it becom...

Isabella Dal Porto 1H

Lavelle discussed in class how light rays are streams of EM energy that are made up of photons. Thus, since a photon is a unit for light and E=hv measures the energy of a photon, the equation is applied to light.

Isabella Dal Porto 1H

Like Karyn said, I would just wait to round to the correct sig figs after doing all the calculations. Usually the amount of sig figs depends on the least amount that is provided in the question. If you're using addition/subtraction and multiplication/division, then you base it off the rules for mult...

Isabella Dal Porto 1H

Thank you Hannah!

Isabella Dal Porto 1H

Why is the Rydberg equation only applicable towards hydrogen atoms?

Isabella Dal Porto 1H

There was an example in class that said, "Calculate the De Broglie wavelength of an electron traveling at 5.3x10^{6}m.s^{-1} . Do you think your calculated wavelength, for electrons with similar velocities, could be experimentally verified/detected in this lab?" The solution was \lambda = ...

Isabella Dal Porto 1H

The subscript of two only applies to the element or elements in the parentheses that it is next to. Thus, Mg(N3)2(s) basically means that there is one Mg atom and 6 nitrogen atoms.

Isabella Dal Porto 1H

It has been awhile since I have taken chemistry. I was just wondering if symbols for whether or not a reactant or product is aqueous, liquid, solid, or gas can be identified by looking at the molecular formula alone or if you need to know the chemical properties of the reactant or product to determi...

Isabella Dal Porto 1H

Remember when calculating the maximum mass of copper(II) hydroxide that you multiply that same mol ratio you used previously by the moles of sodium hydroxide and then convert the answer to g copper(II) hydroxide.

Isabella Dal Porto 1H

As Maggie puts it, it is important to note that both combustion and oxidation imply there is burning in the presence of oxygen.

Isabella Dal Porto 1H

Follow-up question...If there is a multiplication/division problem and say 1 mol of _ is being used in the equation, are numbers that are just 1 ignored when considering sig figs? 1 mol only has 1 sig fig but many of the answers to the problems disregard this. Is there a special rule for 1s?

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