CHEMISTRY COMMUNITY

Grace_Remphrey_2J

Hello! I'm a bit confused about galvanic vs electrolytic cells. I am having trouble with the differences between their half-reactions and cell diagrams. Could someone please explain the major differences between the two? Thank you so much!

Grace_Remphrey_2J

Hi! Activation energy is the minimum amount of energy required for a reaction to occur. Free energy of activation is the difference in free energy (deltaG) between reactants and products. Hope this helps!

Grace_Remphrey_2J

A general rule of thumb is that in an isolated system, the internal energy will equal zero. Just something helpful to think of when completing problems like these!

Grace_Remphrey_2J

Hi! This article goes in-depth about how Le Chatelier's principle will counteract changes in different factors of a system in order to reach equilibrium. Hope this helps! https://courses.lumenlearning.com/introchem/chapter/le-chateliers-principle/#:~:text=Le%20Chatelier's%20principle%20is%20an,achie...

Grace_Remphrey_2J

Hi! I think this video has a nice explanation and a pretty clear explanation with tips. Hope this helps! We love Professor Dave lol

https://www.youtube.com/watch?v=N6ivvu6xlog

Grace_Remphrey_2J

\Delta G = \Delta H^{\circ} - T\Delta S^{\circ}, is the formula that directly relates Gibbs free energy to enthalpy and entropy. How can we find deltaS if its not given? delta S = (delta q) / T Hi! To find delta S, you can use the second law of thermodynamics: The change in entropy (delta S) is equ...

Grace_Remphrey_2J

I was wondering about the same thing. I am pretty sure that it was mainly used for the derivation of the integrated rate laws.

Grace_Remphrey_2J

An exothermic reaction can be non-spontaneous when the temperature is high and entropy is negative, as shown in the ∆G = ∆H-T∆S equation.

Grace_Remphrey_2J

Saltwater corrosion of metals happens faster than freshwater because of the increased presence of dissolved ions. These ions allow electrons to move faster on the metal, speeding up the formation of rust. Hope this helps!

Grace_Remphrey_2J

For this problem, I used the Arrhenius equation to calculate the activation energy but rearranged it to solve for Ea. Hope this helps!

Grace_Remphrey_2J

HI! I am a visual learner and this video helped me understand the function of the salt bridge. Hope this helps!

https://www.youtube.com/watch?v=BJzgnjg4Nok

Grace_Remphrey_2J

I was also confused about this and these explanations were super helpful. Thank you!!

Grace_Remphrey_2J

Hi! Since a bomb calorimeter is an isolated system (no energy or matter is being lost/gained), it is a perfect system. Hope this helps!

Grace_Remphrey_2J

Hi! When E naught is positive, the redox reaction is favorable so you can deduce it is spontaneous. When E naught is negative, the reaction is not favorable so you can deduce it is not spontaneous. Hope this helps!

Grace_Remphrey_2J

Hi! I also had this question and this link had a nice explanation in addition to the ones above. Hope this helps!
https://socratic.org/questions/what-is- ... ochemistry

Grace_Remphrey_2J

Work is positive if the system is being compressed. Work is being done on the system. Work is negative if the system is being expanded. Work is being done by the system.

Grace_Remphrey_2J

Since the temperature is held constant, the change in energy is zero. The heat absorbed by the gas equals the work done by the ideal gas on its surroundings. Enthalpy change is also equal to zero because the change in energy zero and the pressure and volume is constant. Hope this helps!

Grace_Remphrey_2J

If the free energy of the formation of a compound is negative, this means that in the reaction for the formation of the compound, the elements (reactants) will tend to combine to form the compound (products). When free energy is positive, the elements are favored in the reaction, so the compound wil...

Grace_Remphrey_2J

- A redox reaction is spontaneous if the standard electrode potential for the redox reaction, Eo(redox reaction), is positive. If Eo(redox reaction) is positive, the reaction will proceed in the forward direction (spontaneous). - If Eo(redox reaction) is negative (Eo(redox reaction) < 0), the reacti...

Grace_Remphrey_2J

I have a question relating to the following two questions: 4C.11 How much heat is needed to convert 80.0 g of ice at 0.0 8C into liquid water at 20.0 8C (see Tables 4A.2 and 4C.1)? 4C.13 An ice cube of mass 50.0 g at 0.0 8C is added to a glass containing 400.0 g of water at 45.0 8C. What is the fina...

Grace_Remphrey_2J

Yes, your reasoning is correct! Good job :)
Negative work indicates that the system is doing work whereas positive work indicates that work is being done on the system.

Grace_Remphrey_2J

Reversible pathway: a slow series of steps and work done on the reversible pathway is greater than irreversible work because the external pressure is nearly equal to the system's pressure. Irreversible pathway: a quick series of steps. Takes less work because the system is pushing against low extern...

Grace_Remphrey_2J

The post that Allan included in his comment is very helpful and I also used it to understand this problem when I was confused. To add, entropy is higher for molecules with more possible orientations for each atom.

Grace_Remphrey_2J

Since the temperature remains constant in isothermal reactions, they are reversible.

Grace_Remphrey_2J

Yes, gas becomes more orderly when it liquifies. During the state change, the energy that is released into the surroundings increases the entropy of its surroundings. According to the second law of thermodynamics, the entropy of the universe is always increasing. Hope this helps!

Grace_Remphrey_2J

Yes I'm pretty sure, heat capacity always has a positive value since it is the amount of energy (heat) required to raise the temperature of the system. Hope this helps!

Grace_Remphrey_2J

Since the surrounding system (the universe) is so large, changes in pressure in the open system would not have a significant effect on the system. As stated above, the example of putting a bucket of water in the ocean.

Grace_Remphrey_2J

In the phase change from liquid water to water vapor, the breaking of hydrogen bonds allows the phase change to occur. The strength of hydrogen bonds explains why water has a high boiling point since H-bonds are difficult to break.

Grace_Remphrey_2J

Since weak acids and bases don't dissociate completely, ICE tables allow us to organize the information so we can determine how much they do dissociate.

Grace_Remphrey_2J

If delta U is 0 then q=-w. This concept stems from the first law of thermodynamics.

Grace_Remphrey_2J

Selecting the correct R constant can be determined by the units used in the calculations. It's super helpful to keep track of units through your calculations so you can choose the right R constant. Hope this helps!

Grace_Remphrey_2J

Heat is not a state function because it depends on the path taken (as explained in the hiking example Dr. Lavelle used in the lectures) rather than just the initial and final conditions. Hope this helps!

Grace_Remphrey_2J

Heat is a transfer of energy due to a temperature difference. Enthalpy is the change in the amount of heat in a system at constant pressure. Remember that for these terms, you can only use heat and enthalpy interchangeably if there is no work being done to the system. Hope this helps!

Grace_Remphrey_2J

I think it'll definitely be helpful to have a strong understanding of calorimeters and for the most part, have the diagram memorized. Hannah's explanation above about the bathtub is a great trick to use!

Grace_Remphrey_2J

I am a bit confused about what the difference is between these statements that are in outline 2. Can someone please explain the difference between the pH of salt solutions vs the pH of a weak acid and its salt? I'm hoping that by explaining the pH of a weak acid and its salt that the third question ...

Grace_Remphrey_2J

I don't think we would have to solve for such values of x because they would be extremely small and therefore insignificant. Hope this helps!

Grace_Remphrey_2J

A phase change occurs when a substance is either heated or cooled and changes from one state to another. For example, when a solid is heated it may change phases to liquid or gas. The reverse can also occur when a change in pressure or temperature causes a change from gas to liquid or solid. Hope th...

Grace_Remphrey_2J

To find the formal concentration of B, find the sum of [B] and [BH+]. Hope this helps!

Grace_Remphrey_2J

Kw is super important when calculating Ka and Kb. If given either Ka or Kb, you can manipulate the formula Kw=Ka*Kb to solve for the unknown. Also, the value of Kw explains why the sum of pH and pOH is 14. Hope this helps!

Grace_Remphrey_2J

K is the equilibrium constant. Kc and Kp specific if the equilibrium constant is in regards to concentration or pressure. Hope this helps!

Grace_Remphrey_2J

Endothermic reactions require heat to occur. Exothermic reactions release heat. These changes are denoted by changes in enthalpy. Hope this helps!

Grace_Remphrey_2J

n short, it is possible to have pH outside of this range but it will be extremely concentrated, resulting in a virtually meaningless pH value. The exception of pH falling in the 1-14 scale can be caused by lowering the concentration of H20 (if not obeying the assumption that water does not have a va...

Grace_Remphrey_2J

In order to maintain equilibrium between the products and reactants, if there is an addition to one side of the reaction, the equation will shift to the opposing side in order to maintain equilibrium.

Grace_Remphrey_2J

Given the equation Kw= Ka*Kb, you can see the relationship between Ka and Kb. Since Ka and Kb are on the same side of the equation, an increase in either Ka or Kb will cause an inverse reaction to the opposing constant.

Grace_Remphrey_2J

Ka is the acidity constant and will be used when working with acids. Kb is the base dissociation constant and will be used when working with bases. The larger the Ka value, the stronger the acid. The larger the Kb value, the stronger the base. Hope this helps!

Grace_Remphrey_2J

Here's a table I find super helpful when looking at the difference between real and ideal gas. Hope this helps!

Grace_Remphrey_2J

Since they are not dissolved in a solvent, solids have no concentration (molL-1). Liquids are not included because their effective concentrations do not change in a reaction. Hope this helps!

Grace_Remphrey_2J

If Kc subscript is very large, ~1000 or more, you will have mostly product species present at equilibrium. If Kc is very small, ~0.001 or less, you will have mostly reactant species present at equilibrium. If Kc subscript is in between 0.001 and 1000, you will have a significant concentration of bot...

Grace_Remphrey_2J

If the pressure in a system increases or the volume decreases, the equilibrium will shift to favor the side of the reaction that involves fewer moles of gas. In contrast, if the volume of a system increases or the pressure decreases, the production of additional moles of gas will be favored. Hope th...

Grace_Remphrey_2J

Since concentration has moles/liter as its units, you cannot have a negative value. Hope this helps!

Grace_Remphrey_2J

Bronsted acids donate H+ ions. Bronsted bases accept H+ ions. Lewis acids accept an electron pair. Lewis bases donate an electron pair. Think: bronsted=H+ AND Lewis=electrons. Hope this helps a bit!

Grace_Remphrey_2J

Organic molecules have carbon-hydrogen bonds. Inorganic molecules do not contain carbon-hydrogen bonds. While carbon can still appear in inorganic molecules, such as in carbon dioxide, it lacks the additional hydrogens that make it organic.

Grace_Remphrey_2J

The ions in the strong acid and base will completely dissociate and the solution will then be neutral.

Grace_Remphrey_2J

Both ions have their outermost electrons located on the same energy level, but they do not have the same ionic radius. The number of protons each species has in its nucleus varies. Potassium, which has an atomic number equal to 19, has 19 protons in its nucleus. Chlorine has 17. In the case of the p...

Grace_Remphrey_2J

Kb and pKb relate to bases. A large Kb value indicates the high level of dissociation of a strong base. A lower pKb value indicates a stronger base. Kb is the base dissociation constant, while pKb is the -log of the constant. These values account for hydroxide ion concentration. pH tells us the conc...

Grace_Remphrey_2J

An amphiprotic substance is one that donates hydrogen ions (protons) and also accepts them. Amphoteric means that they have reactions as both acids and bases.Hope this helps!

Grace_Remphrey_2J

To see if a ligand is a bidentate, tridentate, or hexadentate, you look to see how many lone pairs there are on the different atoms. The best way to see this is by drawing a lewis structure. For example, a bidentate would have two lone pairs, each on different atoms. Hope this helps!

Grace_Remphrey_2J

The angle 109.5 degrees is obtained when all four pairs of outer electrons repel each other equally. The bond angles in tetrahedral structures are less than 109.5° because of the stronger repulsion by their lone pairs of electrons.

Grace_Remphrey_2J

As explained in the posts above, the number of lone pairs on an atom that can be donated will affect the number of possible ligand binding sites.

Grace_Remphrey_2J

I think the rules for comparing polarizability will help with this and similar questions: The greater the number of electrons, the less control the nuclear charge has on charge distribution, and thus the increased polarizability of the atom. The greater the distance of electrons from nuclear charge,...

Grace_Remphrey_2J

The term "monodentate" refers to the ligand binding to the center through only one atom. Some examples of monodentate ligands are chloride ions, water, hydroxide ions, and ammonia. Bidentate ligands have two donor atoms which allow them to bind to a central metal atom or ion at two points....

Grace_Remphrey_2J

A coordination complex is the product of a Lewis acid-base reaction in which neutral molecules or anions (called ligands) bond to a central metal atom (or ion) by coordinate covalent bonds. Compounds that contain a coordination complex are called coordination compounds. Coordination compounds and co...

Grace_Remphrey_2J

Here's the set of rules I typically consult to determine that. Hope this helps! - If the salt's anion is the conjugate base of a strong acid, then its solution will be neutral. - If the salt's anion is the conjugate base of a weak acid, then its solution will be basic. - If the salt's cation is the ...

Grace_Remphrey_2J

Though context would suggest which is better to use, both formulas should produce the same result. There was probably an error in your calculation! Hope this helps.

Grace_Remphrey_2J

The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each of which is ten times ...

Grace_Remphrey_2J

Hi! Here are the general steps I follow when drawing lewis structures. First, determine the total number of valence electrons in a molecule. Second, draw a skeleton for the molecule which connects all atoms using only signal bonds. Third, arrange the remaining electrons to fill as many octets as pos...

Grace_Remphrey_2J

Sigma and pi bonds are chemical covalent bonds. Sigma and pi bonds are formed by the overlap of atomic orbitals. Sigma bonds are formed by end-to-end overlapping and Pi bonds are when the lobe of one atomic orbital overlaps another. Generally, sigma bonds are stronger than pi bonds because sigma bon...

Grace_Remphrey_2J

The seesaw shape maximizes the bond angles of the single lone pair and the other atoms in the molecule. The lone pair is in an equatorial position offering 120 and 90 degree bond angles, compared to only 90 degree bond angles if placed at the axial position. The T shaped structure minimizes the rema...

Grace_Remphrey_2J

In case you still needed an in-depth explanation as well as diagrams and images, here's a super helpful link that I used for studying!

https://study.com/academy/lesson/molecu ... mples.html

Grace_Remphrey_2J

Localized electrons exhibit normal behavior, a localized lone pair remains close to one atom, and a localized bond pair travels between two atoms. Resonance hybrids necessarily contain some "abnormal" electrons. In a delocalized pi bond, instead of sticking near one atom, it visits two ato...

Grace_Remphrey_2J

Sulfur has one more electron pair in its 3s subshell so it can undergo excitation and place the electron in another empty 3d orbital. Now sulfur has 6 unpaired electrons which means it can form 6 covalent bonds to give a total of 12 electrons around its valence shell. Hope this helps with understand...

Grace_Remphrey_2J

I'm more of a visual learner and this video does a great job explaining nomenclature. Even though we don't need to memorize a lot of these structures, I think it's helpful to understand the reasoning behind the names.
https://www.youtube.com/watch?v=peguZTUTgHI
Hope this helps!

Grace_Remphrey_2J

This link is super helpful for understanding and visualizing the periodic table trends. There are definitions as well as diagrams of periodic tables with arrows indicating the trends across the table. Hope this helps! https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Modules_and_Websites_(...

Grace_Remphrey_2J

Hydrogen bonds are weaker than covalent bonds because hydrogen bonds do not involve a formal electron exchange. The formal electron exchange strengthens the bond. In comparison, hydrogen bonds are weaker than covalent and ionic bonds but stronger than most Van der Waals forces.
Hope this helps!

Grace_Remphrey_2J

For shortcuts, I typically consider the following: Lewis Acids: cations, an atom/ion/molecule with an incomplete octet, molecules where the central atom can have more than 8 valence shell electrons, and molecules that have multiple bonds between atoms of different electronegativity. Lewis Bases: ani...

Grace_Remphrey_2J

Fluorine is a small atom with a small amount of space available in its 2p orbital. Because of this, any new electron trying to attach to fluorine experiences lower electron affinity from the electrons already living in the element's 2p orbital. Since chlorine's outermost orbital is a 3p orbital, the...

Grace_Remphrey_2J

Some of the larger questions gave partial credit for some of the multiple-choice answers. Since partial credit was given, we had decimals in our final scores!

Grace_Remphrey_2J

I think as long as you have the common ones memorized, you should be fine! So far, that has been what my TA and Lavelle have said. Just be sure to double-check with your TA just in case!

Grace_Remphrey_2J

The grades are posted on both CCLE and under grades and exams on MyUCLA!

Grace_Remphrey_2J

The grades are posted on both CCLE and under grades and exams on MyUCLA.

Grace_Remphrey_2J

Yes, they are exceptions to the octet rule. I would assume he may mention it in the future or your TA will mention that during discussion. Hope this helped!

Grace_Remphrey_2J

If you still need some help, I would recommend using the value of R that Dr. Lavelle includes on his formula sheet: 3.28984*10^15 Hz. Hope this helped!

Grace_Remphrey_2J

If the problem mentions the Lyman Series, there should be an n=1 somewhere in the equation. The Lyman series is in the ultraviolet while the Balmer series is in the visible and the Paschen, Brackett, Pfund, and Humphreys series are in the infrared.
Hope this helped!

Grace_Remphrey_2J

Hi! The Ml atomic number specifies the orientation in space of an orbital of given energy (n) and shape (l). This number divides the subshell into individual orbitals which hold the electrons; there are 2l+1 orbitals in each subshell. Thus the s subshell has only one orbital, the p subshell has thre...

Grace_Remphrey_2J

Hello! The answers above are super helpful, but I'm definitely a visual learner so I found a youtube video that explains super clearly! Hope this helps.

https://www.youtube.com/watch?v=M5q_YMN4CtY

Grace_Remphrey_2J

First, you need to write the net ionic equation. In a net ionic equation, you do not need to include the spectator ions. So, in this case, you do not need to include NO3 and Na. That means, in the end, the net ionic equation, will be Cu2+ + 2(OH)- yields Cu(OH)2. In part b), you need to find the gra...

Grace_Remphrey_2J

Just be sure to convert the wavelength given in nanometers to meters since the constant c, the speed of light, is in meters.

Grace_Remphrey_2J

Given most of the practice problems in the textbook for this course, I would say they will give us the actual yield! If not, they would give you enough info (theoretical and percent yield) to be able to find it.

Grace_Remphrey_2J

If you still need help, I find videos super helpful for things like these! This is a 3-minute video that is super easy to understand and really gives a detailed yet brief explanation! https://www.youtube.com/watch?v=jHbocq7n1Ew

Grace_Remphrey_2J

Like everyone said above, you should be ok for the first midterm. Once Dr. Lavelle goes over that topic in the lecture/your TA covers it, then it'll probably be expected for you to understand. Otherwise, I think just the well-known compounds are expected to be memorized! Good luck on the midterm!

Grace_Remphrey_2J

Electrons do not stay in excited states for very long - they soon return to their ground states, emitting a photon with the same energy as the one that was absorbed.

Grace_Remphrey_2J

Hi! I believe Dr. Lavelle asked us to use the traditional sig fig rules - in the final answer, use the same number of sig figs as the smallest given value in the original problem. Hope this helped

Grace_Remphrey_2J

Limiting reagent and limiting reactant are the same thing! I think it's easiest to always call it the limiting reactant so you know which side - reactants vs products - the limiting compound will be found (hopefully that makes sense). Just keep in mind that if you see "limiting reagent" it...

Grace_Remphrey_2J

I found that the modules are very helpful to do before each week's lectures. There are a series of objectives for each week that Dr. Lavelle sent us and you can look at them to see which video to do in preparation for the week!

Grace_Remphrey_2J

Hi! Here is my understanding of each of them and their difference: A quantum is a packet of energy that may or may not be light energy. A photon is a packet of light energy. The different is that a photon is light energy, while quanta may not be light energy. To sum up: a quantum may not be a photon...

Grace_Remphrey_2J

I would recommend using the units that the initial problem uses unless the problem states for you to change the units in your final answer. Hope this helps!

Grace_Remphrey_2J

Not a dumb question at all!! An angstrom is a unit of length that represents 10^-10 meter. Typically, it is used as a unit for wavelengths or distances between atoms. Hope that helped!

Grace_Remphrey_2J

Hello!

I would continue to write states of matter when balancing equations as I am pretty sure Dr. Lavelle uses the states of matter throughout his examples during lectures. Plus I'm sure it will be good practice for when we eventually take higher-level chemistry classes.

Hopefully that helps!

Grace_Remphrey_2J

I believe that the ± in "molar mass of 110±10 g/mol" means that the mean molar mass of the compound is 100g/mol, but can vary by one standard deviation (10g/mol). While completing the problem, use the mean value of molar mass.

Grace_Remphrey_2J

Hi! For part A, you need to convert the units of people to moles. You can do so by dividing the world's population (in people) by Avogadro's number (6.022*10^23). This will convert the population of the world to the units you would need for part B. Hoepfully that helps a bit!

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