CHEMISTRY COMMUNITY

Polo Morales 3C

We would use the rate of the slowest reaction, since it would be the one that limits the speed of the overall reaction. Hope this helps!

Polo Morales 3C

Catalysts decrease the activation energy in both directions. Hope this helps!

Polo Morales 3C

Free energy of activation has more to do with the spontaneity whereas the activation energy is the minimum amount of added energy needed to make the reaction proceed. Hope this helps!

Polo Morales 3C

Catalysts basically work by lowering the activation energy of a reaction. They are not used up and they increase the rates of both the reverse and the forward reactions. Hope this helps!

Polo Morales 3C

Thermodynamics seems to have focus more on spontaneity of a forward vs reverse reaction, whereas kinetics focuses on rates. This is just one difference though. Hope this helps!

Polo Morales 3C

During the phase change at 100C, the heat that is being added is going into breaking bonds and changing the liquid into a gas. Therefore, the H2O is not actually getting hotter, although heat is being added. Hope this helps!

Polo Morales 3C

Pascals are a unit of pressure, just like Bar, Atm, etc. 1 atm = 101325 pascals. 1000 Pa = 1kPa. Hope this helps!

Polo Morales 3C

When deltaH is negative, it means that the change in energy of the system is negative, meaning it lost energy. By that same logic, if deltaH is positive, the system has gained energy. Hope this helps!

Polo Morales 3C

At the boiling point, it takes a lot of energy to change H2O from liquid to gas, even without changing its temperature. In other words, a lot of energy must be gained by the H2O at 100C in order to go from liquid to gas. Therefore, the gas H2O molecules at 100C have a lot more energy and can thus ca...

Polo Morales 3C

Bomb calorimeters are incredibly well insulated, so they may be considered isolated systems. They also hold a constant volume, thought not always a constant pressure. Hope this helps!

Polo Morales 3C

Yes. It would be helpful to look at what units you're working with and which ones you need. Hope this helps!

Polo Morales 3C

The equation is U=q+w. Sometimes, however, the value of w is negative. However, this would just be adding a negative value. Therefore, the equation holds true. Hope this helps!

Polo Morales 3C

Isochoric means that the volume is being held constant. Therefore, the system is not losing energy to expansion, and thus no work is done. Hope this helps!

Polo Morales 3C

Hello! To keep it concise, Enthalpy deals with energy,temp,heat, etc. Entropy deals with disorder. Hope this helps!

Polo Morales 3C

Isothermal means that the temperature stays constant. Hope this helps!

Polo Morales 3C

You can change the energy of a system by doing work to it, altering the temperature, adding reactants or products, etc. Hope this helps!

Polo Morales 3C

Delta U = 0 when w=-q. Since the equation is deltaU = w+q. Hope this helps!

Polo Morales 3C

A closed system cannot lose matter to its surroundings, but it may transfer heat and/or energy. Hope this helps!

Polo Morales 3C

Negative work means that the system is losing energy to its environment. It is doing work to its surroundings. Positive work means work is being done to it by the surroundings. Hope this helps!

Polo Morales 3C

Negative work means that the system is losing energy to its environment. It is doing work to its surroundings. Positive work means work is being done to it by the surroundings. Hope this helps!

Polo Morales 3C

An isolated system cannot interact with the environment at all. A closed system might exchange heat or energy with its environment. Hope this helps!

Polo Morales 3C

You would want to pay close attention to the units of the values that you're given. It might help to write out the units and figure out what would cancel and what you're missing. Hope this helps!

Polo Morales 3C

At a constant pressure, some energy is lost to work being done to surrounding molecules that are pushed out of the way. Therefore, it takes more energy to increase temperature by the same amount. Hope this helps!

Polo Morales 3C

In a bomb calorimeter, you would use q=Cn(delta)T, where C is a specific constant for constant volume. Hope this helps!

Polo Morales 3C

You would want to subtract final-inital for the enthalpy. If something was going from gas at 300 C to a solid at 25 C, you would want to consider their enthalpies at each given temperature and account for energy required for phase changes. Hope this helps!

Polo Morales 3C

In order to know which R constant to use, you would need to know which units you are dealing with, and what the units should be for your missing variable. I would recommend writing out all of the units of your known values and working from there. Hope this helps!

Polo Morales 3C

By adding an inert gas, you are increasing pressure due to the fact that there are more total moles of gas in the same volume. Since it's an inert gas and not a reactant nor a product, there is no shift in the reaction toward either side. Hope this helps!

Polo Morales 3C

In simplified terms, enthalpy refers to the total energy of a system whereas heat is the energy being transferred.

Polo Morales 3C

Breaking bonds requires energy and is therefore considered and endothermic process. It takes energy to break stable bonds. Hope this helps!

Polo Morales 3C

We can say this because one substance is gaining the heat that was lost by another substance. Hope this helps!

Polo Morales 3C

I'd suggest breaking down the word and comparing the prefixes. We know that "exo" usually relates to external, exits, etc. We also know that "endo" relates to entering. Another way would be to connect "exo" to "exit", and "endo" to "enter"....

Polo Morales 3C

In thermodynamic, "q" represents heat transfer. It can be used to calculate work in some instances. Hope this helps!

Polo Morales 3C

Unless otherwise specified, it would be safe to assume that room temperature is equivalent to 25 degrees Celsius. Hope this helps!

Polo Morales 3C

It would be better to determine whether a reaction is endothermic or exothermic by identifying whether energy is being added or being released. Hope this helps!

Polo Morales 3C

Melting is an endothermic process. Remember that energy is required to break the intermolecular attractions of liquid molecules. Therefore, the liquid is taking up energy from its environment as it becomes a gas. Hope this helps!

Polo Morales 3C

Melting is an endothermic process. Remember that energy is required to break the intermolecular attractions of liquid molecules. Therefore, the liquid is taking up energy from its environment as it becomes a gas. Hope this helps!

Polo Morales 3C

Consider whether the reactants are gaining or losing energy as the reaction advances. If the reactants absorb heat from their surroundings (thereby cooling them down), the reaction is said to be endothermic. If the reactants release heat into the environment, the reaction is said to be exothermic. H...

Polo Morales 3C

Only gases and aqueous solutions should be included in an ICE table. Solids do not have concentrations. Liquids are in such excess that their "concentrations" do not change significantly. Hope this helps!

Polo Morales 3C

Monoprotic means that it can only release one proton (H+). If you break down the word into "mono" =one, "protic"= dealing with protons, it may be easier to remember this.

Polo Morales 3C

Yes, Ka is the equilibrium constant for a reaction that deals with increase in [H3O+] ions, and therefore helps you determine pH. Kb is the equilibrium constant for a reaction that increases concentration of [OH-], and can thus help you find pOH. Hope this helps!

Polo Morales 3C

Hello! K is basically the term that is used for any equilibrium constant. Kc is specifically the equilibrium constant dealing with molar concentrations. Hope this helps!

Polo Morales 3C

They are not the same. They do, however, have equal values at equilibrium. K=[P]/[R] at equilibrium only. On the other hand, Q=[P]/[R] at any point in the reaction. Therefore, the two values are only equal once a reaction has reached equilibrium.

Polo Morales 3C

Hi! It doesn't make a huge difference which one you use since they are the same values. That being said, it would be best to make sure that you use whichever one you make fewer typing mistakes with, so that you don't accidentally mistype a value. Otherwise, it does not make much of a difference. Hop...

Polo Morales 3C

It wouldn't matter too much which one you call -X and which one you call +X, as long as you use them consistently. When you go to solve for X, the +/- sign will be adjusted to show you which concentrations increased and which ones decreased as the reaction advanced. That being said, the math is easi...

Polo Morales 3C

Q is a ratio of products to reactants at any given time. Q=[P]/[R] at any point in the reaction. K=[P]/[R] at equilibrium. Therefore, they are related in that Q=K at equilibrium.

Polo Morales 3C

Kw is the equilibrium constant for H2O ---> H3O+ + OH-. Kw = [H3O+][OH-] since the H2O concentration changes negligibly. At 25 C, Kw = 10^-14. This can be used to determine Ka or Kb in some problems.

Polo Morales 3C

If Q<K, it means that the reaction has not yet reached equilibrium, and more products have yet to be created. Remember that Q=K at equilibrium and Q = [P]/[R] at any given time. Hope this helps!

Polo Morales 3C

A monoprotic acid is one that can only release one H+. If you ever forget, break down the word into "mono" = one and see that it contains the root "prot" as in proton. Hope this helps!

Polo Morales 3C

Q is the reaction quotient. It is the quotient of [P]/[R] at any given time, and would thus change as a reaction is taking place. K, on the other hand, is the equilibrium constant and is the quotient of [P]/[R] at equilibrium. K does not change as a reaction takes place, but rather Q gets closer to ...

Polo Morales 3C

Since pH = -log[H3O+], a higher pH indicates a lower [H3O+] concentration. Weak bases do not fully dissociate in water, and would thus create fewer H3O+ ions in identical conditions. This would lead to a lower overall [H3O+] concentration, and thus a higher pH. Hope this helps!

Polo Morales 3C

An ion is classified as a spectator ion if it does not react with the surrounding water molecules to form an acid or a base. An example of this would be Cl-. HCl fully dissociates in water due to the weak bond between H and Cl (strong acid). Cl- would thus be more stable as a spectator ion than in a...

Polo Morales 3C

Given that it can be classified as either, it is highly unlikely that we will get a problem on an assessment where we would have to classify as one or the other ourselves. In the event that it did come up in a question, it would likely be specified whether we should treat it as a strong or a weak ac...

Polo Morales 3C

Yes, since we are calculating pH using a known equilibrium constant, the calculated pH will change if the constant changes. As explained in the lecture, temperature does, in fact, affect the equilibrium constant, and therefore the pH. Hope this helps!

Polo Morales 3C

If it is in an aqueous solution then it will donate the proton (H+) to H2O and create a hydronium cation (H3O+). This will thereby lower the pH. Hope this helps!

Polo Morales 3C

A conjugate acid is what is formed when a base accepts a proton (ex: H2O becoming H3O+). A conjugate base is what is formed when an acid donates a proton (ex: CH3COOH becoming CH3COO-). Hope this helps!

Polo Morales 3C

Since there is some overlap between Lewis and Bronsted acids (all Bronsted are Lewis, but not all Lewis are Bronsted), it would probably be specified only if it mattered. In other words, if it didn't specify the type of acid, then it would most likely be both (or it wouldn't matter). Hope this helps!

Polo Morales 3C

When it reacts with water, H2CO3 is formed. From there, the H2CO3 in water breaks down into HCO3- and H3O+, thereby lowering the pH of the rain and making it more acidic. Hope this helps!

Polo Morales 3C

The statement that orbitals must be conserved refers to the fact that if you begin with 1 S orbital and 3 P orbitals, they would hybridize and you would end with 4 SP3 orbitals. Hope this helps!

Polo Morales 3C

The 2 just specifies that it is in Period 2. Hope this helps!

Polo Morales 3C

Not necessarily. It simply means that there are 3 regions of electron density, which could be bonds or lone pairs. Hope this helps!

Polo Morales 3C

For AXE notation, the X should only count the number of atoms that are attached to the central atom, without considering double/triple bonds. In other words, the Xe has 3 Oxygen atoms attached, and thus its AXE notation would be AX3E rather than AX6E.

Polo Morales 3C

That is correct. You have to take into account not only bonds, but regions of electron density in general. Lone pairs happen to be regions of e- density that exert greater repulsion than bonds, and thus they have a different effect on bond angles.

Polo Morales 3C

I think you misinterpreted what he meant when he said "due to the lone pairs". You are correct in thinking that without lone pairs, the shape would be linear and the angle would be 180. However, the 109.5 comes from the hypothetical situation where there were bonds in place of the lone pai...

Polo Morales 3C

It is bent due to the two lone pairs left on the oxygen. These lone pairs exert a great repulsive force and thus create a bent shape in the molecule of H2O.

Polo Morales 3C

The sigma bond will have been the first one formed and will involve end-to-end bonding of orbitals. The pi bonds will form subsequently, and are side-by-side bonds that do not allow for rotation. Hope this helps!

Polo Morales 3C

Atoms of levels 3 and onward may expand their octet.

Polo Morales 3C

You first need to count the regions of electron density (lone pairs + atoms attached). From this, one can keep in mind that 2 regions -> sp , 3 -> sp2, 4 -> sp3, etc. One must also make sure to conserve the total amount of orbitals.

Polo Morales 3C

Yes, pi bonds form only after sigma bonds are formed between two atoms. The second bond in a double bond and third in a triple bond are pi bonds, while the first bond is a sigma bond.

Polo Morales 3C

Ka and pKa have an inverse relationship. A low pKa indicates a strong acid, while a low Ka indicates a weaker acid. Hope this helps!

Polo Morales 3C

The final will be cumulative. That being said, cumulative finals typically focus a bit more on material that has not been on previous tests. I cannot assure you that this is how our final will be, but I would focus my studying a bit more on that. Hope this helps!

Polo Morales 3C

Personally, I'd redo old homework problems and do the recommended textbook problems. I'd also recommend re-watching old lectures to refresh your memory, and watching YouTube videos on things that still don't quite make sense. Finally, I'd focus a bit more on newer and recent material that we haven't...

Polo Morales 3C

It's 140 points, out of 400 total for the class. This means it's worth 35% of our grade in the class.

Polo Morales 3C

Personally, I find youtube videos very helpful. It might also help to form study groups and help each other understand conceptual things. Hope this helps!

Polo Morales 3C

They are counted at the end of each week.

Polo Morales 3C

Remember all of the times where you've had more difficult tasks than this and you've excelled. Trust yourself, you have accomplished more difficult things. Take some time to relax beforehand and treat it as what it is. In the end, it is just a test. Hope this helps!

Polo Morales 3C

VSEPR is an acronym for Valence Shell Electron Pair Repulsion. This theory allows us to predict the molecular shape based on the fact that valence electrons in adjacently bonded atoms repel each other.

Polo Morales 3C

Single bonds between two atoms are sigma bonds, additional bonds are pi bonds.

Polo Morales 3C

A simple way to determine wether a bond is a sigma or a pi bond is that if the if there is a single bond between two atoms it is a sigma bond. Any additional bonds between the two atoms will be pi bonds. Hope this helps!

Polo Morales 3C

Hello! As for everything, "intra" means within and "inter" means between one and another. INTERmolecular means between one molecule and another. INTRAmolecular means within an atom. Hope this helps!

Polo Morales 3C

Dipole-dipole forces are permanently present as they occur between two polar molecules that have permanent dipole moments since electrons are shared unevenly. London dispersion forces are temporary dipole moments present due to the movement of electrons within a molecule they are present in all inte...

Polo Morales 3C

A dipole-dipole force happens between two partially charged molecules of opposite partial charges. An ion-dipole attraction happens between a polar molecule and an ion, which has a formal charge. Hope this helps!

Polo Morales 3C

Al of the quantum concepts that appeared after Friday of Week 3, and therefore did not appear on midterm 1, are available to appear on midterm 2.

Polo Morales 3C

To determine electronegativity you should simply look at the period table. Electronegativity increases as you go up and to the right on the periodic table. Hope this helps!

Polo Morales 3C

Generally, it can be said that covalent bonds are stronger. However, this is just a general assertion and not a set law. Hope this helps!

Polo Morales 3C

No. Ionic bonds are bonds between a metal and a nonmetal. Covalent bonds are between two nonmetals. It is not possible for one to become the other. Hope this helps!

Polo Morales 3C

The main difference would be that dipole-dipole interactions are much stronger intermolecular interactions that dispersion forces since they deal with partial negative and partial positive charges on polar molecules.

Polo Morales 3C

When a molecule is polar it essentially means that the electrons in the covalent bonds are not evenly distributed. This uneven sharing of electrons lead to partially positively charged regions of the molecule and partially negatively charged areas of it as well. Hope this helps!

Polo Morales 3C

Hi! It can be easy to confuse these topics. However, these are two completely different concepts. Ground vs excited states refer to different states of energy of individual electrons in an atom. Covalent and Ionic are adjectives thats that describe two different types of bonds. In covalent bonding, ...

Polo Morales 3C

Having a (-1) as an exponent is a different way of putting the base in the denominator. (Ex: 2^(-1) is the same and 1/2) Likewise, a unit with a (-1) as an exponent is the same as "per unit". Ex: m*s^-1 = m/s = meters per second. Hope this helps!

Polo Morales 3C

I believe that you'd probably only need to worry about this if the question says something along the lines of "Express answer in grams", etc. Also, I'd probably try to use whatever units we were provided with. e.g if the question gave a mass in grams, then the answer should also probable b...

Polo Morales 3C

Yes, if you plugged that into a calculator it would give you the correct answer. You could also simply add (+2) to the exponent of the base 10 of the scientific notation. This would have the same effect as multiplying by 100. Hope this helps!

Polo Morales 3C

I believe that it shouldn't be a big deal whether you use m/s or m*s^(-1), since they both mean the same thing mathematically and physically. Hope this helps!

Polo Morales 3C

I had the same doubt as yourself, since I had also heard some people say that some Midterm material was to be covered in Week 4, but Professor Lavelle's email confirmed that the Midterm will only contain content up to Week 3.

Polo Morales 3C

Momentum and force are not the same thing. Momentum is a concept that describes mass in motion, and is useful to calculate what happens after collisions, among other things. The greater the mass of an object in motion, the more momentum it carries and thus if it were to collide with something it wou...

Polo Morales 3C

We're not absolutely required to memorize it, since it's provided on equation sheets. However, it can only help to have it memorized. Hope this helps!

Polo Morales 3C

Elements in the same group have the same number of valence electrons, and thus tend to have similar properties.

Polo Morales 3C

Hydrogen is located on the far left side of the periodic table, where elements have relatively low electronegative values. However, hydrogen is the exception in the sense that it has a medium electronegative value, much higher than most of the elements in its column. Hope this helps!

Polo Morales 3C

if your calculator has an "answer (ans)" function, then I'd recommend using that and going step by step if you're really concerned about being precise. Otherwise, keep in mid that the exam is multiple choice and 4-5 decimal places are more than enough. Hope this helps!

Polo Morales 3C

If any responses seem too complicated then I will share an analogy that a high school chem teacher taught us when we first started Chemistry.Think of a mole in the same way you think of a dozen. One dozen of donuts is 12 donuts, because the word "dozen" is simply an indicator of a set quan...

Polo Morales 3C

Theoretical yield is the value that you end up with when you finish all of your calculations. That being said, on-paper calculations assume ideal conditions and don't account for real-world variables such as side reactions, impurities, etc. Your actual yield is the value that you determine as the qu...

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