CHEMISTRY COMMUNITY

Susan Chamling 1F

K stands for the equilibrium constant, although K also stands for Kelvin.

Susan Chamling 1F

For an open system energy and matter can be exchanged with the surroundings, while for a closed system only energy can be exchanged with the surroundings. Lastly, an isolated system is not able to exchanged anything with the surroundings.

Susan Chamling 1F

To get the reaction’s overall order, we just take the sum of the individual orders.

Susan Chamling 1F

In general we just think of endothermic reactions as ones which absorb energy, so if the question talks about an absorption of heat or other indication of energy absorption, the reaction is most likely endothermic. On the other hand, if the statement discusses a reaction which releases heat or energ...

Susan Chamling 1F

Oxidation number stand for how the electrons moved, whether that was a gain of electrons (negative oxidation number) or a loss of electrons (positive oxidation number).

Susan Chamling 1F

You're right, if delta V is zero that means no work is done.

Susan Chamling 1F

The Organic Chemistry Tutor has a video briefly covering the different types of systems titled "Open System, Closed System, and Isolated System - Thermodynamics and Physics". Hope the video helps!

Susan Chamling 1F

K should be positive since it's a proportionality constant.

Susan Chamling 1F

K is the equilibrium constant and the subscript just clarifies whether it's from concentrations or partial pressures.

Susan Chamling 1F

K is at equilbrium, so when Q < K it means it favors products while Q > K means it favors reactants.

Susan Chamling 1F

I don't think they can be used interchangeably since they provide different values. I'm fairly certain they are used separately for two different equations.

Susan Chamling 1F

I believe it's actually the opposite, so when work is being done by the system, it is negative since the system loses energy. In contrast, when work is being done on the system, it is positive since the system gains energy.

Susan Chamling 1F

G is not under standard conditions so the question may provide more information in this regard. On the other hand, Gº is under standard conditions (298 K and 1 atm), so we can typically assume these conditions.

Susan Chamling 1F

I think that with an isolated system changes can not be made from outside that system, but they can still be made within the system itself.

Susan Chamling 1F

I believe that K just stands for the Boltzmann constant which equals 1.380649×10^−23 J/K

Susan Chamling 1F

STP is 1 atm and 273.15 Kelvin (or 0* Celsius)

Susan Chamling 1F

I prefer staying with Kelvin mainly because most of the units involved in calculations include Kelvin rather than Celsius.

Susan Chamling 1F

State properties are dependent on the final and initial values, not on the path taken.

Susan Chamling 1F

Enzymes are a type of catalyst, which decreases a reaction's activation energy so that the reaction is able to occur at a faster rate.

Susan Chamling 1F

Hi, I believe they mean basically the same thing for the context of this class.

Susan Chamling 1F

A thermodynamically feasible fuel cell is when the reaction is spontaneous, implying that it has a negative ΔG.

Susan Chamling 1F

Yes, I believe that positive delta H values always indicate endothermic reactions, while negative delta H values always indicate exothermic reactions.

Susan Chamling 1F

State functions do not rely on a pathway but rather the final and initial states.

Susan Chamling 1F

I believe that the entropy of the gas decreases while the energy released causes the entropy of the surroundings to increase.

Susan Chamling 1F

Yes, you can apply the same rules!

Susan Chamling 1F

Hi, I believe the main difference on usage between the two is what units are needed in order to complete the problem. It may help to take note of the different units within the problem, and possibly breaking them down in a sense (such as with Joules) to remember what units are required.

Susan Chamling 1F

I don't think that there is a different between the two for this class.

Susan Chamling 1F

Entropy is basically a measure of the energy unable to participate in work, or a degree of disorder within the system.

Susan Chamling 1F

I believe the relationship between Kelvin and Celsius is linear in the sense that it is a constant of 273 that separates the two rather than an exponential difference.

Susan Chamling 1F

Yes, an increase in temperature means an increase in the energy within the system, which in turn increases the reaction rate.

Susan Chamling 1F

For the gas constant it's important to make sure the units cancel out correctly for the particular problem. But if you really need to, unit conversions are an option.

Susan Chamling 1F

I believe he usually sends us an email or two notifying us about how we performed on the exam and when the results could be expected to be released, so we're usually notified fairly well about the results.

Susan Chamling 1F

To convert from pKa to Ka, you just calculate 10^ (-pKa).

Susan Chamling 1F

I would suggest changing celsius to kelvin since it might be easier in terms of keeping track of units, but as long as you are mindful of which units are using in your calculations, I think it's really up to you.

Susan Chamling 1F

Yes, I believe that if it isn't specified, we assume it's standard temperature and pressure.

Susan Chamling 1F

Just for clarification, one of the first steps is to calculate Ka because we know both Kw and Kb, so we can solve for the third value in the formula (Ka = Kw / Kb). We then use the Ka to find the concentration in terms of the NH4Cl.

Susan Chamling 1F

Make sure you have all of your terms in the correct order and on the same side. If you move a term to the opposite side, remember to change the sign from positive to negative, or vice versa. Also don't forget about the denominator, 2a. When I use the quadratic formula I enter it in parts on my calcu...

Susan Chamling 1F

Hi! Maybe you are forgetting to move the -x and constant value in the quadratic equation to the same side as the x^2? This would cause your positives and negatives to be incorrectly flipped for these terms.

Susan Chamling 1F

Hi, I believe this applies to most monoprotic acids.

Susan Chamling 1F

To find the initial [B], you can add the equilibrium [B] with the x you used for the ICE table.

Susan Chamling 1F

I think from examples in lecture atm tends to be used more often

Susan Chamling 1F

The inverse K provided the K value of the reverse reaction, but can also be helpful when solving a question that requires combining or manipulating several reactions.

Susan Chamling 1F

P = Pressure, typically in atm or bars
V = Volume, Liters
n = # of moles
R = gas constant (which I believe is provided on the equations sheet)
T = temperature, Kelvin

Susan Chamling 1F

I believe that keeping your units in Mol/L is helpful to preventing calculation errors, so it is recommended.

Susan Chamling 1F

Hi! I believe the value will be provided for us on the equations and formulas sheet we’re allowed to use.

Susan Chamling 1F

We use Kc if the problem uses concentrations, but we use Kp if the problem provides partial pressures.

Susan Chamling 1F

Changing the pressure will not change the concentrations because we calculate K through quantity per volume, and an inert gas does not affect the equilibrium reaction.

Susan Chamling 1F

The RICE method is basically the same as the ICE table we can use.

Susan Chamling 1F

The gas constant R is universal and is provided to us on the equations sheet.

Susan Chamling 1F

Use Kelvin because it will cancel with the units for R.

Susan Chamling 1F

I believe bent and angular are synonymous, although for this class we tend to use the term bent more often.

Susan Chamling 1F

The tetrahedral has 4 bond angles of about 109.5* rather than 90* because, with three-dimensional space, we are not limited to a single plane. Since we are trying to give the atoms the highest amount of distance between one another, we would utilize the three-dimensional space so that their placemen...

Susan Chamling 1F

The bond angles should be a bit less than 90* due to the lone pairs.

Susan Chamling 1F

Hi! The wedge indicates the bond coming towards you while the dashed line represents the bond extending further away from your perspective. They’re both supposed to help us visualize the orientation of the bonds in three dimensional space

Susan Chamling 1F

Hi! They aren’t the same shape; seesaw has 5 regions of electron density, one of which is a lone pair (AX4E), whole trigonal pyramidal has 4 regions of electron density, one of which is a lone pair (AX3E).

Susan Chamling 1F

Yes! Even when a molecule has polar bonds within it, those individual interactions do not determine the overall polarity of the molecule on their own. It depends on whether the dipoles within the molecule have something to cancel them out, which results in a nonpolar molecule.

Susan Chamling 1F

CHI3 has the higher melting point because Iodine is a larger atom than Fluorine, which has the smaller atomic radius. Since it is larger, Iodine has higher LDFs and polarizability, and since more energy to break interactions means a higher temperature, CHI3 will have the higher melting point.

Susan Chamling 1F

Polar molecules are when the bonded atoms have an electro negativity difference and asymmetry is observed where dipole forces are not canceled out. On the other hand nonpolar molecules are when electrons are shared equally among the atoms of the molecule or when the dipole forces cancel one another ...

Susan Chamling 1F

Yes, both are considered angular or bent. The general shapes of the structure are described, but the angles depend on what atoms are involved and if lone pairs are present. Because lone pairs are present in this case, the bond angles between the other regions will be a bit less because the lone pair...

Susan Chamling 1F

The shape is bent because in addition to the two atoms that the central atom is bound to, there are also two lone pairs which will had a repelling effect and contribute to the total of four electron density regions. With four regions trying to have the greatest amount of distance between them, the b...

Susan Chamling 1F

Hi! I sometimes have difficulty drawing Lewis Structures too, but what I do to prevent errors is that I always check I have the correct number of electrons that includes the valence electrons of the atoms as well as the charge if applicable. Another thing that helps is noticing how the formula is wr...

Susan Chamling 1F

Dipole arrows will point towards the end which has higher electronegativity. For that question we had to consider how the different dipole forces would create a net dipole force, and in which direction.

Susan Chamling 1F

Pi bonds are probably stronger because they are found in double and triple bonds while sigma bonds are found in any covalent bond.

Susan Chamling 1F

It helps to take into account the 3D shape of the molecule rather than just the Lewis structure, as the Lewis structure may lead us to believe it is nonpolar when it is actually polar, and vice versa. Sometimes I will look at the symmetry of the forces acting on the molecule, because if it is symmet...

Susan Chamling 1F

I agree with previous replies that having a chart for reference is very helpful. I've found that with time and having completed more exercises, it has become easier to recall what types of shape and angle sizes would be associated with the molecule. Drawing out the molecule can also help.

Susan Chamling 1F

I think one method of figuring out if a molecule is polar or not, even when it has dipole forces, is to look at the molecule's structure and determine whether it has symmetry or not. If it has symmetry, in most cases it will not be polar, even when it has dipole forces, because they will cancel out.

Susan Chamling 1F

Electronegativity, Atomic radius, Bond type (Triple, Double, or Single), among other factors will affect bond length and in turn, bond strength. Shorter bonds tend to be stronger than longer bonds, and molecules with stronger bonds typically have a higher boiling point as a result.

Susan Chamling 1F

The general periodic trend for electronegativity is that it increases from left to right for periods and down to up for groups.

Susan Chamling 1F

You typically start by counting the number of valence electrons each atom would normally have, and distributing them accordingly. The central atom tends to be the one with the lowest ionization energy, which is often a Carbon atom. Once you have finished drawing out your bonds and filling out the oc...

Susan Chamling 1F

This link might be helpful as well: www.khanacademy.org/science/physics/qua ... f-the-atom

Susan Chamling 1F

I believe double bonds are stronger than single bonds because the shorter distance between the atoms makes the double bond stronger than the single bond. This might be due to the idea that the pull of the nucleus is stronger the closer the object is to the nucleus.

Susan Chamling 1F

Hydrogen bonding is a type of intermolecular force and dipole-dipole interaction, but is not a coordinate covalent bond.

Susan Chamling 1F

Hello! Ionization energy is the energy needed to remove an electron from an atom (gas phase). The further the electron is from the nucleus, the easier it is to remove. The trend for ionization energy increases as you move right across a period and up a group. On the other hand, Electron affinity is ...

Susan Chamling 1F

I believe it is a conceptual principle that was mentioned in the Quantum Numbers and Atomic Orbitals Lecture, in which it was stated that the Principle Quantum Number (n) determines energy and size

Susan Chamling 1F

I had difficulty determining the plausibility of the structure as well, but I mainly looked at how the charges were dispersed throughout the structure (evenly or not), and if an electronegative atom was holding the charge (I believe my TA mentioned that the more electronegative the atom, the better ...

Susan Chamling 1F

Hund's Rule states that due to electron repulsion electrons in the same subshell, l, will occupy different orbitals with parallel spins and are unpaired. Paired electrons have opposite spins and are in the same orbital.

Susan Chamling 1F

It was mentioned in lecture that an orbital is a math function with three quantum numbers (n, l, m. I think orbitals are 3D representations of the space where an electron can be found rather than indicators of an electron's specific position, especially considering the movement of electrons.

Susan Chamling 1F

E = hv is only used for finding the energy of photons/light, while E = pc can be used for particles with mass.

Susan Chamling 1F

Intensity is proportional to amplitude so that when one increases, so will the other.

Susan Chamling 1F

Hello! I think that, due to the periodic table being arranged in part by the number of protons the element has, similar characteristics can be noted within a certain grouping of elements. This further plays out in the trends that can be seen in the periodic table, such as the trend of electronegativ...

Susan Chamling 1F

Pure water is neutral and is neither acidic or basic. However, depending on the question and context provided, water can act as an acid or base.

Susan Chamling 1F

There can only be whole numbers in an empirical formula, as it is the simplest positive integer ratio of atoms in a compound.

Susan Chamling 1F

Yes, you would want to multiply your coefficients by the same number in order to get whole ratios. As long as you preserve the ratio, multiplying the coefficients is fine.

Susan Chamling 1F

There are multiple methods to measuring a liquid's viscosity, such as measuring the rate at which it flows through a narrow tube. The more viscous the liquid the slower it will flow.

Susan Chamling 1F

The 10x portion does not count as part of your sig figs, as your sig figs should be focused on nonzero values or zeros that are considered significant due to their placement.

Susan Chamling 1F

I think we should try to memorize the order and wavelengths of electromagnetic radiation. One of the TAs covered a question in which we had to know the wavelength, as it wasn't provided

Susan Chamling 1F

I think it would definitely be helpful to understand these concepts, as we will probably have to identify their meanings and different applications in future chem classes. Furthermore, these terms are often used in lab settings, so it would be better to understand what it means when your data is acc...

Susan Chamling 1F

Avogadro's number is the number of objects in one mole of a substance. You can use it to describe the number of atoms, molecules, etc there are in a mole of whatever substance because it is just a number.

Susan Chamling 1F

Black Body refers to a material that could, in theory, absorb all wavelengths of light, which renders it invisible due to no light reflecting off of its surface, which is required for us to see an object.

Susan Chamling 1F

Hi! As previous replies have states, we don't need to memorize a bunch of compounds for now. However, if you want to start practicing how to name compounds, I think there is a section of the textbook fundamentals that covered the topic. I believe it was 1D, but I'm not entirely certain.

Susan Chamling 1F

For the acronym mentioned a couple comments above, the Great Master Knight Did Commit Murder Under No Pretenses, it goes G - giga 10^9 M - mega 10^6 K - kilo 10^3 D - deci 10^-1 C - centi 10^-2 M - milli 10^-3 u - micro 10^-6 n - nano 10^-9 p -pico 10^-12 In this acronym Giga is the prefix with the ...

Susan Chamling 1F

You're correct, the brighter light was caused by an increase in photons. For the experiment they realized that increasing the intensity of the light did not change the energy of the photons, because it is a change in wavelength/frequency that causes that change.

Susan Chamling 1F

Protons and neutrons have a similar mass, which is about 1 amu, while electrons have what is considered negligible mass.

Susan Chamling 1F

The reactant which will run out of moles first in relation to the molar ratios expressed in the chemical equation will be the limiting reactant. For example, if you have 5 moles of Oxygen and 20 moles of Hydrogen, but the molar ratio given by the balanced chemical reaction states that the ratio betw...

Susan Chamling 1F

In order to determine the formula for nitric acid you can refer to what was suggested in the textbook, -ate ions go with -ic acids, while -ite ions go with -ous acids". We know that in most cases acids typically begin with H, and that because its nitric acid, the hydrogen is paired with nitrate...

Susan Chamling 1F

I would recommend maintaining the same units throughout your calculations so that it is less likely that your conversions are off. Before starting to solve the problem, converting the units into Liters would probably be better.

Susan Chamling 1F

Non-zero digits are always significant. On the other hand, zeros are only significant if they are between two non-zero digits (Ex: 3004 has four sig figs) or if they are trailing a digit with a decimal (Ex:30.00 has four sig figs). I believe there is a module reviewing sig figs on the chemistry webs...

Susan Chamling 1F

This question also confused me initially, but I decided to first convert the grams of CO2 and grams of H2O into moles because I knew that is usually one of the steps in solving for the empirical formula. After doing so I realized that it was critical to the problem that we know what mass of oxygen w...

Susan Chamling 1F

I also assumed a 1:1 ratio for the 2-butanone: 3-methyl 3-hexanol. The value provided in my version of the question was 0.30 mL of 2-butanone, which I then converted to grams and then moles. I calculated 0.0034 moles of 2-butanone, so therefore there was 0.0034 moles of 3-methyl 3-hexanol. Next I co...

Susan Chamling 1F

I think a part of balancing equations is intuition and trial and error, but in my own experience I tend to first look at all of the elements involved and then see which one is the most limited in the sense that it appears in the equation a lesser amount of instances than the other elements. I then w...

Search found 101 matches