CHEMISTRY COMMUNITY

Lauren Stack 1C

In a multi-step reaction, there are intermediates. They are something that forms in an earlier step, but are ultimately used as a reactant in a subsequent step. Thus, they are cancelled out in the net/final equation. They are essential to the mechanism of the reaction, but do not end up in the final...

Lauren Stack 1C

Catalysts are no consumed as they appear as an input, but also an output of a reaction. Thus, the amount of catalyst is not decreased by lowering the activation energy.

Lauren Stack 1C

In order to consider this reaction, you have to know that the slow step is the rate determining step. If you make the other steps faster, it still does not change the fact that the slow step is still at the same (slow) rate. As the slow step is the sole factor you consider when determining overall r...

Lauren Stack 1C

Homogeneous catalysts are the same state as the reactants, while heterogeneous catalysts are in a different state. With heterogeneous catalysts, the reactants sit on the surface of the catalyst.

Lauren Stack 1C

Absorption is different from adsorption. In adsorption, the reactants sit on the surface of the catalyst. So thus, I'd believe you'd visualize it as liquid reactants in a pool on top of a solid or gas surrounding the surface of the solid.

Lauren Stack 1C

A was described in class as the frequency factor or pre-exponential factor (includes # of collisions with correct orientation)

Lauren Stack 1C

I don't think he will actually ask us to derive something on the test. Although, knowing how to derive the equations is listed on the outline for the Kinetics section, so I would be familiar enough with them to manipulate the equations.

Lauren Stack 1C

On the Kinetics outline Lavelle lists: Know how to derive the differential and integrated rate laws for zero, 1st and 2nd order reactions Use the Arrhenius equation and rate constants measured at different temperatures to determine activation energy. Use the Arrhenius equation and the activation ene...

Lauren Stack 1C

To be stable, the reaction will have a negative deltaG value, so it is technically spontaneous. Although, there is a very large activation energy which prevents it from proceeding. Thus, it is kinetically trapped in reactant form.

Lauren Stack 1C

An instantaneous rate provides an infinite amount of time points that you can measure the rate. It is more accurate than taking the average between two points because you are looking at the exact rate in time, rather than an approximation between two points where the rate in between the two points c...

Lauren Stack 1C

A negative E values means that the reaction is not spontaneous, while if the E value is positive, then the reaction is spontaneous. You can see this connection through the relation of delta G= -nFE.

Lauren Stack 1C

∆G° is for standard conditions, which ∆G is for non-standard conditions. Therefore, the principle still remains that a negative deltaG would mean that the reaction is spontaneous.

Lauren Stack 1C

Tabled values are typically given in terms of reduction. In order to calculate the entire redox reaction value, you must flip the sign on the half reaction that is showing oxidation.

Lauren Stack 1C

n stands for the number of electrons transferred. You find this value by balancing the two half reactions in a redox situation. Once you balance them, you look at the electron transfer and use that value as n.

Lauren Stack 1C

A salt bridge allows ion transfer to occur. This allows the electrons to keep flowing and maintain a neutral charge. When you don't have a salt bridge, there is another form of ion transfer, such as through a porous disk.

Lauren Stack 1C

A half reaction shows either the oxidation or reduction of elements, and thus shows the relative transfer of electrons. It is useful because it allows us to balance the electrons in a redox reaction.

Lauren Stack 1C

The cathode is where the reduction reaction takes place in a salt bridge circuit. It is usually designated on the right side of the diagram. Conversely, the anode is where the oxidation occurs and is usually found on the left side of the diagram.

Lauren Stack 1C

A half reaction is used when trying to balance a redox reaction for our purposes. One of the half reaction shows the oxidation, while the other demonstrates the reduction. This equations allow you to keep track of the electrons being transferred in order to balance the equation properly.

Lauren Stack 1C

Balancing a redox reaction is a bit different than just comparing normal products and reactants. Here you must keep track of the electrons being transferred. You must balance the two half reactions (one for oxidation, one for reduction) in terms of the electrons as well as the other elements. Thus, ...

Lauren Stack 1C

Rusting itself is a redox reaction, where the iron is oxidized, losing electrons, and oxygen is reduced, gaining electrons. Rust's chemical formula is Fe2O3.

Lauren Stack 1C

lnQ is used when the system is not at equilibrium, while lnK is found at equilibrium. If you think about it, Q = K at equilibrium, so you can see the connection.

Lauren Stack 1C

Gibbs Free Energy is the amount of thermodynamic potential energy available to do work. The equation for it is usually used to determine the energetics of a system, such as if it is spontaneous (Negative deltaG) or not.

Lauren Stack 1C

The degree symbol is to show that the value was found under standard conditions, while the deltaG without the degree symbol will be total change in Gibbs Free Energy, and not restricted to solely standard conditions.

Lauren Stack 1C

Here you must consider the equation for Gibbs Free Energy, which is deltaG = deltaH - TdeltaS. A negative deltaG denotes a spontaneous reaction, while a negative deltaH denotes an exothermic reaction. You can see that in order to make deltaG negative, having a negative deltaH can help, as then the d...

Lauren Stack 1C

The class is point based, so tests are not curved by themselves. The class as a whole is curved or adjusted. In order to pass the class, you must receive half of the available points.

Lauren Stack 1C

I believe knowing these terms would be important background to know regarding various changes to a system through temperature, pressure, etc
Here is a link to a discussion with these terms defined and a few more: viewtopic.php?f=128&t=9661

Lauren Stack 1C

I believe that favorable and spontaneous are used interchangeably. Both mean that a reaction will proceed without an input of energy.

Lauren Stack 1C

Gibbs free energy is the energy in a chemical reaction that can be used to do work. Since enthalpy is the total heat content of a system, you would subtract entropy, which is the unavailable energy that is used for work, with temperature. This gives us the energy that can be used for work. So to cl...

Lauren Stack 1C

1 L*atm is equal to 101.325 J, which allows you to compare various amounts of work.

Lauren Stack 1C

I believe it was "When you're under DePressed, you want to watch TV and get HUGS."
Which comes out at PD TV HUGS (Pressure, density, temperature, volume, enthalpy, internal energy, free energy, and entropy)

Lauren Stack 1C

Heat is defined to be the transfer of energy due to a temperature difference. Enthalpy was defined to be the heat released or absorbed in chemical reactions and physical changes at a constant pressure.

Lauren Stack 1C

Work can be positive or negative, depending on how you look at it. If you compress a piston, there is positive work being done on the system, as there was an input of work to move the piston. Conversely, the work done by the system is negative.

Lauren Stack 1C

The main difference between a closed system and an isolated system revolves around energy. Both closed and isolated systems do not exchange matter (reactants/products) with the surroundings, but closed systems exchange energy with the outside world. Isolated systems do not exchange mass OR energy. T...

Lauren Stack 1C

If you think about the definition of an isolated system, nothing can interact with the surroundings (reactants, products, or energy). Thus, I like to think of it like a very very good thermos. If you leave hot water in it, an isolated system will keep the water heated through insulating the system a...

Lauren Stack 1C

Closed systems are still allowed to exchange energy with the outside world, while isolated systems are not. This is caused by the "isolating" factor of insulation. If you think about a really good thermos or bomb calorimeter, all of the energy should be stored and maintained in the vessel ...

Lauren Stack 1C

Enthalpy is a state function because it only relies on the final and initial values to calculate it. If you use the example of altitude gain while rock climbing, the difference between the final and initial values is the same, regardless of what path you take. Conversely, a path function or non-stat...

Lauren Stack 1C

In lecture, Lavelle was able to add the reactions because it used an intermediate that allowed the two to be combined. N2 (g) + O2 (g) -> 2 NO (g) where delta H = 180kJ 2 NO (g) + O2 (g) -> 2 NO2 (g) where delta H = -122kJ Thus adding them to form a net equation N2 (g) + 2 O2 (g) -> 2NO2 (g) where d...

Lauren Stack 1C

Steam produces a more severe burn than water because it has more energy, even though the two may have the same temperature. http://ibalchemy.com/wp-content/uploads/2015/11/Change-of-State-Water-graph.png You can see in this graph that although the temperature of steam and water may be the same, the ...

Lauren Stack 1C

A state function is a property that is not dependent on path taken to obtain that state, thus these state properties can be added or subtracted. Some examples given in lecture were E, P, V, T, Density, and Heat Capacity. To further explain this using volume, if you compress a gas in a container usin...

Lauren Stack 1C

As mentioned in lecture, the general table of bond enthalpies shows all positive values. In order to determine the correct net reaction enthalpy as seen in method 2, you must convert the appropriate values to negative. (Reactants = positive energy required) --> (Products, energy is released = negati...

Lauren Stack 1C

Based off of the syllabus, it appears that it would cover the first two topics/section (chemical equilibrium and acid/base equilibrium). In sum, it is the material covered in lecture up until Wednesday, because in class Friday Lavelle went over example problems.

Lauren Stack 1C

To answer Alison's question, I am reviewing by re-doing the practice modules on the website, answering all of the textbook practice problems, and reading the assigned textbook pages. Usually that gives me enough repetition to be able to find my weak spots in understanding, which I address in office ...

Lauren Stack 1C

With endothermic reactions, I think of heat as a reactant. Thus, if you apply the logic learned with Le Chatelier's principle, the equilibrium will shift to the right, just as it would if you had added a chemical reactant.

Lauren Stack 1C

K stays constant, no matter the amount/concentration of a product or a reactant added within a given reaction. K, rather, simply describes to concentration ratios of the products and reactants when the reaction has reached equilibrium. No matter the relative initial concentrations, a reaction will m...

Lauren Stack 1C

Q and K are actually calculated using the same formula with products over reactants. The difference between the two lies in when they apply. K ONLY applies to when a reaction has reached equilibrium. On the other hand, Q can represent any time during a reaction. Using Q, you an determine if the reac...

Lauren Stack 1C

To address Daniel's question, the Ideal Gas law only applies to ideal gases. An ideal gas is one where all of the collisions are perfectly elastic. Most common gases interact in this manner most of the time, but under certain conditions (including low temperature/high pressure), gases can begin to a...

Lauren Stack 1C

The quadratic equation is used to solve quadratics in the form of ax^2 + bx + c = 0. The a is the coefficient in front of the x^2 term, b is the coefficient of the x term, and c is a constant. The quadratic equation allows you to solve for x in equations where there are x terms raised to the second ...

Lauren Stack 1C

K is used to represent of products and reactants in a reaction that has reached equilibrium. Q, on the other hand, is calculated the same way as K, but using non-equilibrium concentrations of the reactants and products. Comparing Q to K allows you to [censored] what direction the reaction is moving ...

Lauren Stack 1C

I believe the Kc and Kp stand for Kc (concentration) and Kp (pressure) respectively. Thus you can use Kc or Kp for gases, as they can be represented as either, but for aqueous solutions you can only denote them using concentration (Kc)

Lauren Stack 1C

The ideal gas law equation (PV=nRT) uses Pressure (P), Volume (V), number of moles (n), a universal gas constant (R), and Temperature (T)

Lauren Stack 1C

Lone pairs do count. If you think about how we define hybridization, it is through the electron geometry found in the VSEPR Theory. In order to find this electron geometry, we must count both the number of bonds and the number of lone pair sites in order to find the total number of areas of electron...

Lauren Stack 1C

I also see mistakes on the formula sheet from my test 2. The first test and the midterm had correct formulas from what I can see from my test 1 that I have. I think it should be fixed for the final?? Hopefully??

Lauren Stack 1C

I believe it is helpful to memorize the seven strong acids which are (HBr, HCl, HI, HNO3, HClO4, HClO3, and H2SO4). For strong bases, they are Group 1 hydroxides, alkaline earth metal hydroxides (Ca(OH)2, Sr(OH)2, Ba(OH)2), and Group 1/Group 2 Oxides. This is all summarized in table J.1 of our textb...

Lauren Stack 1C

I believe that the formula sheet for the final should be the same as the other formula sheets provided for the previous exams. It does include the pH=-log[H+] formula, but does not have Ka on it from what I see.

Lauren Stack 1C

The two is simply signifying the number of the row that the element is found. For example, you could apply this to other rows and put a 1 in front of the s when describing the hybridization of something including a Hydrogen (1s).

Lauren Stack 1C

If you are referring to salt, as in table salt, the molecular formula is NaCl. As such, it is an ionic compound that is soluble in water. Thus, it does not affect the pH of a solution, and therefore cannot impact how acidic or basic a solution is.

Lauren Stack 1C

Bent and angular represent the same shape, so you should be able to use them interchangeably. I believe both are accepted on exams.

Lauren Stack 1C

As you would with a strong acid/base, you must take the -log of the concentration of hydronium or hydroxide, but you must multiply the equilibrium constant (Ka) first, which is defined as
Ka= [A-][H+] / [AH]

Lauren Stack 1C

The definition of an acid and base lies in the relative concentrations and characteristics associated with hydronium ion and hydroxide ions. Acids donate protons (H ions), while bases accept these (donate OH-). This can be seen in the basic formula for acid/base reaction: HA (parent acid) + B (paren...

Lauren Stack 1C

A conjugate acid is what the parent base “turns into.” Consequently the conjugate base is what the parent acid “turns into.” If you think about it, whatever contains a hydrogen is marked as an acid, as demonstrated in the basic formula given to us in lecture. HA (parent acid) + B (parent base) -> A-...

Lauren Stack 1C

If you think about the various diagrams we were shown of the orbital hybridization, you can see that the sigma bonds’ orbitals overlap much more than the orbitals of the pi bonds as they directly overlay each other. This diagram I found helped me understand: https://qph.fs.quoracdn.net/main-qimg-a35...

Lauren Stack 1C

I don’t believe you have to write the subscript of one. If you think about the chemical formula of a molecule, like H2O, you only write the subscript on the element that has multiple atoms present (Hydrogen), while you do not write the 1 for the subscript on the oxygen. You can apply this thinking t...

Lauren Stack 1C

In the VSEPR theory that we use to name molecules, only the electrons associated with the central atom are considered. If you look at the VSEPR formula, which involved A-the central atom, X-number of bonds connected to the central atom, and E- number of lone pairs/a radical on the central atom. Thus...

Lauren Stack 1C

Boiling point and melting point can both act as indicators of the relative strength of intermolecular forces and are closely related. The difference between the two lies in the phase or state of the compound. Thus, a boiling point is the temperature that a liquid turns to gas, and a melting point is...

Lauren Stack 1C

There isn’t a direct relationship between polarity and melting point or boiling point. The factor that influences the relative height of such points is the strength of intermolecular forces. These intermolecular forces can be ion-ion, ion-dipole, hydrogen bond, dipole-dipole, etc. Dipoles are create...

Lauren Stack 1C

The various delta symbols do in fact show a partial charge. If you think about a water molecule, the two hydrogens will have a delta positive and the oxygen will have a delta negative. The arrows point towards the negative atom. So the point of the arrow will go towards the oxygen in the case of wat...

Lauren Stack 1C

For each of the different molecular geometry shapes (VSEPR), I am memorizing the possible angles. Otherwise, I believe that is important to understand why an angle might be slightly less than expected (such as 107deg instead of expected 109.5deg) by understanding the role that lone pairs play in rep...

Lauren Stack 1C

I do not believe we need to know exact values for electronegativity. I think that knowing the general periodic trends associated with it are sufficient in that noble gases are not electronegative and electronegativity increases up a column and across a row. Comparing relative electronegativity can b...

Lauren Stack 1C

When calculating formal charge, the order that you do it in should not matter. Formal charge is assigned individually to each atom in a molecule by taking the number of valence electrons and subtracting the sum of the number of bonds and the number of lone electrons. Overall, you want the most elect...

Lauren Stack 1C

What I noted is that you should be able to tell when the bond angles are less than the expected (i.e. less than 109.5 deg in the example you give), but it is also helpful to be able to rank them when comparing various shapes, such as the bond angles on a molecule with one lone pair against a molecul...

Lauren Stack 1C

I believe that exact values of bond strength are determined experimentally through finding the dissociation energy. For our purposes, we can use a provided table of bond strengths and lengths to determine strength. The more bonds there are between atoms, the stronger the bond. Additionally, the shor...

Lauren Stack 1C

A coordinate covalent bond is special because both electrons in the shared lone pair came from the same atom. In a regular covalent bond, each atom in the bond provide an electron. I believe that the strength of a coordinate covalent bond is equivalent to any other covalent bond and its importance i...

Lauren Stack 1C

I would think that we are held responsible for understanding Lewis acids and bases for all of the upcoming assessments. It appears on the syllabus in Focus 3: Chemical bonds. We did not complete all of focus 3 before the midterm, but I assume that the material will be fair game on future tests. I re...

Lauren Stack 1C

As Carbon, Nitrogen, Oxygen, and Fluorine are all located in period 2 of the periodic table, their valence electrons are found in n=2. Thus, they do not have the extra 3d subshell that would allow them to have an expanded octet an must follow the octet guideline. Furthermore, although we try to mini...

Lauren Stack 1C

When atoms are highly polarizable or have high polarizing power, they are able to pull the electrons between them closer to the cation. An ionic bond is formed by the attraction between two oppositely charged atoms. As a covalent bond is defined by a sharing of electrons between the two bonded atoms...

Lauren Stack 1C

Isoelectronic simply means that the atoms being compared have the same number of electrons. This is often demonstrated by ions, like S- being isoelectronic with Cl.

Lauren Stack 1C

Coordinate covalent bonds appear as normal covalent bonds with two electrons shared between two atoms. What makes coordinate bonds special is that the two electrons that are shared both came from one atom, rather than each atom contributing one electron.

Lauren Stack 1C

Atoms with an open d or f orbital can have an expanded octet. Thus, atoms in the n=3 level or greater can have this occur. As for determining if an atom as an expanded octet, it is important to assess its formal charge and adjust the structure accordingly to get the formal charge of all atoms as clo...

Lauren Stack 1C

You want the most electronegative atom to take the negative formal charge. In this case, it is Oxygen and you would want the -1 formal charge to be assigned to it.

Lauren Stack 1C

Solely based off of the visual representation of a Lewis Structure, a covalent bond is represented with a line between two atoms, as they are sharing electrons. In an ionic bond, the atoms are not sharing electrons and are not represented with a line between them.

Lauren Stack 1C

I believe that it is most important to understand the general trends associated with ionization energy. Ionization energy is said to be the energy needed to remove an electron from an atom in the gas phase. Thus, ionization energy decreases down a group and increases across a period.

Lauren Stack 1C

Typically the atom with the lowest electronegativity is the central atom. The only exception to the rule is Hydrogen.

Lauren Stack 1C

The only time to expand into the descriptive x, y, and z is when it is specified in the question or asked for. Otherwise, I believe it is fine to leave the configuration in its simplified form (no x, y, z). The x, y, and z are not necessarily part of the 4 main quantum numbers.

Lauren Stack 1C

I believe that you can leave it as the more simplified version. If you look in the periodic table in the textbook, they list electron configurations for various elements and all of them are left in the simplified form (not displaying the x,y,z)

Lauren Stack 1C

Having resonance does not necessarily mean that there are exactly three ways to draw the Lewis structure. Rather, resonance means that the molecule being examined has more a more complex bonding structure. A Lewis structure is a simplification of what a molecule really is, as demonstrated by the dif...

Lauren Stack 1C

Hydrogen is the only element that has one electron in its ground state. Otherwise, all other elements can be considered multi-electron atoms. Helium could hypothetically be stripped of an electron (even though highly unlikely/extremely difficult because it is highly stable) and become a single-elect...

Lauren Stack 1C

To address Quresh’s question: Momentum is found by multiplying mass times velocity (p=mv). It describes the amount of resistance to stopping that an object in motion has. If you think about two balls rolling at the same velocity but with different weights, the heavier one has more momentum and is th...

Lauren Stack 1C

The exceptions to the expected electron configurations come with Chromium and Copper. Chromium’s electron configuration is [Ar] 3d^5 4s^1. Copper’s is [Ar] 3d^10 4s^1. As for what half filled and full subshells mean, a d subshell can have up to 10 electrons in it, and half-full would be 5 electrons ...

Lauren Stack 1C

A shell is defined by n, which can be whole number values (1, 2, 3, etc). The term subshell refers to the l (s, p, d, f) and the shapes that are made by the expected/potential location of the electron. An orbital is a combination/description of all of the quantum numbers (which are n, l, ml, and ms)...

Lauren Stack 1C

An electron configuration is the symbolic representation of where an electron is located within an atom. Each of the levels within electron configuration denotes a certain amount of energy that an electron possesses. An element can be defined by its electron configuration because its is marked by it...

Lauren Stack 1C

De Broglie's equation is used to find the wavelength.
The equation itself is:
Wavelength = Planck's constant / (mass X velocity)
The units of planck's constant (m^2kg/s) cancel down to meters, as it is divided by mass (kg) and velocity (m/s) respectively.

Lauren Stack 1C

In lecture, Dr. Lavelle said that a particle with less than 10^-15m does not have detectable wavelike properties. So anything larger than that should qualify.

Lauren Stack 1C

I tend to do most of the reading listed on the syllabus above the problem set before I attempt to do any problems. I only read what he has listed online. For example, he omitted section 1C for the Quantum World. I don't take notes on everything, only main formulas or things that are essential or thi...

Lauren Stack 1C

Light has both wave-like and particle-like tendencies. The particle-like behavior is reflected in photons, which I think of as a small package of energy.

Lauren Stack 1C

If you think of the concept that energy is neither created or destroyed, the release of the light reflects a decrease in energy for the atom as a whole. The further the gap between the starting and final energy levels does impact the frequency of the light emitted, thus allowing us to analyze the va...

Lauren Stack 1C

If you are simply converting from grams to moles, or vice versa, having decimals is acceptable, as long as they go along with the rules of significant figures. In the case of 2.44, you have three significant figures listed. If you are making an empirical formula, you should not have decimals for the...

Lauren Stack 1C

The moles of solute remain the same, regardless of the dilution. There is a set number of molecules of the solute in a solution. Even if more solvent is added, the number of molecules of solute will not change, as there is no solute being added or removed. There is simply more solvent being added, w...

Lauren Stack 1C

Wavelength and frequency are inversely related, as when they are multiplied, they result in a constant. I believe that amplitude is a separate value with no relation to the other two. For example, a wave might have a set frequency, and thus a set wavelength to compensate. The amplitude could be any ...

Lauren Stack 1C

The empirical formula shows only the ratio/proportions of atoms of the elements present in a molecule. Conversely, the molecular formula shows the exact number of atoms of each element that are present in a molecule. The way that I remember the difference is the when you want to look at a specific m...

Lauren Stack 1C

As many of us do, I also struggle with stress/jitters before a large exam. Some of the strategies to cope with it that I have found useful are: 1. Take a break from the material and do something active. I personally like going to the gym or running. It helps me get my mind off of the problems at han...

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