CHEMISTRY COMMUNITY

Ashley Presnell 1C

Intermediates are the species involved in a reaction mechanism that are formed in an earlier step but used up in a later step. They are not the same as catalysts which are not consumed in the reaction.

Ashley Presnell 1C

A reaction mechanism is the outline of the specific pathway in which a reaction follows to get the overall reaction. The mechanism details information not present in the overall reaction by including the elementary steps that are involved in the formation of the products.

Ashley Presnell 1C

Since we know at equilibirum the rates of the forward and reverse reactions are equal, I would assume the reverse of a slow reaction rate at equilibrium, by this reasoning, would also therefore be slow.

Ashley Presnell 1C

If looking at options of possible mechanisms for the overall reaction, we can check that the elementary steps align with the experimental rate law and chemical equation by making sure the sum of the elementary reactions aligns with the overall reaction and the rate law.

Ashley Presnell 1C

I am pretty sure it is relative, so we base the rate law off of the slowest step as the rate determining step.

Ashley Presnell 1C

The spontaneity of a reaction is separate from the speed a reaction takes place. Spontaneity refers to the likliness of a reaction to occur as is, energy wise, which does not indicate how fast a reaction would occur once started. A spontaneous reaction is thermodynamically favorable and could occur ...

Ashley Presnell 1C

We need experimental data to find the experimental rate law since the value of k can only be determined from the slope of the concentration of the reaction over time for a zero order, ln(conc) over time for first, and 1/conc for second order.

Ashley Presnell 1C

This is because it is showing the concentration over time of the reaction, and since its linear it means the reagent is decreasing linearly over time which agrees with the zero order rules.

Ashley Presnell 1C

Catalysts can lower the barrier of activation energy, to make it easier for a reaction to start. This means a catalyst can lower the activation energy necessary for a reaction to start, speeding up the reaction overall and requiring less energy.

Ashley Presnell 1C

It kind of follows exponent laws because when you do 3^2 times 3^4 you get 3^6 which is the sum of the two exponents rather than the product of them.

Ashley Presnell 1C

Anode is where the oxidation occurs, and is written on the left of the galvanic cell. The cathode is where reduction occurs, and is on the right of the cell.

Ashley Presnell 1C

My best advice for balancing redox reactions is the process I go through to balance. First I balance all elements that aren't oxygen or hydrogen. Then I add H2O to the side of the half reaction where there is not enough oxygens if the number of oxygens are not balanced. From there, I add H+ to the o...

Ashley Presnell 1C

I think we typically assume to write the cell diagram with the anode on the left (where the oxidation occurs) and the cathode on the right (where the reduction occurs). At least, that is the extent to which I learned from attending lectures in which we discussed electrochemistry and how to set up ga...

Ashley Presnell 1C

Since we are trying to balance the amount of ions, the side with the lower concentration of ions gives out electrons. So the electrons will flow from there to the other side of the cell.

Ashley Presnell 1C

F is actually a constant called Faraday's constant, which is given on the constants and equations sheet to be 96485. We plug this in to solve for unknowns in the equation.

Ashley Presnell 1C

I think in certain cases, since standard reduction potentials are tabulated for the standard hydrogen electrode (meaning they are given like we would use for standard enthalpy of formations of compounds for example), we use these values to calculate electron transfer by comparing it with the standar...

Ashley Presnell 1C

Since the goal is to convert the chemical energy into electrical energy through the transfer of electrons in the galvanic cell, we want to include a salt bridge or porous disk to allow ion transfer between the two half reactions. The purpose of the salt bridge/porous disk is to keep the 2 solutions ...

Ashley Presnell 1C

The galvanic cell is the actual experiment in which we separate the two half reactions of a redox reaction. So within the galvanic cell, there is one side containing the oxidation reaction with the anode, and the other side holds the reduction reaction with the cathode. A galvanic cell also contains...

Ashley Presnell 1C

The acididty of the solution determines what ions are present in the solution. An acidic solution in this case would have H+ ions in solution, which would effect the reaction's progress. If it occurred in a basic solution, there would be OH- present, therefore also potentially affecting the reaction...

Ashley Presnell 1C

Another way that helps me remember what reduction vs oxidation means is the acronym "OIL RIG." It stand for Oxidation Is Lose, Reduction Is Gain. The lose/gain being referred to is the electrons. So if the element studied loses electrons/ increases in oxidation state through the reaction, ...

Ashley Presnell 1C

Usually if you are using bond enthalpies to calculate the enthalpy of the reaction, you are given the bond enthalpies necessary to make that computation. However, if given the reaction's enthalpy, it is sometimes possible to then isolate the bond enthalpy by treating it like an equation in which ent...

Ashley Presnell 1C

Reversible expansion occurs in infinitesimal quantities, making it easy to go in either the forward or reverse reaction. However, an irreversible reaction is quick and would not be able to then go in the reverse reaction. For reversible reactions we use the equation w=-nRT*ln(V2/V1) but for irrevers...

Ashley Presnell 1C

If we keep our units while making calculations, we can easily figure out which value of R to use based off what units are present in the equation an what our final result needs to be. If we are given pressure in atm, we would use the value 0.08206 for the constant R. However when trying to obtain Jo...

Ashley Presnell 1C

I believe so as isothermal just refers to the lack of change in temperature in a reaction. So there could theoretically be a reaction in which the temperature remains constant but is not reversible as implied by an isothermal reversible reaction.

Ashley Presnell 1C

Entropy of a system is a measure of the disorder. Entropy increases for spontaneous processes because it does not take much energy to maintain disorder, whereas it is unfavorable (energy wise) to go to an organized system. The universe trends towards higher entropy.

Ashley Presnell 1C

They all refer to the amount of energy to raise the temperature of something by 1* Celsius, but are specific in what quantity they refer to. Heat capacity of an object would be how much energy is required to make the whole material heat up by 1*C, specific heat would be the amount of heat to raise t...

Ashley Presnell 1C

In an isothermic system, the temperature is constant. However, in a closed system, the system can still exchange energy with the surroundings, meaning the temperature does not have to remain constant as heat can be exchanged.

Ashley Presnell 1C

Heat capacity is dependent on the amount of the material as well. So when comparing two different quantities of the same compound, the larger compound would have a larger heat capacity, which makes sense. It takes a lot more heat to heat up a pool versus a cup of water.

Ashley Presnell 1C

Both a closed system and a isolated system do not involve the exchange of matter from the system to surroundings. However, a closed system can involve the exchange of heat energy between the system and surroundings. An isolated system, on the other hand, involves neither the exchange of energy or ma...

Ashley Presnell 1C

When work is being done on the system, the value of work would be positive, indicating the system is gaining energy. However, when work is being done BY the system, work is negative as it is losing energy, such as when the volume expands, requiring work by the system to do so.

Ashley Presnell 1C

Since his definition of a state variable is a variable in which we can ignore the path taken from the initial to final states, I believe your assumption is correct. When studying state variables like temperature, we ignore how the temperature went from for example 100 degrees Celsius to 50 degrees C...

Ashley Presnell 1C

Heat is one of many forms of energy that is sometimes released from reactions like combustion. Heat is energy that can be transferred from one system to another that can result in temperature changes. However, more specifically heat capacity is a characteristic of materials that details how much hea...

Ashley Presnell 1C

State properties are properties not affected by how the final value was obstained from the initial value. For example, if you were to move forward 10 meters then backwards for 5, your displacement would be 5 meters from your starting point. Like a state variable, it only accounts for your final posi...

Ashley Presnell 1C

Lavelle mentioned that the standard enthalpy of formation of elements in their natural state like O2 for oxygen or N2 for nitrogen would be 0. Since it is the naturally more stable form of the element, it doesn't require energy to form it, but rather would require energy to form a different structur...

Ashley Presnell 1C

I think while the intermolecular forces may be weaker, there is still a brief period in which the temperature remains constant during a phase change, but with stronger forces like hydrogen bonds the constant temperature would be a longer period than without.

Ashley Presnell 1C

If we use the ICE box to figure out the change in concentrations based on the balanced chemical equation, we can usually isolate a single variable x that is causing the change from the initial to equilibrium concentrations. Using the calculated change x from the initial and known equilibrium concent...

Ashley Presnell 1C

Since the equation is on the constants and equations sheet given to us, it isn't 100% necessary to memorize, but rather be able to quickly understand what the ideal gas law reveals about the relationships between different variables. For example, we learned in a lecture that through rearranging the ...

Ashley Presnell 1C

Buffers are helpful not only in labs but in biological systems to minimize changes in pH. There is no universal buffer that works for everything as we choose a buffer dependent on the pH of the desired solution, and choose a pKa close to that pH value to minimize changes in pH. For example, shampoo ...

Ashley Presnell 1C

We use the ideal gases law to be able to convert between concentration of a gas and its pressure or vice versa. This is especially useful if the values given are not all in either units of concentration or units of pressure. For example, if we are given a reaction A+B --> C, and we know Kc but we on...

Ashley Presnell 1C

If given the partial partial pressure of the reactant and Kp, we can use an ICE box to solve for the partial pressures of the products and reactants at equilibrium the same way we solve for equilibrium concentrations using Kc. Once we know all the partial pressures at equilibrium, we solve for the t...

Ashley Presnell 1C

A solutions pH value becomes smaller as the solution becomes acidic, meaning more H3O+ are forming. This means for example, in terms of adding a weak acid/base that is unknown, if the resulting solution has a lower pH than before, the substance was a weak acid as it dissociated into H3O+ and its ocn...

Ashley Presnell 1C

Since K is a representation of the ratio of products to reactants or [P]/[R], a larger K, for example, would mean the numerator is higher and would lead to a higher favoring of the products than for a smaller value of K. This would mean the reaction is shifted right for higher values of K, and shift...

Ashley Presnell 1C

When looking at how temperature affects an equilibrium shift, we have to first determine whether the reaction is endothermic or exothermic. If a reaction is endothermic, an increase in temperature will cause the reaction to favor the products in order to reduce the effects of the change on the syste...

Ashley Presnell 1C

Professor Lavelle briefly mentioned this in one of his recorded lectures, but a very small Equilibrium Constant would indicate that at equilibrium, there are more reactants favored as there is a very small denominator. This means that the reaction favors the formation of reactants as they are more s...

Ashley Presnell 1C

We always make sure to give temperature in terms of Kelvin, which would be the Celsius degree value + 272.15. Then we want to make sure the value we put in for R is in the same units as the pressure we input into the equation. We are given multiple different values of R on the constants and equation...

Ashley Presnell 1C

We make many assumptions such as neglecting attractive forces between molecules or the volumes of the gas molecules when treating a molecule like an ideal gas which is really the "ideal" way a gas would act so we can simplify the relationships between a gas's temperature, pressure, and con...

Ashley Presnell 1C

With what we know right now, it is important to make the assumption that the gases are acting as ideal gases so we can neglect different forces that could be affecting the characteristics of the gas we are considering. For example, when using the ideal gas law, we are neglecting different factors th...

Ashley Presnell 1C

We can't have a pressure of anything but a gas so if we are finding terms of Kp then we would only be taking about an equation in which the equilibrium constant would only include gaseous reagents. However, we can have concentrations of both a gas or an aqueous molecule, therefore we can use both to...

Ashley Presnell 1C

Equilibrium is affected by changes in the molar concentrations of either the reactants or products, changes in temperature, and changes in volume (which would affect the pressure/concentration). When saying pressure affects the response of the system it is because when we decrease volume, for exampl...

Ashley Presnell 1C

Atm is another unit of measuring the pressure of some molecule or system. 1 atm actually equals the average atmospheric pressure at sea level, and we can use the conversion factors given in the constants and equations sheet to convert back and forth between different units of pressure to make sure w...

Ashley Presnell 1C

Since we only calculate Kc using the molar concentrations of the reactants and products, it would be best to convert the given values of the reactants to the molar concentration to be able to get an equation we can plug into the Kc equation once we find the E part of the ICE box. Since we are lookin...

Ashley Presnell 1C

The total pressure of a system is the sum of the individual partial pressures of each gas in the system. So once you calculate the partial pressures of the individual gases in the reaction, you take the sum of them all the find the total pressure. The same relationship can be used to find partial pr...

Ashley Presnell 1C

An ideal gas is when we make assumptions for how a gas will act when we are working out a certain experiment or reaction. For example, when using the ideal gas law to calculate characteristics of a specific gas, we do not take into account factors like inelastic collisions between molecules or the v...

Ashley Presnell 1C

Hard water is water that has more minerals in it. Calcium is a common mineral in hard water. Hard water usually has a high pH, meaning it is more basic than distilled water which has a neutral pH of 7.

Ashley Presnell 1C

Since HF has a really tight bond due to the really high electronegativity and short bond since the Fluorine atom is much smaller relative to HI which is a strong acid because it is much larger atom and has a longer, weaker bond and therefore donates the H atom much easier.

Ashley Presnell 1C

A conjugate acid is what is formed when a base accepts a proton. A conjugate base is what is formed when an acid donates a proton.

Ashley Presnell 1C

If the atom bonded to the H proton are in the same group, then we can determine the relative strength of acids based on the length of the bond. If the bond length is longer it is weaker and therefore easier to lose the H proton and a stronger acid.

Ashley Presnell 1C

Strong bases have conjugate acids that are weak and strong acids have conjugate bases that are weak.

Ashley Presnell 1C

Conjugate means the one correlating to. So the conjugate base of a specific acid would be the specific base that forms when an acid donates a proton. For example, we have HCl which has a conjugate base of Cl-.

Ashley Presnell 1C

They mean the same thing as it just shows the concentration of protons that were gained in a reaction so either H+ or how it is added to water molecules H20 --> H3O+. Both represent the same value when calculating pH of a solution.

Ashley Presnell 1C

Since it has no lone pairs it would be an electron acceptor or a lewis acid.

Ashley Presnell 1C

Is pH of the solution is lower than the pKa it means the solution is more acidic than the weak acid so it will not dissociate. But when the pKa is lower than the pH the acid is more acidic than the solution and will then dissociate.

Ashley Presnell 1C

Molecules with resonance are more stable and therefore stronger acids because that means the ion itself when dissociated is stable.

Ashley Presnell 1C

Ka can be used to analyze the relative strength of acids. A low Ka correlates to a high pKa since p means the -log of something. Therefore an acid with a high Ka is more acidic than one with a low Ka.

Ashley Presnell 1C

Coordination of a compound can be calculated by determining how many points at which a ligand is bonded to the central metal cation.

Ashley Presnell 1C

It helps for me to visualize where the electron density is and how that effects the structure. For example, I memorized the angles for linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral. From there, knowing how the structure would change helps to see why the bond angles make ...

Ashley Presnell 1C

The E is referring to the lone pairs on the central atom since this is the formula for the configuration of electrons in reference to the central atom.

Ashley Presnell 1C

The number of orbitals is conserved in hybridization. If you have 4 atomic orbitals you will therefore have 4 hybrid orbitals.

Ashley Presnell 1C

Hybridization is when we mix or hybridize as the name depicts, the orbitals to explain bond formation in the observed structures we get from VSEPR models. It better explains the experimentally determined structures for example why Carbon likes to form 4 bonds in CH4 by having 4 electrons occupying t...

Ashley Presnell 1C

Since A is the central atom, we do not have a subscript since the 1 is implied and we only deal with one central atom.

Ashley Presnell 1C

I believe that delocalized pi bonds indicate that there are resonance structures in which since the actual molecule is a hybrid of all the resonance structures, the electrons are not necessarily held in the location of one of the pi bonds, but rather are delocalized to be in the hybrid form of these...

Ashley Presnell 1C

Salts are ionic compounds that are produced by a reaction between an acid and base, giving it properties like being able to be dissolved in water.

Ashley Presnell 1C

Using formal charges to determine the structure of a molecule at times will result in a different structure than figuring out which structure minimizes formal charges since these values are not the same.

Ashley Presnell 1C

When electronegativity differences increase, this results in an ionic bond which has a greater strength than covalent bonds between two atoms with very small electronegativity differences.

Ashley Presnell 1C

A general trend I have seen is that for example Cl has 7 electrons already so it would be the one with the extra lone electron because it already had an odd number of electrons!

Ashley Presnell 1C

A coordinate covalent bond is like a covalent bond involving the sharing of electrons between the two atoms, however what makes it a coordinate covalent bond is the fact that one atom is the electron donor for both atoms that are shared.

Ashley Presnell 1C

We can figure out that there are delocalized bonds if there is resonance, revealing that the bonds have bond orders in between whatever is present in the resonance structures. This means the electrons are therefore delocalized since they are in reality in a configuration that is a hybrid of all the ...

Ashley Presnell 1C

Usually you want two different signs of formal charges adjacent to each other since opposites attract. So an arrangement of formal charges along an atom with -1,+1,-1 would be better than -1,-1,+1. It also helps to keep in mind that we prefer to have the less electronegative atom as the central atom...

Ashley Presnell 1C

Usually it is best to have the more electronegative atom have the negative formal charge, rather than something else. We also want to make sure we are reducing the number of atoms that have formal charge that doesn't equal 0 so it would be best to factor those general rules in when deciding which re...

Ashley Presnell 1C

This is why we typically measure bond lengths in Angstroms (10^-10 m), however, when looking at comparing different bond lengths, we know that single bonds are longer than double bonds which are then longer than triple bonds due to the increasing strength as we increase the bond order!

Ashley Presnell 1C

Since radius is to the 6th power and has an inverse relationship, we know that atomic radius has a bigger effect than charge does due to its large power and its inverse relationship to the energy.

Ashley Presnell 1C

Dipole moments can also therefore be used to measure the polarity of a chemical bond within a molecule.

Ashley Presnell 1C

In terms of identifying them as Boron or Beryllium, we can tell the difference because both elements don't follow the octet rule, because it would require a lot of energy for them to gain 5 or 6 electrons to fill their outer energy level. In this case, they both are able to have just a few bonds wit...

Ashley Presnell 1C

Repulsion strength is how lone pairs and bonding electrons repeal each other. The greatest repulsion strength is between 2 sets of lone pair electrons, followed by the interaction between a lone pair and bonding electrons, then followed by the weakest of the 3 repulsion strengths between two sets of...

Ashley Presnell 1C

The most plausible lewis structures are those in which we minimize the formal charges of all atoms in the molecule, so if we have 3 atoms making up the molecule it would be favorable to have a structure that resulted in 0 formal charges for all 3 molecules over something with like a +1,-2,0 formal c...

Ashley Presnell 1C

In general, we can tell if it's covalent or ionic based on the distance between the two atoms on the periodic table. If it is between a metal and non-metal it will generally be an ionic bond, and if it's between two elements near each other on the table it will tend to be covalent. This is a good gu...

Ashley Presnell 1C

Dipoles cancel out when the molecule is symmetrical. For example in CO2, the two dipole vectors are pointing away from each other, with the partially positive charge in the central carbon atom, and the two oxygen atoms being partially negative. Since they are symmetrical, the two dipole vectors canc...

Ashley Presnell 1C

Since Fluorine is in group 17, it has 7 valence electrons and with its high electron affinity and ionization energy, it tends to want a -1 charge by gaining one more electron to have similar electron configuration to neon, a stable noble gas. Because of this, it would be hard to force Fluorine to fo...

Ashley Presnell 1C

If an atom is trying to form more bonds than electrons that are able to be fit into the s and p orbitals, period 3 elements will fill their d-orbitals. Not 100% sure if I completely understood the question, but for example Sulfur can form 6 bonds to create SO4 (2-) because it starts to fill up the 3...

Ashley Presnell 1C

Resonance structures can have different formal charge distributions as bonds are not placed in the same places, affecting the formal charges of inidivual atoms in a molecule. Since the actual structure is an average of the resonance structures, it will be more heavily skewed to more stable structure...

Ashley Presnell 1C

They share the same concepts of how acids are species that accept electrons/donate protons whereas bases donate electrons/accept protons. The overall reaction between bases and acids tend to be neutralizing reactions, which seems similar to what happens between lewis bases/acids when they form coord...

Ashley Presnell 1C

Radicals are special exceptions with an unpaired valence electron. This makes them highly reactive, and also only exist for very short periods of time. An example would be CH3 which is formed in the flame of burning hydrocarbons.

Ashley Presnell 1C

We have two exceptions that cause us to fill up the d orbital halfway/ full before the 4s orbital because a half filled/ full d orbital has a lower energy than a filled 4s orbital, therefore we want to have a more stable electron configuration which is why we have the exceptions of copper and chromi...

Ashley Presnell 1C

We would keep mass in kg since Joules is measured in kg*m^2/s^2. We also would then keep distance and wavelength measurements in meters to make sure quantities cancel out.

Ashley Presnell 1C

Ionic radius follows a similar trend to atomic radius but has differences when looking at the trend of a cation versus an anion.

Ashley Presnell 1C

While electrons within a shell do repel each other, the more electrons in a shell will actually cause the atomic radius to decrease (which is why atomic radius decreases as you go left to right on the periodic table). This is because there are more electrons/ negative charge to be pulled into the po...

Ashley Presnell 1C

Since shielding causes electrons to feel less of a pull from the nucleus, this does affect how greatly the nucleus can pull in the electrons, causing the atomic radius to increase!

Ashley Presnell 1C

In the equation we were given, the work function and threshold energy both represent the same thing in terms of energy necessary to excite an electron enough for it to eject the electron.

Ashley Presnell 1C

Spin is represented by the 4th quantum number which indicates its spin state as +1/2 or -1/2. Two electrons in an orbital spin opposite directions, which is why no two electrons have the same four quantum numbers.

Ashley Presnell 1C

By conservation of energy, energy is not created or destroyed, so in order to decrease the excess energy we would decrease the energy of the incident wave as the threshold energy is usually constant for a specific material. To decrease the energy of the incidence wave, we would increase the waveleng...

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