CHEMISTRY COMMUNITY

Kelly Tran 1J

Catalysts will not be included in the overall rate law because it is "consumed' in one step and then produced in another.

Kelly Tran 1J

As others have stated above, an increase in temperature increases the rate constant, k. Similarly, a decrease in temperature decreases k.

Kelly Tran 1J

Yes, if you are reversing the reaction you would flip the sign of Enaught. However, keep in mind that the value of Enaught will not change if you multiply the reaction by a factor.

Kelly Tran 1J

If Q < K, the equilibrium will shift to the right and products are favored. If Q > K, the equilibrium will shift to the left and reactants are favored.

Kelly Tran 1J

The slow step of a mechanism is the rate limiting step; it determines the rate of the overall reaction. You can identify the slow step from a mechanism by determining whether the rate law of that step matches the rate law of the overall reaction.

Kelly Tran 1J

If [A] is halved and [B] is tripled, you would multiply the initial rate by (1/2)^1 (because [A] is first order) and 3^2 (because [B] is second-order). --> Rate = (1/2)^1 x 3^2 x 0.0480 M/s Similarly, if [A] is tripled and [B] is halved, you would multiply the initial rate by 3^1 and (1/2)^2. --> Ra...

Kelly Tran 1J

Hi! Yes, you are correct! The rate laws for the reactions of elementary steps can be written using the balanced chemical equation and its stoichiometric coefficients. However, as Jaden pointed out, it is important to note that although intermediate species can be written in the rate laws of the elem...

Kelly Tran 1J

The order of the reaction will determine what should be plotted. A first order reaction is a straight line plot of ln[A] vs time. A second order reaction is a straight line plot of 1/[A] vs time. A zeroth order reaction is a straight line plot of [A] vs time. ([A] is the concentration of the reactant)

Kelly Tran 1J

The order of reaction is not based on the stoichiometric coefficients; it is calculated using experimental data. The order of reaction is the sum of the order of each reactant.

Kelly Tran 1J

No, the order does not matter in the cell diagram. You would involve Pt(s) in the cell diagram as an inert conductor to transfer electrons when there are no conducting solids.

Kelly Tran 1J

I use the acronym LEO to remember that Oxidation is the Lost of Electrons and the acronym GER to remember that Reduction is the Gaining of Electrons. An oxidation half-reaction is a reaction in which a species is losing electrons. A reduction half-reaction is a reaction in which a species is gaining...

Kelly Tran 1J

The reagent that would oxidize Zn to Zn^2+ but not Sn to Sn^2+ would have a higher standard reduction potential than that of Zn to Zn^2+ and a lower standard reduction potential than that of Sn to Sn^2+. In other words, standard reduction potential of Zn to Zn^2+ < standard reduction potential of re...

Kelly Tran 1J

The better/best oxidizing agents are the species that are more likely to be reduced. So, the species with the higher/highest reduction potential will be the better/best oxidizing agent.

Kelly Tran 1J

The purpose of the salt bridge is to keep the solutions in the oxidation half-reaction and the reduction half-reaction neutral. The salt bridge prevents charge buildup by allowing anions to enter the anode side and cations to enter the cathode side. This will allow the solutions to stay neutral so t...

Kelly Tran 1J

Since E naught is an intensive property, the value of E naught will not change since it does not depend on how many times the reaction occurred. So, for example, if you multiplied the reaction by a factor of 2, you would not multiply the E naught value by 2; it will remain the same.

Kelly Tran 1J

Hi! The n value is the number of moles of electrons transferred, so your n value would be 6 and not 1. Hope this helps!

Kelly Tran 1J

If the forward reaction is R (reactants) --> P (products), the reverse reaction would be P --> R.

Kelly Tran 1J

Work done BY the system (the system does work) is negative. Work done ON the system is positive.

Kelly Tran 1J

As others have stated above, delta H = q at constant pressure. It is also good to keep in mind that the term "isobaric" refers to conditions of constant pressure.

Kelly Tran 1J

As others have stated above, delta n refers to the net change in moles of gases, so you would only consider the moles of gases and ignore the moles of solids and liquids.

Kelly Tran 1J

For isolated systems, q = 0 because there is no heat transfer, and w = 0 because there is also no volume change as nothing can go in or out. This means that delta U = 0 as well.

Kelly Tran 1J

The R you would use depends on the units! Use R = 8.314 J/mol.K or R = 0.08206 L.atm/mol.K depending on the units of the other terms.

Kelly Tran 1J

If the reaction is endothermic, an increase in temperature will shift the equilibrium toward the products. If the reaction is exothermic, an increase in temperature will shift the equilibrium toward the reactants.

Kelly Tran 1J

The R you would use in the equation w = -nRT*ln(V2/V1) is R = 8.314 J/(K*mol) so that the units will cancel out. When you are solving the ideal gas law equation PV=nRT, you would use R = 0.08206 (L*atm/(K*mol)).

Kelly Tran 1J

If work is being done BY the system, then work is a negative value. If work is being done ON the system, then work is a positive value. Whenever something, such as the system in this context, is doing work, its value for work will be negative.

Kelly Tran 1J

If the system is undergoing compression, work is positive as work is being done on the system. If the system is undergoing expansion, work is negative because work is being done by the system (the system is doing work).

Kelly Tran 1J

You can add 273 or 273.15 to your°C to convert degrees celsius to degrees kelvin. Using 273.15 is slightly more accurate but your answer should not be different if you use 273.

Kelly Tran 1J

To calculate the standard molar entropy of vaporization, there are 3 steps. Step 1 is to heat the water from 40.0 °C to its normal boiling point, (100 °C) by using C*ln(T2/T1). Step 2 is to allow the water to vaporize at the boiling point (100 °C). This value is given in the problem. Step 3 is to co...

Kelly Tran 1J

If the value of work is negative, it means that the system is doing work on the surroundings. If the value of work is positive, it means that work is done on the system, meaning the surroundings are doing work on the system.

Kelly Tran 1J

Delta U is the change in internal energy of a system, which consists of the heat absorbed/released from a system and the work done by/on the system. The equation to calculate delta U is deltaU = q + w.

Kelly Tran 1J

q = mCdeltaT is used to calculate the specific heat capacity. q = CdeltaT is used to calculate the heat capacity.

Kelly Tran 1J

As others have said above, you would assume [H3O+] = [OH-] are equal since the water is neutral, which means that [H3O+] = [OH-] = x. Then, you would plug in x and the given Kw into the equation Kw = [H3O+] x [OH-], which would equal Kw = (x) x (x) = x^2.

Kelly Tran 1J

Reversible expansions do more work than irreversible expansions because since the system is at equilibrium, the internal and external pressures are approximately the same, so when the external pressure slowly decreases by a small value such as a millionth, the internal pressure will undergo a small ...

Kelly Tran 1J

Hi! Changes in pressure (by changing the volume) only affects gases since gases are compressible. If the pressure increases (decreasing the volume), the equilibrium would shift to the side with less amount of moles of gas, but if there are equal moles of gases on both sides of the reaction, the equi...

Kelly Tran 1J

Let's say that you are given the reaction: A + B <--> C and the K for this reaction. If you reverse this reaction to C <--> A + B, the K for this reaction would be 1/K. (If you reverse the reaction, you take the inverse of the K). If you multiply the reaction by a coefficient, for example 2A + 2B <-...

Kelly Tran 1J

If K < 10^-4 , you can make the assumption that x is a really small value, which means you can use the shortcut of approximation. To be safe, you should confirm whether you can make the approximation by calculating the percent ionization. If (x/initial concentration) x 100 is less than 5%, your appr...

Kelly Tran 1J

Raising the temperature will either increase or decrease K. If the reaction is endothermic, raising the temperature will cause an increase in K. If the reaction is exothermic, raising the temperature will cause a decrease in K.

Kelly Tran 1J

In this problem water is not affecting the equilibrium because it is in its liquid state. Solids and liquids are omitted from the equilibrium constant expression, and hence do not affect the equilibrium, because the change in their concentrations are negligible.

Kelly Tran 1J

K being greater/less than 10^-3, and K being greater/less than 1 indicates whether the products/reactants are or not strongly strongly favored. If K > 10^3, products are strongly favored. If K < 10^-3, reactants are strongly favored. If K > 1, products are slightly favored. If K < 1, reactants are s...

Kelly Tran 1J

Hi! To calculate the Ka from the given pH and concentration, first you would convert the pH to [H3O+]. To do this conversion, you would plug in the pH to this equation: [H3O+] = 10^-pH. Next, I would set up an ice table using the given initial concentration in order to organize the expressions for t...

Kelly Tran 1J

Hi! If K < 10^-4, then you can make an approximation and leave out x in the denominator. To confirm whether your approximation is valid, you can do the 5% rule. If (x/initial concentration) x 100 is less than 5%, your approximation is valid and you can carry on with your calculations. However, if (x...

Kelly Tran 1J

Hi! Since strong acids/bases completely dissociate, we can assume that the concentration of H3O+ ions is equal to the concentration of the strong acid, and similarly we can assume that the concentration of OH- ions is equal to the concentration of the strong base. This is why ice tables are not need...

Kelly Tran 1J

Hi! If K < 10^-4, then you can make your approximation of x. However, if you are unsure about whether or not you can make the approximation, you can calculate the % ionization to determine whether the approximation is valid. So, if (x/initial concentration) x 100 < 5%, your approximation is valid. I...

Kelly Tran 1J

I believe that percentage ionization applies to both acids and bases. Percentage deprotonation applies to acids, since acids are proton donors and give up protons. Percentage protonation applies to bases, since bases are proton acceptors and pick up protons.

Kelly Tran 1J

Hi! A large Ka/Kb and a small pKa/pKb correlates with a stronger acid/base. In other words, the stronger the acid, the larger its Ka value and the smaller its pKa value. Similarly, the stronger the base, the larger its Kb value and the smaller its pKb value. A small Ka/Kb and a larger pKa/pKb correl...

Kelly Tran 1J

The change in equilibrium, denoted by the "C" row, is determined by the stoichiometric coefficients. Whether the change in x is a positive or negative value depends on whether the reactant or product is being used up. For example, if the reactant is being used up, then the change will be -...

Kelly Tran 1J

Hi! If K < 10^-4, then you can approximate when solving for x. If you are unsure about whether or not your approximation is valid, or if you want to check to see if your approximation is valid, you can substitute values into this expression: (x/initial concentration) x 100. If the value is less than...

Kelly Tran 1J

Hi! To reiterate what others have said, when water is a solvent (in liquid form), it would not be included in the expression for K because it is present in large excess. However, when water is in a gas form, it would be included in the expression for K. Hope this helps!

Kelly Tran 1J

We do not include solids and liquids (solvents) in the expression for K because their concentrations essentially do not change. For example, the change in concentration of solvents are so small that the change is insignificant. In other words, if you take the initial concentration and subtract a rea...

Kelly Tran 1J

Hi! The total pressure is the sum of the partial pressures of the reactants and products (gases) at equilibrium. Hope this helps!

Kelly Tran 1J

Since the reactions are reversible, there are 2 reactions: the forward reaction and the reverse reaction. In the forward reaction, the reactants are on the left side and the products are on the right side. In the reverse reaction, the product of the forward reaction is the reactant of the reverse re...

Kelly Tran 1J

If the pressure increases by decreasing the volume, then the equilibrium will shift to the side with the lesser amount of moles of gas.

Kelly Tran 1J

I would go with what Dr. Lavelle stated in lecture. If Ka < 10^-4, you can approximate to solve for x. If you are unsure, you can check to see if your approximation is valid by determining whether the value of x you solved for is less than 5% of the initial concentration. If it is, then the approxim...

Kelly Tran 1J

Increasing pressure (by decreasing volume) only applies to gases because for liquids and solids, changing the pressure does not change the volume. Therefore, you would only consider the moles of gases.

Kelly Tran 1J

[H30+] and [OH-] must be the same/equal in a neutral solution at 25C because the equilibrium constant for water, Kw, does not change. Since Kw = 1.0 x 10^-14 and is a constant, it will not change. This means that [H30+] = [OH-], and the only value that works for those concentrations is 1.0 x 10^-7.

Kelly Tran 1J

The concentrations of pure substances (solids and liquids) are not involved in the calculation of the equilibrium constant, K, of chemical reactions because the change in their concentrations is so small, it is negligible. For example, if you have $1 million and you lose $1, you would still say that...

Kelly Tran 1J

Yes, you can use the approximation method when K < 10^-4. In today's lecture (Lecture #4), Dr. Lavelle mentioned that you can use approximations not just for cubic equations, but also for quadratic equations as long as K < 10^-4.

Kelly Tran 1J

Both Q and K are calculated in the same way by calculating the ratio of [P] / [R]. If the chemical reaction is at equilibrium, you are calculating for K, but if the chemical reaction is not at equilibrium, you are calculating for Q.

Kelly Tran 1J

As others have expressed above, changing the pressure by changing the volume will cause the reaction to change because changing the volume changes the concentration of the products and reactants. On the other hand, changing the volume by adding an inert gas will not cause the reaction to change beca...

Kelly Tran 1J

As others have stated above, only the moles of gasses are considered when determining the effect of changing the pressure.

Kelly Tran 1J

The reaction quotient Q is used when you are calculating the ratio of the concentration of products not at equilibrium to the concentration of reactants not at equilibrium. In other words, you are calculating Q when the reaction is not at equilibrium.

Kelly Tran 1J

Homogeneous equilibrium refers to all of the reactants and products being in the same phase. Heterogeneous equilibrium refers to at least one or more of the reactants or products being in different phases. The molar concentration of a pure substance (solid or liquid) does not change in a reaction, s...

Kelly Tran 1J

When Qc > Kc, the reverse reaction is favored (reactants are favored).
When Qc < Kc, the forward reaction is favored (products are favored).
When Qc = Kc, neither reactants nor products are favored.

Kelly Tran 1J

Pure liquids are not involved in the calculation for the equilibrium constant because their change in concentration is so small that the change is negligible. Professor Lavelle used money as an example to illustrate this concept. For example, if you had $1 million and you gained or lost $1, you woul...

Kelly Tran 1J

Q is the reaction quotient and K is the equilibrium constant. Both Q and K are calculated in the same way; however, the difference between the two is that Q is calculated when the reaction is not at equilibrium whereas K is calculated when the reaction is at equilibrium. In other words, Q = [P] / [R...

Kelly Tran 1J

The units will tell you whether you are calculating for Kc or Kp. If the molar concentration is given, you are calculating for Kc. If the units of atm/bar is given, you are calculating for Kp.

Kelly Tran 1J

The first statement means that the concentration of the reactants and the concentrations of the products are the same. For example, [R] = [P] = 1.0 M. This statement would be false because the concentrations of the reactants and products do not have to be the same values. The second statement means ...

Kelly Tran 1J

Arrows indicating a dipole moment point in the direction of the more electronegative atom.

Kelly Tran 1J

pKa is the -log(Ka) and it tells you how acidic the compound is (the strength of the acid). The lower the pKa value, the stronger the acid. The higher the pKa value, the weaker the acid.

Kelly Tran 1J

Yes, you are correct. Bronsted acids are proton donors while bronsted bases are proton acceptors, and lewis acids are lone pair acceptors while lewis bases are lone pair donors.

Kelly Tran 1J

A lewis acid is an electron lone-pair acceptor, and a lewis base is an electron lone-pair donor. A bronsted acid is a proton donor, and a bronsted base is a proton acceptor. The difference between lewis acids/bases and bronsted acids/bases is what you are referring to. If you are describing the tran...

Kelly Tran 1J

The bond angle would be less than 109.5 due to the tetrahedral arrangement. The exact value of the bond angles depends on the atoms being bonded.

Kelly Tran 1J

[OH-] is the concentration of hydroxide ions (OH-) whereas pOH is the -log of [OH-]. In other words, pOH is a value that indicates how basic the solution is.

Kelly Tran 1J

Seesaw and trigonal pyramidal are not the same shape. Seesaw has 5 regions of electron density (1 of which is a lone pair while 4 are bonding pairs). Trigonal pyramidal has 4 regions of electron density (1 of which is a lone pair while 3 are bonding pairs).

Kelly Tran 1J

As others have said above, wedges and dashes are used to help you visualize the shape and structure of the molecule. If you had a 3-d model of the molecule in front of you, a wedge indicates that the bond is facing towards you while a dash indicates that the bond is facing away from you.

Kelly Tran 1J

Yes, lone pairs come into play in hybridization since it is a region of electron density and regions of electron density contribute to hybridization.

Kelly Tran 1J

When calculating the pH, pOH, [H+], and [OH-] of a solution, it is important to keep these formulas/equations in mind:
[H+] [OH-] = 1.0 x 10^-14
pH + pOH = 14
pH = -log[H+]
pOH = -log[OH-]

Kelly Tran 1J

To add on, pH is the -log of [H3O+] (hydronium ion concentration) whereas pKa is the -log of the Ka value or acid dissociation constant. The lower the pKa value, the stronger the acid, and the higher the pKa value, the weaker the acid.

Kelly Tran 1J

Yes, a coordinate covalent bond connects the ligands to the transition metal ion. The ligand is contributing both electrons since it forms a coordinate covalent bond with the transition metal ion.

Kelly Tran 1J

Bronsted bases and lewis bases are essentially the same; the only difference is how you use the term to describe the molecule/compound. When referring to protons, bronsted bases are used to indicate that it is a proton acceptor. When referring to electrons, lewis bases are used to indicate that it i...

Kelly Tran 1J

To reiterate what others have said, a lewis acid is an electron lone pair acceptor while a Bronsted acid is a proton donor.

Kelly Tran 1J

A lewis acid is an electron acceptor. BF3 is a lewis acid since it is electron deficient, which means that it can accept a lone pair of electrons.

Kelly Tran 1J

A bronsted acid is a proton donor whereas a bronsted base is a proton acceptor. This is similar to lewis acids and bases where lewis acids are electron acceptors whereas lewis bases are electron donors.

Kelly Tran 1J

You can determine whether a ligand is neutral by calculating its formal charge or by memorizing which ligands are neutral. Calculating the formal charge allows you to determine the charge of the ligand, which will help you calculate the oxidation number of the transitional metal since the individual...

Kelly Tran 1J

Since the Cl and H20 are outside of the brackets, they do not interact directly with the transition metal and therefore are named as they normally are. The rules for naming coordination compounds only apply to the molecules/ions inside of the brackets.

Kelly Tran 1J

You would use the prefixes bis-, tris-, tetrakis-, or pentakis- if the ligand has the prefixes di-, tri-, or tetra- in its name or if the ligand is polydentate. For your example the name of the coordination compound is bisethylenediammine.

Kelly Tran 1J

Hi! A sigma bond is a bond that is formed when two orbitals, each with 1 electron, interact end-to-end. A pi bond, on the other hand, is a bond that is formed when two orbitals, each with 1 electron, overlap side-by-side. All single bonds are sigma bonds. A double bond has one sigma bond and one pi ...

Kelly Tran 1J

Since bond angles are experimentally determined, we are not able to definitively state what the bond angles between atoms are. However, we can use the VSEPR model to estimate what the bond angle should be. Identifying the electron arrangement of the molecule will help us qualitatively determine the ...

Kelly Tran 1J

A single bond is a sigma bond. A sigma bond is when 2 orbitals, each with 1 electron, interact end-to-end to form a bond. When two atoms are bound by more than one covalent bond, one of those bonds will be a sigma bond, and the additional bonds will be pi bonds.

Kelly Tran 1J

The coordination number is the number of bonds present within the molecule. In [Fe(CN)6]^4-, the coordination number is 6 since there are 6 things bonded to the central atom.

Kelly Tran 1J

When naming the shape of a molecule, you would only consider the position of the bound atoms (bonding pairs). Considering the regions of electron density (bonding pairs and lone pairs) allows you to determine the electron arrangement of the molecule. Having different atoms surrounding the central at...

Kelly Tran 1J

As others have said above, bond order is the number of bonds present between 2 atoms. If there is a single bond between 2 atoms, the bond order is 1. If there is a double bond between 2 atoms, the bond order is 2. If there is a triple bond between 2 atoms, the bond order is 3.

Kelly Tran 1J

To determine if a covalent bond is strong, you can determine how many bonds the molecule has. Triple bonds indicate the strongest bond, double bonds indicate a stronger bond, and single bonds are the weakest bonds. You can also use the atomic radius to determine the bond length as well. For example,...

Kelly Tran 1J

Ionic bonds are typically formed between a metal and a nonmetal while covalent bonds are typically formed between 2 nonmetals. An atom on the far left of the periodic table and an atom on the far right would form an ionic bond since the electronegativity difference is higher while 2 atoms close toge...

Kelly Tran 1J

Hi! Lone pairs occupy a larger volume, and the repulsion strength between a lone pair and a bonding pair is greater than that of a bonding pair and a bonding pair. Due to this, the lone pairs push down on the bonded pairs, distorting (decreasing) the bond angles. Hope this helps!

Kelly Tran 1J

The octet rule is more of a guideline as there are some exceptions to it. For example, an expanded valence shell is an exception to the octet rule. Atoms in period 3 or higher can accommodate more than 8 valence electrons.

Kelly Tran 1J

Sigma bonds are present in every covalent bond (so they are present in single, double, and triple bonds), while pi bonds are present in double and triple bonds. For example, if there is a single bond, it is a sigma bond. In a double bond there is 1 sigma bond and 1 pi bond, and in a triple bond ther...

Kelly Tran 1J

I'm not sure if this is true, but I think they technically can? For example, a molecule can have polar bonds, which describes a polar characteristic. However, the molecule may be nonpolar overall if the dipole moments cancel out, which describes a nonpolar characteristic.

Kelly Tran 1J

The electron repulsion between lone pairs is stronger than the repulsion between bonding pairs since lone pairs occupy a larger volume. In other words, since lone pairs occupy a larger volume, they are able to push down on the bonded pairs, which is why lone-lone pair repulsion is stronger compared ...

Kelly Tran 1J

I agree with the above posts. Radicals are exceptions to the octet rule since they have an unpaired electron or an odd number of electrons. Since, CH3 and OH have 7 electrons, there will be an unpair electron in the lewis structure.

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