CHEMISTRY COMMUNITY

MaryBanh_2K

Substance A decomposes in a first-order reaction and its half-life is 355 s. How much time must elapse for the concentration of A to decrease to (a) one-eighth of its initial concentration; (b) one-fourth of its initial concentration; (c) 15% of its initial concentration; (d) one-ninth of its initia...

MaryBanh_2K

The presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kJ?mol−1 to 75 kJ?mol−1. (a) By what factor does the rate of the reaction increase at 298 K, all other factors being equal? (b) By what factor would the rate change if the ...

MaryBanh_2K

According to the solutions manual, " At equilibrium, rates of forward and reverse reactions are equal, not rate constants?" Is there such thing as a rate constant of a forward or reverse reaction or are they just referred to as rates?

MaryBanh_2K

What are the correct units for t? The solutions manual leaves it in minutes but aren't the correct units in seconds?

MaryBanh_2K

When solving for k, do both of these derivations mean the same thing: (ln([Ao]/[[A]))/t AND (ln[A]/[Ao])/-t? The book uses the first equation but I'm not sure if the two equations mean the same thing because I am getting a different answer.

MaryBanh_2K

What's the difference between minimum potential and maximum potential? Does minimum potential mean Standard E Cell and maximum potential mean Wmax? If so, what does this mean conceptually?

MaryBanh_2K

Why can we assume the cell can do work when the E value at the Cathode is bigger than the E value at the Anode?

MaryBanh_2K

For 6M5, the cell diagram included Hg(l). Why wasn't there a solid metal included at the oxidation side? Does Hg(l) still work as a conductor even if it is in liquid form?

MaryBanh_2K

Are liquids the only thing we don't include in cell diagrams?

MaryBanh_2K

Does the standard delta G (with the degree sign) mean the reaction is at equilibrium? Can you also find standard delta G (with the degree sign) with the Q value or does it only with the equilibrium constant, K?

MaryBanh_2K

A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis? Does the minimum potential mean t...

MaryBanh_2K

How do we know Cobalt is a solid in 6M11 part a?

MaryBanh_2K

I know a more negative (less positive) standard reduction potential leads to a stronger metal as a reducing agent. For this problem, how do we know which standard reduction potential to use in the appendix when there are many of them for the same element?

MaryBanh_2K

A student was given a standard Cu(s)|Cu2+(aq) half-cell and another half-cell containing an unknown metal M in 1.00 M M(NO3)2(aq) and formed the cell M(s)|M+1(aq)||Cu2+(aq)|Cu(s). The cell potential was found to be -0.689 V. What is the value of E(M+2/M)? In this problem, im assuming the Cu(s)|Cu2+(...

MaryBanh_2K

When you balance redox reactions and you end up with the same amount of added electrons on the same side, how do you know which equation to flip to cancel out the electrons? Do we flip the anode or the cathode or is it dependent on the E value of each?

MaryBanh_2K

d) Balance 1/2 rxns: Pt(s) | O2 | H+ || OH- | O2 For part d, I tried balancing the oxidation half-reaction by adding to waters on the right to balance out the oxygens. That would make 5 H+ in total so I balanced out those H+s by adding 5H+ to the left side. The final charge I got on the left was 5 a...

MaryBanh_2K

When it comes to balancing the equation for the cell reaction for each of the following galvanic cells, if OH- is given is there another method we follow? How do we find the two balanced 1/2 reactions for the oxidation and reduction rxns in this problem?

MaryBanh_2K

Will the charge of O2 always be -2 even if it stands alone? Can someone explain the charges of different kinds of oxygen such as O and O3 and up?

MaryBanh_2K

For homework 6K5, when balancing the O3 --> O2 reaction, the solutions manual shows that H2O cancels out after balancing the H. Why would this occur?

MaryBanh_2K

The following reaction is used in the acidic solution in the Breathalyzer test to determine the level of alcohol in the blood:

H+(aq) + (Cr2O7)-2(aq) + C2H5OH(aq) ---> (Cr)3+(aq) + C2H4O(aq) + H2O(l)

Is the overall net charge of both C2H5OH and C2H4O zero or one?

MaryBanh_2K

A student was given a standard Cu(s)|Cu2+(aq) half-cell and another half-cell containing an unknown metal M in 1.00 M M(NO3)2(aq) and formed the cell M(s)|M+1(aq)||Cu2+(aq)|Cu(s). The cell potential was found to be -0.689 V. What is the value of E(M+2/M)? I'm confused about this problem. How can you...

MaryBanh_2K

The textbook's definition of cell potential is vague. Is it a measure of how much voltage or electrical energy a cell has? How does this relate to the half-reactions of redox reactions and oxidation? Is the electrical energy caused by the movement or the difference in electrons on both sides?

MaryBanh_2K

I'm confused about how an electrochemical cell operates. I understand that oxidation occurs at the anode and reduction occurs at the cathode, but overall what is the charge of the cell and what is the meaning of this circuit?

MaryBanh_2K

I understand that reaction quotient (Q) measures the relative amounts of products and reactants at any time in the reaction at any particular point and equilibrium constant (K) describes the reaction at equilibrium. I also know that K and Q can be compared so that we can tell which way the reaction ...

MaryBanh_2K

Why do we solve for delta G of the reaction using the delta G with the degree sign? I know that the degree sign indicates that the reaction is at standard temperature and pressure but what is the significance of this?

MaryBanh_2K

How do we know when we can use PV=nRT to find a missing value? When we are given the change in one or more of these variables, do we plug it in as delta for the variable(s)? For example, if we want to find Pressure and the problem gives us the change in Volume and moles, would we solve for P using t...

MaryBanh_2K

An ice cube of mass 50.0 g at 0.0 8C is added to a glass containing 400.0 g of water at 45.0 8C. What is the final temperature of the system (see Tables 4A.2 and 4C.1)? Assume that no heat is lost to the surrounding. For this problem, I understand that we find the total heat for ice and total heat f...

MaryBanh_2K

Can someone explain when to use the ideal gas constant for monatomic ideal gases? What is are some examples of a monoatomic ideal gas?

MaryBanh_2K

I understand that heat capacity at a constant volume is (delta U)/(delta T) bc at constant volume delta U equals q. However, why is heat capacity at constant pressure (delta H)/(delta T)?

MaryBanh_2K

When can we assume enthalpy (delta H) and heat (qp) are equal? Can we always use them interchangeably? Why or why not?

MaryBanh_2K

An expansion is reversible when the temperature is constant. This process is gradual and requires more work. It is reversible because everything is at equilibrium and therefore entropy is equal to zero. During a reversible expansion, work is negative and the system is losing energy by expanding; how...

MaryBanh_2K

Why aren't heat and work state functions?

MaryBanh_2K

What is the significance of finding the heat capacity?

MaryBanh_2K

What is the conceptual significance of having the negative sign in the equation: w=-(external pressure) x (change in volume)?

MaryBanh_2K

What keywords would help you determine whether a system is closed or isolated? I find the two very similar and am having difficulty differentiating them when looking at examples.

MaryBanh_2K

For homework problem 4A.9: A piece of copper of mass 20.0 g at 100.0 8C is placed in a vessel of negligible heat capacity but containing 50.7 g of water at 22.0 8C. Calculate the final temperature of the water. Assume that no energy is lost to the surroundings. The solutions manual states that we so...

MaryBanh_2K

What is the conceptual meaning of the internal energy change and how do we calculate it?

MaryBanh_2K

How do pKa and pKb relate to pH and pOH?

MaryBanh_2K

When we look at the changes and effects using Le Chatelier's Principle, is Partial Pressure different from Pressure? For example, if the Partial Pressure of one of the products increases, will there be an increase in the Partial Pressure of the reactants. On the other hand, if Pressure increases in ...

MaryBanh_2K

When we decide whether or not to exclude the "minus x" in the denominator do we compare the K value to 10^-3 or 10^-5?

MaryBanh_2K

For problem 6D)15, how do we find pH? How do you find the Ka value that we use for the equation to figure out the x value?

MaryBanh_2K

How do we know when to compare K to a value greater than or less than 1 and when to compare K to the values 10^3 and 10^-3?

MaryBanh_2K

In class, Lavelle mentioned something called the 5 % rule. I didn't really understand this concept. Can someone explain when to use this? Does it only apply to acids and bases ICE calculations?

MaryBanh_2K

Why do solutions of weak acids have higher pH values than solutions of strong acids at the same concentration? Does this have something to do with the fact that weak acids have stronger conjugate bases?

MaryBanh_2K

How do you calculate the percentage ionization of a weak acid or a weak base? What does this calculation mean conceptually?

MaryBanh_2K

How do we know when to use the ICE table for acids and bases? Do we have to memorize which are strong acids and strong bases?

MaryBanh_2K

Why is the activity of pure substances equal to zero?

MaryBanh_2K

What is the purpose of having alternative forms of the equilibrium constant?

MaryBanh_2K

What is the difference between the Activity of a Substance J (denoted a sub j) and the Activity Coefficient?

MaryBanh_2K

What is the purpose of the ideal gas law and which reactions can use it as an approximation?

MaryBanh_2K

When does the amount of reactant and product affect the reaction? In HW 5G1, these two statements are false: An equilibrium rxn is not affected by increasing the concentration of products. If one starts with a higher pressure of reactant, the equilibrium constant will be larger. In this problem are ...

MaryBanh_2K

HI is a stronger acid than HCl because I has a larger atom radius than Cl and HI has a weaker bond than HCl which makes HI dissociate completely very easily.

However, when looking at HOI and HOCl, why is HOCl a stronger acid?

MaryBanh_2K

When do you use "ferrate" when naming molecular compounds?

MaryBanh_2K

In this problem, we had to assign a hybridization scheme to the Sb atoms. In the solutions manual, the single bond between C and H is sigma(C 2sp^2, H 1s) what does the 2 and 1 represent? Is if the n value of each atom?

MaryBanh_2K

How is NH3 a base?

MaryBanh_2K

Why is water always a monodentate ligand if there are two pairs of lone pairs?

MaryBanh_2K

What is the difference between a structural isomer and a stereoisomer?

MaryBanh_2K

How do we determine the charge of a cation?

MaryBanh_2K

Why is acetic acid considered a weak acid?

MaryBanh_2K

In a reaction, how can you tell if a molecule/ion has been incompletely or completely deprotonated?

MaryBanh_2K

Since water can donate a proton and accept a proton, is it considered both a bronsted acid and bronsted base? If so, what are other compounds that have this characteristic?

MaryBanh_2K

How do linear molecules have an sp hybridization?

MaryBanh_2K

If we are given a molecule with multiple carbons like C5H5N, will the lewis structure will always be in the form of a ring of carbons (and one N)? Also, do we refer to the central atoms as the carbon or is there no central atom?

MaryBanh_2K

For 2E19d on the homework, is SnCl2 a radical? In other words, does the central atom, Sn, not need to fill its octet? Which atoms can this trend occur in?

MaryBanh_2K

Why does the bond angle between two hybrid orbitals increase as the s-character of the hybrids is increased?

MaryBanh_2K

From my understanding, the boiling point and melting point both increase as the intermolecular forces increase in strength but what is the difference between the two?

MaryBanh_2K

What is the difference between octahedral, square pyramidal, and square planar?

MaryBanh_2K

Is there a conceptual way of how you can determine the molecular geometric shape of a molecule or do we just have to memorize the amount of bonding and lone pairs of different molecular geometric shapes and assign the shape that way?

MaryBanh_2K

What's the difference between the electron geometric shape and the molecular geometric shape of a molecule?

MaryBanh_2K

If there are lone pairs around the central atom, will the bond angles always be less than the intended degrees? For example, SO2 has one lone pair and has bond angles of less than 120 degrees. On the other hand, BCl3 has no lone pairs and has bond angles of 120 degrees.

MaryBanh_2K

How can we tell if a molecule has lone pairs of electrons on the central atom or not?

MaryBanh_2K

How do you find the maximum wavelength in which an electron can be ejected?

MaryBanh_2K

1.43 What is the minimum uncertainty in the speed of an electron confined to within a lead atom of diameter 350. pm? Model the atom as a one-dimensional box with a length equal to the diameter of the actual atom. In this problem, does the 350 pm represent delta x? Will it always be talking about the...

MaryBanh_2K

How do you find the number of photons a light can generate if you are given the amount of energy the light emits and its wavelength?

MaryBanh_2K

When energy is absorbed, is the n value going up or down?

MaryBanh_2K

What is delta p and delta x in the Heisenberg Indeterminacy (Uncertainty) Equation?

MaryBanh_2K

Why are resonance structures more reactive?

MaryBanh_2K

What is the difference between radicals and biradicals?

MaryBanh_2K

If we are given a list of molecules, such as CF4, CCl4, and CBr4, how can we tell which molecule is predicted to have the strongest CX bond, where X is a halogen? (reference: problem 2D15)

MaryBanh_2K

When we do Lewis Dot Diagrams, how do we know which atoms can have expanded valence shells? Also, if they are able to expand their valence shells, how many extra valence electrons are they able to possess?

MaryBanh_2K

For 2A5 in the homework, how come when we find the ground state e-configuration for Bi+3 we include 6s^2 but we don’t include it for the ground state e- configuration for TI+3?

MaryBanh_2K

Why are Phosphorus, Sulfur, and Chlorine able to accommodate more than 8 valence electrons? Are there any other elements with this characteristic?

MaryBanh_2K

When given a set of lewis structures like problem 2C15 in textbook where there are four resonance structures shown, how do we know which has the lowest energy?

MaryBanh_2K

Which elements mostly show up in the center of the Lewis Structure and why?

MaryBanh_2K

In the lecture, Lavelle mentioned that transition metals vary in valence electrons. Mn has 7 valence electrons and it is in the seventh column in the transition metal groups. How do we know when to determine a transition metal’s valence electrons based on column number and when not to?

MaryBanh_2K

What is the importance of finding the formal charge of an atom?

MaryBanh_2K

What is linear momentum and how do we solve for it?

MaryBanh_2K

Why are there gaps and certain chunks of vertical lines on the atomic spectra and what do they represent?

MaryBanh_2K

In problem 1A.3, what does it mean by the “extent of change in the electrical field”? Is it referring to the amplitude of the wave? In that case, if the frequency decreases, will the extent of change also decrease?

MaryBanh_2K

What is the difference between classical mechanics and quantum mechanics?

MaryBanh_2K

What happens if the energy of light matches the threshold energy level? What would happen to the electron(s) on the metal surface?

MaryBanh_2K

What is the de Broglie particle-wave duality for the election and proton? How do we derive it?

MaryBanh_2K

What is the difference between the Lynam and Balmer series?

MaryBanh_2K

Can someone explain what a photon exactly is and how it relates to the Photoelectric Effect? I can't seem to comprehend it in simple terms.

MaryBanh_2K

The wavelength of an electron can be determined with the de Broglie equation: Wavelength = Planck's constant/ (Mass x Velocity).

MaryBanh_2K

Frequency, denoted as Greek letter nu, represents the number of waves that passes a given point in a certain amount of time. Wavelength, written as Greek letter lambda, is the distance between two points on two adjacent waves. Frequency and wavelength are inversely proportional. This means short wav...

MaryBanh_2K

Hi Candice! The limiting reaction is when a reaction has more of one reactant and less of another causing the amount of product to be limited. Therefore, it is very unlikely for there to be only two limiting reactants. In that case, they would have to be the same amount of reactants which would not ...

MaryBanh_2K

The molar mass does not change when you have an ion. For example, Fe and Fe3+ both have a molar mass of 55.845g/mol. The only difference between the atom (Fe) and ion (Fe3+) is that Fe3+ has 3 electrons. The molar mass remains the same because electrons do not have a large mass compared to the entir...

MaryBanh_2K

When finding the mass percentage, is there a certain decimal we are supposed to round to?

MaryBanh_2K

Problem: A student prepared a solution of sodium carbonate by adding 2.111 g of the solid to a 250.0-mL volumetric flask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transfer into a flask to obtain (a) 2.15 mmol Na; (b) 4....

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