CHEMISTRY COMMUNITY

dana hu 1B

The catalyst is the component that does not change in the overall reaction. Intermediates are determined to be consumed by a later step. A catalyst is added to the reaction to increase the reaction rate.

dana hu 1B

The unit is J/C. It is used to indicate the potential difference which is also the same as the energy transferred between compounds.

dana hu 1B

I think of it as the limiting step compares to the excess step that is being processed because the overall reaction cannot come to completion until the slowest step comes to completion. It is also to examine the slow step rather than the fast.

dana hu 1B

when you calculate for half-life, it is usually set in seconds.

dana hu 1B

Enthalpy is a state function because it depends only on the state of the system and not on the path taken to reach its value. Heat & work are the forms of energy in transit. They appear only when there occurs any change in the state of the system and the surroundings. They don't exist before or ...

dana hu 1B

A certain reaction has an enthalpy of ΔH=54 kJ and an activation energy of Ea=86 kJ.
What is the activation energy of the reverse reaction?

I am sure what equation incorporated enthalpy to determine the Ea of the reverse reaction.

dana hu 1B

A certain reaction has an activation energy of 32.43 kJ/mol. At what Kelvin temperature will the reaction proceed 7.00 times faster than it did at 331 K?

know I have to use lnK=(Ea/RT)+(lnA), how do i incorporate a second temperature?

thank you

dana hu 1B

Definitely not thermodynamic. All those equations and concepts are hard to retain.

dana hu 1B

Hello, I was wondering where can I find the material from one of the Chemical kinetics TA review sessions? I was not able to make any of the times provided for the section and was wondering if there were additional slide info and practice problems that were provided. If anyone can assist me on where...

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Hello, A particular reactant decomposes with a half‑life of 145 s when its initial concentration is 0.269 M. The same reactant decomposes with a half‑life of 213 s when its initial concentration is 0.183 M. How can I determine the order without doing trial and error, calculating the 1st, 2nd, 0 orde...

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If [N2O5]0=0.0635 mol⋅L−1, what will be the concentration of N2O5 after 2.6 h?

By using the first-order half-life equation, [A]t=[A]0*e^-kt, what unit is the time?

dana hu 1B

For the question: Dinitrogen pentoxide, N2O5, decomposes by first‑order kinetics with a rate constant of 3.7×10−5 s−1 at 298 K. What is the half‑life, in hours, of N2O5 at 298 K? I used the equation t1/2=0.693/k and plugged in the rate constant for k and got 18729.729sec then convert to hours is 674...

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Would any of you guys know the percent concentration of what topics will the final reflect? I'm assuming that 50% is going to be on electrochemistry and kinetic, but correct me if I am wrong?

dana hu 1B

Hello, To clarify, the number of reactants correlates with the order number, right. It is determined by the number of reactants colliding at the same time, and that's why the more reactant, it is more unlikely for collision, right? If there is one reactant then that's first order, two reactants=seco...

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Hello, What would the potential of a standard hydrogen electrode (S.H.E.) be under the given conditions? [H+]=0.89 M pH2=1.4 atm T=298 K I'm not sure how to start and form the equation for this problem. How should I approach this reaction? How do I incorporate the 1.4 atm in the nernst equation? Tha...

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Hello, In delta G=-nFE and in Nernst equation... I'm a bit confused on the exact way to solve for n, electron transferred. I understand that if both half-reactions share the same moles of electrons then that would be defined as "n", but what about if both reactions are different? would I m...

dana hu 1B

Thank you for your response

I then got this which is also wrong:
2MnO4-(aq0 + 4H2O(l) + 3S+2(aq) -> 2MnO2(s) +3S(s) +8OH-(g)

What did I do wrong here? Are my states wrong?

dana hu 1B

hello,

I balanced 1/2 reactions and combine them together to get this equation:
H2 MnO4- + 8 H+ + 3 S2- = 2 MnO2 + 4 H2O + 3 S

Why is this wrong? The electron is balanced and so are the ions.

dana hu 1B

Hello,

I am a bit confused about how to determine each ions' charge and its oxidation in order to balance the equation.
Au + HNO3 + HCl -> HAuCl4 + NO2 + H2O

Thank you!

dana hu 1B

Hello,
I was able to balance my equation to 2Ag+ + Cu -> 2Ag + Cu2+, but I am not sure how to type that in the answer box. (not sure what I'm suppose to enter in a balanced overall reaction because I'm not allowed to type in the ions) Any help would be greatly appreciated.

dana hu 1B

In adiabatic process occurs without transferring heat or mass between the system and its surroundings. Therefore Q is zero, with no heat gain or lost system. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work

dana hu 1B

The forward reaction is the direction of reactants to products (left to right).
The reverse is products producing reactants (backward direction)

dana hu 1B

Hello, I need help stepping up this problem. Finding T final, how 2 equations connects, etc. 5) Suppose that 50.0 g of water at 20.0 C is mixed with 65.0 g of water at 50.0°C at constant atmospheric pressure in a thermally insulated vessel. Calculate delta S and delta S total for the process. Thank ...

dana hu 1B

Chem_Mod wrote:Please include the number of your problem (ie 4A.19) to help us better assist you

Sorry about that. It's from topic 4G exercise, problem 1. Thank you!

dana hu 1B

Hello,

Why is HBr gas has a higher molar entropy at 298K than HF gas?
Both have two atom and 2 position at same pressure and state. What other factors should I be considering?\

Thank you!

dana hu 1B

Hello, I am not understanding how to approach answering this question. 1)Nanotechnologists have found ways to create and manipulate structures containing only a few molecules. However, orienting the molecules in specific ways to assemble such structures can be difficult. Calculate the entropy of a s...

dana hu 1B

Hello, I first used the Gibbs free reaction equation of products- reactants=-242020 after converting to J/mol. Then I used the delta G knot=-RTlnK and got 2.653 for K. Can some one tell me why I am still getting the wrong answer? Thank you Hi, use -242020 to calculate the equilibrium constant. I di...

dana hu 1B

Hello,
For this problem, I followed all the steps and unit conversion but still got k=1. Does anyone know what I could have done wrong?
Here is what I got for delta G:
delta G= -0.24207 J/mol (is this correct?)

dana hu 1B

Hello,
I was able to add all the delta H (-1777.1 KJ) and delta S (140000 kJ/K) separately to enter in the deltaG=deltaH-T(deltaS) equation but am still getting it wrong. I got delta G= -41721777.1 kJ. Can someone explain to me what I did wrong. Thank you!

dana hu 1B

[censored], can someone help me with this sapling problem 15?

A+BC⟶2D⟶D
deltaH knot=539.0 kJ
delta H knot=−699.1 kJ
delta S knot=360.0 J/K
delta S knot=−110.0 J/K

calculate delta G knot at 298 K for the reaction

A+B⟶2C

solve delta G knot.

Thank you.

dana hu 1B

Hello,
I first used the Gibbs free reaction equation of products- reactants=-242020 after converting to J/mol. Then I used the delta G knot=-RTlnK and got 2.653 for K. Can some one tell me why I am still getting the wrong answer? Thank you

dana hu 1B

Hello,
What is the correlation between Entropy, delta S, and Enthalpy, delta H? How to determine when it is increasing or decreasing on a heat curve?
Thank you!

dana hu 1B

Hello
regarding using the equation of q=n*C*deltaT, how can I identify (for future reference) that this equation is the best fit for solving this word problem?
Thank you!

dana hu 1B

Hello,
Regarding sapling 15, I keep getting -1.08, but it is wrong. I used the PV=nRT and w=-Pdelta T equation but am still getting the wrong answer. Any help would be appreciated.
Thank you!

dana hu 1B

For the second part of the question of finding the heat of combustion per gram of compound B, I got 6.5007 from multiplying calorimeter constant (part 1 answer) by the change in temperature (5.65 celsius) then divided by mass of compound B. For some reason it is wrong and I cant figure out why. Than...

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Hello, I keep getting c=0.608 for question 17 and I am not sure that I did wrong. Here is the question: An 80.0 g sample of a gas was heated from 25 ∘C to 225 ∘C. During this process, 346 J of work was done by the system and its internal energy increased by 6265 J. What is the specific heat of the g...

dana hu 1B

Hello, At constant volume, the heat of combustion of a particular compound, compound A, is −3005.0 kJ/mol. When 1.405 g of compound A (molar mass =118.67 g/mol) is burned in a bomb calorimeter, the temperature of the calorimeter (including its contents) rose by 7.953 ∘C. What is the heat capacity (c...

dana hu 1B

Hello,
it would depend on what your given and final units are and what units need to be canceled out. To list a few often used units of R are 8.314 4621(75) J K−1 mol−1, 5.189 × 1019 eV K−1mol−1, 0.082 057 46(14) L atm K−1 mol−1,1.985 8775(34) cal K−1 mol−1, 1.985 8775(34) × 10−3 kcal K−1 mol−1, etc.

dana hu 1B

Hello, I have been having a hard time solving sapling question 18 from week 3/4. 18) A 0.253 mol sample of Ar(g), initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 16.9 K. Calculate the amount of heat q required to bring...

dana hu 1B

Hello, Can someone explain how to find the final temperature? (would be using the pv=nrt equation?) 11) A hot lump of 42.4 g of aluminum at an initial temperature of 88.4 °C is placed in 50.0 mL H2O initially at 25.0 °C and allowed to reach thermal equilibrium. What is the final temperature of the a...

dana hu 1B

Hello, how do I solve this? 5I.19 A reaction mixture that consisted of 0.400 mol H2 and 1.60 mol I2 was introduced into a flask of volume 3.00 L and heated. At equilibrium, 60.0% of the hydrogen gas had reacted. What is the equilibrium constant K for the reaction H2(g)+I2(g)⇌2HI(g) at this temperatu...

dana hu 1B

Hello,
I got K= 4 x 10^31. Is that correct? I'm not sure how I can check. I choose equations 1 and 4 and added the reactants together and products separately.
Thanks.

dana hu 1B

You are correct but if you recall the ice chart, be add and subtract x base if it a reactant or product.

dana hu 1B

Hello,
I'm a bit confused about Sapling hw #8 for weeks 3 and 4. How to solve enthalpy with mass included and heat energy. Does this require PV=nRT equation? I know Lavelle hasn't gone over it yet but I would like to know how it. Thank you

dana hu 1B

Hello,
What is the difference between the two forms of enthalpy and how do you identify which is which in a reaction? (If you can show me two different example reaction that would be great)

Thank you.

dana hu 1B

Hello, This is the reaction: B(aq)+H2O(l)↽−−⇀BH+(aq)+OH−(aq)Kb=[BH+][OH−][B] In the chemical reaction, B represents the amine. [ OH− ] = [ BH+ ] because same mole ratio 1:1. Use the pH to determine the pOH and then the [ OH− ]. pOH=14.00−pH Then do the inverse of log 10^(your pOH), which is x. Then ...

dana hu 1B

Hello, I believe all the material will cover up to equilibrium, acid and bases, and therdynamics. Many people are saying up to today's lecture, 1/22, but I feel like he may have more lectures next week. Is the midterm taken during our discussion hour like 14A (because mine is would be on a Tuesday, ...

dana hu 1B

Can someone help me with question number 5: The Kb for an amine is 5.333×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.242 ? Assume that all OH− came from the reaction of B with H2O. I am thrown off my the given pH and keep getting the wrong answer (82.3%...

dana hu 1B

Hello,
When given Kb of the weak base in the question to find pH, why is it necessary to convert to Ka? In Lavelle's Friday lecture, he did an example like that, Ka+Kb=Kw=10^-14. Why can't I just use Kb as the equilibrium constant?
Thank you!

dana hu 1B

Hello, This is the question I am stuck on: The Ka of a monoprotic weak acid is 0.00743. What is the percent ionization of a 0.143 M solution of this acid? I found that x=0.03258 and tried to solve for the % ionization= 0.03258/0.143= 22.8%, but it was wrong. Can anyone identify what I did wrong? Tha...

dana hu 1B

Hello,
When is it appropriate to assume that x is so small therefore to be considered zero when calculating for the equilibrium constant? Also, would it affect sig fig condition in the end?
Thank you!

dana hu 1B

Hello,
how do you determine which side of the equilibrium reaction is a negative or positive change in concentration (in an ICE chart solution)?
Thank you

dana hu 1B

Q is a quantity that changes as a reaction system approaches equilibrium. (have not yet reached equilibrium; reaction in progress)
K is the numerical value of Q at the "end" of the reaction when equilibrium is reached.

dana hu 1B

Hello, Can someone explain the process of solving this equation? I'm a bit confused about where to start and how to manipulate the multiple equations to be a specific K value. And help would be appreciated. Thank you!

dana hu 1B

X will just be a placeholder until you have reached using the quadratic formula. Plug all the equilibrium equations into the Kp equation. Then isolate all the numbers and variables to one side, equaling 0. Now use the quadratic formula to figure out the value of the x (should have two positive value...

dana hu 1B

Hello. I ran into a problem where after solving all the values to plug into solving the Kc and then using the quadratic formula, what happens when I end up with two different positive concentrations?
Thank you!

dana hu 1B

Hello! For Chem 14B, I cannot get into the second quarter sapling material (I remember purchasing a subscription that would cover my second quarter). When I click the link in ccle, it said I need to use the university's learning management system. Is anyone have the same issue?
thank you!

dana hu 1B

Hello, I am confused why HF is not a strong acid. Isn't electronegativities between the two ions great, like HCl, and it is polar?
thank you!

dana hu 1B

Hello! Lavelle hasn't really elaborated on the Schrodinger wave function and how to apply it in a problem? Does anyone know the main premise/purpose of the equation and maybe an example problem?
Thank you!

dana hu 1B

Hello! Does anyone have any insight into the wave properties of electron diffraction and how its caused?
thank you

dana hu 1B

Hello! I am still having trouble differentiating lewis and bronsted lowry acids and bases because they are so similar? If anyone has examples or a description to tell them apart, that would be great!
Thank you!

dana hu 1B

Hello!
I'm a bit confused about how to tell if a substance can be an acid and a base and how it would bond with water as an acid and base. What are the main characteristics for a substance to be determined as an amphoteric?
Thank you!

dana hu 1B

Hello!
Ka = [H+] [A-]/ [HA]
Ka is the measures the strength of an acid. A stronger acid will have a greater [H+] concentration and hence a greater Ka.
A larger Ka means a smaller pKa
pKa = - log Ka

dana hu 1B

hello! Metallic oxides are basic in nature because they react with dilute acids to form salt and water. They also react with water to form metal hydroxides which are alkaline in nature because these metal hydroxides release OH- ions in solution. Non-metals react with the oxides and form the acidic o...

dana hu 1B

Hello!
There is a difference between mixing water and other liquids to dissolve a solution. An aqueous solution only uses water as a solvent. For mixing other liquids, that a liquid solution, a solution that uses a liquid other than water as a solvent.

dana hu 1B

hello! The strength of an acid in an organic compound is proportional to the stability of the acid’s conjugate base. In other words, an acid that has a more stable conjugate base will be more acidic than an acid that has a less stable conjugate base. It likes to have electrons around it and, therefo...

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H3PO4 isn't a strong acid because phosphorus is not electronegative enough. In order for H3PO4 to be a strong acid, a proton must be able to easily fall off. In order for a proton to fall off, there must be a pulling force that shifts electron density away from the H atoms that are attached to the l...

dana hu 1B

pKa is the negative value of the logarithmic of Ka. pH is the logarithmic value of the inverse of H + concentration.
To indicate acidity, pKa indicates whether an acid is a strong acid or a weak acid while pH indicates whether a system is acidic or alkaline.

dana hu 1B

Hello! Can someone explain to me how I can determine the coordination compound number of Ba[FeBr4]2 and K3[CoF6]? I am stuck with how to draw the lewis structures of these compounds to find the coordination number, especially with the 3 Potassiums.
Thank you!

dana hu 1B

Hello. I understand how to find the basic coordination number and oxidation number, but I'm a bit confused about how it would change with another outside bracket charge.
example:[PtCl6]2-
without the outside charge Pt oxidation # is 6. so what does 2- do to it? do I multiply?
thanks

dana hu 1B

I have yet to start the homework, but just by looking at your answer I worked backwards to get the formula. [Co(NH3)5Cl]Cl. The Cl inside and outside both have a -1 charge, and ammine has no charge. Adding the two -1 charges from the chlorine ions would make a -2 total charge, but since everything ...

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Hello! For 1 in sapling, I got Pentaamminechlorocobalt(III)chloride and it's saying it's wrong. Is my oxidation state wrong, formatting,etc? Also if anyone has a helpful way of determining oxidation states of metal, please let me know. I'm still struggling with it. Thank you!

dana hu 1B

a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves the formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from covalent to ionic. d...

dana hu 1B

what dentate is CO3-2?
Can't it be monodentate and bidentate bc metals can bond with the two oxygen ligands? correct me if I am wrong. Thank you!
Also the same situation with oxalate...

dana hu 1B

Anna Yang 2A wrote:Why is H2O a monodentate ligand? I thought it would be at least bidentate.

In H2O, both lone pairs are on the oxygen. There would be only one binding site between H2O and the central metal. So it is a monodentate.

dana hu 1B

Step 1: Find the Total Number of Valence Electrons. In this step, add up the total number of valence electrons from all the atoms in the molecule. Step 2: Find the Number of Electrons Needed to Make the Atoms "Happy". Step 3: Determine the Number of Bonds in the Molecule. Step 4: Choose a ...

dana hu 1B

The reason water has a bent shape is that the two lone pair of electrons are on the same side of the molecule. They really repel each other as they are only attracted to the oxygen atom in the water molecule.

dana hu 1B

hello! no that is not the case. Resonance molecular structure will not always be the same shape.

dana hu 1B

Cl is more electronegative because it is further to the right and up on the periodic table.

dana hu 1B

because all 4 of the oxygen surrounding As is canceling out each individual vectors, therefore it is nonpolar.

dana hu 1B

wow! Thank you so much!

dana hu 1B

determine the empirical formula first and the empirical mole ratio will help you draw the lewis structure and so on

dana hu 1B

Yes, you're correct. Because when there are only single bonds (and, therefore, only sigma bonds), there can't be resonance since all bonds are the same. Thus, resonance can only exist when a molecule has at least one double bond (for example, ), and, as we learned, a double bond consists of 1 sigma ...

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sp Hybridization: sp hybridization is observed when one s and one p orbital in the same main shell of an atom mix to form two new equivalent orbitals. The new orbitals formed are called sp hybridized orbitals. It forms linear molecules with an angle of 180° This type of hybridization involves the mi...

dana hu 1B

determine valence electrons total and lewis structure of determining the number of bonding and lone pairs will help determine its shape.

dana hu 1B

I would recommend drawing out the structure. The horizontal plane creates a triangle that is 120 and the vertical plane creates 90.

dana hu 1B

gravity has very little effect on the molecular structure of the earth due to the earth's atmosphere. This is because it suffers roughly a billion collisions with other molecules in that second. So you don't see an influence of gravity on an individual atom simply because other influences are far la...

dana hu 1B

I would say be familiar with all the possible molecular shapes. Just base on textbook problems, there is a high possibility the final will ask beyond the basics.

dana hu 1B

Expectations of breaking the octet rule: An electron or molecule which contains unpaired electrons in its outermost shell or valence shell is considered as free radical. Elements like hydrogen, lithium, helium do not obey the octet rule. Another exception of the octet rule is transition elements. Du...

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Hybridization is the concept of mixing atomic orbitals into new hybrid orbitals suitable for the pairing of electrons to form chemical bonds in valence bond theory. Hybrid orbitals are very useful in the explanation of molecular geometry and atomic bonding properties. VSEPR theory to determine the g...

dana hu 1B

I heard that it will be during the discussion section and will remain to be a multiple-choice (same format). Again nothing had been determined so I might be wrong.

dana hu 1B

Elements like hydrogen, lithium, helium do not obey the octet rule. They can only lose or gain one electron in order to become stable due to which they follow the octet rule. Another exception of the octet rule is transition elements. Due to the presence of d-orbitals, they can hold 18 electrons in ...

dana hu 1B

oh got it! So do I have to have all 5 posts every week or I disperse the number of posts whenever, but make sure I have 40 by the end of this week?

dana hu 1B

A delocalized pi bond tells us there is resonance in the lewis structure of the molecule because a certain pi bond can exist in more than one configuration.
it should be o3 and co3-2

dana hu 1B

The main difference between electron geometry and molecular geometry structure is that electron geometry is found by taking both lone electron pairs and bonds in a molecule whereas molecular geometry is found using only the bonds present in the molecule.

dana hu 1B

hello does anyone know how the discussion grades are counted? I have attended every discussion zoom session and did the worksheet problems and receives a grade of 2?!? Did I miss something?

dana hu 1B

its 60, 109.5, 120, 180.
60 is from the angle of the triangle rings, 109.5 is from the tetrahedral bonding arrangement, 120 is from the trigonal planner, trigonal bipyramid, or seesaw, and 180 is linear.

dana hu 1B

hello! the main difference between polar and nonpolar bonds is that polar bonds occur between elements with different electronegativity whereas non-polar bonds occur between with the same electronegativity.

dana hu 1B

you are correct. The most favorable structure is the linear structure. Due to its reactivity, cyclopropenylidene is only seen terrestrially in the laboratory and in extreme environments.

dana hu 1B

hello does anyone know how the discussion grades are counted. I have attended every discussion zoom session and did the worksheet problems and receives a grade of 2?!? Did I miss something?

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