CHEMISTRY COMMUNITY

Aya Shokair- Dis 2H

It explains it well in the book. What I understood from it, is that steady state is assuming that the intermediate formed in the reaction mechanism stays at a constant, low concentration. Most times when you write the rate law for each elementary reaction, and then combine them to form the overall r...

Aya Shokair- Dis 2H

A change in volume means expansion work is occurring!

Aya Shokair- Dis 2H

I don't think we need to memorize anything.
Just if we plot the [A] vs time, and we get a linear line. Then we know that it is zero order

Aya Shokair- Dis 2H

From my notes "reversible work does more work because pushing against a constant P but in irrversible work, you are pushing against a smaller P."

I don't know if that helps

Aya Shokair- Dis 2H

When calculation the change in entropy we use the basic equation of:
ΔS= q(rev)/T

I remember reading in the book that we assume all the work done is reversible when we use work to calculate ΔS. (ΔU=0, so q=-w)

Aya Shokair- Dis 2H

A bomb calorimeter does mean there is no change in volume (ΔV=0). A bomb calorimeter is an isolated system, meaning that there is no heat transfer between the the system (bomb calorimeter) and surrounding. And the surrounding isn't doing work on the system, nor is the system doing work on the surrou...

Aya Shokair- Dis 2H

Isobaric means constant P. ΔU=w + q
At constant P, the change in heat is equal to the change in enthalpy by definition.
At constant P, w= -P(ex)ΔV.

So, the ΔU= ΔH -P(ex)ΔV in isobaric conditions.

Aya Shokair- Dis 2H

Yeah, I agree with the above post. In this way, a lot of product from the first step will be produced and not used up until there is sufficient energy for the second, slower reaction.

Aya Shokair- Dis 2H

In the attached pictures, the textbook is using the standard hydrogen electrode to determine the standard cell potentials of different electrodes. How did they determine one to be positive and one to be negative? I understand that if the cathode is on the right of the cell, then the cell potential i...

Aya Shokair- Dis 2H

Varsha Sivaganesh 1A wrote:Also, when the reaction is irreversible, $\Delta$ S_surroundings = 0.

I don't think that's true.

Aya Shokair- Dis 2H

A sample of 1 mol of gas initially at 1 atm and 298K is heated at constant pressure to 350K, then the gas is compressed isothermally to its initial volume and finally it is cooled to 298K at constant volume. Which of the following values is 0? a. ΔSsurr and ΔG b. ΔSsys and ΔSsurr c. q and w d. W e. ...

Aya Shokair- Dis 2H

^^ Yes! So did I, would it be wrong to use ∑∆G(products)-∑∆G(reactants)?

Aya Shokair- Dis 2H

We are meant to know the entire chapter 11. The new sections are 11.3 and 11.11-11.13.
The other parts of chapter 11 were covered in chem 14a.

Electrochemistry is not on the midterm, so you're right no redox reactions.

Aya Shokair- Dis 2H

Oh, I think I can answer my own question lol. When you have an increase in thermal entropy due to an increase in temperature, the system is allowed more possible configurations or mircostates. So that's how it takes into account thermal entropy. With an increase in temperature, there is an increase ...

Aya Shokair- Dis 2H

From my understanding, I thought Boltzmann's equation was used to calculate only the positional entropy with out taking into account the thermal entropy. So ideally, if there is any positional entropy left at K=0. However, in the book it says that the Boltzmann formula enables us to calculate the ab...

Aya Shokair- Dis 2H

Thank you!

Aya Shokair- Dis 2H

No work is done in a free expansion, thus w=0. If it was a isothermal free expansion, you can go on to say delta U= 0. So that w=-q. since w=0, q=0. You can go on even further to say whether its a irreversible or reversible process. If it is a reversible process, then the process is at equilibrium, ...

Aya Shokair- Dis 2H

So for heat capacity, the more substance you have the more heat is required to raise it by 1 degree C.
However, for specific heat capacity, it does not take into account how much substance you have because it is the heat required to raise 1 gram of a substance by 1 degree C.

Aya Shokair- Dis 2H

In an isothermal, reversible free expansion, delta S tot= 0 because it is an equilibrium.
So, delta S sys= -delta S surr

Aya Shokair- Dis 2H

^^ that is in an irreversible isothermal free expansion

Aya Shokair- Dis 2H

There is no work down on a free expansion. When you are looking at an isothermal free expansion, you know that delta U= 0. So that means -w=q. We just said that there is no work done on a free expansion, so both q & w would equal 0. Thus no heat transferred into the surroundings, so the entropy ...

Aya Shokair- Dis 2H

What is the heat capacity at constant P for a diatomic ideal gas?
I know C(p) is 5/2R for a monoatomic ideal gas.

Aya Shokair- Dis 2H

In isochoric conditions, the change in V is constant/zero. Thus, that means there must be a change in P. However, we can calculate the change in enthalpy by using this formula: delta H= nC(p)delta T In the formula we are assuming constant P, but that isn't the case right? Can someone explain that to...

Aya Shokair- Dis 2H

When a reaction is at equilibrium or when a reaction is reversible. The delta S total = 0. So delta S surroundings= -delta S system

Aya Shokair- Dis 2H

Container A is fi lled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The containers all...

Aya Shokair- Dis 2H

When you add more of a substance into the system, you are increasing the internal energy by increasing the potential energy.
Remember that internal energy is equal to KE + PE.

Aya Shokair- Dis 2H

1 bar is approx. 1 atm!
They are interchangeable.

Aya Shokair- Dis 2H

What are three ways you can increase the internal energy?
(chap 8, excerise 2)

Aya Shokair- Dis 2H

I think the only way you can add energy to an open system is by adding or removing the amount of substance.
For example, adding 1 gram of glucose to a system with 9 grams of glucose increases the potential energy.

Aya Shokair- Dis 2H

A 50.0-g ice cube at 0.0 C is added to a glass containing 400.0 g of water at 45.0 C. What is the fi nal temperature of the system (see Tables 8.2 and 8.3)? Assume that no heat is lost to the surroundings. I understand that q(ice)=-q(water) So i imagined that we would solve it like this m(ice) x C...

Aya Shokair- Dis 2H

You would have to compare bonds of the reactants with bonds of the products.
Another way to solve for the heat of the reaction, would to break ALL the bonds of the reactants and form all the bonds of the products.
This way you won't miss any bonds, but it is a bit more math!

Aya Shokair- Dis 2H

Perhaps it works best with the scope of this class.
A diluted solution might not significantly differ in its specific heat compared to the pure solvent for it to be taken into account.

Aya Shokair- Dis 2H

In class today, Dc. Lavelle said that there are three ways to change the energy of a system. One of the ways was to heat or cool the system and he specifically referred to closed systems. Can this idea be used on open systems as well? Or would the added heat be released to the surroundings bc it isn...

Aya Shokair- Dis 2H

Yes! They were giving us the change in temperature. The change in temperature will be the same in Celsius or K.

Aya Shokair- Dis 2H

Molar heat capacity! with units: J/(mol K)

Aya Shokair- Dis 2H

Bond formation is always exothermic, so a negative H. Bond breaking is endothermic, so a positive H. When looking at a reaction, you must draw all the lewis structures of the reactants and products to understand which bonds are broken and which are newly formed. We do this to calculate the heat of t...

Aya Shokair- Dis 2H

Enthalpy is the heat released or absorbed by a system at constant pressure. ΔH Standard enthalpy has the same definition, however it is measure enthalpy of objects in their standard states.ΔH° Standard states for a liquid, solid, and gas occur at 1 bar, typically at 25C° For solutions the standard s...

Aya Shokair- Dis 2H

I know the rules regarding what makes a strong acid (binary or oxyacid).
Did we go over any rules on what makes a strong base?
Is it right to think that it's conjugate acid must be stable and weak relatively?

Aya Shokair- Dis 2H

You can think of heat as a reactant in exothermic reactions!

Aya Shokair- Dis 2H

He was referring to if you add a small quantity of a weak acid and you calculate the pH/ [H3O+], you'll get what looks like a strong base. He was saying that should make you question it because why would adding a small amount of weak acid result in a strong base? So, he brought of the point that the...

Aya Shokair- Dis 2H

When I think of Lewis, I think of electrons because of the lewis structures we've been doing. So, I know that lewis acids/bases are concerning electrons. Lewis acids accept electrons and lewis bases donate electrons. Bronsted acids/bases are what I typically think of when I think of acids and bases-...

Aya Shokair- Dis 2H

When you write out the complete ionic equation you include all the species of that reaction. You might notice that you will have unchanged species on either side. So, when you write the net ionic equation, you cross off those unchanged species on either side because they aren't directly involved in ...

Aya Shokair- Dis 2H

A lewis acid and a Bronsted acid are describing the same species, however looking at different aspects. A lewis acid is able to accept electrons. A Bronsted acid donates protons (H+).

Aya Shokair- Dis 2H

They are able to react in the presence of both an acid and a base.

Aya Shokair- Dis 2H

The 2 in front of sp is referring to the principal level the orbital lies in!

Aya Shokair- Dis 2H

Hi, I am slightly confused because I was determining the polarity of NH3 and I came to the answer that it's polar because it contains polar bonds making the entire molecule polar. Overall, the hydrogens are more positively charged than the nitrogen. However, I remember in class Professor Lavelle say...

Aya Shokair- Dis 2H

I feel like it will be helpful to refer to the p orbitals and their shape/orientation. Each p-orbital are orientated along an axis. In two atoms, with p-orbital bonding, one of the three orbitals will interact head on. The other one/two will be parallel to the other atoms p-orbitals.

Aya Shokair- Dis 2H

Yes, if you can imagine. You have two atoms that both contain p-orbitals. When they form a bond, 1 of the 3 p-orbitals of each atom interact head-on with a lot of overlap. The other 2 orbitals are parallel to its partner orbital in the other atom. These orbitals will form pi bonds.

Aya Shokair- Dis 2H

Radial node is a circular area with zero density, which means no electrons will be found there. Radial plane is a flat region (plane) with zero electron density.
To find the total number of nodes in an orbital= n-1
To find number of angular nodes= l
To find number of radial nodes= n-l-1

Aya Shokair- Dis 2H

No, bond length and ionic character are not correlated. Ionic character is just referring to the electrons.

Aya Shokair- Dis 2H

n is any number above 1. So it can be 1,2,3,4....
l is [0,..., n-1]
ml is [-l,l]

So, for example, if you had n=6.
possible values for l=0,1,2,3,4,5. If we pick an electron in the 3 orbital
ml=-3,-2,-1,0,1,2,3

Hope that helps!!

Aya Shokair- Dis 2H

Hi,
I know that Doctor Lavelle and the book says that electron affinity is not really periodic, but we still have to be able to compare elements and determine which would be higher/lower electron affinity energy. How are we supposed to do that?

Aya Shokair- Dis 2H

I haven't solved this problem yet, but I'd assume that you look up the Ionization Energy for Argon (I predict will be relatively high). It will most likely be in units of kJ/mol, so you'll have to convert it to J/atom. This energy will be the amount of energy required to remove the electron in gaseo...

Aya Shokair- Dis 2H

For large, everyday objects the Heisenberg's Uncertainty Principle does not apply because the indeterminacy of momentum and position are so small that they're negligible. For example, when a baseball passes between two lasers, we are 100% certain of the path it took and the velocity/momentum it trav...

Aya Shokair- Dis 2H

Yes, correct me if I'm wrong but I think of a node as having zero possibility of an electron being in that space.

Aya Shokair- Dis 2H

Test 3 is covering material up to Oct. 27th.

Aya Shokair- Dis 2H

This question is asking you to determine the empirical formula which, by definition, is the ratio between the atoms in the molecule. So, by assuming that you're working with 100 g of Vanillin, you can convert each mass by composition percent to grams. For example, 63.15% C could be expressed as 63.1...

Aya Shokair- Dis 2H

Yes, I second the statement above. Doctor Lavelle said he'll give you the chemical formulas for all the questions on the test on Friday.

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