Search found 58 matches

by Aya Shokair- Dis 2H
Tue Mar 13, 2018 8:22 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Steady-State v Pre equilibrium?
Replies: 2
Views: 144

Re: Steady-State v Pre equilibrium?

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...
by Aya Shokair- Dis 2H
Tue Mar 13, 2018 8:14 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Test 1 #3
Replies: 4
Views: 287

Re: Test 1 #3

A change in volume means expansion work is occurring!
by Aya Shokair- Dis 2H
Tue Mar 13, 2018 8:10 pm
Forum: Zero Order Reactions
Topic: Applications
Replies: 2
Views: 218

Re: Applications

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
by Aya Shokair- Dis 2H
Tue Mar 13, 2018 8:08 pm
Forum: Calculating Work of Expansion
Topic: Irreversible and reversible
Replies: 1
Views: 87

Re: Irreversible and reversible

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
by Aya Shokair- Dis 2H
Tue Mar 13, 2018 8:00 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: entropy in reversible/irreversible processes
Replies: 1
Views: 196

Re: entropy in reversible/irreversible processes

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)
by Aya Shokair- Dis 2H
Tue Mar 13, 2018 7:56 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bomb Calorimeter
Replies: 2
Views: 261

Re: Bomb Calorimeter

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...
by Aya Shokair- Dis 2H
Tue Mar 13, 2018 7:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Isobaric
Replies: 1
Views: 111

Re: Isobaric

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.
by Aya Shokair- Dis 2H
Tue Mar 13, 2018 7:46 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-Equilibrium Method Conditions
Replies: 2
Views: 105

Re: Pre-Equilibrium Method Conditions

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.
by Aya Shokair- Dis 2H
Mon Feb 19, 2018 5:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Determining the sign of a cell potential
Replies: 1
Views: 96

Determining the sign of a cell potential

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...
by Aya Shokair- Dis 2H
Wed Feb 14, 2018 2:16 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Delta S(tot)
Replies: 5
Views: 359

Re: Delta S(tot)

Varsha Sivaganesh 1A wrote:Also, when the reaction is irreversible, Ssurroundings = 0.


I don't think that's true.
by Aya Shokair- Dis 2H
Tue Feb 13, 2018 7:38 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: UA Karen Week 4 #6 [ENDORSED]
Replies: 1
Views: 138

UA Karen Week 4 #6 [ENDORSED]

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. ...
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 11:43 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.83
Replies: 4
Views: 192

Re: 11.83

^^ Yes! So did I, would it be wrong to use ∑∆G(products)-∑∆G(reactants)?
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 10:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Midterm w18 -Last subject?
Replies: 2
Views: 144

Re: Midterm w18 -Last subject?

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.
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 6:30 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Boltzmann Equation
Replies: 3
Views: 298

Re: Boltzmann Equation

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 ...
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 6:28 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Boltzmann Equation
Replies: 3
Views: 298

Boltzmann Equation

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...
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 5:54 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 2
Views: 144

Re: Free Expansion

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, ...
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 5:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Extensive vs Intensive
Replies: 3
Views: 148

Re: Extensive vs Intensive

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.
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 5:44 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 4
Views: 188

Re: Free Expansion

In an isothermal, reversible free expansion, delta S tot= 0 because it is an equilibrium.
So, delta S sys= -delta S surr
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 5:41 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 4
Views: 188

Re: Free Expansion

^^ that is in an irreversible isothermal free expansion
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 5:40 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 4
Views: 188

Re: Free Expansion

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 ...
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 5:36 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Heat Capacity at constant P for a diatomic ideal gas
Replies: 2
Views: 156

Heat Capacity at constant P for a diatomic ideal gas

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.
by Aya Shokair- Dis 2H
Mon Feb 12, 2018 5:35 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isochoric Conditions
Replies: 1
Views: 123

Isochoric Conditions

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...
by Aya Shokair- Dis 2H
Sun Feb 11, 2018 7:29 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Delta S total
Replies: 2
Views: 143

Re: Delta S total

When a reaction is at equilibrium or when a reaction is reversible. The delta S total = 0. So delta S surroundings= -delta S system
by Aya Shokair- Dis 2H
Sun Feb 11, 2018 7:22 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.35
Replies: 2
Views: 222

9.35

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...
by Aya Shokair- Dis 2H
Wed Jan 24, 2018 10:27 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Changing the energy of a system
Replies: 6
Views: 242

Re: Changing the energy of a system

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.
by Aya Shokair- Dis 2H
Sun Jan 21, 2018 9:08 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Open System
Replies: 7
Views: 333

Open System

What are three ways you can increase the internal energy?
(chap 8, excerise 2)
by Aya Shokair- Dis 2H
Sun Jan 21, 2018 7:04 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Heating/Cooling A System
Replies: 4
Views: 227

Re: Heating/Cooling A System

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.
by Aya Shokair- Dis 2H
Thu Jan 18, 2018 9:25 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.41
Replies: 3
Views: 175

8.41

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...
by Aya Shokair- Dis 2H
Thu Jan 18, 2018 10:16 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Breaking or forming
Replies: 5
Views: 164

Re: Bond Breaking or forming

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!
by Aya Shokair- Dis 2H
Wed Jan 17, 2018 10:57 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific Heat Capacity
Replies: 5
Views: 208

Re: Specific Heat Capacity

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.
by Aya Shokair- Dis 2H
Wed Jan 17, 2018 10:55 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Heating/Cooling A System
Replies: 4
Views: 227

Heating/Cooling A System

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...
by Aya Shokair- Dis 2H
Wed Jan 17, 2018 10:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.25
Replies: 2
Views: 113

Re: 8.25

Yes! They were giving us the change in temperature. The change in temperature will be the same in Celsius or K.
by Aya Shokair- Dis 2H
Wed Jan 17, 2018 10:47 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cm
Replies: 3
Views: 157

Re: Cm

Molar heat capacity! with units: J/(mol K)
by Aya Shokair- Dis 2H
Wed Jan 17, 2018 10:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Breaking or forming
Replies: 5
Views: 164

Re: Bond Breaking or forming

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...
by Aya Shokair- Dis 2H
Wed Jan 17, 2018 10:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy vs Standard Enthalpy
Replies: 1
Views: 109

Re: Enthalpy vs Standard Enthalpy

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...
by Aya Shokair- Dis 2H
Sat Dec 09, 2017 8:45 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong Bases? [ENDORSED]
Replies: 2
Views: 376

Strong Bases? [ENDORSED]

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?
by Aya Shokair- Dis 2H
Sat Dec 09, 2017 1:04 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic Reaction
Replies: 3
Views: 277

Re: Exothermic Reaction

You can think of heat as a reactant in exothermic reactions!
by Aya Shokair- Dis 2H
Sat Dec 09, 2017 1:00 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: calculating pH
Replies: 3
Views: 186

Re: calculating pH

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...
by Aya Shokair- Dis 2H
Sat Dec 09, 2017 12:51 pm
Forum: Lewis Acids & Bases
Topic: Lewis Acids/Bases vs Bronsted Acids/Bases
Replies: 3
Views: 196

Re: Lewis Acids/Bases vs Bronsted Acids/Bases

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-...
by Aya Shokair- Dis 2H
Sat Dec 09, 2017 12:48 pm
Forum: Balancing Chemical Reactions
Topic: Fundamentals J
Replies: 2
Views: 182

Re: Fundamentals J

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 ...
by Aya Shokair- Dis 2H
Sun Dec 03, 2017 5:22 pm
Forum: Lewis Acids & Bases
Topic: Distinguishing Lewis Acid
Replies: 2
Views: 150

Re: Distinguishing Lewis Acid

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+).
by Aya Shokair- Dis 2H
Sun Dec 03, 2017 5:19 pm
Forum: Amphoteric Compounds
Topic: Amphiprotic compounds
Replies: 3
Views: 352

Re: Amphiprotic compounds

They are able to react in the presence of both an acid and a base.
by Aya Shokair- Dis 2H
Sat Nov 25, 2017 5:24 pm
Forum: Hybridization
Topic: Question 4.95
Replies: 2
Views: 155

Re: Question 4.95

The 2 in front of sp is referring to the principal level the orbital lies in!
by Aya Shokair- Dis 2H
Sat Nov 25, 2017 5:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polarity of NH3?
Replies: 4
Views: 1874

Polarity of NH3?

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...
by Aya Shokair- Dis 2H
Sat Nov 18, 2017 9:50 pm
Forum: Hybridization
Topic: Double sigma v. pi bonds
Replies: 4
Views: 180

Re: Double sigma v. pi bonds

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.
by Aya Shokair- Dis 2H
Sat Nov 18, 2017 9:47 pm
Forum: Hybridization
Topic: sigma/pi bond
Replies: 4
Views: 256

Re: sigma/pi bond

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.
by Aya Shokair- Dis 2H
Thu Nov 09, 2017 5:06 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Radial Nodes/Planes
Replies: 2
Views: 179

Re: Radial Nodes/Planes

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
by Aya Shokair- Dis 2H
Thu Nov 09, 2017 5:01 pm
Forum: Bond Lengths & Energies
Topic: Bond Length
Replies: 3
Views: 227

Re: Bond Length

No, bond length and ionic character are not correlated. Ionic character is just referring to the electrons.
by Aya Shokair- Dis 2H
Sun Nov 05, 2017 11:07 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Shell, subshell, and orbital
Replies: 5
Views: 310

Re: Shell, subshell, and orbital

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!!
by Aya Shokair- Dis 2H
Sun Nov 05, 2017 11:01 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity [ENDORSED]
Replies: 6
Views: 455

Electron Affinity [ENDORSED]

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?
by Aya Shokair- Dis 2H
Sun Oct 29, 2017 8:52 pm
Forum: Trends in The Periodic Table
Topic: 2.97
Replies: 2
Views: 268

Re: 2.97

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...
by Aya Shokair- Dis 2H
Sun Oct 29, 2017 8:46 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Two multiple choice questions I was stuck on ...
Replies: 2
Views: 259

Re: Two multiple choice questions I was stuck on ...

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...
by Aya Shokair- Dis 2H
Sun Oct 22, 2017 9:26 pm
Forum: *Shrodinger Equation
Topic: What is a node?
Replies: 5
Views: 348

Re: What is a node?

Yes, correct me if I'm wrong but I think of a node as having zero possibility of an electron being in that space.
by Aya Shokair- Dis 2H
Sun Oct 22, 2017 9:24 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Test 3 [ENDORSED]
Replies: 5
Views: 369

Re: Test 3 [ENDORSED]

Test 3 is covering material up to Oct. 27th.
by Aya Shokair- Dis 2H
Tue Oct 03, 2017 11:54 pm
Forum: Empirical & Molecular Formulas
Topic: F. 9
Replies: 2
Views: 529

Re: F. 9

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...
by Aya Shokair- Dis 2H
Tue Oct 03, 2017 11:43 pm
Forum: Molarity, Solutions, Dilutions
Topic: Writing formulas
Replies: 4
Views: 333

Re: Writing formulas

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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