Search found 48 matches

by Vicky Lu 1L
Wed Feb 13, 2019 1:29 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heating water + cooling
Replies: 2
Views: 17

Re: Heating water + cooling

If we start out with qtotal = qsystem + qsurrounding, you can get qsystem=-qsurrounding if no energy can be lost to the surrounding. Therefore, if you pick ice to be your system and water to the be surrounding, qice=-qwater. which means that heat gained by ice will be from the heat of water, (making...
by Vicky Lu 1L
Wed Feb 13, 2019 1:23 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: state function
Replies: 4
Views: 14

Re: state function

Work is not a state function along with heat and cell potential. Internal energy is a state function as at equilibrium, there is a set amount as delta Utotal = deltaU system + deltaU surrounding. Work and heat are path functions, so you can't find its value based on final - initial.
by Vicky Lu 1L
Wed Feb 13, 2019 1:17 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: Finding W (degeneracy)
Replies: 4
Views: 22

Re: Finding W (degeneracy)

If you are given mols of a substance, Avogadro's number (NA) will appear in the the raised power, times the number of amount of identical molecules/particles.
For example, when calculating the residual entropy of 1 mol of C6H5Br, w = 6 ^ 1*NA, therefore S = Kb*ln (6^1NA) = NA*Kb*ln6.
by Vicky Lu 1L
Tue Feb 05, 2019 10:58 pm
Forum: Calculating Work of Expansion
Topic: work done by system or on system
Replies: 3
Views: 12

Re: work done by system or on system

q (heat) is positive when its has key words such as absorbed/gain energy and is negative when it released/emitted/loses energy. w (work) is positive when work is done on the system and negative when the system does or is doing the work.
by Vicky Lu 1L
Tue Feb 05, 2019 8:32 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Quick Conceptual question
Replies: 7
Views: 35

Re: Quick Conceptual question

Enthalpy (H) refers to the heat in the system while entropy (S) can be thought of as the disorder of the system. They are connected by delta G = delta H - T*delta S. For enthalpy, use the 3 methods: Standard Enthalpy of Formation, Bond Enthalpy, and Hess's Law. In Entropy, changes in volume would us...
by Vicky Lu 1L
Tue Feb 05, 2019 7:27 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reversible Processes
Replies: 2
Views: 16

Re: Reversible Processes

A reversible process is a process whose direction can be "reversed" by inducing very very small changes to a system via its surroundings. Most of the time it occurs with a constant temperature/isothermic.
by Vicky Lu 1L
Mon Jan 28, 2019 10:53 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 2
Views: 19

Re: Bond Enthalpies

To add, this is why bond enthalpy is the least accurate of the three methods since its value is made up from the average of data of many different molecules of different reactions.
by Vicky Lu 1L
Mon Jan 28, 2019 10:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Breaking Bonds
Replies: 4
Views: 22

Re: Breaking Bonds

It is best to draw out the Lewis structures of all the reactants and the products in order to tell which bonds are broken/formed. From there, look for the difference in the reactants to the products of each atom to atom bond in order to tell what the net difference is. From the net difference, you w...
by Vicky Lu 1L
Mon Jan 28, 2019 10:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law (Method 1)
Replies: 4
Views: 30

Re: Hess's Law (Method 1)

Since we do not know the delta H of the net reaction, we have to rely on the delta Hs of the intermediate reactions that can lead us to the net reaction. It is not necessarily adding the two delta H as we have to make sure first the you use the intermediate reactions correctly that would lead you th...
by Vicky Lu 1L
Thu Jan 24, 2019 12:08 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Specific Notation
Replies: 5
Views: 25

Re: Specific Notation

Notation does matter when calculating K. Use brackets when dealing with concentration such as [PCl5]. Brackets are not require if you write out the value of the concentration of PCl5. As for the gaseous states, you don't not use brackets. If you want, you can use parentheses around P PCl5 like so (P...
by Vicky Lu 1L
Wed Jan 23, 2019 11:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reactions at Equilibrium
Replies: 1
Views: 13

Re: Reactions at Equilibrium

I believe that the question will inform the reaction's reactant and/or products. And to know which way the reaction will run, compare Q and K. If Q>K, then the reaction will favor the reactant while if Q<K, then the reaction will favor the product.
by Vicky Lu 1L
Wed Jan 23, 2019 11:50 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Problem 12.45 (6th edition)
Replies: 2
Views: 16

Re: Problem 12.45 (6th edition)

The trend is that the a smaller pKa/larger the Ka, the stronger the acid and the larger the pKb/smaller the Kb, the stronger the acid. Likewise, the smaller the pKb/larger the Kb, the stronger the base and the larger the pKA/smaller Ka, the stronger the base.
by Vicky Lu 1L
Wed Jan 16, 2019 11:32 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert Gases
Replies: 5
Views: 44

Re: Inert Gases

Adding an inert gas won't have an effect on the equilibrium composition as inert gases do not want to interact/react as they are already stable.
by Vicky Lu 1L
Wed Jan 16, 2019 11:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Conjugates
Replies: 5
Views: 37

Re: Conjugates

The conjugate seesaw describes the relationship between an acid and its conjugate base and also a base with tis conjugate acid. The acid or base and their conjugate are inversely proportionate in terms of strength. This is a seesaw as when the acid or base is stronger, the weaker the conjugate acid ...
by Vicky Lu 1L
Wed Jan 16, 2019 11:17 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentration
Replies: 4
Views: 26

Re: Concentration

K stands for Equilibrium Constant which describes the reaction at equilibrium. Q is the reaction quotient which describes the reaction at any point in time. We compare K and Q as it will tell us whether the reaction is favoring the reactant, products, or neither. If Q>K, then he reaction favors the ...
by Vicky Lu 1L
Thu Jan 10, 2019 10:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q and K
Replies: 13
Views: 79

Re: Q and K

The difference between Q and K is that Q is an expression that can be used to describe the composition of the reaction mixture at any time of the reaction. And also between Q and K, the reaction quotient Q at equilibrium is equal to the equilibrium constant K.
by Vicky Lu 1L
Thu Jan 10, 2019 10:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K vs Kp [ENDORSED]
Replies: 4
Views: 48

Re: K vs Kp [ENDORSED]

K in general is an expression to describe the composition of the reaction at equilibrium. Kp is for concentration of partial pressure of the reactants/products while Kc is used in concentration of the reactants/products. Solid and liquids aren't included in the equilibrium constant expression, only ...
by Vicky Lu 1L
Tue Jan 08, 2019 10:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Leaning to the left/right
Replies: 4
Views: 35

Re: Leaning to the left/right

I believe this phrase is talking about which side the equilibrium will move/shift, to the left or right side of the reaction. It is talking about moving back and forth between the forward and backward reaction.
by Vicky Lu 1L
Mon Dec 03, 2018 10:57 pm
Forum: Naming
Topic: Order of Ligand Naming
Replies: 6
Views: 59

Re: Order of Ligand Naming

If there are multiple ligands, the order the ligands are named should follow alphabetical order. If the coordinate compound is PtCl2(NO2)2, then the Cl would be named before the NO2.
by Vicky Lu 1L
Mon Dec 03, 2018 10:54 pm
Forum: Naming
Topic: Prefix bis, tris, tetrakis, etc. [ENDORSED]
Replies: 5
Views: 99

Re: Prefix bis, tris, tetrakis, etc. [ENDORSED]

Di-, tri-, and tetra- should be used for multiple monodentate ligands while bis-, tris-, tetrakis- would be used for for multiple polydentate ligands.
by Vicky Lu 1L
Mon Dec 03, 2018 10:39 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Acids and Bases?
Replies: 2
Views: 42

Re: Bronsted Acids and Bases?

Lewis Acid accepts e- pair and Lewis Base donates e- pairs. Bronsted Acid donates H+ and Bronsted Base accepts H+. Bronsted Acid and Base only involve Hydrogen while Lewis Acid and Base deals with all atoms/molecules. All Bronsted Acids/Bases are Lewis Acids/Bases are Lewis Acids/Bases for this reas...
by Vicky Lu 1L
Tue Nov 27, 2018 10:51 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: ion-ion bond vs. H-bond
Replies: 4
Views: 65

Re: ion-ion bond vs. H-bond

Ion-ion bonds are stronger than hydrogen bond. Ion-ion bonds result in solids as seen in an example with Na+ and Cl-. Together Na+ and Cl- will form an ordered lattice. Hydrogen bonding comes second as this is still the strongest type of intermolecular forces since the difference in electronegativit...
by Vicky Lu 1L
Tue Nov 27, 2018 10:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw Shape Bond Angles
Replies: 8
Views: 78

Re: Seesaw Shape Bond Angles

The bond angles in a see saw shape molecule are less than 120 in equatorial and less than 90 in axial.
by Vicky Lu 1L
Tue Nov 27, 2018 10:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Angle Distorted
Replies: 4
Views: 45

Re: Angle Distorted

Angle distortion means that the angles in the bond has been changed from the typical bond angle arrangement. This is most likely the result of lone pair repulsion which allows electrons in the lone pair to push the other regions of electron density in the molecule away, making the bond angles now di...
by Vicky Lu 1L
Sat Nov 24, 2018 12:53 am
Forum: Ionic & Covalent Bonds
Topic: Bond Lengths
Replies: 10
Views: 112

Re: Bond Lengths

Due to resonance, the most stable structure of the nitrate will be an average of the bonds nitrate holds which is both a single and double bond. As an overall molecule, nitrate's structure will even out and be an inbetween version of a single and double bond. Therefore, the average of 120 and 140 is...
by Vicky Lu 1L
Sat Nov 24, 2018 12:49 am
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR RULE 3
Replies: 4
Views: 72

Re: VSEPR RULE 3

If would make sense if single, double, triple bonds are considered the same as each of these bond still has the same purpose of linking atoms to the other atoms. Each atom holds electrons and therefore each bond is linked to one region of electron density.
by Vicky Lu 1L
Sat Nov 24, 2018 12:40 am
Forum: Bond Lengths & Energies
Topic: H bonding
Replies: 12
Views: 123

Re: H bonding

As hydrogen bonding is on the stronger side of intermolecular forces, it requires more energy to break this bond. This results in high boiling points since it requires more energy to separate the molecules.
by Vicky Lu 1L
Thu Nov 15, 2018 9:28 pm
Forum: Octet Exceptions
Topic: The center atom
Replies: 20
Views: 202

Re: The center atom

O would be the central atom since it is the least ionization energy and can form more bond than the H and Cl. It would not H since H can only have one bond and it would not be Cl either since can normally only form one bond.
by Vicky Lu 1L
Thu Nov 15, 2018 9:21 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 10
Views: 107

Re: Formal Charge

It is better to follow and determine molecular structures base on the formal charger as there are exceptions to the octet rule. Formal charge is the best way to make sure the Lewis structure is in the most stable state it can be as well as writing out the right Lewis structure since the formal charg...
by Vicky Lu 1L
Thu Nov 15, 2018 9:18 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Vespr Formula
Replies: 6
Views: 68

Re: Vespr Formula

The VSEPR formula is simply the letter A follow by X with a subscript of how many atoms are attached to the central atom you pick and E with the subscript of the number of lone pairs of electrons attached to the central atom as well.
by Vicky Lu 1L
Thu Nov 08, 2018 9:08 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Van Der Waal forces
Replies: 3
Views: 517

Re: Van Der Waal forces

Dipoles have intermolecular forces that are between two or more different molecules. Dipole-dipole forces are between opposite partial charges on two different polar molecules that wants to attract each other. In an induced dipole-dipole, it is a coercive force in which the one causes the other to b...
by Vicky Lu 1L
Thu Nov 08, 2018 8:58 pm
Forum: Octet Exceptions
Topic: Octet vs formal charge
Replies: 15
Views: 135

Re: Octet vs formal charge

I believe having the correct formal charge is more important than having a full octet. As seen in some examples with radicals and expanded octets, it is alright if the atom does not have an entire octet, however, your formal charges between the atoms should be equal to the formal charge of the molec...
by Vicky Lu 1L
Mon Nov 05, 2018 3:29 pm
Forum: Octet Exceptions
Topic: Expanded Octet [ENDORSED]
Replies: 5
Views: 81

Re: Expanded Octet [ENDORSED]

Elements are allowed an expanded octet if they are n=3 and after. They are able to do so as there is a d orbital where they can be electrons in. Since n=3, l can be 0, 1, or 2 and therefore corresponds with s, p, and d orbitals.
by Vicky Lu 1L
Wed Oct 31, 2018 9:49 pm
Forum: Lewis Structures
Topic: Central Atom
Replies: 13
Views: 150

Re: Central Atom

The central atom is normally determined by the element with the lowest ionization energy, in your case with the example, CH3OH, carbon. However, if its finding the Lewis structure for HOCO for example, then you would write it straight out like that (H-O-C-O) since it is written in that manner.
by Vicky Lu 1L
Wed Oct 31, 2018 9:41 pm
Forum: Ionic & Covalent Bonds
Topic: p block atoms
Replies: 4
Views: 79

Re: p block atoms

Atoms from n=3 and on, such as P, S, and Cl can have more than 8 valence electrons as they had a d-orbital to put electrons there. They are able to have an expanded octet since there is an empty orbital (d) that is not used. Atoms on row 2 can't have expanded octets.
by Vicky Lu 1L
Wed Oct 31, 2018 9:34 pm
Forum: Ionic & Covalent Bonds
Topic: octet rule
Replies: 11
Views: 121

Re: octet rule

The octet rule concerns atoms wanting to share their electrons in order to complete their valence shell and be the most stable they can. To do this, atom want to either complete their last orbital shell or get rids of some on the last and share/lend it to another atom. They would want to share and h...
by Vicky Lu 1L
Tue Oct 23, 2018 10:03 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Bohr Frequency Condition
Replies: 2
Views: 71

Re: Bohr Frequency Condition

En is actually the energy of an electron in a energy level which is denoted by n. If it is a problem dealing with atomic spectra and the Rydberg Equation, such as asking to find the frequency of a proton that was emitted as it transitioned from the 5th or 3rd energy level, then you have 2 n and ther...
by Vicky Lu 1L
Tue Oct 23, 2018 9:43 pm
Forum: Quantum Numbers and The H-Atom
Topic: Principle Quantum #
Replies: 5
Views: 112

Re: Principle Quantum #

n is the energy level. It describes the type of orbital the electron will be located in. If n=1, then it is at the ground state/first energy level where energy is the lowest. The higher the n, the more energy there are at those energy levels.
by Vicky Lu 1L
Tue Oct 23, 2018 9:31 pm
Forum: Student Social/Study Group
Topic: Questions about Heisenberg
Replies: 5
Views: 148

Re: Questions about Heisenberg

For uncertainty questions, delta v depends on the part after the ±. So in the case of your example, 23 ± 0.1 m/s, just multiple the uncertainty part (± 0.1 m/s) by two as the possible values is up and down at 22.9 m/s and 23.1 m/s.
by Vicky Lu 1L
Thu Oct 18, 2018 8:16 pm
Forum: Properties of Light
Topic: calculating wavelength
Replies: 10
Views: 245

Re: calculating wavelength

You should use De Broglie to solve for the wavelength of a mass. Atoms and objects have mass but light does not. The p (momentum) of De Broglie can be split into (mass*velocity) and that is where mass can be seen. Between the two formula, it is best to just list all the given values and put question...
by Vicky Lu 1L
Thu Oct 18, 2018 8:04 pm
Forum: Properties of Light
Topic: color of light
Replies: 11
Views: 131

Re: color of light

Both can be used to determine the color of visible light. You can identity the specific color of light by mainly by wavelength but if you know the wavelength you find the frequency of light and compare it to what color that would be as well, by the equation speed of light = frequency x wavelength. T...
by Vicky Lu 1L
Thu Oct 18, 2018 7:44 pm
Forum: *Shrodinger Equation
Topic: Using the Equation
Replies: 2
Views: 60

Re: Using the Equation

The Schrodinger's Wave Question is meant to describe where electrons are in an atom and basically the physical changes of the quantum state of an atom that occurs over time. It's just important to know that Ψ represent the height of the wave at position x,y,z and Ψ^2 is the probability of finding an...
by Vicky Lu 1L
Thu Oct 11, 2018 9:24 pm
Forum: Empirical & Molecular Formulas
Topic: Is it possible for the Empirical and Molecular formula to be the same? [ENDORSED]
Replies: 8
Views: 205

Re: Is it possible for the Empirical and Molecular formula to be the same? [ENDORSED]

Empirical and molecular formula can be the exact same as each other. The empirical formula is the simplest ratio of elements in that molecule, however, the molecular formula is merely the exact/actual ratio of elements. It could be that a molecule is in both its empirical and molecular formula alrea...
by Vicky Lu 1L
Thu Oct 11, 2018 9:02 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Mass percent composition [ENDORSED]
Replies: 4
Views: 168

Re: Mass percent composition [ENDORSED]

Mass percent composition is the proportion of an element of that whole molecule. It would be the mass of that element divided by the entire molar mass of a compound.
by Vicky Lu 1L
Thu Oct 11, 2018 8:57 pm
Forum: Significant Figures
Topic: sig figs in periodic table
Replies: 6
Views: 150

Re: sig figs in periodic table

It is best to use the all the significant figures from the periodic table as well as solving your way through a problem with multiplication, division, addition, etc. This way the calculation will be as exact as possible for the final answer. Only by the very end do you round the answers according to...
by Vicky Lu 1L
Mon Oct 01, 2018 9:17 pm
Forum: SI Units, Unit Conversions
Topic: Naming Compounds
Replies: 8
Views: 165

Re: Naming Compounds

There is no trick to memorizing and knowing how to write in molecular terms for cases such as Calcium Sulfide. It is something to either study or pick up. I was say the best way to know the name of compounds would be to learn the common polyatomic ions in groups according to the patterns in their na...
by Vicky Lu 1L
Mon Oct 01, 2018 9:08 pm
Forum: SI Units, Unit Conversions
Topic: Grams/mole
Replies: 12
Views: 208

Re: Grams/mole

g/mol and g.mol^-1 are two different notation but they mean the same things. the ^-1 denotes that mol will be in the denominator. I like to use g/mol to see it fully written out and for it to already be in that form when I use it to solve problems.
by Vicky Lu 1L
Mon Oct 01, 2018 8:44 pm
Forum: General Science Questions
Topic: Periodic Table
Replies: 16
Views: 319

Re: Periodic Table

I tend to use the entirety of the atomic weight listed for that element on the periodic table. I only round at the very end for the final answer and that depends on how many significant figures are used in the given values that is stated at the very beginning from the question.

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