## Search found 67 matches

Sun Mar 17, 2019 10:16 pm
Forum: Experimental Details
Topic: Psuedo First Order
Replies: 4
Views: 652

### Re: Psuedo First Order

A pseudo first order reaction is like a second order reaction that acts like a first order reaction under certain conditions.
Sun Mar 17, 2019 1:01 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Replies: 2
Views: 302

In an adiabatic reaction q =0 while in an isothermal reaction, delta T = 0.
Sat Mar 16, 2019 10:40 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy
Replies: 1
Views: 245

### Re: Enthalpy

It depends on whether C is given in per moles or per grams (molar heat capacity or specific heat capacity).
Sat Mar 16, 2019 10:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: ∆G and work
Replies: 3
Views: 584

### Re: ∆G and work

I believe that delta G is the measure of the maximum amount of energy available for work.
Sat Mar 16, 2019 10:37 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: q and delta H
Replies: 6
Views: 499

### Re: q and delta H

I think q = delta H under constant pressure. I also think that delta H implies constant pressure already so they can be used interchangeably but I am not sure.
Sat Mar 16, 2019 9:51 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Free Expansion
Replies: 3
Views: 346

### Re: Free Expansion

When a system expands, it is doing work on the surroundings which means it would be losing energy. Therefore, work is negative. If the surroundings were to do work on the system, then work would be positive because the system is gaining energy.
Sat Mar 16, 2019 9:49 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 2
Views: 285

### Re: Catalysts

To expand on the above, a homogeneous catalyst is a catalyst of the same phase as the reactants while a heterogeneous catalyst is one that is of a different phase than the reactants.
Sun Mar 10, 2019 9:43 pm
Forum: Zero Order Reactions
Topic: Meaning of Zero, First, and Second Order?
Replies: 4
Views: 145

### Re: Meaning of Zero, First, and Second Order?

Remember you can also relate order numbers to individual reactants themselves or also the overall reaction order.
Sun Mar 10, 2019 9:41 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: What does the Arrhenius Equation tell us?
Replies: 1
Views: 87

### Re: What does the Arrhenius Equation tell us?

If you look at the Arrhenius equation, you will see that increasing temperature increases the number to which e is taken to the power of (T is in the denominator and the number is negative so the number becomes a smaller negative). This increases the value of K. If activation energy decreases, then ...
Sun Mar 10, 2019 9:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Morris Review
Replies: 4
Views: 422

### Re: Morris Review

He said he would post the slides online but if you still want notes I can send them!
Sun Mar 03, 2019 11:47 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: liquid and gaseous states in a cell diagram
Replies: 3
Views: 152

### Re: liquid and gaseous states in a cell diagram

To continue the answers above, remember to use a single line when referencing a porous disc versus the double line used for a salt bridge.
Sun Mar 03, 2019 11:29 am
Forum: General Rate Laws
Topic: Kinetics
Replies: 3
Views: 139

### Re: Kinetics

When you are looking at a chemical reaction, the rate at which each reactant and product is changing might be different from one another. A unique rate would be the rate of change for any species in a chemical reaction divided by its stoichiometric coefficient. Unique rates should be the same for ea...
Sun Mar 03, 2019 11:22 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+ and OH
Replies: 3
Views: 188

### Re: H+ and OH

Sometimes in the homework, the solutions would include KOH instead of OH. Is there a reason for this and should we include salts in our cell diagrams too?
Sun Feb 24, 2019 9:24 pm
Forum: Balancing Redox Reactions
Topic: Salt bridge
Replies: 1
Views: 83

### Re: Salt bridge

In the cell, electrons move from the anode to the cathode which would make the cathode extremely negatively charged. If left like this, electrons would not travel toward the cathode any longer due to the buildup of a negative charge there. The salt bridge helps maintain a neutral state for both solu...
Sun Feb 24, 2019 9:18 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Spontaneous?
Replies: 13
Views: 398

### Re: Spontaneous?

I think the only way to be sure of spontaneity is when ΔG is negative (when ΔH −TΔS is negative) though I could be wrong.
Sun Feb 24, 2019 9:15 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Spontaneous Process
Replies: 2
Views: 89

### Re: Spontaneous Process

A process is spontaneous when ΔG is negative (when ΔH < TΔS).
Sun Feb 17, 2019 7:44 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Calculating entropy
Replies: 4
Views: 134

### Re: Calculating entropy

When we calculate the two independently, we are essentially splitting it up into steps which is allowed since entropy is a state function. First we change the volume and then we change the temperature to reach the final form.
Sun Feb 17, 2019 7:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Intensive vs extensive
Replies: 4
Views: 148

### Re: Intensive vs extensive

I would assume that Gibbs free energy is an extensive property since the feasibility of a reaction depends on factors such as the amount of matter/availability of reactants, etc. Please correct me if I'm wrong!
Fri Feb 15, 2019 8:19 pm
Forum: Calculating Work of Expansion
Topic: Work without change in volume
Replies: 8
Views: 520

### Re: Work without change in volume

If there is no change in volume, no work will be done. If you are referring to an isothermal process with constant pressure, then I'm pretty sure work = -(external P)(Delta V).
Sun Feb 10, 2019 7:57 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Using R
Replies: 10
Views: 355

### Using R

How do I know which R to use and when? Thanks.
Sun Feb 10, 2019 7:51 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Effects of Constant Volume or Temp
Replies: 1
Views: 73

### Re: Effects of Constant Volume or Temp

Constant volume means that no work is done and so delta U is equal to q. When temperature is constant, delta U is equal to 0.
Sun Feb 10, 2019 7:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U = (3/2)nRT
Replies: 2
Views: 118

### U = (3/2)nRT

When do we use the equation U = 3/2 nRT? I saw this on the constants and equations sheet but I have no idea when to use it.
Sun Feb 03, 2019 11:25 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: kJ vs J
Replies: 9
Views: 227

### Re: kJ vs J

Either should be fine as long as you are consistent in your calculations and make sure that everything matches up properly.
Thu Jan 31, 2019 5:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Extensive vs. Intensive
Replies: 5
Views: 450

### Re: Extensive vs. Intensive

I am not entirely sure about extrinsic versus intrinsic though I think they are similar. Intrinsic properties are ones that do not depend on outside factors / amount of substance such as boiling point/density whereas extrinsic properties depend on outside factors / amount of substance such as weight...
Thu Jan 31, 2019 11:25 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity
Replies: 5
Views: 210

### Re: Heat Capacity

To build on, heat capacity is therefore an extensive property because heat capacity is the heat required to raise the temperature of an object by 1 degree celsius. The heat required to raise the temperature of an object depends on how much of the object there is or the amount of substance.
Thu Jan 24, 2019 11:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Favoring
Replies: 4
Views: 240

### Re: Equilibrium Favoring

I think that the question is asking what the reaction favors when it is at equilibrium (as opposed to when we use Q to see which direction the reaction will go when it is not at equilibrium). I do not remember the exact numbers but I believe in the first few lectures Dr. Lavelle talked about the rea...
Thu Jan 24, 2019 11:37 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: determining x for weak acids and bases
Replies: 6
Views: 395

### Re: determining x for weak acids and bases

I think that you can ignore the x when you are adding it or subtracting it to some constant (e.g. 1.0-x) because the difference that x will make on the number is insignificant when x is that small. It is important to note that x does not equal zero though.
Thu Jan 24, 2019 7:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW 6A.21
Replies: 1
Views: 90

### Re: HW 6A.21

Because you know that the solution is neutral water (pH ~7), the hydronium and hydroxide concentrations must equal each other and balance each other out.
Fri Jan 18, 2019 4:27 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert Gases
Replies: 5
Views: 209

### Re: Inert Gases

Concentration is dependent on the number of moles and volume (n/v). Though adding inert gas does change the pressure, it changes neither of the number of moles nor the volume which means concentration stays the same! If you changed pressure by changing the volume, then concentration would change and...
Fri Jan 18, 2019 4:10 pm
Forum: Ideal Gases
Topic: The Difference between Q and Kc [ENDORSED]
Replies: 18
Views: 1795

### Re: The Difference between Q and Kc[ENDORSED]

As said above, Q has the same formula as Kc but can be calculated at anytime, not just when a reaction is at equilibrium. To explain the comparison a little more, when Q < Kc, a forward reaction will be favored. This is because Q is calculated as [products] / [reactants]. If Q is smaller than Kc, we...
Fri Jan 18, 2019 3:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When is X negligible.
Replies: 6
Views: 165

### Re: When is X negligible.

As the others mentioned before, the general rule is that you can disregard the X when the K value is smaller than 10^-3. Afterward, you can also confirm that the X you get is less than 5% of the initial concentration in order to double check that your approximation is valid.
Sat Jan 12, 2019 6:23 pm
Forum: Ideal Gases
Topic: K and Q
Replies: 7
Views: 277

### Re: K and Q

They have the same formula but don't equal each other because K is calculated using molarities at equilibrium but Q is calculated using molarities at any point in time during the reaction. We can then use Q and compare it to K to see at where the reaction is at. If Q<K, then a forward reaction is fa...
Sat Jan 12, 2019 6:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp and Kc
Replies: 1
Views: 87

### Re: Kp and Kc

Kp is the equilibrium constant calculated using partial pressure (of gases). Kc is the equilibrium constant calculated using concentration of products and reactions at equilibrium. You can convert between partial pressure and concentration through PV = nRT. where P = (n/v)RT and n/v is concentration.
Sat Jan 12, 2019 6:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solving for K
Replies: 7
Views: 182

### Re: Solving for K

We use brackets in our calculation for Kc because we are using the molarity/concentration which is denoted with brackets. I don't think its necessary to use brackets when solving for Kp because we are using partial pressure though I'm not sure.
Sat Dec 08, 2018 8:57 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: A X5 E
Replies: 6
Views: 268

### Re: A X5 E

AX5E is square pyramidal!
Sat Dec 08, 2018 8:54 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Diamagnetic vs. Paramagnetic
Replies: 1
Views: 285

### Re: Diamagnetic vs. Paramagnetic

I find that drawing out the orbitals and filling in the electrons help. That way you can easily visualize whether there are unpaired electrons (paramagnetic) or no unpaired electrons (diamagnetic).
Sat Dec 08, 2018 8:47 pm
Forum: Naming
Topic: bis-, tris-, etc.
Replies: 4
Views: 332

### Re: bis-, tris-, etc.

You use bis-, tris-, and tetrakis- when the ligand name already has di-, tri-, tetra-, etc or if they are polydentate. For oxalate, you would use bis-, tris-, etc as it is bidentate.
Sat Dec 08, 2018 8:38 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: inter- and intra-
Replies: 5
Views: 866

### Re: inter- and intra-

The greater the difference in electronegativity between two atoms, the greater the ionic character of their bond. I think the number mentioned in class was that if the value of electronegativity is greater than 2, than the bond is considered generally ionic.
Sat Dec 08, 2018 8:35 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: determining the coordination compound
Replies: 1
Views: 115

### Re: determining the coordination compound

If you are talking about the coordination number, the coordination number is the number of ligands bound to the central atom!
Sat Dec 08, 2018 8:34 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligands
Replies: 1
Views: 97

### Re: Ligands

Do you mean what it means for it to be cis? Cisplatin is a chemotherapy drug that forms a coordination compound with DNA, particularly guanine, to stop cell division.
Sat Dec 01, 2018 3:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar Molecules
Replies: 12
Views: 290

### Re: Polar Molecules

It would be best to, from the Lewis structure, figure out the shape of the molecule through VSEPR and use the electronegativity of each atom to determine the total dipole movement.
Sat Dec 01, 2018 2:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Dissociation energy
Replies: 7
Views: 253

### Re: Dissociation energy

When bonds are formed, energy is released (negative) as atoms move toward a more stable state. The opposite, the breaking of bonds, would therefore require an input of energy (positive) in order to pull atoms away from that stable state.
Sat Dec 01, 2018 2:40 pm
Forum: Lewis Acids & Bases
Topic: Lewis and Bronsted
Replies: 8
Views: 312

### Re: Lewis and Bronsted

The two are essentially the same but they relate the ions through different means. The Lewis definition relates two ions using the transfer of electrons. A Lewis acid is an electron acceptor while a Lewis base is the electron donor. The Bronsted definition relates the two through protons in which a ...
Sat Nov 24, 2018 10:35 pm
Forum: Sigma & Pi Bonds
Topic: Sigma Bonds
Replies: 2
Views: 127

### Re: Sigma Bonds

In a double bond, one will always be a sigma bond and one will always be a pi bond. In a triple bond, one will always be a sigma bond and two will be pi bonds. This is because, in order to form sigma bonds, the orbitals need to align end to end. Afterward, the lobes can only align in a parallel form...
Sat Nov 24, 2018 9:05 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: Polarity and Boiling Point
Replies: 3
Views: 874

### Re: Polarity and Boiling Point

Molecules with higher polarity have greater dispersion forces and therefore stronger dipole-dipole interactions. This greater intermolecular attraction force leads to a higher boiling point. This explains why water (with all its hydrogen bonds) has a high boiling point.
Sat Nov 24, 2018 8:35 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: molecular shape vs molecular geometry
Replies: 3
Views: 73

### Re: molecular shape vs molecular geometry

Looking at VSEPR notations might help. For AX4, a molecule without lone pairs, both its molecular and electron geometry are tetrahedral. For AX3E, its molecular geometry would be trigonal pyramidal but its electron geometry is tetrahedral.
Sun Nov 18, 2018 10:09 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Energy of Intermolecular Forces
Replies: 6
Views: 273

### Re: Energy of Intermolecular Forces

Breaking bonds generally requires an addition of energy. The opposite, forming bonds, is a release of energy which explains the negative number.
Sun Nov 18, 2018 10:03 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular shape vs electron geometry
Replies: 4
Views: 148

### Re: Molecular shape vs electron geometry

An example would be AX3E. Its molecular geometry would be trigonal pyramidal but its electron geometry is tetrahedral. For those without lone pairs on the central atom such as AX4, both its molecular and electron geometry is tetrahedral.
Sun Nov 18, 2018 9:50 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Sigma and Pi Bonds
Replies: 5
Views: 265

### Re: Sigma and Pi Bonds

A single bond will always be a sigma bond, a double bond will be a sigma bond and a pi bond, and a triple bond will be a sigma bond and two pi bonds. The first bond is able to overlap head-on which allows the bound atoms to rotate. However, the second and third bonds are forced to bond side by side ...
Fri Nov 09, 2018 7:16 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Placement of the 3d orbital
Replies: 1
Views: 171

### Re: Placement of the 3d orbital

The 4s orbital comes before the 3d orbital because the 4s shell actually has a lower energy level than the 3d orbital. However, if the 4s orbital is filled (2 electrons), then its energy level rises to higher than the 3d orbital which is why we write it after the 3d (exceptions: Chromium and Copper).
Thu Nov 08, 2018 2:22 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Electronegativity
Replies: 6
Views: 252

### Re: Electronegativity

I think that oxygen is more electronegative. Oxygen is smaller than chlorine, with chlorine having a whole other shell of electrons which means that valence electrons in oxygen feel a stronger force.
Thu Nov 08, 2018 1:01 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge & Stable lewis structures
Replies: 6
Views: 338

### Re: Formal Charge & Stable lewis structures

To add on to the previous posts, it is also most desirable to have the lowest possible charge on the central atom for stability though this is not always possible.
Sun Nov 04, 2018 12:48 am
Forum: Octet Exceptions
Topic: Lewis acids and bases
Replies: 4
Views: 114

### Re: Lewis acids and bases

A lewis base simply donates an electron within a coordinate covalent bond and a lewis acid accepts an electron in a coordinate covalent bond!
Sun Nov 04, 2018 12:43 am
Forum: Trends in The Periodic Table
Topic: Ionization Energy: Oxygen
Replies: 1
Views: 50

### Re: Ionization Energy: Oxygen

This is because oxygen's 2p orbitals has 4 electrons (1 paired, 2 unpaired). Losing one electron from the pair would create a half filled stable orbital which is desired, hence the low ionization energy!
Sun Nov 04, 2018 12:36 am
Forum: Lewis Structures
Topic: Drawing Lewis Structures
Replies: 4
Views: 212

### Re: Drawing Lewis Structures

Unless the question asks you specifically to draw all the resonance structures, I think that one is okay.
Sun Oct 28, 2018 11:10 am
Forum: Ionic & Covalent Bonds
Topic: Replacement for Modules
Replies: 7
Views: 330

### Re: Replacement for Modules

In addition to the resources stated above, I also really enjoy going through worksheets from workshops, step-up sessions, etc. You can just look them up on chem community!
Sun Oct 28, 2018 11:06 am
Forum: Ionic & Covalent Bonds
Topic: ionization energy [ENDORSED]
Replies: 4
Views: 108

### Re: ionization energy[ENDORSED]

After the first electron is removed, the ratio of protons to electrons increases and therefore the pull on the remaining electrons increases. This raises the ionization energy.
Sun Oct 28, 2018 11:04 am
Forum: DeBroglie Equation
Topic: Kg vs Grams
Replies: 6
Views: 429

### Re: Kg vs Grams

I think something that would help would be to write out the units for all parts of the equation. In h/mv, h is given in kg.m^2.s^-1. In order to cancel out the kg, the mass "m" needs to be in kilograms as well. The velocity should cancel out m.s^-1 and leave meters for λ.
Sun Oct 21, 2018 9:07 am
Forum: DeBroglie Equation
Topic: de broglie post module q 35 [ENDORSED]
Replies: 2
Views: 105

### Re: de broglie post module q 35[ENDORSED]

You would just solve this as you normally do. λ = h/p = h/mv h = 6.626 x 10^-34 m = 275 kg v = 34.72 m/s λ = (6.626 x 10^-34)/(275*34.72) = 6.94 x 10^-38 m A car does not have wavelike properties as only very small objects have measurable wavelike properties. As objects become larger, wavelike prope...
Sun Oct 21, 2018 8:37 am
Forum: Properties of Light
Topic: Test 2
Replies: 7
Views: 338

### Re: Test 2

I would focus on the topics explored in the last four video modules and all the information given up until Friday's lecture.
Sun Oct 21, 2018 8:35 am
Forum: Photoelectric Effect
Topic: spectral lines
Replies: 6
Views: 245

### Re: spectral lines

Both work since wavelength is the inverse of frequency. It just depends on what you are trying to solve for in the problem! I think that something of this topic will most likely appear on the exam.
Sat Oct 13, 2018 11:02 pm
Forum: Balancing Chemical Reactions
Topic: Test 1 and Future Tests
Replies: 5
Views: 445

### Re: Test 1 and Future Tests

Maybe you could try balancing in steps one element at a time just in case a mistake is made so you can receive partial credit.
Sat Oct 13, 2018 10:02 pm
Forum: Significant Figures
Topic: sig fig calculations
Replies: 3
Views: 450

### Re: sig fig calculations

For addition and subtraction, you use the least number of decimal points from the given values and for multiplication, you use the least number of sig figs from the given values.
Sat Oct 13, 2018 9:56 pm
Forum: Administrative Questions and Class Announcements
Topic: Writing in Pen
Replies: 13
Views: 568

### Re: Writing in Pen

If you really dislike writing in pen, I would just ask your TA whether he/she cares! My TA said she did not mind whether we use pen or not.
Fri Oct 05, 2018 11:46 am
Forum: Molarity, Solutions, Dilutions
Replies: 3
Views: 434

I think here we need to use the M1V1 = M2V2 formula. I would first find the molarity of the original solution by converting 5.00 grams of KMnO4 into moles for the moles of solute and then divide it by the volume of the solution. (0.0316 mol/0.1500 L = 0.211 mol/L) Now you have the initial molarity (...
Fri Oct 05, 2018 8:56 am
Forum: Limiting Reactant Calculations
Topic: Excess Reactant Calculation
Replies: 2
Views: 122

### Re: Excess Reactant Calculation

After identifying the limiting reactant, determine how much of the other reactant is used up by converting the grams of the limiting reactant to moles and, using the stoichiometric coefficients for the ratio, determining how many moles of the other reactant is used up. Convert that number to grams a...
Fri Oct 05, 2018 8:16 am
Forum: Empirical & Molecular Formulas
Topic: Post-Module Assessment Q22
Replies: 3
Views: 168

### Re: Post-Module Assessment Q22

After finding the empirical formula (C5H12O5), calculate its molar mass which should be about 152.15 g/mol. The question should give the molar mass of the compound. Divide that number by the 152.15 g/mol you just calculated to find the ratio between the molecular and empirical formula. Use that rati...