Search found 50 matches

by Clara Hu 1G
Thu Mar 15, 2018 10:34 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Equations for different types of reactions
Replies: 1
Views: 199

Re: Equations for different types of reactions

For reversible, PV=nRT, and w=-nRTln(). For irreversible, w=-PV.
by Clara Hu 1G
Thu Mar 15, 2018 10:26 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.111
Replies: 1
Views: 79

Re: 11.111

In this homework problem, the second K is actually 10 times smaller than the first, so you would actually divide the first K by 10 rather than how you did 10 times the first K.
by Clara Hu 1G
Thu Mar 15, 2018 4:26 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal energy change = 0
Replies: 2
Views: 138

Re: Internal energy change = 0

The change in internal energy will be 0 for all isothermal expansions, whether the expansion is reversible or irreversible.
by Clara Hu 1G
Wed Mar 07, 2018 5:29 pm
Forum: First Order Reactions
Topic: First Order Integrated Rate Law
Replies: 3
Views: 176

Re: First Order Integrated Rate Law

They can both be used because ln of any number is equal to 2.303log of the same number.
by Clara Hu 1G
Wed Mar 07, 2018 5:13 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Diamond/Graphite
Replies: 4
Views: 690

Re: Diamond/Graphite

According to thermodynamics, the reaction from diamond to graphite is spontaneous and favorable. However, because kinetics rather than thermodynamics is controlling this reaction, it occurs extremely slowly. So, diamond is kinetically stable, but thermodynamically unstable.
by Clara Hu 1G
Wed Mar 07, 2018 5:05 pm
Forum: Zero Order Reactions
Topic: Units of K based on the order
Replies: 3
Views: 264

Re: Units of K based on the order

Because the rate of the reaction should have the units of mol/L s, for zero order, rate=k, so k has the units of mol/Ls. For first order, the units of k times concentration (mol/L) needs to be mol/L s, so the units of k are s^-1. For second order, the units of k times (mol/L)squared needs to be mol/...
by Clara Hu 1G
Fri Mar 02, 2018 12:57 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 15.3 [ENDORSED]
Replies: 7
Views: 277

Re: 15.3 [ENDORSED]

In part c it is asking for the unique rate of the reaction, so you divide the rate for the certain term by its stoichiometric coefficient.
by Clara Hu 1G
Fri Mar 02, 2018 12:47 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.97
Replies: 1
Views: 135

Re: 14.97

Ka is the equilibrium constant for the dissociation of acids, so in this problem you would calculate it the same way you calculate regular k.
by Clara Hu 1G
Fri Mar 02, 2018 12:39 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Straight line
Replies: 7
Views: 334

Re: Straight line

Also, if you plot a straight line with [A] vs t, it is zero order. ln[A] vs t means that it is first order, and 1/[A] vs t is second order.
by Clara Hu 1G
Fri Feb 23, 2018 1:09 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: ln vs log [ENDORSED]
Replies: 5
Views: 208

Re: ln vs log [ENDORSED]

Using log makes it easier to find the pH because pH= - log [H+].
by Clara Hu 1G
Fri Feb 23, 2018 1:06 pm
Forum: First Order Reactions
Topic: Reaction order
Replies: 4
Views: 192

Re: Reaction order

Also, the overall reaction order is found by adding together the reaction orders of the substances whose concentrations affect the reaction rate.
by Clara Hu 1G
Fri Feb 23, 2018 1:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13d
Replies: 3
Views: 167

Re: 14.13d

This is what happens in a concentration cell.
by Clara Hu 1G
Wed Feb 14, 2018 1:49 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: What does E stand for?
Replies: 3
Views: 219

Re: What does E stand for?

E is cell potential, which is an intensive property, and its units are in Volts, which is J/C.
by Clara Hu 1G
Wed Feb 14, 2018 1:38 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Difference between Gibbs Free Energy and standard Gibbs Free Energy
Replies: 2
Views: 399

Re: Difference between Gibbs Free Energy and standard Gibbs Free Energy

Gibbs Free Energy is energy associated with chemical reactions and is equal to . Standard Gibbs Free Energy is when things are occurring at a standard state, which I believe should be 25 degrees C and 1 atm.
by Clara Hu 1G
Fri Feb 09, 2018 12:53 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta g
Replies: 2
Views: 117

Re: delta g

I think that Delta G is the free energy change of a reaction. Delta G r is the Gibbs Free Energy of the reactants and Delta G r knot is the standard free energy for the reactants.
by Clara Hu 1G
Fri Feb 09, 2018 12:47 pm
Forum: Balancing Redox Reactions
Topic: Anode vs cathode
Replies: 6
Views: 141

Re: Anode vs cathode

Also, the anode, oxidation half reaction, is always on the left, while the cathode, reduction half reaction, is always on the right.
by Clara Hu 1G
Fri Feb 09, 2018 12:44 pm
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: 9.73
Replies: 1
Views: 355

Re: 9.73

S total must be greater than zero, or positive, to be spontaneous. This is part of the Second Law of Thermodynamics.
by Clara Hu 1G
Wed Jan 31, 2018 5:04 pm
Forum: Phase Changes & Related Calculations
Topic: Example in Lecture
Replies: 4
Views: 194

Re: Example in Lecture

For this example, at 333K when deltaG=0, Br2(l) and Br2(g) are at equilibrium or boiling point, so if the temperature increases above 333K, the forward process would be favored and Br2 would vaporize to the gas phase only.
by Clara Hu 1G
Wed Jan 31, 2018 4:52 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Phase change question demonstrated in Lecture
Replies: 4
Views: 202

Re: Phase change question demonstrated in Lecture

When delta H is positive, it takes a very high temperature for entropy to dominate and cause delta G to become negative. So delta H + is only spontaneous at high temperatures.
by Clara Hu 1G
Wed Jan 31, 2018 4:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: State functions [ENDORSED]
Replies: 7
Views: 239

Re: State functions [ENDORSED]

Heat and work are not state functions because work is proportional to the distance traveled, meaning that the path taken does matter.
by Clara Hu 1G
Wed Jan 24, 2018 11:30 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimetry
Replies: 4
Views: 172

Re: Calorimetry

It doesn't really matter if the change in temperatures are in Kelvin or Celsius because the Kelvin is in the same scale as Celsius, just +273, just make sure that the initial and final temperatures are both either in Kelvin or Celsius.
by Clara Hu 1G
Wed Jan 24, 2018 11:25 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calculating heat (q)
Replies: 4
Views: 324

Re: Calculating heat (q)

You would use q=mc(delta)T if you knew the mass of a substance and had the specific heat capacity while you would use q=nc(delta)T if you knew the number of moles and had the molar heat capacity because you want the final units of q to be in Joules.
by Clara Hu 1G
Wed Jan 24, 2018 11:17 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy of a gas
Replies: 2
Views: 151

Re: Entropy of a gas

Entropy decreases when an ideal gas is compressed because the volume decreases and pressure increases.
by Clara Hu 1G
Wed Jan 17, 2018 4:15 pm
Forum: Phase Changes & Related Calculations
Topic: 8.91
Replies: 1
Views: 93

Re: 8.91

For 8.91, I first used q=mC \Delta T to find the amount of heat needed to raise the liquid water by 5°C, which was 0.312kJ. Then, I divided it by 0.5 hours to find the amount of heat transferred per hour, which was 0.624 kJ/hr. I multiplied that by 10.5 hours which was the time it took an ice cube t...
by Clara Hu 1G
Wed Jan 17, 2018 4:09 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: calculating specific heat
Replies: 5
Views: 242

Re: calculating specific heat

When using specific heat capacity to get q, only the mass and change in temperature are needed because the equation is q=mC \Delta T. The units for q is in joules and specific heat is in J/g°C, so when you multiply the specific heat by the mass (g) and change in temperature, (°C), you are left with ...
by Clara Hu 1G
Wed Jan 17, 2018 4:03 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bomb Calorimeters
Replies: 2
Views: 301

Re: Bomb Calorimeters

Bomb Calorimeters are isolated systems as nothing exchanges with the surroundings because the bomb calorimeter is insulated and does not allow heat energy to transfer to the surroundings.
by Clara Hu 1G
Fri Jan 12, 2018 1:25 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What type of system is a Bomb Calorimeter?
Replies: 4
Views: 515

Re: What type of system is a Bomb Calorimeter?

Also, a Bomb Calorimeter is used during dconstant Volume calorimetry because the reaction chamber is a fixed volume.
by Clara Hu 1G
Thu Jan 11, 2018 3:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: #39 from Chapter 8
Replies: 3
Views: 184

Re: #39 from Chapter 8

You would use the specific heat capacity when you have the mass, while you would use molar heat capacity when you know the amount of moles because specific heat capacity measures the joules of heat needed to raise one gram of a substance by one degree C, while molar heat capacity measure the joules ...
by Clara Hu 1G
Thu Jan 11, 2018 3:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Most Stable Forms
Replies: 4
Views: 218

Re: Most Stable Forms

An example of when the enthalpy of formation is 0 is when two Oxygen atoms form O2. This is because O2 is the natural form of oxygen.
by Clara Hu 1G
Thu Dec 07, 2017 12:54 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Relative Acidity Concept Question
Replies: 4
Views: 238

Re: Relative Acidity Concept Question

In the example given in class, hypochlorous acid was the most acidic out of HClO, HBrO, and HIO because CL has the highest electronegativity which stabilizes the negatively charged O by withdrawing electron density.
by Clara Hu 1G
Thu Dec 07, 2017 12:42 pm
Forum: Amphoteric Compounds
Topic: Amphoteric vs amphiprotic
Replies: 2
Views: 351

Re: Amphoteric vs amphiprotic

Also, on the periodic table, there is a diagonal band of amphoteric oxides found between the metal oxides (bases) and nonmetal oxides (acids) that form amphoteric compounds.
by Clara Hu 1G
Thu Nov 30, 2017 10:42 am
Forum: Lewis Structures
Topic: 4.7A Homework
Replies: 3
Views: 497

Re: 4.7A Homework

For SOCl2, the oxygen atom and two chlorine atoms are each bonded to sulfur by a single bond, and sulfur also has a lone pair to complete the octet. Then, because there are four areas of electron density with one lone pair, the shape is trigonal pyramidal.
by Clara Hu 1G
Thu Nov 30, 2017 10:39 am
Forum: Lewis Structures
Topic: 4.9
Replies: 1
Views: 141

Re: 4.9

Iodine has d-orbitals so it has an expanded octet and can accommodate more than 8 valence electrons. ICl3 is T-shaped because it has 5 areas of electron density with 2 lone pairs, and the Cl-I-Cl bond angle is less than 90 degrees because of the repulsion from the lone pairs.
by Clara Hu 1G
Wed Nov 22, 2017 3:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T-shaped and Trigonal Pyramidal
Replies: 6
Views: 365

Re: T-shaped and Trigonal Pyramidal

T-shaped structures have 5 regions of electron density with 2 lone pairs, while Trigonal Pyramidal structures have 4 regions of election density with 1 lone pair.
by Clara Hu 1G
Wed Nov 22, 2017 3:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.9 Problem
Replies: 4
Views: 227

Re: 4.9 Problem

For ICl3, there are 5 regions of electron density, but only 3 are occupied by atoms, so there are two lone pairs, which means that it is T shaped.
by Clara Hu 1G
Fri Nov 17, 2017 6:51 pm
Forum: Biological Examples
Topic: Cobalt
Replies: 4
Views: 292

Re: Cobalt

The biological function of cobalt is that it is found in vitamin B12.
by Clara Hu 1G
Wed Nov 15, 2017 3:39 pm
Forum: Hybridization
Topic: Unhybridized Orbitals
Replies: 2
Views: 147

Re: Unhybridized Orbitals

Like in the example that was done in class with C2H4, the unhybridized 2p orbitals on each C atom overlapped side-to-side to form the pi bond.
by Clara Hu 1G
Wed Nov 08, 2017 12:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Beryllium Octet Rule
Replies: 6
Views: 1275

Re: Beryllium Octet Rule

The Boron in BF3 does not have a full octet because BF3 is a Lewis Acid, and the empty p-orbital on B can accept an electron lone pair from a Lewis Base.
by Clara Hu 1G
Wed Nov 08, 2017 12:35 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.11a
Replies: 2
Views: 135

Re: 4.11a

When the VSEPR formula is AX4E, the shape is always seesaw. The 5 pairs of electrons are arranged in trigonal bipyramidal, with 4 bonding pairs and 1 lone pair. Since only 4 of the 5 positions are occupied by atoms, they form the seesaw shape.
by Clara Hu 1G
Fri Nov 03, 2017 1:23 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent/ Ionic Bond
Replies: 5
Views: 276

Re: Covalent/ Ionic Bond

Common examples of molecules with covalent bonds are HI, HBr, and HCl, whereas salts like KCL, KF, and LiF have ionic bonds.
by Clara Hu 1G
Fri Nov 03, 2017 12:50 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic Bonds w/ Covalent Character
Replies: 2
Views: 199

Re: Ionic Bonds w/ Covalent Character

To add on, large, electron rich anions, can be highly distorted, so they have more covalent character, and are described as being highly polarizable. Small, highly charged cations, which have high polarizing power, cause large distortions and also lead to more covalent character.
by Clara Hu 1G
Thu Oct 26, 2017 9:43 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic vs. Covalent Bonds [ENDORSED]
Replies: 8
Views: 435

Re: Ionic vs. Covalent Bonds [ENDORSED]

So just to add on, in the case of KCl, K becomes a cation with a charge of +1 while Cl forms an anion with charge -1, so the attraction between the positive and negative charges causes them to form an ionic bond.
by Clara Hu 1G
Thu Oct 26, 2017 11:19 am
Forum: Ionic & Covalent Bonds
Topic: covalent bond
Replies: 7
Views: 534

Re: covalent bond

It is true because non-metals do not form cations because their ionization energies are too high, so they share electrons to form covalent bonds.
by Clara Hu 1G
Thu Oct 19, 2017 11:12 am
Forum: *Shrodinger Equation
Topic: Electron Spin
Replies: 6
Views: 433

Re: Electron Spin

Also, an electron that spins up and an electron that spins down can be paired in an orbital, while electrons with the same spin avoid each other and cannot be in the same orbital because no two electrons can have the same set of four quantum numbers.
by Clara Hu 1G
Thu Oct 19, 2017 10:56 am
Forum: *Shrodinger Equation
Topic: What is a node?
Replies: 5
Views: 348

Re: What is a node?

Also, at a node, the wavefunction is zero, so the electron density at the node is also zero, and the probability of finding an electron there is zero.
by Clara Hu 1G
Thu Oct 12, 2017 2:34 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in Kinetic Energy
Replies: 2
Views: 173

Re: Uncertainty in Kinetic Energy

Yes, you would use the equation E=mv2 and plug in v,which is the uncertainty for velocity, to get the uncertainty in kinetic energy.
by Clara Hu 1G
Wed Oct 11, 2017 4:53 pm
Forum: Photoelectric Effect
Topic: CH.1 #33 pt B
Replies: 3
Views: 269

Re: CH.1 #33 pt B

For part b, use . Because you know the velocity of the ejected electron and the frequency of the radiation, you can solve for the work function, which is the energy required to remove the electron, and get 1.66 x 10-17 J.
by Clara Hu 1G
Wed Oct 04, 2017 5:01 pm
Forum: Empirical & Molecular Formulas
Topic: L.39
Replies: 5
Views: 347

Re: L.39

After converting the amount of oxygen to moles (0.025mol), also convert the 1.50g of tin to moles, which is 0.0126 mol. Then because you have the amount of oxygen and tin in moles you can get the empirical formula because you know the ratio of tin to oxygen. You have Sn0.0126O0.025, and because 0.01...
by Clara Hu 1G
Mon Oct 02, 2017 4:49 pm
Forum: Molarity, Solutions, Dilutions
Topic: Finding the Concentration of a Specific Ion in Solutino [ENDORSED]
Replies: 2
Views: 324

Re: Finding the Concentration of a Specific Ion in Solutino [ENDORSED]

For finding the concentration of potassium ions, first find the amount in moles of KCl, K2S, and K3PO4 in the solution. Then, split each compound and calculate the total amount in moles of potassium ions, which is 0.0229 moles. Then find the concentration of the potassium ions by dividing the number...

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