Search found 50 matches

by Christy Zhao 1H
Sat Mar 17, 2018 4:44 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: UA Practice Final 1D and 1E
Replies: 3
Views: 143

Re: UA Practice Final 1D and 1E

Because the anode metal is a solid, the Ecell won't be affected. Ecell is dependent on concentration and temperature.
by Christy Zhao 1H
Sat Mar 17, 2018 4:28 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding E
Replies: 3
Views: 177

Re: Finding E

If you flip the sign, use Ecell=Eanode+Ecathode. If you don't flip the sign, use Ecell= Ecathode-Eanode.
by Christy Zhao 1H
Sat Mar 17, 2018 3:58 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 2
Views: 217

Re: 9.13

Both equations are also given on the constants sheet. And the C value can be Cv at constant volume, or Cp at constant pressure.
by Christy Zhao 1H
Sat Mar 10, 2018 11:30 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding n
Replies: 15
Views: 717

Re: Finding n

If a half reaction is multiplied by 2 to get an equal number of moles of electrons in both half reactions to be able to cancel each other out, then yes n=2.
by Christy Zhao 1H
Sat Mar 10, 2018 11:16 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.53
Replies: 3
Views: 241

Re: 8.53

How do you know to use the equation ?
by Christy Zhao 1H
Sat Mar 10, 2018 10:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 Question 2
Replies: 4
Views: 184

Re: Test 2 Question 2

Adding on to the comment above, you can also use the equation to solve for K.
by Christy Zhao 1H
Sun Mar 04, 2018 4:09 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 891158

Re: Post All Chemistry Jokes Here

Why can't chemists prank their friends?
They lack the element of surprise.
by Christy Zhao 1H
Sun Mar 04, 2018 3:35 pm
Forum: Second Order Reactions
Topic: Slope of second order reaction
Replies: 3
Views: 173

Re: Slope of second order reaction

The integrated rate laws of the zero and first-order have a -kt, while the second-order has a +kt. Since the integrated rate laws correspond to y=mx+c (m=k), the slope depends on k.
by Christy Zhao 1H
Sun Mar 04, 2018 2:39 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Straight line
Replies: 7
Views: 308

Re: Straight line

Adding on to the comment above, -k would be for zero and first-order reactions, and k would correspond to second-order reactions.
by Christy Zhao 1H
Sat Feb 24, 2018 9:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Strongly Reducing Metals
Replies: 5
Views: 184

Re: Strongly Reducing Metals

The opposite goes for oxidizing agents; the more positive the standard cell potential, the stronger the oxidizing agent.
by Christy Zhao 1H
Sat Feb 24, 2018 9:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Creating a Cell Diagram with solids
Replies: 2
Views: 128

Re: Creating a Cell Diagram with solids

Are there any other special cases like liquid Hg where it can be considered as an electrode?
by Christy Zhao 1H
Sun Feb 18, 2018 11:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 4
Views: 133

Re: Salt Bridge

A salt bridge allows the flow of ions to complete the electrical circuit without affecting the cell potential.
by Christy Zhao 1H
Sun Feb 18, 2018 11:27 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: electrolytic cells
Replies: 3
Views: 177

Re: electrolytic cells

Electrolysis occurs in electrochemical cells and drives reactions in their nonspontaneous directions through an electric current.Electrolysis can be used to to predict how much products form from an electric current flow.
by Christy Zhao 1H
Sun Feb 18, 2018 10:59 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Nernst Equation
Replies: 6
Views: 274

Re: Nernst Equation

If you were confused with the subscript, page 571 says, "The subscript r is always the signal that we are using this 'molar' form."
by Christy Zhao 1H
Thu Feb 08, 2018 11:12 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.17
Replies: 10
Views: 334

Re: 11.17

Here is the link to the errors in the solution manual for future reference!
https://lavelle.chem.ucla.edu/wp-conten ... rs_6Ed.pdf
by Christy Zhao 1H
Thu Feb 08, 2018 11:07 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 9
Views: 374

Re: Spontaneity

On page 348 of the textbook, there is a helpful diagram that shows that a negative change in Gibbs free energy is spontaneous.
by Christy Zhao 1H
Thu Feb 08, 2018 10:53 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: exothermic
Replies: 5
Views: 197

Re: exothermic

Since the flask is getting colder, it is an endothermic reaction because the flask(as the surroundings) is losing heat. Therefore, the heat from the flask is going into the reaction.
by Christy Zhao 1H
Sun Feb 04, 2018 3:39 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: How do we find out if a system is favorable? [ENDORSED]
Replies: 7
Views: 1702

Re: How do we find out if a system is favorable? [ENDORSED]

Adding to the comment above, the system is spontaneous when delta G is negative because G is energy, and decreases in energy are spontaneous.
by Christy Zhao 1H
Sun Feb 04, 2018 3:34 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.65
Replies: 6
Views: 215

Re: 9.65

The compound becomes more unstable when the change in entropy is negative and temperature increases. So, after the standard entropies of formation are calculated, PCl5 would be the compound that is less stable since it is negative.
by Christy Zhao 1H
Sun Feb 04, 2018 3:22 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible systems
Replies: 7
Views: 274

Re: Reversible systems

Yes, you would calculate the change in entropy for the change in volume and the change in pressure, and add the entropy changes together.
by Christy Zhao 1H
Sun Jan 28, 2018 2:29 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Adiabatic system
Replies: 6
Views: 192

Re: Adiabatic system

Adding on to the post above, pg. 268 of the textbook says that in an adiabatic system, the change in internal energy is equal to the work done.
by Christy Zhao 1H
Sun Jan 28, 2018 2:25 pm
Forum: Calculating Work of Expansion
Topic: Homework 8.11
Replies: 6
Views: 232

Re: Homework 8.11

Keep in mind that for reversible expansion processes, the work done is the maximum work possible, therefore more work is done compared to irreversible expansion processes.
by Christy Zhao 1H
Sun Jan 28, 2018 1:46 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 891158

Re: Post All Chemistry Jokes Here

What do hungry chemists eat?
Gram (Graham) crackers
by Christy Zhao 1H
Sun Jan 21, 2018 10:56 am
Forum: Calculating Work of Expansion
Topic: Work done on / work done by system
Replies: 5
Views: 171

Re: Work done on / work done by system

When work is done to the system, energy is added and work is positive. When work is done by the system, energy leaves the system and work is negative.
by Christy Zhao 1H
Thu Jan 18, 2018 10:46 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: open system
Replies: 6
Views: 249

Re: open system

Another example is an uncovered pot of hot water. Matter is leaving the system through the steam, and energy as heat is also lost.
by Christy Zhao 1H
Thu Jan 18, 2018 10:33 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Reversible, Irreversible
Replies: 4
Views: 195

Re: Reversible, Irreversible

Also, keep in mind that a reversible process does more work than an irreversible process.
by Christy Zhao 1H
Sun Jan 14, 2018 11:23 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question about Question 8.7
Replies: 3
Views: 199

Re: Question about Question 8.7

On the other hand, if work was done by the system, the internal energy of the system would have decreased.
by Christy Zhao 1H
Sun Jan 14, 2018 10:50 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Systems
Replies: 7
Views: 296

Re: Systems

An example would be a hot cup of water. Heat from the hot water is released into its surroundings, and matter can be exchanged by drinking some of the water, or through the steam that is released into the air.
by Christy Zhao 1H
Sun Jan 14, 2018 10:38 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Closed system and Midterm
Replies: 3
Views: 416

Re: Closed system and Midterm

In section 8.1 of the book, it gives an example of a closed system: a cold pack. Energy can be exchanged, but not matter.
by Christy Zhao 1H
Sat Dec 09, 2017 2:01 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium Part 2 Module Question #27
Replies: 2
Views: 189

Re: Chemical Equilibrium Part 2 Module Question #27

Adding on, you should get 0.05 M H2O for the initial concentration, and you know x=0.040 from H2. The equilibrium concentration for H2O is 0.05-x, and plugging in x you would get 0.01 M H2O.
by Christy Zhao 1H
Sat Dec 09, 2017 1:01 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligand Order
Replies: 2
Views: 211

Re: Ligand Order

Yes, ligands are written in alphabetical order when writing the formula. Toolbox 17.1 goes into detail about writing chemical formulas.
by Christy Zhao 1H
Sat Dec 02, 2017 11:48 pm
Forum: Amphoteric Compounds
Topic: Amphoteric and amphiprotic compounds
Replies: 4
Views: 244

Re: Amphoteric and amphiprotic compounds

An amphiprotic example would be water since there are hydrogen atoms and is able to donate a proton, and the oxygen has lone pairs and is able to accept a proton.
by Christy Zhao 1H
Sat Dec 02, 2017 11:27 pm
Forum: Amphoteric Compounds
Topic: amphoteric properties
Replies: 3
Views: 173

Re: amphoteric properties

Substances that are amphoteric can act as an acid or base, so they can donate protons or accept protons.
by Christy Zhao 1H
Sun Nov 26, 2017 11:38 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Molecular Shape
Replies: 3
Views: 162

Re: Determining Molecular Shape

"Because single bonds and multiple bonds are treated as equivalent in the VSEPR model, it does not matter which of the Lewis structures contributing to a resonance structure we consider" (pg. 112).
by Christy Zhao 1H
Sun Nov 26, 2017 11:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs vs. Bonding Pairs
Replies: 6
Views: 302

Re: Lone Pairs vs. Bonding Pairs

Bonding pairs are held in place by two atoms unlike lone pairs, so lone pairs are able to take up a larger space.
by Christy Zhao 1H
Sun Nov 19, 2017 1:53 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent or linear?
Replies: 11
Views: 625

Re: Bent or linear?

Adding on, it would be linear because single and multiple bonds are treated as the same in the VSEPR model.
by Christy Zhao 1H
Thu Nov 16, 2017 5:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Exercise 4.7 and 4.9
Replies: 2
Views: 136

Re: Exercise 4.7 and 4.9

Since lone pairs have a greater electron repulsion than electrons in bonds, these lone pairs push the bonded atoms closer together.
by Christy Zhao 1H
Sun Nov 12, 2017 3:48 pm
Forum: Bond Lengths & Energies
Topic: Bond Length
Replies: 8
Views: 880

Re: Bond Length

The larger the bonding atoms are, the distance between them is also larger, and the bond becomes weaker.
by Christy Zhao 1H
Sun Nov 12, 2017 3:05 pm
Forum: DeBroglie Equation
Topic: When to use DeBroglie Equation
Replies: 4
Views: 178

Re: When to use DeBroglie Equation

This equation works for particles with momentum, and it has wave-like properties with wavelength.
by Christy Zhao 1H
Sun Nov 05, 2017 10:08 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 8
Views: 405

Re: Formal Charge

Keep in mind that the formal charge of the model should add up to the overall charge of the atom.
by Christy Zhao 1H
Sun Nov 05, 2017 1:39 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: d and s blocks
Replies: 16
Views: 684

Re: d and s blocks

The electronic configuration is written based on the principle quantum number(n), in the order of increasing energy. S blocks have a greater n value than d blocks.
by Christy Zhao 1H
Sun Oct 29, 2017 4:47 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Quick Question about SO4
Replies: 8
Views: 682

Re: Quick Question about SO4

It can be determined by calculating the formal charge of the element. The lower the number of formal charges, the more stable the structure.
by Christy Zhao 1H
Sun Oct 29, 2017 3:33 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Difference between subshell and orbital [ENDORSED]
Replies: 9
Views: 1082

Re: Difference between subshell and orbital [ENDORSED]

A wave function and orbital have the same meaning. In the textbook it says, "wavefunctions of electrons in atoms are called atomic orbitals."
by Christy Zhao 1H
Sun Oct 22, 2017 7:15 pm
Forum: *Shrodinger Equation
Topic: What is a node?
Replies: 5
Views: 324

Re: What is a node?

Just to reiterate, keep in mind that the node is where the wavefunction passes through zero, it doesn't just reach zero.
by Christy Zhao 1H
Sun Oct 22, 2017 6:52 pm
Forum: Properties of Light
Topic: Planck's Constant
Replies: 10
Views: 450

Re: Planck's Constant

You also use Planck's constant in the equation relating the kinetic energy of an ejected e- to the energy of an incident photon.
by Christy Zhao 1H
Sun Oct 15, 2017 8:01 pm
Forum: Properties of Light
Topic: Excitation of electrons
Replies: 5
Views: 235

Re: Excitation of electrons

Adding on, one photon interacts with one electron, and each photon must have enough energy to eject one electron to be absorbed. So if 1 million photons are absorbed, 1 million electrons are excited to a higher energy level.
by Christy Zhao 1H
Sun Oct 15, 2017 7:21 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Balmer, Lyman, Paschen, and Bracket Series
Replies: 3
Views: 199

Re: Balmer, Lyman, Paschen, and Bracket Series

I'm still a bit confused about the Balmer and Lyman series. Are we just supposed to know that Balmer series are in the visible region and Lyman series are in the UV region?
by Christy Zhao 1H
Wed Oct 04, 2017 11:58 pm
Forum: Empirical & Molecular Formulas
Topic: Trouble in finding the Molecular Formula
Replies: 6
Views: 747

Re: Trouble in finding the Molecular Formula

I understand that we have to multiply the mole ratios to get as close to whole numbers as possible, but to what extent would the decimal be considered too far from a whole number? For example if I get 1.86, would I still be able to round that to 2?
by Christy Zhao 1H
Wed Oct 04, 2017 11:12 pm
Forum: Molarity, Solutions, Dilutions
Topic: E 29 part c
Replies: 3
Views: 655

Re: E 29 part c

I'm confused with part d. How would I go about to find what fraction of the total mass of the sample was due to oxygen?

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