Search found 62 matches
- Sat Mar 16, 2019 1:12 pm
- Forum: Ideal Gases
- Topic: Bar for partial pressure [ENDORSED]
- Replies: 4
- Views: 686
Bar for partial pressure [ENDORSED]
Do we always use unit in bar when calculating partial pressure equilibrium constants?
- Sat Mar 16, 2019 11:23 am
- Forum: Administrative Questions and Class Announcements
- Topic: LYNDON'S PORK RAMEN REVIEW
- Replies: 37
- Views: 7374
Re: LYNDON'S PORK RAMEN REVIEW
Will you post the answers here as usual?
- Thu Mar 14, 2019 9:30 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Reducing power
- Replies: 1
- Views: 195
Re: Reducing power
The rule for reducing power is that the more negative the standard potential E is, the greater reducing power.
- Thu Mar 14, 2019 9:27 pm
- Forum: General Rate Laws
- Topic: Rate Law and Unique Rates
- Replies: 1
- Views: 224
Re: Rate Law and Unique Rates
I think the question will specify. If they are asking for formation rate, they will explicitly say which species. The rate law equals unique rate. You can recall from the integral rate law process.
- Thu Mar 14, 2019 9:22 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Rate of Formation
- Replies: 1
- Views: 249
Re: Rate of Formation
rate of formation is approached by unique rates, while experimental rate law is directly from the data (remember the tables?)
- Fri Mar 08, 2019 1:26 pm
- Forum: First Order Reactions
- Topic: First Order Decay
- Replies: 2
- Views: 337
Re: First Order Decay
I think no. You can only ensure a decay reaction as first order reaction when the half-life is a constant.
- Fri Mar 08, 2019 1:24 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: reaction orders
- Replies: 2
- Views: 260
Re: reaction orders
It implies the reaction mechanism and is related to molecularity.
- Fri Mar 08, 2019 1:21 pm
- Forum: First Order Reactions
- Topic: Units
- Replies: 2
- Views: 268
Re: Units
There is a general formula: if x is the overall order of the reaction, the unit of k is (M)^(1-x)/s. M is mol/L
- Fri Mar 01, 2019 8:11 pm
- Forum: Balancing Redox Reactions
- Topic: Max Potential
- Replies: 3
- Views: 435
Re: Max Potential
Max potential is related to delta G by delta G= -nFE
- Fri Mar 01, 2019 8:10 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: rate of change
- Replies: 4
- Views: 754
Re: rate of change
By the stochemiistry coefficients, and the unique rates.
- Fri Mar 01, 2019 8:08 pm
- Forum: General Rate Laws
- Topic: Unique rates
- Replies: 5
- Views: 636
Re: Unique rates
Yes. Unique rate is spontaneous rate, which will definitely change with time. But we usually talk about the initial rate.
- Fri Feb 22, 2019 3:39 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing problem
- Replies: 3
- Views: 513
Re: Balancing problem
In this reaction, Cl2 is both oxidized and reduced. Try to identify the oxidation number of each "Cl" in this reation.
- Fri Feb 22, 2019 3:37 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Delta G=0 at equilibrium
- Replies: 4
- Views: 2489
Re: Delta G=0 at equilibrium
The total delta G of a reaction equals the total delta G of products minus that of all the reactants. At equilibrium, there is no difference between the delta G of the reactants and the products, so that total delta G equals 0.
- Fri Feb 22, 2019 3:24 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy
- Replies: 2
- Views: 254
Re: Gibbs Free Energy
Gibbs free energy is the available energy that can do useful work. They are related by the equation delta G= delta H- T*delta S.
- Fri Feb 15, 2019 4:28 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Equation based on equilibrium
- Replies: 5
- Views: 474
Re: Equation based on equilibrium
Actually, it should be G=G knot + RTlnQ. It implies that the reaction is not at equilibrium.
- Fri Feb 15, 2019 4:24 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: delta G knot
- Replies: 4
- Views: 796
Re: delta G knot
Like the concept in enthalpy. Delta G knot is the change in G under standard conditions (1 atm or 1 M). Delta G can be the change of free energy of the whole process(reaction).
- Fri Feb 15, 2019 4:22 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: system v surroundings entropy
- Replies: 4
- Views: 671
Re: system v surroundings entropy
I think the book wrote that way because we usually can find out S(system) so that we relate that to S(surroudings).
- Fri Feb 08, 2019 5:28 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Reversible and isothermal
- Replies: 2
- Views: 364
Re: Reversible and isothermal
In a reversible system, energy lost through doing work by the system will be replenished to the system through inputting heat. It is very efficient and slow. Reversible system usually is isothermal, which means no temperature change.
- Fri Feb 08, 2019 5:25 pm
- Forum: Calculating Work of Expansion
- Topic: Reversible Expansion
- Replies: 3
- Views: 342
Re: Reversible Expansion
For an irreversible system, work is done under constant pressures and energy is lost as heat. For a reversible system, each energy lost by doing work will come back to the system as heat, and it is more efficient.
- Fri Feb 08, 2019 5:23 pm
- Forum: Calculating Work of Expansion
- Topic: Nonexpansion work
- Replies: 2
- Views: 246
Re: Nonexpansion work
Maybe it is free expansion. The internal energy doesn't change because as long as there is no volume change no work can be done. The system expands due to an increase in entropy.
- Fri Feb 01, 2019 8:45 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: reversible expansion
- Replies: 3
- Views: 309
Re: reversible expansion
Usually, questions will give initial and final volumes or the change in height.
- Fri Feb 01, 2019 8:28 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: 3 methods for enthalpy calculation
- Replies: 10
- Views: 1912
Re: 3 methods for enthalpy calculation
Our TA says you just need to examine the giver conditions to choose methods. But definitely remember using bond enthalpy is the least accurate.
- Fri Feb 01, 2019 8:25 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Enthalpy
- Replies: 3
- Views: 395
Re: Enthalpy
I think enthalpy can be calculated under any condition, but maybe most questions will give a constant pressure, just temperature.
- Fri Jan 25, 2019 4:13 pm
- Forum: Phase Changes & Related Calculations
- Topic: Elements in different states
- Replies: 2
- Views: 257
Re: Elements in different states
Not really. I think we only are supposed to know the standard state.
- Fri Jan 25, 2019 4:07 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard States
- Replies: 1
- Views: 171
Re: Standard States
Pure liquid and solid are naturally considered as in their standard state. The standard state for a solution is defined as 1 M. The standard state for an element is its most stable phase at 1 atm.
- Fri Jan 25, 2019 4:01 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Solving bond enthalpies
- Replies: 3
- Views: 258
Re: Solving bond enthalpies
Breaking bonds requires energy, resulting in positive enthalpy while forming bonds release energy, resulting in negative enthalpy. In other words, the enthalpy change made by reactants is positive while that made by forming products is negative.
- Fri Jan 18, 2019 5:21 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Buffers - weak acid
- Replies: 4
- Views: 3191
Re: Buffers - weak acid
Buffer solution usually consists of a pair of conjugate weak acid and base. The variation in pH results from the Kc of acid/base.
- Fri Jan 18, 2019 5:12 pm
- Forum: Ideal Gases
- Topic: Pressure in terms of mols
- Replies: 3
- Views: 430
Re: Pressure in terms of mols
It depends on how you decrease the pressure. You can either increase the volume or introduce other unrelated gases.You can then relate the change in pressure with the change in moles.
- Fri Jan 18, 2019 5:03 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Pure Solids and Pure Liquids
- Replies: 4
- Views: 442
Re: Pure Solids and Pure Liquids
No. Water is only considered in the calculation when it is in gas phase.
- Fri Jan 11, 2019 4:48 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Table Help
- Replies: 3
- Views: 232
Re: ICE Table Help
The is no keyword I think. But it always works in equilibrium problems.
- Fri Jan 11, 2019 4:46 pm
- Forum: Ideal Gases
- Topic: Pressure and volume
- Replies: 4
- Views: 440
Re: Pressure and volume
Not always. For instance, when the pressure is increased by adding inert gas and the container is not changed, the volume stays the same.
- Fri Jan 11, 2019 4:44 pm
- Forum: Ideal Gases
- Topic: Reaction Quotient
- Replies: 5
- Views: 503
Re: Reaction Quotient
Yes...
- Fri Dec 07, 2018 5:33 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: aqueous solutions of salts
- Replies: 2
- Views: 489
Re: aqueous solutions of salts
NO3 is the conjugate base for strong acid that will get a proton from water to form OH- in the solution.
- Fri Dec 07, 2018 4:00 pm
- Forum: Lewis Acids & Bases
- Topic: Weak Acids/Bases?
- Replies: 5
- Views: 696
Re: Weak Acids/Bases?
You are supposed to remember all the strong acid and bases, according to a UA. Then the rest are all weak ones.
- Fri Dec 07, 2018 3:59 pm
- Forum: Lewis Acids & Bases
- Topic: How to tell if an ion is acidic or basic?
- Replies: 1
- Views: 218
Re: How to tell if an ion is acidic or basic?
You need to tell it from Lewis structures because the charges of ions stem from formal charges which also depend on the valence electrons of the atoms that from the ion.
- Fri Nov 30, 2018 3:57 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Amines and strength of acid
- Replies: 4
- Views: 410
Re: Amines and strength of acid
Amines are weak bases, becasue they are proton acceptors by the definition of Bronsted base and they are lone pair donor by the definition of Lewis base.
- Fri Nov 30, 2018 3:50 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Charges
- Replies: 4
- Views: 502
Re: Charges
You can usually know the overall charge of the complex from the question. Utilize your knowledge for the charges of the most common ligands to calculate the ones unknown.(usually only one)
- Fri Nov 30, 2018 3:48 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Chelate
- Replies: 2
- Views: 240
Re: Chelate
Chelate is the complex containing a ligand that forms a ring of atoms that includes the central metal atom. Because a ring structure is formed, I think the complex is more stable.
- Wed Nov 21, 2018 5:26 pm
- Forum: Hybridization
- Topic: Electron Density vs Shape?
- Replies: 6
- Views: 661
Re: Electron Density vs Shape?
Electron density refers to all regions that have electrons, which includes lone pairs. However, when we name shapes, only atoms are counted.
- Wed Nov 21, 2018 5:23 pm
- Forum: Hybridization
- Topic: Purpose of hybridization
- Replies: 4
- Views: 361
Re: Purpose of hybridization
Hybridization allows you to figure out how bonds are formed by displaying the electron regions in the real case that is most stable for the lowest maintaining energy.
- Wed Nov 21, 2018 4:10 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular Size
- Replies: 3
- Views: 340
Re: Molecular Size
In most cases, an increase in molecular size attributes to an increase in the size electro regions of the atoms that construct the molecule, so an increase in size will make the intermolecular interaction stronger.
- Fri Nov 16, 2018 5:01 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Repulsion Strength
- Replies: 7
- Views: 674
Re: Repulsion Strength
I remember in the lecture this came after the discussion about bond angles. When lone pairs are involved, VSEPR can only predict the bond angles within a interval but cannot predict the angle precisely.
- Fri Nov 16, 2018 4:53 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: VSEPR Models with 5 bonding regions
- Replies: 3
- Views: 353
Re: VSEPR Models with 5 bonding regions
I think it became complicated from 5 bonding regions because the increasing chance of lone pair getting involved. You can simply first ignore the difference between bonded and lone pair regions and regard them all as atoms to get the intuitive shape and remove the atom to reconsider if it is a lone ...
- Fri Nov 16, 2018 4:30 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: tetrahedral vs trigonal planar
- Replies: 9
- Views: 1059
Re: tetrahedral vs trigonal planar
You can simply distinguish them with the number of atoms as the above posts say, or imagine the shape based on Lewis structures. Pay attention to lone pairs.
- Sat Nov 10, 2018 9:36 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: Induced Dipole-Induced Dipole names?
- Replies: 4
- Views: 850
Re: Induced Dipole-Induced Dipole names?
It was not clarified on the lecture but in the discussion, our TA cataloged it to diple-diple interactions.
- Sat Nov 10, 2018 9:25 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: how to know which shape it is
- Replies: 6
- Views: 650
Re: how to know which shape it is
The first step is drawing Lewis structure and see how the bonded pairs electrons repel each other, according to VSEPR. For example, BeCl2 is linear because there are two bonded pairs of electrons around the central atom Be, while BF3 is trigonal planar because there are 3 bonded pairs around the cen...
- Sat Nov 10, 2018 9:18 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Drawing Lewis Structures with VSPER
- Replies: 5
- Views: 514
Re: Drawing Lewis Structures with VSPER
Lewis structure illustrates 2-D structures while the molecular shape is 3D. So it does not necessarily need to correspond to each other. Lewis structures only need to give a guideline to molecular shapes.
- Fri Nov 02, 2018 2:37 pm
- Forum: Lewis Structures
- Topic: Expanded octets
- Replies: 6
- Views: 607
Re: Expanded octets
Only elements after period 3. For instance, elements in period 3 has unoccupied d orbitals which enable them to expand their electro clouds.
- Fri Nov 02, 2018 2:35 pm
- Forum: Trends in The Periodic Table
- Topic: Electron Affinity???
- Replies: 3
- Views: 420
Re: Electron Affinity???
Sulfur has a higher effective nuclear charge which can attract electrons more strongly.
- Fri Nov 02, 2018 2:20 pm
- Forum: Trends in The Periodic Table
- Topic: Diagonal Relationship
- Replies: 3
- Views: 359
Re: Diagonal Relationship
Do you mean elements that are at diagonal positions on the periodic table have similar properties.
- Sat Oct 27, 2018 10:18 pm
- Forum: Octet Exceptions
- Topic: do we nee to memorize the octet exceptions?
- Replies: 6
- Views: 986
Re: do we nee to memorize the octet exceptions?
I think so. But there is only 4 of them.
- Sat Oct 27, 2018 10:17 pm
- Forum: Ionic & Covalent Bonds
- Topic: Electron Affinity vs. Ionization Energy [ENDORSED]
- Replies: 4
- Views: 454
Re: Electron Affinity vs. Ionization Energy [ENDORSED]
They are not the same. Electron affinity has no clear periodicity, and elements on the top left of the period table tend to have higher electro affinity. On the otehr hand, ionization energy display clear periodicity.
- Sat Oct 27, 2018 10:13 pm
- Forum: Ionic & Covalent Bonds
- Topic: Lowest Ionization Energy [ENDORSED]
- Replies: 7
- Views: 703
Re: Lowest Ionization Energy [ENDORSED]
Ionization energy has periodicity.
- Fri Oct 19, 2018 3:56 pm
- Forum: Properties of Electrons
- Topic: Rydberg formula
- Replies: 5
- Views: 436
Re: Rydberg formula
You can use the one written in the textbook, which the professor didn't cover in lecture. That one is more straight forward to calculate the problems you mentioned. But he also said that he prefer students to use the equation he covered, which will also be used in exams.
- Fri Oct 19, 2018 3:53 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Incorrect Atomic Model
- Replies: 6
- Views: 452
Re: Incorrect Atomic Model
With the given delta x, which is the diameter of the atom, we can calculate the minimum delta momentum with the Heisenberg uncertainty principal (the equation). Because the minimum velocity calculated then is larger than the velocity of light, which should be the largest velocity possible, the model...
- Fri Oct 19, 2018 3:47 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg Uncertainty Equation
- Replies: 3
- Views: 279
Re: Heisenberg Uncertainty Equation
The question will usually clarify which variable it is asking, so there is no particular sequence in solving such problems.
- Fri Oct 12, 2018 10:28 am
- Forum: Einstein Equation
- Topic: calculating kinetic energy
- Replies: 5
- Views: 321
Re: calculating kinetic energy
That should be kg. We use SI units in all equations.
- Fri Oct 12, 2018 9:47 am
- Forum: Properties of Light
- Topic: Threshold Energy
- Replies: 11
- Views: 789
Re: Threshold Energy
Threshold energy is the least energy needed to remove an electro of certain metal. Different metals have different threshold energy.
- Fri Oct 12, 2018 9:46 am
- Forum: Properties of Light
- Topic: Do I need to memorize the Light Spectrum? [ENDORSED]
- Replies: 13
- Views: 899
Re: Do I need to memorize the Light Spectrum? [ENDORSED]
I think we should at least remember the range of UV and visible light.
- Sat Oct 06, 2018 12:37 am
- Forum: Empirical & Molecular Formulas
- Topic: When finding empirical formula
- Replies: 4
- Views: 471
Re: When finding empirical formula
I think yes. Only in that way you could find the ratio of moles.
- Sat Oct 06, 2018 12:36 am
- Forum: Balancing Chemical Reactions
- Topic: States of Matter
- Replies: 11
- Views: 2094
Re: States of Matter
Aqueous solution is the solution that the solvent is water. I actually think the chemical equations are designed to show the process of the experiments. To better represent the process, the states of reactant can help clarify the experiment.
- Fri Oct 05, 2018 11:06 pm
- Forum: Limiting Reactant Calculations
- Topic: Limiting reagents
- Replies: 12
- Views: 810
Re: Limiting reagents
In one step-reactions, there will only be one limiting reactant. It is possible that all the substance involved in a reaction is completely consumed, in which there are no limiting reagents or all the reactants are limiting.