## Search found 62 matches

Sat Mar 16, 2019 1:12 pm
Forum: Ideal Gases
Topic: Bar for partial pressure [ENDORSED]
Replies: 4
Views: 452

### 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: 5392

### 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: 101

### 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: 91

### 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: 119

### 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: 124

### 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: 112

### 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: 133

### 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: 188

### 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: 374

### 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: 258

### 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: 166

### 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: 460

### 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: 117

### 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: 201

### 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: 274

### 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: 420

### 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: 155

### 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: 148

### 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: 93

### 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: 134

### 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: 594

### 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: 184

### 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: 124

### 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: 90

### 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: 88

### 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: 2994

### 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: 163

### 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: 198

### 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: 155

### 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: 190

### 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: 239

### Re: Reaction Quotient

Yes...
Fri Dec 07, 2018 5:33 pm
Forum: Identifying Acidic & Basic Salts
Topic: aqueous solutions of salts
Replies: 2
Views: 321

### 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: 279

### 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: 81

### 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: 158

### 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: 196

### 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: 143

### 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: 262

### 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: 160

### 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: 169

### 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: 298

### 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: 127

### 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: 503

### 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: 323

### 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: 284

### 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: 246

### 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: 341

### 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: 225

### 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: 176

### 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: 591

### 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: 163

### 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: 321

### 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: 238

### 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: 278

### 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: 152

### 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: 124

### 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: 325

### 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: 383

### 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: 216

### 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: 812

### 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: 352

### 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.