## Search found 58 matches

Sat Mar 17, 2018 12:03 am
Forum: Zero Order Reactions
Topic: graph of 0 order
Replies: 10
Views: 623

### Re: graph of 0 order

It would be a negative slope linear line. Y axis is reaction concentration, whose interaction is A0. The x axis is time, as time goes, the reactants consumes and its concentration decreases
Sat Mar 17, 2018 12:00 am
Forum: First Order Reactions
Topic: Negative Orders
Replies: 5
Views: 328

### Re: Negative Orders

It can be negative, which means as the substances decreases , the reaction rates increases. Try to think of the relationships between products and forward reaction
Fri Mar 16, 2018 11:59 pm
Forum: Limiting Reactant Calculations
Topic: Reactant vs. Reagent [ENDORSED]
Replies: 23
Views: 12628

### Re: Reactant vs. Reagent[ENDORSED]

Reactant is something that truest reacts ( chemical changes)
Regent is things that is used in the chemical reaction, which do not necessarily to be chemically changed
Fri Mar 16, 2018 11:56 pm
Forum: General Rate Laws
Topic: Writing out states for rate laws
Replies: 4
Views: 445

### Re: Writing out states for rate laws

I think we do not have to do so. But it is necessary to make sure that the units are all correct
Sun Mar 11, 2018 1:38 pm
Forum: First Order Reactions
Topic: Log vs ln
Replies: 9
Views: 542

### Re: Log vs ln

Since you can get the answer in both ways so that I don't see a real need to convert ln to log. If it makes calculation easier for you, then it is o.
Sun Mar 11, 2018 1:37 pm
Forum: Zero Order Reactions
Topic: graph of 0 order
Replies: 10
Views: 623

### Re: graph of 0 order

The graph is a linear line with time against [A]. The slope is negative, which equals to -k. The interaction point with y-axis is [A]0, which is the initial concentration of the reactant.
Sun Mar 11, 2018 1:34 pm
Forum: General Rate Laws
Topic: Stoichiometric coefficients and order
Replies: 5
Views: 469

### Re: Stoichiometric coefficients and order

You can tell the reaction rate equation by simply looking at its chemical equation.
Rate equation is determined by experiment.
Only it works if the chemical reaction is a mechanical step of the reaction.
Sun Mar 11, 2018 1:32 pm
Forum: General Rate Laws
Topic: Unique Reaction Rates [ENDORSED]
Replies: 33
Views: 63118

### Re: Unique Reaction Rates[ENDORSED]

I will say the rate of a chemical reaction is the change in concentration over the change in time and is a metric of the "speed" at which a chemical reactions occurs.
And Unique rate is the rate occurs per unit of each molecules
Fri Mar 02, 2018 9:20 am
Forum: Zero Order Reactions
Topic: Units of k [ENDORSED]
Replies: 13
Views: 497

### Re: Units of k[ENDORSED]

Since Rate= mol•L^-1•S^-1
AND [A]= mol•L-1

First order rate = K1*[A]

And calculate the unit of K1
Fri Mar 02, 2018 9:15 am
Forum: General Rate Laws
Topic: Unique Rate [ENDORSED]
Replies: 5
Views: 307

### Re: Unique Rate[ENDORSED]

If 2A+3B—>5C
Unique rate equals to -1/2 * d[A]/dt = -1/3 * d[B]/dt=+1/5 * d[C]/dt
Fri Mar 02, 2018 9:12 am
Forum: *Complex Reaction Coordinate Diagrams
Topic: Unique Rate. [ENDORSED]
Replies: 4
Views: 1084

### Unique Rate.[ENDORSED]

What’s unique rate in a chemical reaction?
Fri Feb 23, 2018 1:27 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: homework 14.51
Replies: 1
Views: 158

### homework 14.51

why the cell uses two silver electrode then Ecell is zero
isn't Ecell depending on the concentration of solutions ?? ( which means the K=1)
Fri Feb 23, 2018 1:19 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Homework 14.41
Replies: 2
Views: 150

### Homework 14.41

Why the solution manuals writes Ecell*=0 for b) part as the concentration of H+ are not equal for reactants and products.
Fri Feb 23, 2018 12:40 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Textbook Problem
Replies: 2
Views: 144

### Textbook Problem

The textbook writes that (RT/F) ln 10 = (0.026 93 V) * 2.303 = 0.0592 V at 25 C, Ecell =Ecell'- (ET/F)ln10*og{H+} =Ecell'+ .0592 V* pH It is on the page 591, which is section 14.11 why equation changes the sign from "plus" to "minus" if (RT/F) ln 10 = (0.026 93 V) * 2.303 = 0.059...
Sun Feb 18, 2018 8:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 2
Views: 144

### Re: Cell Diagrams

Usually, anode is on the left, and the cathode is on the right. There are a wire connects the two part together. Besides, it needs a salt bright to balance the charge difference.
Sun Feb 18, 2018 8:04 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Change in Entropy in Surroundings [ENDORSED]
Replies: 2
Views: 184

### Re: Change in Entropy in Surroundings[ENDORSED]

First, you can think of that everything is constant in the universe
Then, since Stotal=q(total)/T
Qtotal=zero
Stotal=0
Sun Feb 18, 2018 7:56 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 2
Views: 171

### Re: Concentration Cells

For example, when a cell has lower concentration of glucose of the cell than that outside of the cell, It needs to use Na+,K+pump to create electrochemical gradient. The pump does work and create concentration difference to produce potential energy to perform actions
Sun Feb 18, 2018 7:52 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst equation
Replies: 2
Views: 154

### Re: Nernst equation

These two equation are essentially the same. There are two different form of the same equation. The only difference is that log has 10 as its base and ln has e as its base. However, adding the constant make the two value the same. If you want to apply the same thing to other equation, I would sugges...
Sun Feb 11, 2018 6:15 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: entropy and moles
Replies: 2
Views: 402

### Re: entropy and moles

TURE, remember the equation S=k*lnW, and W=(number of different micro-states for each molecule) ^ (number of molecule)
if the number of molecules increases, S definitely increases
Sun Feb 11, 2018 6:11 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Equation
Replies: 4
Views: 142

### Re: Entropy Equation

Yes, you can only use the equation s=Qrev/T when it is a reversible expansion.
Sun Feb 11, 2018 6:05 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: signs
Replies: 3
Views: 165

### Re: signs

That's how Pro.Lavelle emphasizes in the lecture.
Positive signs mean gaining ENG and Negative signs mean giving ENG.
Probably for more accurate calculation and emphasize the direction of ENG flows.
Sun Feb 04, 2018 2:23 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat transfer to a liquefied gas.
Replies: 2
Views: 174

### Re: Heat transfer to a liquefied gas.

I think it is because vaporization always happens with lost of energy of the liquid.
Sun Feb 04, 2018 2:22 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test Number 1
Replies: 9
Views: 420

### Re: Test Number 1

you can figure it out it two ways (question:A balloon filled with gas is expanded to a larger volume and lower pressure while maintaining the same temperature. Answer yes or no if heat is being transferred in the process. ) 1:since it is a isothermal expansion, delta T=0, then delta U=0. there is no...
Sun Feb 04, 2018 2:17 pm
Forum: Calculating Work of Expansion
Topic: Calculating Work of Expansion
Replies: 4
Views: 225

### Re: Calculating Work of Expansion

Since Dr.Lavelle did mention it specifically, i think we could just use these equations. What matters is whether you understand the question and how to solve it, but not the mathematical calculation demonstration on equation
Fri Jan 26, 2018 12:41 am
Forum: Calculating Work of Expansion
Topic: Irreversible Expansion
Replies: 3
Views: 210

### Re: Irreversible Expansion

First, reversible process is one that can be reversed by an infinitely small change in infite-small change for example, 2 systems are both under 2 atm pressure, they could push/pull each other with a tiny small change in volume, it works the same for both directions however, if the 2 system are one ...
Fri Jan 26, 2018 12:38 am
Forum: Calculating Work of Expansion
Topic: 8.17 Work done by a system
Replies: 6
Views: 321

### Re: 8.17 Work done by a system

Work done by a system: the energy of system released to do work, which means the system loses ENG
Work done on the system: the energy done by the surroundings, like compressing the air, which means the internal energy of the system increases
Thu Jan 25, 2018 11:38 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Homework 8.57
Replies: 2
Views: 196

### Homework 8.57

Why on the solution manuals
the answer use the sum of enthalpy of reactant to minus the sum of enthalpy of products???
or do i misunderstand the meaning of ∆Hc is it meaning the enthalpy of formation ???
Fri Jan 19, 2018 4:04 am
Forum: Calculating Work of Expansion
Topic: 8.3 Homework
Replies: 4
Views: 272

### Re: 8.3 Homework

the truth is totally opposite.
when work is done by the system, w is negative (expand
when work is done by the environment to the system, w is positive (compress
Fri Jan 19, 2018 4:01 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Homework 8.15
Replies: 3
Views: 213

### Re: Homework 8.15

when the system lost heat to its surrounding, q is negative
Fri Jan 19, 2018 3:56 am
Forum: Calculating Work of Expansion
Topic: Homework 8.11
Replies: 8
Views: 459

### Re: Homework 8.11

Expand isothermally means that temperature stays the same, which means there is no heat transfer.All energy transfer comes form doing work. It applies to the isothermal expanding equation w=-nRT ln ( V2/V1)
Mon Jan 15, 2018 9:33 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Bond Enthalpies
Replies: 7
Views: 621

### Re: Bond Enthalpies

NO HAS A DOUNVLE BOND
BUT NO2 HAS A resonnance structure, which means the strenth of the bond is between double bond and single bond
Therefore, NO has higher bond enthalpy
Mon Jan 15, 2018 9:29 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 8.1 part c [ENDORSED]
Replies: 8
Views: 561

### Re: 8.1 part c[ENDORSED]

Since the purpose of the device is measure the heat of the substance released by burining it. Therefore, there should be no heat transfer between the device and environment
Mon Jan 15, 2018 9:27 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Closed Versus Isolated System
Replies: 3
Views: 201

### Re: Closed Versus Isolated System

A isolated system is totally separate with the outside environment; however, a closed system could still exchange heat with the outside environment.
Sat Dec 09, 2017 9:56 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Question in adding H20 in equilibrium reaction
Replies: 2
Views: 366

### Question in adding H20 in equilibrium reaction

The photosynthesis reaction, 6 CO2(g) + 6 H2O(l) ⇌ C6H12O6(aq) + 6 O2(g), is endothermic. What effect will the following changes have on the equilibrium composition.

why the answer isn't no effect since water is not part of Equilibrium constand
Wed Dec 06, 2017 9:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework 11.89 [ENDORSED]
Replies: 1
Views: 115

### Homework 11.89[ENDORSED]

when calculating the equilibrium constant of the chart.

question 1: In solution manuals, why does it use kPa as unit but not atm??
question 2: Even if it use kPa, why it use the percentage value like 5/100 but not just 5 (kpa)
Sun Dec 03, 2017 4:06 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Why is NH3 a base while NH4 an acid? H2S03? [ENDORSED]
Replies: 2
Views: 3018

### Re: Why is NH3 a base while NH4 an acid? H2S03?[ENDORSED]

Because NH4 has a proton to donate
NH3 can accept a proton
Therefore, based on the Bronsted principle.

NH4 is Bronsted acid
NH3 is Bronsted base
Sun Dec 03, 2017 3:43 pm
Forum: Ideal Gases
Topic: Q and K [ENDORSED]
Replies: 35
Views: 1431

### Re: Q and K[ENDORSED]

K is the equilibrium constants of the reaction, which is only changed with the temperature. However, Q is the reaction rate at any time of the reaction, which will be changed with add/remove of the substance,volume,and concentrations. In the other words, we say Q includes K; K is one value of Q in t...
Tue Nov 28, 2017 2:10 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Homework Question 4.73 (b)
Replies: 1
Views: 205

### Homework Question 4.73 (b)

usually, we said if the central atom of molecule has lone pairs, it is radical.
Why CH3 ; CH4; CH3 ; CH2; CH22 ; CH22 are all not radical??
Tue Nov 28, 2017 12:21 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Homework Question 4.25 (a)
Replies: 1
Views: 145

### Homework Question 4.25 (a)

for the molecule CH2Cl2 I think there are 2 ways to draw its lewis structure. one is that we draw the two H atom in the opposite direction; so do the Cl atoms. second one is we draw the two H atom next to each other; so do the Cl atoms. i think for the first one, the molecule is non-polar and the se...
Mon Nov 27, 2017 10:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX4E2 lone pairs
Replies: 2
Views: 288

### Re: AX4E2 lone pairs

The two lone pairs are farthest apart when they are on opposite sides of the central atom.
The AX4e2 adopt both equatorial positions and square planar arrangement.
Mon Nov 27, 2017 10:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Electron Arrangement and Molecular Shape
Replies: 4
Views: 214

### Electron Arrangement and Molecular Shape

It is different to describe Electron Arrangement and Molecular Shape?
For example, what's the Electron Arrangement and Molecular Shape of SO3 ^-2?
what's the Electron Arrangement and Molecular Shape of NH3??
Tue Nov 21, 2017 9:09 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reaction progress [ENDORSED]
Replies: 2
Views: 212

### Re: Reaction progress[ENDORSED]

Usually, the x-axis is time, and the y-axis is the concentration of reactants. It looks like the picture shown in the following links.
https://chem.libretexts.org/Core/Physic ... _Rate_Laws
Tue Nov 21, 2017 9:07 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Why do lone pairs take up more space than bonds?
Replies: 5
Views: 3011

### Re: Why do lone pairs take up more space than bonds?

Because lone paris have the strongest repulsion force to each other.
Tue Nov 21, 2017 9:06 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: What does it mean exactly that the reactions are at equilibrium?
Replies: 3
Views: 317

### Re: What does it mean exactly that the reactions are at equilibrium?

When the reaction are at equilibrium, the reaction rate and the reverse reaction rate are equal( although the concentrations could be different)
In that case, the reaction rate will increasing gradually reaching the equilibrium point instead of being equilibrium immediately.
Tue Nov 21, 2017 8:57 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Order of Orbitals
Replies: 10
Views: 642

### Re: Order of Orbitals

Yes, it matters. You need to follow the Aufbau Principle, and write the orbitals from lowest energy to highest energy.
Tue Nov 21, 2017 8:55 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7951
Views: 1123462

### Re: Post All Chemistry Jokes Here

In Arctic, a bear drop into the lake and looking for help:
"HELP, i'm dissolving"
Another brown bear get there and explains:
"dude, bears are insoluble"
....
"That's easy for you to say, you are not polar....."
Tue Nov 21, 2017 8:51 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Difference Between Kp and Kc
Replies: 4
Views: 599

### Re: Difference Between Kp and Kc

Kc And Kp. K and K are the equilibrium constants of gaseous mixtures. However, the difference between the two constants is that Kc is defined by molar concentrations, whereas Kp is defined by the partial pressures of the gasses inside a closed system
Tue Nov 21, 2017 8:49 am
Forum: Properties of Light
Topic: Amplitude properties
Replies: 4
Views: 399

### Re: Amplitude properties

Amplitude is independent from frequency and wavelength.
Amplitude decides the brightness of light( the number of photons)
The higher the frequency is , the more energy light has.
Frequency and wavelength are reversely related.
Tue Nov 21, 2017 8:45 am
Forum: Limiting Reactant Calculations
Topic: Reactant vs. Reagent [ENDORSED]
Replies: 23
Views: 12628

### Re: Reactant vs. Reagent[ENDORSED]

A reagent is a substance or compound added to a system to cause a chemical reaction, or added to test if a reaction occurs. The terms reactant and reagent are often used interchangeably—however, a reactant is more specifically a substance consumed in the course of a chemical reaction.
Tue Nov 21, 2017 8:41 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Temperature in Kp measurements
Replies: 2
Views: 199

### Re: Temperature in Kp measurements

You need to distinguish between rate and equilibrium position. Temperature always increases the rate of reactions (because it increases the collision frequency and the average energy of the particles reacting.) But the effect of temp on the equilibrium depends on whether the reaction is exo or endot...
Tue Nov 21, 2017 8:36 am
Forum: Ideal Gases
Topic: Chemical equilibrium [ENDORSED]
Replies: 9
Views: 896

### Re: Chemical equilibrium[ENDORSED]

Yes, it is possible! Adding more product and changing the surrounding temperature and pressure will influence the chemical equilibrium.
Sun Nov 19, 2017 4:31 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Naming Coordination Compounds
Replies: 4
Views: 279

### Re: Naming Coordination Compounds

Add -o to the end of the anion name : for example cyanide-->cyano
YES, ammonia and chlorine are both ligands in [Co(NH3)5Cl]Cl*2h20
Sun Nov 19, 2017 3:35 pm
Forum: Naming
Topic: Terminology
Replies: 4
Views: 242

### Re: Terminology

In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs.
Sun Nov 12, 2017 8:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 4
Views: 309

### Re: Bond Angles

Yes. It is one of the important parts that are mentioned on the outline of chapter 4.
Thu Nov 09, 2017 4:16 am
Forum: Bond Lengths & Energies
Topic: Homework Question 3.87 Strongest&Weakest CX bond [ENDORSED]
Replies: 1
Views: 339

### Homework Question 3.87 Strongest&Weakest CX bond[ENDORSED]

3.87 Which do you predict to have the strongest CX bond, where X is a halogen: (a) CF4, (b) CCl4, or (c) CBr4? Explain.

if we use length strength, cf4 is the strongest.
if we use electronegativity to judge, cf4 is the weakest.

how should we solve the problem???
Thu Nov 09, 2017 3:29 am
Forum: Ionic & Covalent Bonds
Topic: How to define Ionic&Covalent Bonds? [ENDORSED]
Replies: 1
Views: 191

### How to define Ionic&Covalent Bonds?[ENDORSED]

How to define the Ionic&Covalent Bonds if the electronegativity difference is between 1.5 to 2
Thu Nov 09, 2017 3:18 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron config of elements in 5d and 6d
Replies: 4
Views: 512

### Re: Electron config of elements in 5d and 6d

You do not have to count the f-block square
for Osmium, it should be 5d6
Thu Nov 09, 2017 3:08 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron config of elements in 5d and 6d
Replies: 4
Views: 512

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