## Search found 63 matches

Mon Mar 19, 2018 3:15 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: arrhenius equation
Replies: 1
Views: 282

### Re: arrhenius equation

A is the pre-exponential factor. It is the fraction of molecules that would react if the activation energy was zero (if Ea is 0, e^0/RT would be 1 so your arrhenius equation would be k=a).

A is usually determined with experimental data, since it's different for different reactions.
Mon Mar 19, 2018 3:09 am
Forum: Balancing Redox Reactions
Topic: periodic trends
Replies: 3
Views: 361

### Re: periodic trends

the oxidizing power increases as you go to the right and up (similar to electronegativity). The reducing power is the opposite, with elements like lithium being a strong one.
Sun Mar 18, 2018 10:39 am
Forum: Balancing Redox Reactions
Topic: test 2
Replies: 5
Views: 500

### Re: test 2

you use the deltaG=-nFE equation.
Fe2+ + e- -> Fe2+ deltaG1 = -(1)(F)(0.77)
Fe2+ + 2e- => Fe(s) deltaG2 = -(2)(F)(-0.44)

Add them up, then solve for E.
deltaG1+deltaG2 = -(3)(F)(E).

Which is -0.037 V.
Sun Mar 11, 2018 11:09 pm
Forum: Balancing Redox Reactions
Topic: redox
Replies: 6
Views: 417

### Re: redox

LEO the lion says GER.

a loss of electrons is oxidation, so the oxidizing agent is what makes the loss of electrons happen, aka what gets more electrons by oxidizing something else.

The reducing agent is what causes the gain of electrons, so it gives up electrons to reduce something else.
Sun Mar 11, 2018 10:34 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-equiliibrium?
Replies: 3
Views: 281

### Re: Pre-equiliibrium?

pre-equilibrium: basically when the process is not at equilibrium. Since the rate of reaction measures how fast the reaction progresses UNTIL equilibrium (before it reaches equilibrium)
Sun Mar 11, 2018 10:33 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: k and Ea
Replies: 4
Views: 547

### Re: k and Ea

you can think about it this way... the equilibrium constant k is basically products/reactants. If the activation energy is super high, then it's harder to form products since we have to first overcome this barrier. So when the numerator is smaller, k is smaller.
Sun Mar 04, 2018 10:15 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate determining reaction
Replies: 3
Views: 228

### Re: Rate determining reaction

The rate determining step would be the slowest step of the reaction. You would calculate the rate based on the slower step.
Sun Mar 04, 2018 10:12 pm
Forum: General Rate Laws
Topic: Rate laws
Replies: 4
Views: 307

### Re: Rate laws

Well, we could possibly be asked to calculate the order of the reaction with respect to a certain substance given a table of concentrations.
Sun Mar 04, 2018 10:02 pm
Forum: First Order Reactions
Topic: Derivations
Replies: 6
Views: 413

### Re: Derivations

Also, as general comprehension of formulas, we should know the theory behind where they came from.
Sun Mar 04, 2018 9:59 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8244
Views: 1438351

### Re: Post All Chemistry Jokes Here

Dang girl you are a 10.

On a pH scale.

Because you are basic.
Thu Mar 01, 2018 12:16 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 15.3 [ENDORSED]
Replies: 7
Views: 447

### Re: 15.3[ENDORSED]

Since it 10^-3 mol is the same as 1 mmol, it's the same thing. Convention maybe just wanted the answer to be in standard moles.
Thu Feb 22, 2018 1:10 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.107
Replies: 1
Views: 207

### 14.107

14.107 What range (in volts) does a voltmeter need to have to measure pH in the range of 1 to 14 at 25 C if the voltage is zero when pH = 7?

When using the formula E=RT/nF lnK, why is n = 1? Is it always this way, or is there something in this problem specifically that tells us we have one mol?
Thu Feb 22, 2018 12:40 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cathode vs Anode
Replies: 4
Views: 322

### Re: Cathode vs Anode

I think by convention you put the anode first, because then when you read it from left to right your eyes follow the flow of electrons from anode to cathode. So, oxidation (anode) -> reduction (cathode) site.
Thu Feb 22, 2018 12:33 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.19
Replies: 2
Views: 207

### Re: 14.19

Yeah, what's given to us is the cell potential. The question is asking for the M2/M couple, which is the cathode. So rearranging the potential = cathode-anode will give us the correct answer, -0.689+0.34=-0.349 V.
Thu Feb 15, 2018 3:13 pm
Forum: Phase Changes & Related Calculations
Topic: Specific heat of water or ice?
Replies: 6
Views: 489

### Re: Specific heat of water or ice?

Water is only ice below 0 degrees, so we would use the specific heat of ice below that and then include the heat of fusion at 0 degrees then the specific heat of water above 0 degrees. So we use ice -> phase change -> water. Your delta temperature for the ice should have 0 as the final, and the delt...
Thu Feb 15, 2018 3:09 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: log vs. ln [ENDORSED]
Replies: 2
Views: 249

### Re: log vs. ln[ENDORSED]

the NERNST equation can be written with both ln and log, there's just an added constant for log. So for ln: E = E-RT/nF(lnQ) but for log: E = E-2.303RT/nF(logQ)
Thu Feb 15, 2018 3:01 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: s vs. delta s
Replies: 7
Views: 448

### Re: s vs. delta s

most of the times in calculations it's delta s, because we are measuring the entropy of some reaction and therefore take the entropy of the products minus reaction (thus a change in entropy).
Wed Feb 07, 2018 11:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: quiz question #7
Replies: 1
Views: 201

### Re: quiz question #7

I don't know what "five steps of enthalpies we have to calculate" are but number 7 was about making iced-tea. So the enthalpy of fusion from ice melting is 30grams*(1mol/18.01grams)*(6010Joules/mol) which you add to the heat(q=mcDeltaT) of your now water to get the total q_ice. for referen...
Wed Feb 07, 2018 11:33 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.1
Replies: 4
Views: 338

### Re: 9.1

100/(20+273.15)=0.341 Joules/(Kelvin second)
Wed Feb 07, 2018 11:13 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.103
Replies: 4
Views: 307

### Re: 9.103

As given, is there no way to figure out what deltaG is? In order to do this problem, is the only way to search up the deltaG of the entire reaction by some appendix?
Wed Feb 07, 2018 10:57 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.103
Replies: 4
Views: 307

### Re: 9.103

So how would you tell whether the equations, A and B, are spontaneous or not?
Wed Feb 07, 2018 10:35 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.103
Replies: 4
Views: 307

### 9.103

How can we determine if a reaction is spontaneous by just looking at it? Especially in the context of this case. 9.103 A scientist proposed the following two reactions to produce ethanol, a liquid fuel: C 2H4(g) + H2O(g) -> CH3CH2OH(l) (A) C 2H6(g) + H2O(g) -> CH3CH2OH(l) + H2(g) (B) Assume standard...
Wed Jan 31, 2018 11:51 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Midterm
Replies: 6
Views: 390

### Re: Midterm

Both probably, but it's always helpful to understand concepts before you can carry out computations.
Wed Jan 31, 2018 11:50 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: what exactly is free energy?
Replies: 5
Views: 350

### Re: what exactly is free energy?

Free energy is like all the energy in the universe available to be released or consumed through reactions taking place. The Gibbs free energy is a measure of "usable" energy in the system. Basically how much energy you have available to do work. So when we have deltaG, we are looking at th...
Wed Jan 31, 2018 11:35 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.13
Replies: 5
Views: 294

### Re: 9.13

it tells us to assume ideal gas conditions, which means we assume 1 mol of gas.
Sun Jan 28, 2018 9:50 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal Reversible
Replies: 3
Views: 415

### Re: Isothermal Reversible

not all isothermal reactions are reversible. for a thermodynamic process to be reversible, it must maintain equilibrium with its surroundings at all instances. So, the process must progress slowly without acceleration. The expansion of an ideal gas into a vacuum is isothermal. It is expanding into e...
Sun Jan 28, 2018 9:23 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp for an ideal gas
Replies: 2
Views: 200

### Re: Cp for an ideal gas

Here's one proof, scroll down to the second half of the page for Cp (the first half is Cv) http://physics.bu.edu/~redner/211-sp06/class24/class24_heatcap.html and also you might ask where the Energy = 3/2 * nRdeltaT comes from, which is explained conceptually in the following video: https://www.khan...
Sun Jan 28, 2018 9:16 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Difference between systems? [ENDORSED]
Replies: 8
Views: 602

### Re: Difference between systems?[ENDORSED]

An open system freely exchanges energy and matter with its surroundings. The simplest example of this is boiling water, where both water can leave in the form of vapor and it gives off heat. A closed system only exchanges energy with its surroundings, so this is like boiling water with a lid on. You...
Sun Jan 21, 2018 11:50 pm
Forum: Student Social/Study Group
Topic: First Test Topics
Replies: 2
Views: 442

### Re: First Test Topics

basically, nothing about the isothermal reversible reaction calculations.
Sun Jan 21, 2018 11:47 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Heat and systems
Replies: 3
Views: 279

### Re: Heat and systems

Heat transfers from a higher point of temperature to a lower one. So look at a problem and determine if the system losing heat or gaining heat.
Sun Jan 21, 2018 11:44 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Entropy of an Isolated System
Replies: 4
Views: 335

### Re: Entropy of an Isolated System

isolated systems always go towards thermodynamic equilibrium, and that is a state with maximum entropy. An example is if you have an ice cube in a room, and the room is an isolated system, the total entropy inside the room will increase as the ice melts. The system is exchanging heat within itself a...
Sun Jan 21, 2018 11:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: closed sysytem
Replies: 3
Views: 227

### Re: closed sysytem

mercury in a thermometer: no matter can escape, but heat can. We can see that when the temperature is hot the mercury expands, causing the thermometer to have a higher reading. The mercury is affected by the heat of the surroundings. That's a simple explanation. But no matter escapes because as we s...
Mon Jan 15, 2018 4:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units of Pressure
Replies: 3
Views: 305

### Re: Units of Pressure

Also, Dr. Lavelle noted that for our calculations we can kind of equate atm and bar since they are so similar in value.
Mon Jan 15, 2018 4:54 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Units
Replies: 2
Views: 172

### Re: Units

Or, you can always do dimensional analysis and see which units cancel out when calculating.
Mon Jan 15, 2018 4:53 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy Trends
Replies: 2
Views: 204

### Re: Enthalpy Trends

Yeah, also stable bonds like staying as such so it would take more energy to break them. A bond with a weak enthalpy would be able to dissolve without much input.
Sat Dec 09, 2017 10:29 pm
Forum: Administrative Questions and Class Announcements
Topic: Practice Test Fall 2017 [ENDORSED]
Replies: 19
Views: 2622

### Re: Practice Test Fall 2017[ENDORSED]

There is a question on the final practice test, number 22, that asks how many O2 molecules can myoglobin bind and how many myoglobins form a hemoglobin. I know biologically the answer is each myoglobin can bind one oxygen and hemoglobin is composed of 4 myoglobins, but what is the chemical explanati...
Fri Dec 08, 2017 12:35 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Acid Strength
Replies: 5
Views: 562

### Re: Acid Strength

I think you might be mistaken, HCl is a stronger acid than HF.

There are 7 common strong acids and HCl is on that list, HF is not.
Fri Dec 08, 2017 12:29 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: 12.7
Replies: 2
Views: 314

### Re: 12.7

For part a, the conjugate base to HClO3 is ClO3-. The lewis structure has a central Cl atom, connected to two oxygen atoms with double bonds and a third oxygen with a single bond. The double bonded oxygens have 2 lone pairs each while the single bond connected oxygen has 3 lone pairs (6 total lone e...
Thu Nov 30, 2017 10:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Table 11.2
Replies: 4
Views: 296

### Re: Table 11.2

K is Kp, the equilibrium constant based on the partial pressures. The relationship between Kc and Kp is Kp = Kc(RT)^delta(n). This can be derived from the ideal gas equation (PV=nRT) by letting P = nRT/V (and n/V is the concentration, so this is P = [gas]RT) and plugging that in to the Kp equation (...
Thu Nov 30, 2017 10:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Units for K and Q [ENDORSED]
Replies: 5
Views: 732

### Re: Units for K and Q[ENDORSED]

You just have to use the same constant for all your calculations. Since the units eventually cancel out to render K unitless, it doesn't really matter as long as it's all the same (so don't use atm for one molecule and bar for another, but if you use atm for all then all the atms cancel anyways). Si...
Wed Nov 22, 2017 1:55 pm
Forum: Naming
Topic: Question 17.29a
Replies: 3
Views: 227

### Re: Question 17.29a

Ferrous means iron. Ever notice that the symbol for iron is Fe instead of like... Ir (actually iridium)? It's derived from latin. Another example is Copper, which you might expect to be Co (that's actually cobalt) but Copper is actually Cu... stands for cupric, also latin for copper. Tin is another ...
Wed Nov 22, 2017 1:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: 17.33 (whole)
Replies: 3
Views: 476

### Re: 17.33 (whole)

Polydentate ligands is basically when you bind a bunch of these given molecules to a central metal atom or ion. So how many bonds does each molecule make with the metal? I'll give the easiest example, part c, which is water. This is monodentate because only the oxygen atom is a donor atom that has e...
Thu Nov 16, 2017 9:24 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8244
Views: 1438351

### Re: Post All Chemistry Jokes Here

Aren't you all glad we have this chemistry community forum? It makes 14A less of a cheMYSTERY for us all :)
Thu Nov 16, 2017 9:16 pm
Forum: Ionic & Covalent Bonds
Topic: SiO2
Replies: 4
Views: 2770

### Re: SiO2

You know that the Si-O bonds are polar because of their location on the periodic table. We know that C-O bonds are polar, since oxygen is more electronegative than carbon, and Silicon is in the same group as carbon -> Si-O bonds are also expected to be polar.
Thu Nov 16, 2017 9:04 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: bond angle
Replies: 4
Views: 479

### Re: bond angle

The bond angle for something is the angle between your central atom and the two directly attached to it. For example, in water the bond angle is the angle created by H-O-H. For a trigonal bipyramidal molecule like PF5, the bond angles are either 120 or 90 degrees. See the attached graphic... It's ea...
Thu Nov 09, 2017 1:23 pm
Forum: Dipole Moments
Topic: Finding Dipole Moments
Replies: 3
Views: 504

### Re: Finding Dipole Moments

And when drawing the arrows for dipole movements, it always goes from the less electronegative atom -> more electronegative atom. It's a measure of polarity, and the large electronegativity difference, the larger dipole movement force.
Thu Nov 09, 2017 1:17 pm
Forum: DeBroglie Equation
Topic: Diffraction Patterns
Replies: 2
Views: 234

### Re: Diffraction Patterns

When waves run into each other they either contructively build or destructively become weaker. So when we measure "how much" wave we get at each location, we get a diffraction pattern that shows where waves added up and where they canceled out. The following gif representation of how diffr...
Thu Nov 09, 2017 1:13 pm
Forum: Dipole Moments
Topic: Polarity
Replies: 5
Views: 615

### Re: Polarity

You can look for either lone pair electrons or polar bonds. If we take two molecules, CO2 and H2O which may both seem to be linear in shape because they have 3 atoms each, we find that actually CO2 is linear while H2O is bent. Because the lone pair electrons on water repel the hydrogens and force a ...
Thu Nov 02, 2017 5:35 pm
Forum: Trends in The Periodic Table
Topic: Diagonal relationships
Replies: 1
Views: 140

### Re: Diagonal relationships

Many chemical properties are related to size of an atom or how many protons/electrons it contains. For two elements diagonal to each other, they differ by one group (vertical column of periodic table) and share similar characteristics. Size decreases when you move from left to right, and increases w...
Thu Nov 02, 2017 5:29 pm
Forum: Lewis Structures
Topic: Lewis Structures for Ions?
Replies: 1
Views: 220

### Re: Lewis Structures for Ions?

Yeah, add or subtract the amount of electrons (add one electron for 1-, add two for 2-, remove one for 1+, remove 2 for 2+, etc.) then put your whole molecule in brackets [these things] and put the charge in the corner so ammonium would be [NH4]+ (except it would be nitrogen as the central atom with...
Tue Oct 31, 2017 10:26 pm
Forum: Trends in The Periodic Table
Replies: 2
Views: 262

With the loss of an electron, the remaining electrons in a cation are drawn closer to the nucleus. With the gain of an electron, the electron cloud of anions grows larger because electrons repel each other. Generally, increasing electrons (increasing negative charge) leads to increased ionic size an...
Mon Oct 23, 2017 12:00 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: electron configuration for cation of Cr? [ENDORSED]
Replies: 1
Views: 130

### Re: electron configuration for cation of Cr?[ENDORSED]

[Ar](3d^5)
You lose electrons from the largest number shell first (4th shell) here
and if you had even less electrons like it was Cr3+ then it would be [Ar](3d^3)
Mon Oct 23, 2017 11:23 am
Forum: *Shrodinger Equation
Topic: Double derivative [ENDORSED]
Replies: 3
Views: 371

### Re: Double derivative[ENDORSED]

A double derivative is the same as a second derivative. Find the derivative of your function. Then, take another derivative -> you now have a double derivative.
Mon Oct 23, 2017 11:20 am
Forum: Administrative Questions and Class Announcements
Topic: Where is BruinCast?
Replies: 2
Views: 285

### Where is BruinCast?

Where can I find Bruincast for 14A? I know that they are on CCLE under the media tab but the CCLE links to Lavelle's website not the CCLE chem14A website... so anyone know where it is??
Fri Oct 20, 2017 2:18 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Atomic Orbitals
Replies: 2
Views: 204

### Re: Atomic Orbitals

Also the f orbital. So if the p orbital is two lobes, aka two ellipses, the d orbital would be (generally) like a double p with 4 lobes. And the f is (generally) like a triple p with 6 lobes (because one p has 2 lobes, so triple that would be 6 total). It's also arranged similarly, 6 ellipsoids orie...
Fri Oct 20, 2017 2:07 am
Forum: DeBroglie Equation
Topic: Help with the concept of De Broglie's
Replies: 8
Views: 548

### Re: Help with the concept of De Broglie's

Yeah, the wavelength exists but is very small and imperceivable. The entire concept of De Broglie's is to propose that all matter has wave-like properties, such as wavelengh. It is usually applied to describe the wave-like nature of an electron, but can still be used for larger objects. Just doesn't...
Fri Oct 20, 2017 2:03 am
Forum: DeBroglie Equation
Topic: Homework Problems
Replies: 3
Views: 299

### Re: Homework Problems

You can still turn in questions from chapter 1 as long as they're not the same as the ones you turned in last week. Since the email Lavelle sent out told us specifically which hw problems would be covered on the test, doing the hw from this section would be good preparation.
Fri Oct 20, 2017 12:36 am
Forum: DeBroglie Equation
Topic: CHAPTER 1 QUESTION 33!!!
Replies: 8
Views: 623

### Re: CHAPTER 1 QUESTION 33!!!

Back to your original question, I understand it like this. You cannot use the Ek = 0.5mv^2=hc/lambda because we are calculating the wavelength for an electron, and there is a given velocity (3.6x10^3 km/s, in the problem) for this. Electrons don't travel at the speed of light (the constant c, in the...
Fri Oct 13, 2017 1:30 am
Forum: Limiting Reactant Calculations
Topic: volume of stock solution needed to make 250ml of 0.650M NaOH
Replies: 1
Views: 979

### Re: volume of stock solution needed to make 250ml of 0.650M NaOH

If we used 250 mL of stock solution as you said, we would have 250 mL of 2.00 M NaOH. This is not what we want. What we want is 250 mL of 0.650 M NaOH. The stock solution is the solution calculated in Q2A. What you know about this stock is that it is 2.00 M NaOH, as given in the problem. So given th...
Sun Oct 08, 2017 10:03 pm
Forum: Properties of Light
Replies: 3
Views: 304

Yes, I think you're right. I mean, would you want to (or could you) read under either UV or infrared light rays? They aren't even visible to the human eye.
Sun Oct 08, 2017 9:52 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant
Replies: 9
Views: 2406

### Re: Limiting Reactant

When calculating for the limiting reactant, you need to not only find how many moles of each (cause usually you're given the reactants in grams of mass) you have, but how many moles of one reactant is needed in relation to the other reactants. For example, if your equation is X + 3Y -> 2Z then every...
Fri Oct 06, 2017 9:46 pm
Forum: Limiting Reactant Calculations
Topic: Is either Method better?
Replies: 4
Views: 379

### Re: Is either Method better?

Often, the problem will ask how much product is formed given two amounts of reactant. In this case, straight up calculating and comparing how much product would be formed from using all of each reactant would simultaneously give you the answer to how much product you actually get. Then, you can simp...
Thu Oct 05, 2017 10:14 pm
Forum: Administrative Questions and Class Announcements