## Search found 50 matches

Fri Mar 16, 2018 5:27 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: delta S sys and delta S surr
Replies: 2
Views: 701

### Re: delta S sys and delta S surr

They are different because one system would be releasing heat, while the other is absorbing the heat.
Fri Mar 16, 2018 5:21 pm
Forum: Calculating Work of Expansion
Topic: Conversion of R
Replies: 7
Views: 535

### Re: Conversion of R

You would have to see what units you are using or solving for. If you are trying to find joules, you will be using 8.314
Fri Mar 16, 2018 5:17 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation energy and temp
Replies: 3
Views: 231

### Re: Activation energy and temp

Activation energy and temperature have a great influence on the rate constant k, but not on each other.
Fri Mar 16, 2018 5:16 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Which is which k?
Replies: 4
Views: 260

### Re: Which is which k?

As long as you are consistent with what temperature you assign the k's, then it shouldn't matter.
Fri Mar 16, 2018 5:15 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: rate law
Replies: 5
Views: 491

### Re: rate law

You would also be able to tell the order of the reactin by looking at the rate constant, assuming its given. For instance
1/s would be first order.
Thu Mar 15, 2018 8:57 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Profiles
Replies: 1
Views: 100

### Re: Reaction Profiles

Previous finals have questions where a reaction profile is given and we have to name certain parts of it. So just be comfortable with it, and know what each part of the profile stands for/ is.
Thu Mar 15, 2018 8:55 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Collision theory for Reaction Mechanisms
Replies: 2
Views: 197

### Re: Collision theory for Reaction Mechanisms

More than likely, we'll be dealing with unimolecular and bimolecular reactions, maybe some termolecular reactions, and this is basically the chances of atoms colliding with each other. The chances the atoms collide in the necessary ways decrease as the amount of atoms increases.
Thu Mar 15, 2018 8:51 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Final Pseudo Equilibrium
Replies: 1
Views: 163

### Re: Final Pseudo Equilibrium

Yes, my plf and T.A both said we should know what it is and how to use it.
Thu Mar 15, 2018 8:03 pm
Forum: First Order Reactions
Topic: Slope of 1st order RXNs
Replies: 9
Views: 633

### Re: Slope of 1st order RXNs

First order integrated rate law: ln[A]= -k*t+ln[A]
y= m*X + B

Zero Order Integrated Rate Law: [A]=−kt+[A]initial
Y= m*X+B
Thu Mar 15, 2018 8:00 pm
Forum: First Order Reactions
Topic: Exam 3: Question 6
Replies: 2
Views: 262

### Exam 3: Question 6

How would we determine which rate constant to use given the following facts: 1st order reaction, proceeds for 10 minutes and that only 71.9% of the initial concentration of reactants remain.
Thu Mar 15, 2018 7:54 pm
Forum: Zero Order Reactions
Topic: Units of k
Replies: 12
Views: 997

### Re: Units of k

The easiest way to determine the units of the rate constant k is to use the following "formula":
M^(1-X)/S
where x is the order of the reaction. Examples:
Zero Order: M(^1-0)/S ----> units: M/S
First Order: M^(1-1)/S ----> units: 1/S and so on
Thu Mar 15, 2018 7:51 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Question 15.63
Replies: 2
Views: 206

### Re: Question 15.63

As long as you are consistent with what k you are associating with that particular temperature, it shouldn't matter.
Thu Mar 15, 2018 7:49 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: endothermic reaction.
Replies: 5
Views: 352

### Re: endothermic reaction.

This question was answered in a newer post, so im just going to quote what that person said: 'In an endothermic process, the potential energy of the products is higher than that of the reactants. Its reverse process will be exothermic. In the endothermic process, the reaction must build up activatio...
Thu Mar 15, 2018 7:47 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation and constant
Replies: 3
Views: 253

### Re: Arrhenius Equation and constant

Can someone also expand conceptually on what "Exhibiting Arrhenius behavior" entails in regards to rate constants? The closest answer I've gotten so far is that the Arrhenius equation shows the relationship between k, temperature and activation energy. To put it simply, the higher Ea is, ...
Thu Mar 15, 2018 7:44 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 1
Views: 137

### Re: 15.63

I got confused with this question at first, but you get .59 after plugging in the values into the equation and solving. The only problem is that the -.59 the manual shows should actually be a positive .59 in order to get e^(.59)=1.8
Thu Mar 15, 2018 7:39 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius equation and order of rxn
Replies: 3
Views: 226

### Re: Arrhenius equation and order of rxn

Order doesn't apply to the arrhenius equation since all you're doing is finding k or ea. If you were given k, you could figure out what order it is from the units alone, but that wouldn't affect how you solve using the formula.
Wed Mar 14, 2018 11:04 pm
Forum: General Rate Laws
Topic: Distinguishing Different Types of Constants
Replies: 3
Views: 245

### Re: Distinguishing Different Types of Constants

My T.A said that you can write small notations near the K's to distinguish them, for instance, the equilibrium constant can be written as K(eq) to help you distinguish from small k(fwd)/k(rev).
Also, if there are multiple steps, you can write a little 1 or 2 next to the k's to clear it up anymore.
Wed Mar 14, 2018 11:01 pm
Forum: General Rate Laws
Topic: Powers of Concentrations in Rate Law`
Replies: 2
Views: 168

### Re: Powers of Concentrations in Rate Law`

You can write the rate law from the the formula itself, A+B -> C, r=k[A][B], but you wouldnt know what order it is until you find the exponents to each reactant, most likely from a data table.
Wed Mar 14, 2018 10:58 pm
Forum: General Rate Laws
Topic: Rate Law
Replies: 6
Views: 628

### Re: Rate Law

The rate law is determined by r=K[A][B][C], where A B C are reactants. You would determine the overall order through a data table, by finding the exponents of each reactant and adding them together.
Wed Mar 14, 2018 10:54 pm
Forum: First Order Reactions
Topic: 15.85
Replies: 3
Views: 297

### Re: 15.85

Since it is in the transition phase, it is very unstable because it is forming and breaking a bond at the same time. You would have to draw the molecule with on bond being broken, and another being added in its place in order to get the final product.
Wed Mar 14, 2018 10:51 pm
Forum: First Order Reactions
Topic: Negative Orders
Replies: 5
Views: 411

### Re: Negative Orders

A previous post stated that their T.A told them that we should be comfortable with negative orders for the final, but we shouldn't worry about fractions or stuff like that.
Wed Mar 14, 2018 10:41 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: k and Ea
Replies: 4
Views: 498

### Re: k and Ea

You can see the relationship by looking at the equation: k=Ae^(-Ea/RT); an e to a small number will give you a small k, whereas an e to a big number will give you a large k. In other words, the bigger Ea is, the smaller the value of k will be and vice versa.
Wed Mar 14, 2018 10:36 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Net rate of formation of products
Replies: 2
Views: 230

### Re: Net rate of formation of products

The net rate of formation is the rate of the slow step without any intermediates; so you would have to use k/k' to replace it and so on. Your final step should never have intermediates in it.
Wed Mar 14, 2018 10:34 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step
Replies: 4
Views: 246

### Re: Slow Step

The step treated at equilibrium is the slow step, and any step after that doesn't really matter. All we care about is the slow step and the steps that come before it.
Wed Mar 14, 2018 10:33 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: k' reverse reaction constant
Replies: 6
Views: 489

### Re: k' reverse reaction constant

Just a heads up, k' can also be written as k-1, but yeah, its just a different notation to distinguish the forward from the reverse reaction rate.
Wed Mar 14, 2018 10:31 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Finding the slow step
Replies: 5
Views: 426

### Re: Finding the slow step

Someone asked that question in my discussion today, the T.A said that the (slow) and (fast) steps will be given, so we shouldn't worry about it.
Wed Mar 14, 2018 10:30 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalyst and Intermediate
Replies: 5
Views: 415

### Re: Catalyst and Intermediate

Yeah, a catalyst will be used in the first step and be regenerated in the last step, whereas an intermediate is formed in the first step and used in the second step. In other words, the intermediate will be cancelled out whereas the catalyst will not. You will be able to see and use both of them.
Wed Mar 14, 2018 10:25 pm
Forum: First Order Reactions
Topic: Determining Reaction Order
Replies: 5
Views: 439

### Re: Determining Reaction Order

You can also determine reaction order from the rate constant:
K=1/s first order
K=1/M*S second order
K=1/M^2*S third order
You get these units for k by doing this: K= M^(1-X)/S; where X is the order of the reaction. Just a helpful hint to find those units :)
Wed Mar 14, 2018 10:21 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: to find k
Replies: 4
Views: 356

### Re: to find k

The r (rate constant) you find from a data table containing concentrations and rate, will be the same for all entries, that is because concentration does not affect the rate constant, only the rate.
Wed Mar 14, 2018 10:19 pm
Forum: General Rate Laws
Topic: rate law vs integrated rate law
Replies: 2
Views: 713

### Re: rate law vs integrated rate law

Integrated rate law gives you the slope of the tangent at any point in the graph. In other words, it tells you how fast/slow the reaction is going at that point.
Sat Dec 09, 2017 10:33 pm
Forum: Sigma & Pi Bonds
Topic: Triple Bond
Replies: 2
Views: 253

### Re: Triple Bond

Single Bond = 1 sigma bond
Double Bond = 1 sigma bond; 1 pi bond
Triple Bond = 1 sigma bond, 2 pi bonds
Sat Dec 09, 2017 10:13 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Shell, subshell, and orbital
Replies: 5
Views: 448

### Re: Shell, subshell, and orbital

For a value of l greater than 4, what would the orbital be? Are there orbitals beyond f orbitals that we don't cover in this class, or is it simply that any l that is 5 or above is considered an f orbital? After the f orbital, its the g orbital. We rarely use the f orbital, so using the g orbital i...
Sat Dec 09, 2017 9:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: SiO2 Polar or Nonpolar
Replies: 2
Views: 5890

### Re: SiO2 Polar or Nonpolar

SiO2 has a linear shape, and since the elements at each end are the same, the pull is canceled out, making the overall compound non-polar.
Sat Dec 09, 2017 9:48 pm
Forum: Hybridization
Topic: sp3 hybridization
Replies: 6
Views: 532

### Re: sp3 hybridization

Bonds, even if they are single/double/triple, will count as one area of electron density. Lone pairs will also count as an area of electron density. So in this case, sp3 means that the atom has 4 areas of electron density.
Sat Dec 09, 2017 9:46 pm
Forum: Photoelectric Effect
Topic: Number of photons and intensity
Replies: 2
Views: 174

### Re: Number of photons and intensity

No, increasing the number of photons will not remove an electron from the metal. The only way to remove it is to increase the energy, by increasing the frequency. E=frequency x Plank's Constant.
Sat Dec 09, 2017 9:44 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Lewis Structures and Formal Charge
Replies: 7
Views: 832

### Re: Lewis Structures and Formal Charge

Yeah, check your formal charges to make sure the lewis structure makes sense. For example, if a Flourine in your structure ended with a positive charge, it's pretty clear that there is a mistake.
Sat Dec 09, 2017 9:39 pm
Forum: Ideal Gases
Topic: Kc and shifting of reaction
Replies: 3
Views: 469

### Re: Kc and shifting of reaction

If you are given all the initial concentrations, the first thing you should do is calculate Q by plugging it into the (Products)/(Reactants Formula) in order to determine the shift. If you don't, you might get the wrong signs for X in your ICE table.
Sat Dec 09, 2017 9:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 7
Views: 602

### Re: ICE table

Can somebody explain the 5% rule when approximating x please? Is K being less than 10^-3 enough to be able to approximate or does it also have to follow the 5% rule? The 5% rule and K being less than 10^-3 go hand in hand. The concentrations of the acids/bases are so little, that it should end up b...
Sat Dec 09, 2017 9:30 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T-shaped and Trigonal Pyramidal
Replies: 6
Views: 472

### Re: T-shaped and Trigonal Pyramidal

T-shaped: AX(3)E(2)
Trigonal Pyramidal: AX(3)E(1)
Sat Dec 09, 2017 9:26 pm
Forum: Lewis Structures
Replies: 1
Views: 168

Yes, radicals, or unpaired single electrons, can also participate in resonance to increase their stability.
Mon Nov 06, 2017 3:07 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: d orbital or s orbital first?
Replies: 5
Views: 394

### Re: d orbital or s orbital first?

The way I remembered it is that s comes before d if d has no electrons; once it does, d always comes before s.
Mon Nov 06, 2017 3:01 pm
Forum: Trends in The Periodic Table
Topic: Comparing Cations and Parent Atom Atomic Radius
Replies: 2
Views: 382

### Re: Comparing Cations and Parent Atom Atomic Radius

I know that atomic radii decreases from left to right across a period as the effective atomic number increases, and they increase down a group as successive shells are occupied. Also that cations are smaller than their parent atoms and anions larger. However, when comparing for example, Cs+1 and Ba...
Thu Oct 19, 2017 8:26 pm
Forum: Properties of Light
Topic: Lyman and Balmer series.
Replies: 4
Views: 313

### Re: Lyman and Balmer series.

Should we know the approximate numbers of the different wavelengths? Yes, that will be helpful, but as long as you understand the concept and know what higher/lower wavelengths mean, you should be fine. For instance, a microwave will have a long wavelength, low frequency, and low energy, whereas an...
Thu Oct 19, 2017 8:23 pm
Forum: Properties of Light
Topic: Converting Units [ENDORSED]
Replies: 11
Views: 773

### Re: Converting Units[ENDORSED]

My T.A stated that as long as the questions don't specify the SI units, you can write you answer in meters or nm etc.. But if it does specify a specific unit, always write your final answer in that unit.
Thu Oct 19, 2017 8:20 pm
Forum: Properties of Light
Topic: the quantum world
Replies: 7
Views: 474

### Re: the quantum world

As long as you understand the concepts of wavelengths and frequencies you should be good. ie, larger wavelength, lower frequency, lower energy and vice versa. You should also know the wavelength of the visible lights, red=700nm, violet=400nm
Thu Oct 19, 2017 8:18 pm
Forum: Properties of Light
Topic: EM spectrum
Replies: 6
Views: 484

### Re: EM spectrum

I noticed that one of the questions asked us what visible color is of the wavelength 486. Should I know the exact ranges of when purple becoming blue since the answer was blue? I took the test today and nothing was asked regarding the color of the wavelength; however, my t.a did mention a couple of...
Thu Oct 12, 2017 6:47 pm
Forum: Properties of Light
Topic: Chapter 1 #3
Replies: 9
Views: 559

### Re: Chapter 1 #3

With respect to Part C, is there a relationship between the extent of change in an electrical field and the frequency of electromagnetic radiation? According to the solutions manual: "Yes, The Electrical Field corresponds to the amplitude; as the frequency decreases the waves broaden and the e...
Thu Oct 05, 2017 4:28 pm
Forum: Empirical & Molecular Formulas
Topic: Identifying Empirical and Molecular Formulas [ENDORSED]
Replies: 13
Views: 5436

### Re: Identifying Empirical and Molecular Formulas[ENDORSED]

When writing an empirical or molecular formula, how do you know in what order to write the elements? For example, how would you know to write Na3AlF6 rather than AlNa3F6 or Na3F6Al? Our discussion asked that exact same question today, and our T.A told us that generally, the metal atom goes first fo...
Thu Oct 05, 2017 4:23 pm
Forum: Molarity, Solutions, Dilutions
Topic: Writing formulas
Replies: 4
Views: 438

### Re: Writing formulas

Both statements above are correct; however, my T.A did state that after this Friday's test, we will have to memorize the names and formulas of the compounds. They will not be written down for us anymore.
Thu Oct 05, 2017 4:10 pm
Forum: Significant Figures
Topic: Number of sig figs in answer
Replies: 8
Views: 753

### Re: Number of sig figs in answer

Hey, I had the same question too, but after asking my T.A and watching several youtube lessons on sig figs, it is always better to have a couple sig figs in your calculations and once you arrive at your final calculation, you round up the significant figures. For instance, if I knew I only needed 3 ...