## Search found 50 matches

Fri Mar 16, 2018 5:41 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Fast or Slow
Replies: 8
Views: 282

### Re: Fast or Slow

The step that has a rate law that matches the overall rate law is the slow step. When finding the rate law for a step remember to look out for intermediates as they should not be in the rate law for the step. If we happen to have an intermediate present in the rate law for the step we have to replac...
Fri Mar 16, 2018 4:41 pm
Forum: *Aldehydes
Topic: Carbonyl -> Aldehydes and Ketones [ENDORSED]
Replies: 5
Views: 689

### Re: Carbonyl -> Aldehydes and Ketones[ENDORSED]

The difference between them is that aldehydes are at the end as they have at least one hydrogen attached to them while ketones continue as they do not have a hydrogen attached rather two carbon chains.
Fri Mar 16, 2018 3:32 pm
Forum: Phase Changes & Related Calculations
Topic: 15.85
Replies: 2
Views: 195

### Re: 15.85

The molecularity also corresponds to the overall order of a reaction.
For example:
Unimolecular is 1st order
Bimolecular is 2nd order
Termolecular is 3rd order
Thu Mar 08, 2018 6:19 pm
Forum: General Rate Laws
Topic: Reaction Rates
Replies: 4
Views: 181

### Re: Reaction Rates

Yes we always want positive reaction rates.
For reactants we have: rate = -delta[R]/delta t
For products we have: rate = delta[P]/delta t
Thu Mar 08, 2018 6:14 pm
Forum: General Rate Laws
Topic: 15.17 type problems
Replies: 4
Views: 175

### Re: 15.17 type problems

I show work in these problems by: 1) Specifying which reactant I'm finding the order of 2) Taking the ratio of the initial rates for the two experiments 3) Taking the ratio of the concentrations for the two experiments 4) Solve for n in: (ratio of concentrations)^n=(ratio of initial rates) 5) The va...
Thu Mar 08, 2018 5:59 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19 (a)
Replies: 3
Views: 251

### Re: 15.19 (a)

Yes it is okay to round up to 9.
When you take the ratios of the concentrations you should get 3.
Then we solve for n in 3^n=9 which is n=2 making this second order.
Fri Mar 02, 2018 7:20 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate Constant [ENDORSED]
Replies: 3
Views: 127

### Re: Rate Constant[ENDORSED]

The rate constant k can be seen as the proportionality constant that relates the rate of the reaction to the product of the concentrations of the reactants. An example of the equation would be: rate=k[A]^n[B]^m
Fri Mar 02, 2018 7:02 pm
Forum: Zero Order Reactions
Topic: Zero Order Reactions [ENDORSED]
Replies: 3
Views: 133

### Re: Zero Order Reactions[ENDORSED]

In lecture it was also mentioned that when the rate of the reaction is independent of the concentration of the reactant, which implies a zero order reaction, it often occurs when a catalyst or enzyme is required.
Fri Mar 02, 2018 6:55 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: What is the order of the reaction? [ENDORSED]
Replies: 4
Views: 155

### Re: What is the order of the reaction?[ENDORSED]

In class we also discussed the different plots that go with each reaction: First order means a straight line plot of ln[reactant] vs time Second order means a straight line plot of 1/[reactant] vs time Zero order means a straight line plot of [reactant] vs time [reactant] means concentration of the ...
Sun Feb 25, 2018 9:46 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: K and Q at equilibrium
Replies: 5
Views: 205

### Re: K and Q at equilibrium

For concentration cells, E° is always 0 V.
Sun Feb 25, 2018 9:40 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: calculating n
Replies: 9
Views: 375

### Re: calculating n

When we get the two half reactions and balance the charges by adding electrons, we have to make the electrons added to each half reaction equal by multiplying each reaction by a number that will do so. Once the number of electrons added to both half reactions is equal, the number of electrons added ...
Sun Feb 25, 2018 9:22 pm
Forum: Balancing Redox Reactions
Topic: Half Reaction Order
Replies: 9
Views: 257

### Re: Half Reaction Order

A pattern that I have noticed while doing problems is that when it is an oxidation half reaction the electrons go on the right and when we have a reduction half reaction the electrons are on the left.
Sun Feb 18, 2018 3:11 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta S total and delta G
Replies: 2
Views: 247

### Re: delta S total and delta G

Depending on the signs of delta H and delta S, the sign of delta G will be positive or negative and we can therefore determine if a reaction is spontaneous or not. To guarantee spontaneity we need delta H to be negative and delta S to be positive.
Sun Feb 18, 2018 2:46 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Is Enthalpy a State Function?
Replies: 2
Views: 184

### Re: Is Enthalpy a State Function?

An example of two properties that are not state functions are w (work) and q (heat).
Since H (enthalpy) is a state function, it can be added and subtracted which is why we are able to use Hess's Law.
Sun Feb 18, 2018 2:40 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: First Law
Replies: 5
Views: 531

### Re: First Law

When we have an adiabatic system q=0 and delta U=w because in an adiabatic system there is no heat flow.
Fri Feb 09, 2018 6:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.15
Replies: 8
Views: 380

### Re: 11.15

We need to use this Gibbs Free Energy equation because it includes K (the equilibrium constant) which is given in the question. We can also use the partial pressures given in the question to calculate Q which is also needed to solve for delta G. This equation contains values that we were either give...
Fri Feb 09, 2018 5:53 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Temperature and Spontaneity
Replies: 2
Views: 117

### Re: Temperature and Spontaneity

The chart we went over in lecture goes: Delta S (+) and Delta H (-) means spontaneous at all temperatures Delta S (+) and Delta H (+) means spontaneous at high temperatures Delta S (-) and Delta H (-) means spontaneous at low temperatures Delta S (-) and Delta H (+) means not spontaneous at any temp...
Fri Feb 09, 2018 5:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Entropy
Replies: 7
Views: 211

### Re: Entropy

This is what I think:
S°m would be the Standard Molar Entropy
S°r would be the Standard Reaction Entropy
S°f would be the Standard Entropy of Formation
Sat Feb 03, 2018 9:35 pm
Forum: Phase Changes & Related Calculations
Topic: Closed Systems [ENDORSED]
Replies: 8
Views: 459

### Re: Closed Systems[ENDORSED]

For a closed system, we can change the energy of the system by heating or cooling it as well as by doing work on it. An example in the notes of work done on the system is compressing a piston or letting the system do work on the surroundings causing the piston to move out. For an open system, we can...
Sat Feb 03, 2018 9:15 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Universe [ENDORSED]
Replies: 3
Views: 149

### Re: Universe[ENDORSED]

Since the universe is an isolated system, it follows the first law of thermodynamics which is that the internal energy of an isolated system is constant. Therefore, the energy of the universe is constant.
Sat Feb 03, 2018 8:28 pm
Forum: Phase Changes & Related Calculations
Topic: Degeneracy
Replies: 4
Views: 183

### Re: Degeneracy

Some of the examples we were given for finding the degeneracy,W, are:
For 2 particles both in one of two states: W=(2)^2=4
For 1 particle in one of two states: W=(2)^1=2
From this we can get the general idea that W = # of states^# of particles
Fri Jan 26, 2018 11:39 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Assigning system/surroundings
Replies: 5
Views: 210

### Re: Assigning system/surroundings

The system would be the specific object we are interested in and the surroundings would be everything else. In the lecture notes it states: system+surroundings=universe
Fri Jan 26, 2018 11:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law [ENDORSED]
Replies: 7
Views: 278

### Re: Hess's Law[ENDORSED]

I agree that it will depend on the question and what we've covered in class. I feel like for the most part we would be given the reactions we need and the one we are looking for however there was a homework problem where we needed to know the combustion equations.
Fri Jan 26, 2018 10:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat capacity vs Specific Heat capacity
Replies: 5
Views: 172

### Re: Heat capacity vs Specific Heat capacity

Heat capacity is an extensive property because it depends on the amount of the substance while specific heat capacity is an intensive property.
Sun Jan 21, 2018 7:53 pm
Forum: Phase Changes & Related Calculations
Topic: Question 8.87- Breaking phase changes up into steps [ENDORSED]
Replies: 4
Views: 464

### Re: Question 8.87- Breaking phase changes up into steps[ENDORSED]

Doing a phase change and raising the temperature of the system require different equations and constant values. Breaking up the problem into different steps keeps everything organized because of the different equations and constant values you need to use for each step. It is easier to do the steps s...
Sun Jan 21, 2018 7:31 pm
Forum: Phase Changes & Related Calculations
Topic: Equations to know
Replies: 6
Views: 203

### Re: Equations to know

Based on my experience in 14A, we will be given the equations and constants we need to know and then some. So it is important to know which equations and constants we are focused on, what each variable stands for, and how the constants and equations relate to each other because some problems require...
Sun Jan 21, 2018 7:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.61
Replies: 3
Views: 133

### Re: 8.61

Whenever you need to switch the equation remember that you need to multiply the enthalpy value given by negative one which changes its sign.
Sun Jan 14, 2018 11:50 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard States
Replies: 4
Views: 223

### Re: Standard States

In lecture it was also mentioned that carbon's standard state is graphite.
Sun Jan 14, 2018 11:32 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature and Heat
Replies: 4
Views: 170

### Re: Temperature and Heat

When a phase change is occurring the temperature of the sample stays the same because the heat that is being added to the sample is being used to break the bonds of the sample instead of raise the temperature. For example, if we have ice that has reached its freezing point, the heat that is being ap...
Sun Jan 14, 2018 11:12 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Differences between Bomb and Coffee Cup Calorimeters?
Replies: 2
Views: 318

### Re: Differences between Bomb and Coffee Cup Calorimeters?

The bomb calorimeter has constant volume while the coffee cup calorimeter has constant pressure. Since the coffee cup calorimeter has constant pressure, it gives us enthalpy values.
Sun Dec 10, 2017 2:58 pm
Forum: Quantum Numbers and The H-Atom
Topic: How many electrons with given quantum numbers including ml
Replies: 3
Views: 237

### Re: How many electrons with given quantum numbers including ml

To add on, if we are also given the spin quantum number, which can either be + or - 1/2, then only one electron can correspond to that because in each orbital one electron has +1/2 spin while the other one has -1/2 spin.
Sun Dec 10, 2017 2:52 pm
Forum: Dipole Moments
Topic: Dipole Occurence
Replies: 4
Views: 306

### Re: Dipole Occurence

The dipole moments cancel out when the molecule is composed of the same atoms symmetrically around the central atom.
Sun Dec 03, 2017 5:08 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ICE box
Replies: 3
Views: 327

### Re: ICE box

Don't forget to add the appropriate coefficients to x when making your ice box.
Sun Dec 03, 2017 5:03 pm
Forum: Sigma & Pi Bonds
Topic: When do Sigma and Pi bonds occur?
Replies: 4
Views: 295

### Re: When do Sigma and Pi bonds occur?

Sigma bonds are when two orbitals interact end to end and overlap while pi bonds are when two orbitals overlap side by side.
Sun Dec 03, 2017 4:50 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Difference betwen constant and quotient?
Replies: 4
Views: 346

### Re: Difference betwen constant and quotient?

We need to compare the equilibrium constant and the reaction quotient in order to figure out the direction a reaction is going.
Sun Dec 03, 2017 4:41 pm
Forum: Naming
Topic: Trans & Cis Naming
Replies: 3
Views: 170

### Re: Trans & Cis Naming

When we are able to see the lewis structure we can see if we need to use cis or trans. We can't just assume cis or trans because depending on the prefix, the molecule can be polar or nonpolar. In the example given in class, when cis was used we had a polar molecule while when trans was used we had a...
Sun Nov 26, 2017 7:32 pm
Forum: Trends in The Periodic Table
Topic: Radius
Replies: 6
Views: 283

### Re: Radius

Both atomic radius and ionic radius decrease across a period.
With ionic radius, the cations decrease then the anions decrease.
Sun Nov 26, 2017 7:08 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Molecules in Subscript
Replies: 3
Views: 161

### Re: Molecules in Subscript

We write P subscript molecule when we are looking for Kp. The P subscript molecule notation means the partial pressure of the molecule.
Mon Nov 20, 2017 12:50 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Naming; VSEPR
Replies: 3
Views: 188

### Re: Naming; VSEPR

This means that there is one central atom (A) and five atoms attached to the central atom (X^5). Since there is no E there are no lone pairs of electrons.
Mon Nov 20, 2017 12:34 am
Forum: Lewis Structures
Topic: Best way to start Lewis Structures
Replies: 12
Views: 472

### Re: Best way to start Lewis Structures

I usually start by counting all the valence electrons and finding out the central atom, which is the one with the lowest ionization energy. I start with one bond between the central atom and remaining atoms and then fill in the remaining electrons keeping the formal charge as low as possible.
Sun Nov 12, 2017 8:35 pm
Forum: Lewis Structures
Topic: Exceptions
Replies: 4
Views: 222

### Re: Exceptions

The actual electron configurations are:
Chromium: [Ar]3d^5 4s^1
Copper: [Ar]3d^10 4s^1
Sun Nov 12, 2017 8:27 pm
Forum: Bond Lengths & Energies
Topic: Bond Length
Replies: 3
Views: 217

### Re: Bond Length

Adding on to the previous response, since single bonds are longer, they are weaker than triple bonds which are shorter and stronger.
Sun Oct 29, 2017 10:35 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Determining Formal Charge [ENDORSED]
Replies: 3
Views: 221

### Re: Determining Formal Charge[ENDORSED]

When we see a formal charge of 0, it is the most stable structure.
Sun Oct 29, 2017 9:46 pm
Forum: Quantum Numbers and The H-Atom
Topic: Ionization Energy
Replies: 3
Views: 205

### Re: Ionization Energy

When looking at trends in the periodic table, ionization energy increases across a period. Therefore, elements on the left, which are mostly metals, have lower ionization energy than the elements on the right, which are nonmetals.
Sun Oct 22, 2017 5:10 pm
Forum: Quantum Numbers and The H-Atom
Topic: D-Orbital
Replies: 4
Views: 292

### Re: D-Orbital

If you wanted to write the subscripts to be more specific they would be:
x^2-y^2
xy
xz
yz
z^2
Sun Oct 22, 2017 4:44 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d Orbital [ENDORSED]
Replies: 2
Views: 130

### Re: 3d Orbital[ENDORSED]

When we look at the order of elements in the periodic table, we notice that the first two elements in the fourth row are part of the s-block. Therefore, 4s has a lower energy than 3d. However, for multi electron atoms after atomic number 20, 4s has a higher energy than 3d.
Sun Oct 15, 2017 7:32 pm
Forum: Properties of Light
Topic: Question about speed of light rounding
Replies: 4
Views: 227

### Re: Question about speed of light rounding

I think using the value Dr. Lavelle provided on the constants and equations sheet will be the safest option then at the end round the result to the appropriate sig figs based on the problem.
Sun Oct 15, 2017 7:14 pm
Forum: Properties of Electrons
Topic: Threshold level and Work Function [ENDORSED]
Replies: 6
Views: 421

### Re: Threshold level and Work Function[ENDORSED]

Yes! When the kinetic energy of an ejected electron is zero, then the work function must equal the energy of the photon hitting the metal surface.
Sun Oct 08, 2017 8:34 pm
Forum: Balancing Chemical Reactions
Topic: Physical States [ENDORSED]
Replies: 2
Views: 223

### Re: Physical States[ENDORSED]

When writing physical states, you can use the following symbols:
solid (s)
liquid (l)
gas (g)
aqueous solution (aq)
Sun Oct 08, 2017 8:18 pm
Forum: SI Units, Unit Conversions
Topic: Prefixes [ENDORSED]
Replies: 6
Views: 413

### Re: Prefixes[ENDORSED]

The symbols for each of the prefixes we went over in class are:

G (giga)
M (mega)
k (kilo)
d (deci)
c (centi)
m (milli)
µ (micro)
n (nano)
p (pico)

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