Search found 52 matches
- Sat Mar 17, 2018 4:43 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: isothermal = no internal energy change
- Replies: 4
- Views: 751
Re: isothermal = no internal energy change
for isothermal reactions, delta U = 0 which means that q=-w. however, it does not necessarily mean that q=0. Even though temperature is the same, heat can and will still be transferred to counter the work being done so that the internal energy remains at 0. q is only 0 is the system is "adiabat...
- Fri Mar 16, 2018 1:00 pm
- Forum: Calculating Work of Expansion
- Topic: Midterm Q5
- Replies: 2
- Views: 445
Midterm Q5
On the solutions for the midterm, it says that after solving for work = -158, delta u = +158. Why is this the case? Even though work=delta u if q=0
- Wed Mar 14, 2018 8:30 pm
- Forum: General Rate Laws
- Topic: Unimolecular
- Replies: 5
- Views: 783
Re: Unimolecular
Unimolecular means that there is only one reactant in the reaction so by nature, the rate of rxn is k(A) which is always going to be first order. Bimolecular means there are two reactants (even if they are the same molecule but just separated into two reactants) so the rate = k(a)(b) or rate = k(a)(...
- Wed Mar 14, 2018 8:25 pm
- Forum: General Rate Laws
- Topic: Test 3 Question 8
- Replies: 1
- Views: 237
Re: Test 3 Question 8
First convert your time into seconds. Then understand that A0 = 5M and At = 2M. using this information and the fact that its second order, solve for k using the half life equation. Once you have k (and the given concentrations), use the second order equation to solve for time.
- Wed Mar 14, 2018 8:23 pm
- Forum: General Rate Laws
- Topic: Test 3 Question 6
- Replies: 1
- Views: 234
Re: Test 3 Question 6
you want to start by converting time and then use ln(A0/.766A0) = k(time) to solve for k. then using that k, you can match which equation it is for
- Tue Mar 06, 2018 5:12 pm
- Forum: General Rate Laws
- Topic: Coefficients
- Replies: 6
- Views: 948
Re: Coefficients
Coefficients play a role in the unique rate law that states where aA --> bB, the rate = (-1/a)(dA/dt) = (1/b)(dB/dt). Because of this, you can identify how and individual product/reaction rate compares to another based on it's coefficient as shown in 15.1.
- Tue Mar 06, 2018 5:10 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Self Test 15.3Ba
- Replies: 1
- Views: 330
Re: Self Test 15.3Ba
Based on reading the question, my initial reaction would be that it is zero-order for the OH- because I see no other possibility for the concentration change of OH- to not affect the rate. Considering that the definition of a zero-order reaction is that the rate is not dependent on concentrations, I...
- Sun Mar 04, 2018 9:43 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Cell potential and Gibbs free energy
- Replies: 1
- Views: 261
Re: Cell potential and Gibbs free energy
You do this when you are trying to get the cell potential of a half reaction or you are given cell potentials of half reactions. For some reason, half reaction cell potentials are not state functions so you cannot just add or subtract them.
- Sun Mar 04, 2018 9:42 pm
- Forum: Zero Order Reactions
- Topic: K limiting rate
- Replies: 3
- Views: 465
Re: K limiting rate
Because it's the rate constant so a large value of K will make the reaction faster where a lower K will cause a slower reaction
- Wed Feb 28, 2018 11:14 pm
- Forum: Zero Order Reactions
- Topic: Real Life Example
- Replies: 2
- Views: 522
Real Life Example
Can someone give me a real life example of when a zero order reaction would take place?
- Wed Feb 28, 2018 11:12 pm
- Forum: General Rate Laws
- Topic: Significance
- Replies: 3
- Views: 502
Re: Significance
While what this person said ^^ is true, it can be helpful to look at the equations to understand exactly how to see the effects in each order. For example, in a second order overall reaction, the ratio change to one of the reactants (if the other(s) remain the same) changes the rate by that same rat...
- Mon Feb 26, 2018 2:43 pm
- Forum: General Rate Laws
- Topic: Overall Order
- Replies: 2
- Views: 366
Overall Order
What's the difference between between the order for each reaction and the overall order when solving for orders using a table such as in 15.17? How do you solve for overall order?
- Mon Feb 26, 2018 2:12 pm
- Forum: General Rate Laws
- Topic: Unique Rate [ENDORSED]
- Replies: 4
- Views: 518
Unique Rate [ENDORSED]
What is a unique rate of reaction?
For example, in question 15.5 it gives us the unique rate and asks us to find the individual rates of rxn. How do they relate?
For example, in question 15.5 it gives us the unique rate and asks us to find the individual rates of rxn. How do they relate?
- Tue Feb 13, 2018 10:12 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Reversible Expansion and Total Entropy
- Replies: 1
- Views: 307
Re: Reversible Expansion and Total Entropy
because it is constantly equilibrating so no total entropy is ever created (this is very unrealistic but in a perfect world this would occur). be sure to understand however that individual reactions are still causing entropy
- Tue Feb 13, 2018 10:10 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Qrev
- Replies: 2
- Views: 1056
Re: Qrev
Just to add on as a word of caution: be careful when using that equation that your problem states that the reaction is reversible. Sometimes you can forget and try to use it anyway but that doesn't work obviously
- Tue Feb 13, 2018 10:07 pm
- Forum: Calculating Work of Expansion
- Topic: Formula for reversible vs irreversible
- Replies: 1
- Views: 274
Re: Formula for reversible vs irreversible
Reversible work is w=-nRTln (Pf/Pi)
Irreversible work is w=-PdeltaV
Irreversible work is w=-PdeltaV
- Tue Feb 13, 2018 10:06 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: 8.49
- Replies: 3
- Views: 452
Re: 8.49
yes if temperature is necessary to solve the problem. Typically it is stated though (like in all Lavelle's practice problems and old midterms)
- Tue Feb 13, 2018 10:03 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Energetically Favorable and Spontaneity
- Replies: 1
- Views: 249
Re: Energetically Favorable and Spontaneity
As far as I am concerned, anything that is spontaneous is favorable for the products. A reaction however that is not spontaneous favors the reactants (or its spontaneous in the other direction)
- Tue Feb 13, 2018 10:01 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Gibbs free energy
- Replies: 3
- Views: 452
Re: Gibbs free energy
delta G not is delta G at standard conditions
- Sun Feb 04, 2018 5:36 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: The sign of the change in Gibb's Free Energy
- Replies: 6
- Views: 780
Re: The sign of the change in Gibb's Free Energy
To expand, if a reaction is spontaneous, it can occur more easily and often so it would be more favorable than a reaction that requires a specific environment and has a more difficult proceeding.
- Sun Feb 04, 2018 5:30 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat Capacities of Dense Elements
- Replies: 2
- Views: 323
Re: Heat Capacities of Dense Elements
Density and heat capacity are inversely proportional I believe! not sure about the second part of your question as much though.
- Sun Feb 04, 2018 5:25 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 9.35
- Replies: 4
- Views: 438
Re: 9.35
Highly active molecules are moving more and are causing more entropy because their movement causes disorder while the less active molecules aren't moving as much and therefore aren't creating as much entropy.
- Sun Jan 28, 2018 6:43 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Distribution
- Replies: 3
- Views: 397
Re: Distribution
Each distribution of the energy at the molecular level characterizes a microstate of the system. The entropy is measure of the number of microstates that are accessible at given total energy.
- Sun Jan 28, 2018 6:40 pm
- Forum: Environment, Fossil Fuels, Alternative Fuels
- Topic: biodiesel fuel [ENDORSED]
- Replies: 4
- Views: 1595
Re: biodiesel fuel [ENDORSED]
1.Biodiesel has higher lubricity (it is more "slippery") than petroleum diesel. This is a good thing, as it can be expected to reduce engine wear. 2. Biodiesel contains practically no sulfur. This is also a good thing, as it can be expected to result in reduced pollution from engines using...
- Sun Jan 21, 2018 11:53 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.31
- Replies: 3
- Views: 259
8.31
On 8.31, the solution states that the molar heat capacity of a monatomic ideal gas at constant pressure is = 5/2 R and later states that the molar heat capacity of a monatomic ideal gas at constant volume is = 3/2 R. What does this mean and how can you find it?
- Sun Jan 21, 2018 11:27 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.49
- Replies: 1
- Views: 121
8.49
How do we know temperature for 8.49? We are giving an equation and a delta H. Are we assuming its at a certain condition?
- Sun Jan 21, 2018 11:24 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.65, where did that equation come from?
- Replies: 3
- Views: 417
Re: 8.65, where did that equation come from?
I was wondering the same thing... Is there possibly a chart or something that we should be using to get that equation or would it be given?
- Sun Jan 21, 2018 11:23 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.57
- Replies: 1
- Views: 202
8.57
would we be given the equations that were used to solve for the final equation we wanted or would we have to know those off the top of our head?
Ex. given: C2H2 + 2H2 > C2H6
used: C2H2 +5/2O2 > 2CO2 +H2O
C2H6+ 7/2O2 > 2 CO2 +H2O
H2 + 1/2O2 > H2O
Ex. given: C2H2 + 2H2 > C2H6
used: C2H2 +5/2O2 > 2CO2 +H2O
C2H6+ 7/2O2 > 2 CO2 +H2O
H2 + 1/2O2 > H2O
- Sun Jan 14, 2018 12:36 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Calorimeter
- Replies: 10
- Views: 1019
Re: Calorimeter
This probably won't be a huge topic but simply more of an example for how specific heat is measured. The example gives you a little more depth into understanding that specific heat capacity is an intensive property (meaning it doesn't depend on the amount of substance)
- Sun Jan 14, 2018 12:33 pm
- Forum: Phase Changes & Related Calculations
- Topic: Extensive vs Intensive
- Replies: 2
- Views: 341
Re: Extensive vs Intensive
An extensive property is a property that depends on the amount of matter in a sample. Mass and volume are examples of extensive properties. An intensive property is a physical property that doesn't rely on the size of the system such as density.
- Fri Jan 12, 2018 1:23 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: heat capacity of a gas at constant pressure
- Replies: 1
- Views: 149
heat capacity of a gas at constant pressure
Are we required to calculate/determine the Cp or Cv or should we be finding that in a table somewhere in the textbook?
- Sat Dec 09, 2017 2:23 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Difference between % calculations
- Replies: 2
- Views: 399
Re: Difference between % calculations
It is helpful to think of these calculations as percent yield. Also the numerator and denominator can represent molarity or moles
- Sat Dec 09, 2017 2:21 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Difference in Calculating pH for Strong and Weak Acids
- Replies: 3
- Views: 843
Re: Difference in Calculating pH for Strong and Weak Acids
It is also worth mentioning that when you are calculating the pH of strong vs weak acids, you can get a general check of your calculations because a weak acid is going to have a pH closer to 7 where as a strong acid is going to have a pH closer to 0
- Sat Dec 02, 2017 1:01 pm
- Forum: Bronsted Acids & Bases
- Topic: Identifying Bronsted Acids and Bases [ENDORSED]
- Replies: 3
- Views: 783
Identifying Bronsted Acids and Bases [ENDORSED]
I know that a bronsted acid is a proton donor and a bronsted base is a proton acceptor but is there a technique to identifying which a compound is? For example, KOH or H2SO3
- Sat Dec 02, 2017 12:59 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kc [ENDORSED]
- Replies: 3
- Views: 372
Re: Kc [ENDORSED]
If the reaction requires heat (endothermic), then the reaction will favor products and more products are made therefore affecting K. If the reaction gives off heat (exothermic), then the reaction favors reactant formation and K will be affected.
- Sun Nov 26, 2017 5:47 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium Composition
- Replies: 1
- Views: 263
Re: Equilibrium Composition
Often one of those K values will be too large (ex. it is larger than the concentration of one of the compounds)
- Sun Nov 26, 2017 1:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Test #4
- Replies: 1
- Views: 213
Test #4
Up to what chapter 11 hw problems does test #4 cover?
- Sun Nov 19, 2017 2:47 pm
- Forum: Naming
- Topic: writing chemical formula based on name
- Replies: 4
- Views: 320
writing chemical formula based on name
How do you know what order the elements or compounds go when writing the chemical formula if you are given the full name? Example would be 17.31
- Fri Nov 17, 2017 2:23 pm
- Forum: Hybridization
- Topic: 4.35
- Replies: 2
- Views: 283
4.35
How is what 4.33 and 4.35 are asking different? I was able to do 4.33 but 4.35 is confusing me so I must be missing something in the question. Is "state the hybridization" different from "identify the hybrid orbitals"?
- Sun Nov 12, 2017 7:27 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 4
- Views: 607
Bond Angles
Are we going to have to know the bond angles for each of the basic VESPR shapes for the test?
- Tue Nov 07, 2017 7:26 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Trends of Polarizing Power
- Replies: 4
- Views: 13914
Trends of Polarizing Power
Can someone explain to me what makes an element or ion more or less polarizing? Is there a periodic trend to follow or something polarizing power is proportionally related to?
- Thu Nov 02, 2017 10:13 pm
- Forum: Octet Exceptions
- Topic: Knowing Chemical Formulas??
- Replies: 1
- Views: 197
Knowing Chemical Formulas??
For the test are we going to have to know what the chemical formula for certain names compounds or will the formulas be given? For example, will we need to know that "perchlorate ion" is ClO4 (-)?
- Thu Nov 02, 2017 10:07 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: 5a,c ; 19b,e ; 21d
- Replies: 2
- Views: 430
5a,c ; 19b,e ; 21d
why for these problems listed above does the solutions manual state that the D orbital is filled to 10 even if it is not one of the exceptions? For example Ga3+ would put you at Ni which would typically be (Ar)3d^8 4s^2 but instead the correct answer is (Ar)3d^10? The same thing goes for Cu+, Sn4+, ...
- Fri Oct 27, 2017 5:15 pm
- Forum: Trends in The Periodic Table
- Topic: 2.55
- Replies: 1
- Views: 162
2.55
Can someone help me with 2.55? It is asking for the valence-shell configuration of a) alkali metals, b) group 15, c) group 5 transition metals, and d) Cu, Ag, Au. I have the solutions manual so I saw the answers but I couldn't figure out how they got them.
- Fri Oct 27, 2017 5:15 pm
- Forum: Trends in The Periodic Table
- Topic: 2.55 [ENDORSED]
- Replies: 1
- Views: 201
2.55 [ENDORSED]
Can someone help me with 2.55? It is asking for the valence-shell configuration of a) alkali metals, b) group 15, c) group 5 transition metals, and d) Cu, Ag, Au. I have the solutions manual so I saw the answers but I couldn't figure out how they got them.
- Tue Oct 24, 2017 11:47 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: chapter 2 Q29
- Replies: 1
- Views: 229
chapter 2 Q29
can someone help me with parts B and D on question 29? Question reads: how many electrons can have the following quantum numbers in an atom...
B) I don't understand how when n=4 and l=2, only two electrons can have these quantum numbers.
Same thing for D when n=3, l=2, and m=1...
B) I don't understand how when n=4 and l=2, only two electrons can have these quantum numbers.
Same thing for D when n=3, l=2, and m=1...
- Wed Oct 18, 2017 8:26 pm
- Forum: Properties of Electrons
- Topic: Hydrogen series
- Replies: 5
- Views: 602
Re: Hydrogen series
For this test, you only need to know Lyman and Balmer simply for which "n" level an electron begins at or returns to.
- Wed Oct 18, 2017 8:22 pm
- Forum: *Shrodinger Equation
- Topic: Electron Spin
- Replies: 6
- Views: 1113
Electron Spin
What's the difference between an electron being spun up vs being spun down? What does that mean?
- Tue Oct 10, 2017 1:54 pm
- Forum: Properties of Electrons
- Topic: Balmer vs Lyman series [ENDORSED]
- Replies: 5
- Views: 763
Re: Balmer vs Lyman series [ENDORSED]
What do the lines represent in the series? I remember something about them marking a transition but I'm not sure to what.
- Tue Oct 10, 2017 1:52 pm
- Forum: Properties of Light
- Topic: Photo electric effect
- Replies: 3
- Views: 418
Photo electric effect
What is the point of determining the threshold amount of light that causes the electrons to be emitted? Why do we focus on the photo electric effect/what does it teach us about the quantum world?
- Wed Oct 04, 2017 3:07 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Accuracy vs Precision [ENDORSED]
- Replies: 5
- Views: 3393
Re: Accuracy vs Precision [ENDORSED]
Accuracy is when you continue to hit near the mark or say the center of a target but your collection of shots are a little bit scattered. Precision is when you continue to hit one specific mark over and over again (very close together) but the mark you're hitting is not the center of the target or y...
- Wed Oct 04, 2017 3:00 pm
- Forum: Balancing Chemical Reactions
- Topic: Balancing Chemical equations too slow... any advice? [ENDORSED]
- Replies: 18
- Views: 3795
Re: Balancing Chemical equations too slow... any advice? [ENDORSED]
Definitely balancing Oxygen last helps but keep in mind that if the Oxygen is in form of O AND O2, then when you keep it for the end, there's a chance you will have to double everything to make whole numbers for coefficients. Also in general, just think of it like a puzzle: look at the big picture f...