Search found 52 matches

by Rachel Brown 3A
Sat Mar 17, 2018 4:43 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal = no internal energy change
Replies: 4
Views: 321

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...
by Rachel Brown 3A
Fri Mar 16, 2018 1:00 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q5
Replies: 2
Views: 197

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
by Rachel Brown 3A
Wed Mar 14, 2018 8:30 pm
Forum: General Rate Laws
Topic: Unimolecular
Replies: 5
Views: 356

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)(...
by Rachel Brown 3A
Wed Mar 14, 2018 8:25 pm
Forum: General Rate Laws
Topic: Test 3 Question 8
Replies: 1
Views: 101

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.
by Rachel Brown 3A
Wed Mar 14, 2018 8:23 pm
Forum: General Rate Laws
Topic: Test 3 Question 6
Replies: 1
Views: 88

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
by Rachel Brown 3A
Tue Mar 06, 2018 5:12 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 6
Views: 227

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.
by Rachel Brown 3A
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: 93

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...
by Rachel Brown 3A
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: 100

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.
by Rachel Brown 3A
Sun Mar 04, 2018 9:42 pm
Forum: Zero Order Reactions
Topic: K limiting rate
Replies: 3
Views: 156

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
by Rachel Brown 3A
Wed Feb 28, 2018 11:14 pm
Forum: Zero Order Reactions
Topic: Real Life Example
Replies: 2
Views: 132

Real Life Example

Can someone give me a real life example of when a zero order reaction would take place?
by Rachel Brown 3A
Wed Feb 28, 2018 11:12 pm
Forum: General Rate Laws
Topic: Significance
Replies: 3
Views: 138

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...
by Rachel Brown 3A
Mon Feb 26, 2018 2:43 pm
Forum: General Rate Laws
Topic: Overall Order
Replies: 2
Views: 118

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?
by Rachel Brown 3A
Mon Feb 26, 2018 2:12 pm
Forum: General Rate Laws
Topic: Unique Rate [ENDORSED]
Replies: 4
Views: 175

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?
by Rachel Brown 3A
Tue Feb 13, 2018 10:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible Expansion and Total Entropy
Replies: 1
Views: 124

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
by Rachel Brown 3A
Tue Feb 13, 2018 10:10 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Qrev
Replies: 2
Views: 236

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
by Rachel Brown 3A
Tue Feb 13, 2018 10:07 pm
Forum: Calculating Work of Expansion
Topic: Formula for reversible vs irreversible
Replies: 1
Views: 106

Re: Formula for reversible vs irreversible

Reversible work is w=-nRTln (Pf/Pi)
Irreversible work is w=-PdeltaV
by Rachel Brown 3A
Tue Feb 13, 2018 10:06 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.49
Replies: 3
Views: 161

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)
by Rachel Brown 3A
Tue Feb 13, 2018 10:03 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Energetically Favorable and Spontaneity
Replies: 1
Views: 102

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)
by Rachel Brown 3A
Tue Feb 13, 2018 10:01 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Gibbs free energy
Replies: 3
Views: 124

Re: Gibbs free energy

delta G not is delta G at standard conditions
by Rachel Brown 3A
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: 200

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.
by Rachel Brown 3A
Sun Feb 04, 2018 5:30 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacities of Dense Elements
Replies: 2
Views: 117

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.
by Rachel Brown 3A
Sun Feb 04, 2018 5:25 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.35
Replies: 4
Views: 116

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.
by Rachel Brown 3A
Sun Jan 28, 2018 6:43 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Distribution
Replies: 3
Views: 121

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.
by Rachel Brown 3A
Sun Jan 28, 2018 6:40 pm
Forum: Environment, Fossil Fuels, Alternative Fuels
Topic: biodiesel fuel [ENDORSED]
Replies: 2
Views: 431

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...
by Rachel Brown 3A
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: 110

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?
by Rachel Brown 3A
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: 73

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?
by Rachel Brown 3A
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: 159

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?
by Rachel Brown 3A
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: 86

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
by Rachel Brown 3A
Sun Jan 14, 2018 12:36 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Calorimeter
Replies: 10
Views: 446

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)
by Rachel Brown 3A
Sun Jan 14, 2018 12:33 pm
Forum: Phase Changes & Related Calculations
Topic: Extensive vs Intensive
Replies: 2
Views: 141

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.
by Rachel Brown 3A
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: 91

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?
by Rachel Brown 3A
Sat Dec 09, 2017 2:23 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Difference between % calculations
Replies: 2
Views: 152

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
by Rachel Brown 3A
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: 187

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
by Rachel Brown 3A
Sat Dec 02, 2017 1:01 pm
Forum: Bronsted Acids & Bases
Topic: Identifying Bronsted Acids and Bases [ENDORSED]
Replies: 3
Views: 212

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
by Rachel Brown 3A
Sat Dec 02, 2017 12:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc [ENDORSED]
Replies: 3
Views: 186

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.
by Rachel Brown 3A
Sun Nov 26, 2017 5:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Composition
Replies: 1
Views: 109

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)
by Rachel Brown 3A
Sun Nov 26, 2017 1:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Test #4
Replies: 1
Views: 111

Test #4

Up to what chapter 11 hw problems does test #4 cover?
by Rachel Brown 3A
Sun Nov 19, 2017 2:47 pm
Forum: Naming
Topic: writing chemical formula based on name
Replies: 4
Views: 159

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
by Rachel Brown 3A
Fri Nov 17, 2017 2:23 pm
Forum: Hybridization
Topic: 4.35
Replies: 2
Views: 123

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"?
by Rachel Brown 3A
Sun Nov 12, 2017 7:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 4
Views: 262

Bond Angles

Are we going to have to know the bond angles for each of the basic VESPR shapes for the test?
by Rachel Brown 3A
Tue Nov 07, 2017 7:26 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Trends of Polarizing Power
Replies: 4
Views: 4136

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?
by Rachel Brown 3A
Thu Nov 02, 2017 10:13 pm
Forum: Octet Exceptions
Topic: Knowing Chemical Formulas??
Replies: 1
Views: 132

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 (-)?
by Rachel Brown 3A
Thu Nov 02, 2017 10:07 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 5a,c ; 19b,e ; 21d
Replies: 2
Views: 208

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+, ...
by Rachel Brown 3A
Fri Oct 27, 2017 5:15 pm
Forum: Trends in The Periodic Table
Topic: 2.55
Replies: 1
Views: 111

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.
by Rachel Brown 3A
Fri Oct 27, 2017 5:15 pm
Forum: Trends in The Periodic Table
Topic: 2.55 [ENDORSED]
Replies: 1
Views: 162

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.
by Rachel Brown 3A
Tue Oct 24, 2017 11:47 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: chapter 2 Q29
Replies: 1
Views: 115

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...
by Rachel Brown 3A
Wed Oct 18, 2017 8:26 pm
Forum: Properties of Electrons
Topic: Hydrogen series
Replies: 5
Views: 336

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.
by Rachel Brown 3A
Wed Oct 18, 2017 8:22 pm
Forum: *Shrodinger Equation
Topic: Electron Spin
Replies: 6
Views: 432

Electron Spin

What's the difference between an electron being spun up vs being spun down? What does that mean?
by Rachel Brown 3A
Tue Oct 10, 2017 1:54 pm
Forum: Properties of Electrons
Topic: Balmer vs Lyman series [ENDORSED]
Replies: 5
Views: 485

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.
by Rachel Brown 3A
Tue Oct 10, 2017 1:52 pm
Forum: Properties of Light
Topic: Photo electric effect
Replies: 3
Views: 221

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?
by Rachel Brown 3A
Wed Oct 04, 2017 3:07 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Accuracy vs Precision [ENDORSED]
Replies: 5
Views: 1227

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...
by Rachel Brown 3A
Wed Oct 04, 2017 3:00 pm
Forum: Balancing Chemical Reactions
Topic: Balancing Chemical equations too slow... any advice? [ENDORSED]
Replies: 18
Views: 1540

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...

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