Search found 27 matches

by Brenda Melano 3H
Sat Mar 12, 2016 8:56 am
Forum: General Science Questions
Topic: Sig Figs
Replies: 1
Views: 677

Sig Figs

With questions that require the use of 'n'- the number of mols- should we use this to determine the number of sig figs we use? For the most part, n has one sig fig... I noticed in the past exams that problems varied between using n as determining sig figs and not using n. Please enlighten me!
by Brenda Melano 3H
Sat Mar 05, 2016 8:54 am
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: Priority groups (2011 Final Exam #7B)
Replies: 1
Views: 384

Priority groups (2011 Final Exam #7B)

The answer for the structure of CH3CH2CHC(Cl)COOH says that the molecule is Z or cis. However, the carboxylic group is drawn opposite of the ethyl group on the other side of the double bond. I was wondering why this is. I would have thought that it would be trans or E because the carboxylic group wo...
by Brenda Melano 3H
Mon Feb 29, 2016 8:24 am
Forum: *Alkanes
Topic: Carbo cations
Replies: 1
Views: 311

Carbo cations

How do we know when a carbocation will form in a reaction? Or should we just know how it reacts with other reactants?
by Brenda Melano 3H
Sun Feb 28, 2016 7:26 pm
Forum: *Alkenes
Topic: hex-2,4-diene Z and E components
Replies: 1
Views: 353

hex-2,4-diene Z and E components

Hello,
I have a attached an image of hex-2,4-diene. This form of the molecule has both a Z and E component. Which is listed first if they are both equidistant from both ends? Does it matter?
Thank you
by Brenda Melano 3H
Mon Feb 15, 2016 11:30 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Frequency Factors
Replies: 2
Views: 390

Re: Frequency Factors

What would the units and size of values for A be? Would this value be given to us? In most of the examples, they don't provide any values for A... so I was wondering if there were any examples where we would have to use this parameter and figure out what it was based on the rxn somehow..
by Brenda Melano 3H
Tue Feb 09, 2016 10:42 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: change of entropy in irreversible reaction (8.11)
Replies: 1
Views: 343

change of entropy in irreversible reaction (8.11)

This is a problem from the 5th edition text book. 3L of Nitrogen gas was compressed to .5 L. The temp increased to 28.1 degrees celsius from 18.5. They asked for the change in entropy. When calculating the change of entropy due to temp change, the solutions manual used R instead of Cv (which I thoug...
by Brenda Melano 3H
Thu Feb 04, 2016 1:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Equilibrium and Galvanic Cells
Replies: 2
Views: 416

Re: Equilibrium and Galvanic Cells

When a cell is at equilibrium, I understand that the concentrations of the products and reactants are equal. At this point the cell no longer has a voltage. This must mean that the cells start off with different concentrations. Which concentrations are ideal to start off with when creating a cell?
by Brenda Melano 3H
Mon Feb 01, 2016 11:55 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: change in entropy of vibrationally active molecules
Replies: 1
Views: 339

change in entropy of vibrationally active molecules

On Midterm 2011 #2B, the question asks which container would have a larger change in entropy- a container of 1 mol of vibrationally active materials and a container with 1 mol of non-vibrationally active molecules (of the same type) when increased to the same temp. I thought that the container with ...
by Brenda Melano 3H
Sun Jan 31, 2016 11:10 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: How molecular characteristics affect heat capacity
Replies: 2
Views: 596

How molecular characteristics affect heat capacity

What contributes most to the heat capacity of a substance- the number of bonds, the size of the molecules, or the mass of the molecules?
by Brenda Melano 3H
Thu Jan 28, 2016 9:53 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Higher molar heat capacity?
Replies: 3
Views: 981

Re: Higher molar heat capacity?

Say that two molecules had the same complexity but a few atoms were different than those found in the original compound. Would the heavier have the higher molar heat capacity?
by Brenda Melano 3H
Sat Jan 23, 2016 2:46 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Isothermal Irreversible Free Expansion
Replies: 2
Views: 308

Re: Isothermal Irreversible Free Expansion

To keep a reaction at constant temperature, do you just keep the reaction in a large amount of water so that it can absorb all the heat? Is this a way to do it or are there any ways to keep a reaction at a constant temperature?..
by Brenda Melano 3H
Sat Jan 23, 2016 2:37 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Delta S equation
Replies: 2
Views: 3766

Re: Delta S equation

This question goes back to change in w=-p*change in V. Then you integrate both sides: w= -integral from V2 to V1 of (P*dV). You then substitute nRT/V for P and take the nRT out of the integral since they are constant. Then you integrate 1/V from V2 to V1 which simplifies into ln(V2/V1). In the end y...
by Brenda Melano 3H
Sun Jan 17, 2016 5:15 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies vs. Mean Bond Enthalpy
Replies: 2
Views: 1322

Re: Bond Enthalpies vs. Mean Bond Enthalpy

I think mean bond enthalpy is the average enthalpy needed to break a certain type of bond (say a C-H bond) for all molecules with that (C-H) bond. Bond enthalpy or bond dissociation enthalpy is the energy needed to break a C-H bond in one particular molecule. I would assume that we use the average b...
by Brenda Melano 3H
Fri Jan 08, 2016 4:52 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature Dynamics in Enthalpies
Replies: 6
Views: 824

Re: Temperature Dynamics in Enthalpies

If there is water vapor above naturally occuring bodies of water, why don't we feel these high temperatures when we are in this water vapor? Is it because the energy from the molecules dissipate quickly into the air? Or because there is a higher concentration of water vapor above a pot of boiling wa...
by Brenda Melano 3H
Thu Jan 07, 2016 12:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating the enthalpy of formation for TNT ch.8, #51
Replies: 1
Views: 399

Calculating the enthalpy of formation for TNT ch.8, #51

the reaction for TNT is 4(C7H5N3O6)+21(O2)---> 28(CO2)+10(H2O)+6(N2) First we have to calculate the enthalpy of the reaction using enthalpies of formation. However, the text book only included 3 enthalpies of formation in the calculation. 28(-393)+10(-1042)-4(-67)=-13168 Why did they leave out the e...
by Brenda Melano 3H
Wed Dec 02, 2015 1:22 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: When to use Henderson Hasselbalch
Replies: 2
Views: 486

When to use Henderson Hasselbalch

Is there ever a time we should no use the Henderson-Hasselbalch equation? The textbook says that we should only use it when the concentrations of the weak acid and the conjugate base are much greater than the concentration of the hydronium concentration. I understand we would not want to use it for ...
by Brenda Melano 3H
Sun Nov 29, 2015 9:00 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: H2+I2----> 2HI equilibrium shift
Replies: 1
Views: 1201

H2+I2----> 2HI equilibrium shift

If Kc=4.3*10^-5, and a small amount of I2 is added, neither the products or reactants are favored. I assumed that the change would favor products, but I am assuming that this is not the case because there is already a much larger concentration of reactants at equilibrium. Will someone please explain...
by Brenda Melano 3H
Fri Nov 20, 2015 6:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Converting from Moles to Pressure
Replies: 3
Views: 677

Re: Converting from Moles to Pressure

Also, when plugging in values into PV=nRT, make sure you are using the correct R value. There are many different R values but just make sure to use the one with units that match with the given temperature and with the desired units of pressure.
by Brenda Melano 3H
Tue Nov 03, 2015 8:12 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Ionization energy based on valence- shell e-
Replies: 3
Views: 967

Re: Ionization energy based on valence- shell e-

Say we had a molecule with 2 electrons in the pi2p orbitals and another molecule with 1 electron in the pi2p orbitals. Would the molecule with 2 electrons have a lower ionization energy because of repulsion or would both molecules have equal ionization energies because both electrons are at equal en...
by Brenda Melano 3H
Sun Nov 01, 2015 9:40 am
Forum: Lewis Structures
Topic: "SO" Lewis Structures
Replies: 1
Views: 311

"SO" Lewis Structures

We have been told a number of times in class that reducing formal charge on atoms leaves us with the most stable lewis structures. I also understand that there are exceptions to this rule and that we should memorize them. However, I find many contradictions for some of the structures among all our s...
by Brenda Melano 3H
Sun Nov 01, 2015 8:26 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Expanded Octet
Replies: 1
Views: 336

Re: Expanded Octet

You know when a molecule has an expanded octet when the number of total electrons you have in a molecule exceeds the electrons that fit onto the lewis structure with all atoms having a full valence shell (8 valence e- for most electrons but 1 for hydrogen and 3 for boron). Typically, the peripheral ...
by Brenda Melano 3H
Sat Oct 24, 2015 9:54 am
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR Practice
Replies: 31
Views: 9483

Re: VSEPR Practice

Lewis structure of SO2.JPG I came up with another lewis structure for SO2 that has a formal charge of 0 for all atoms. However, when I checked my answer, I noticed it was not included. Is this a valid lewis structure? I thought it would be better, in general, to always answer with a lewis structure...
by Brenda Melano 3H
Sun Oct 18, 2015 7:54 pm
Forum: Lewis Structures
Topic: unpaired electrons for 02
Replies: 2
Views: 438

unpaired electrons for 02

How could we tell from the lewis structure of O2 that it has two unpaired electrons, therefore making it paramagnetic?
by Brenda Melano 3H
Mon Oct 12, 2015 9:48 am
Forum: Lewis Structures
Topic: Lewis Structure for NO3-
Replies: 1
Views: 370

Lewis Structure for NO3-

photo-2.JPG
lewis structure of NO3
On one of the midterms the answer for a question that asked for the lewis structure of NO3^1- gave this answer. However, doesn't this answer have two oxygens with the formal charge of -1? which would make NO3 ^2-?
by Brenda Melano 3H
Sat Oct 10, 2015 4:19 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Negative sign in the Schrodinger equation
Replies: 3
Views: 922

Re: Negative sign in the Schrodinger equation

I think what the Schrodinger equation (the one on our constants sheet with a negative sign) is saying is that the total energy of the particle* its wave function is equal to the potential Energy*wave function - kinetic energy of particle*the wave function. I don't know if you took physics in high sc...
by Brenda Melano 3H
Thu Oct 08, 2015 11:33 am
Forum: Quantum Numbers and The H-Atom
Topic: degenerate levels
Replies: 1
Views: 346

degenerate levels

What exactly is a degenerate level? Does it only apply to s,p,d,f orbitals? Does it also apply to spins?...
by Brenda Melano 3H
Thu Oct 01, 2015 6:57 am
Forum: Properties of Light
Topic: how material absorbs or reflects light
Replies: 3
Views: 581

how material absorbs or reflects light

I am confused about how we see the colors of objects. We have always been told that an object absorbs light and reflects light and that the light it reflects is the light we see. Is the light it reflects the energy that the electrons absorb and then re-emits? If so, what happens to the energy of the...

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