Search found 50 matches

by Alex Nechaev 1I
Mon Mar 12, 2018 8:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams- Line Notation
Replies: 4
Views: 191

Re: Cell Diagrams- Line Notation

Yes, and the electrodes should go on either side as well.
by Alex Nechaev 1I
Mon Mar 12, 2018 8:18 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: anode vs cathode in non standard cell diagram
Replies: 5
Views: 198

Re: anode vs cathode in non standard cell diagram

The anode is usually on the left for our purposes, and they probably will not switch it up since we haven't seen any examples in class or on homework proving otherwise.
by Alex Nechaev 1I
Mon Mar 12, 2018 8:16 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q vs. K
Replies: 8
Views: 431

Re: Q vs. K

K can be used calculate the final concentrations at equilibrium for a reaction using an ICE table and the natural progression of the reaction, from left to right or from right to left. Q expresses the relative ratio of products to reactants at a given instant.
by Alex Nechaev 1I
Tue Mar 06, 2018 10:46 pm
Forum: General Rate Laws
Topic: 15.3
Replies: 4
Views: 167

Re: 15.3

Since there is already a negative sign in the formula for determining the reaction rate of a reactant, the subtraction of concentrations that would come out negative becomes positive. I think that reaction rates are just always expressed as positive values.
by Alex Nechaev 1I
Tue Mar 06, 2018 10:42 pm
Forum: General Rate Laws
Topic: Coefficients affecting order & molecularity
Replies: 2
Views: 103

Re: Coefficients affecting order & molecularity

I thought they were related at first as well, but the coefficients actually play no role in determining reaction order. For this, you look at concentrations and reaction rate.
by Alex Nechaev 1I
Tue Mar 06, 2018 10:40 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 6
Views: 228

Re: Coefficients

Coefficients do affect unique rates, but not the general rate law or determining formation or consumption of products or reactants.
by Alex Nechaev 1I
Tue Mar 06, 2018 10:38 pm
Forum: General Rate Laws
Topic: 15.5
Replies: 2
Views: 73

Re: 15.5

It could have something to do with the fact that for unique rate you have to divide by the stoichiometric coefficient, but I do think that in this case you are supposed to multiply by 3.
by Alex Nechaev 1I
Tue Mar 06, 2018 10:34 pm
Forum: General Rate Laws
Topic: Specification of Reactant/Product
Replies: 3
Views: 99

Re: Specification of Reactant/Product

The question will usually be asking for the formation of products if asking for reaction rate, so generally whichever species is the product will be the one to which the rate refers.
by Alex Nechaev 1I
Tue Mar 06, 2018 10:32 pm
Forum: First Order Reactions
Topic: k
Replies: 16
Views: 625

Re: k

Adam Enomoto 1L wrote:Reaction A: k = 2.3 M-1s-1
Reaction B: k = 1.8 Ms-1
Reaction C: k = 0.75 s-1

How do we know which one is a zero order reaction just given the units?

I would just try to memorize the units for at least the first few orders.
by Alex Nechaev 1I
Wed Feb 21, 2018 10:32 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell diagram [ENDORSED]
Replies: 2
Views: 100

Re: cell diagram [ENDORSED]

Here's the general layout of a cell diagram
by Alex Nechaev 1I
Wed Feb 21, 2018 10:28 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagrams
Replies: 2
Views: 78

Re: Cell diagrams

The electrodes are also included on either side of the cell diagram as the first and last elements.
by Alex Nechaev 1I
Wed Feb 21, 2018 10:26 am
Forum: Balancing Redox Reactions
Topic: Determining acidic or basic solution
Replies: 3
Views: 151

Re: Determining acidic or basic solution

The problem will usually tell you whether the solution is acidic or basic.
by Alex Nechaev 1I
Wed Feb 21, 2018 10:13 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: redox
Replies: 7
Views: 295

Re: redox

Just remember opposites. The element being oxidized is the reducing agent and the element being reduced is the oxidizing agent.
by Alex Nechaev 1I
Wed Feb 21, 2018 10:10 am
Forum: Balancing Redox Reactions
Topic: redox agent
Replies: 5
Views: 179

Re: redox agent

Just remember opposites. The oxidizing agent is being reduced, and the reducing agent is being oxidized.
by Alex Nechaev 1I
Wed Feb 21, 2018 10:06 am
Forum: Balancing Redox Reactions
Topic: 3A Determining reduction vs oxidation
Replies: 4
Views: 141

Re: 3A Determining reduction vs oxidation

I always like to use OIL RIG (Oxidation Is Losing, Reduction is Gaining) to remember which elements are being oxidized and reduced. Once you know this, remember that the element being oxidized is the reducing agent and the element being reduced is the oxidizing agent.
by Alex Nechaev 1I
Mon Feb 12, 2018 4:16 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: closed vs isolated
Replies: 11
Views: 552

Re: closed vs isolated

Knowing whether a system is closed or isolated only tells you whether it can exchange energy with its surroundings or not. Don't assume that pressures and volumes are constant unless the problem specifically states that they are.
by Alex Nechaev 1I
Mon Feb 12, 2018 4:13 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: When to use + sign
Replies: 11
Views: 386

Re: When to use + sign

204918982 wrote:So should we always put a + sign on positive answers for change calculations on tests/exams?

I would say yes, since the examples we have done in class and the solutions in the manual all include the + sign for positive answers.
by Alex Nechaev 1I
Mon Feb 12, 2018 4:08 pm
Forum: Phase Changes & Related Calculations
Topic: Origins of Internal Energy
Replies: 2
Views: 105

Origins of Internal Energy

Are we going to need to know the difference between translational, rotational, and vibrational energy?
by Alex Nechaev 1I
Mon Feb 05, 2018 2:17 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: negative entropy [ENDORSED]
Replies: 10
Views: 344

Re: negative entropy [ENDORSED]

Negative entropy simply means that there is a decrease in disorder, or rather an increase in order of the system.
by Alex Nechaev 1I
Mon Feb 05, 2018 2:07 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta S vs Delta U [ENDORSED]
Replies: 5
Views: 414

Re: Delta S vs Delta U [ENDORSED]

Delta S is the entropy of the system, and can be positive or negative to describe that change. Delta U is the change in the internal energy of the system.
by Alex Nechaev 1I
Mon Feb 05, 2018 2:02 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Clausius Inequality
Replies: 1
Views: 77

Re: Clausius Inequality

This is basically just a mathematical explanation of the second law of thermodynamics. It gives us a way to determine whether a cyclical process is reversible or irreversible.
by Alex Nechaev 1I
Tue Jan 23, 2018 11:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Exothermic
Replies: 7
Views: 203

Re: Exothermic

If a system's temperature increases, that means that heat is being released from the reaction to increase the temperature of its surroundings. Don't think of the system itself as the reaction, but rather as the surroundings of that reaction whose change in temperature determines whether the reaction...
by Alex Nechaev 1I
Tue Jan 23, 2018 10:59 pm
Forum: Calculating Work of Expansion
Topic: expansion work
Replies: 2
Views: 115

Re: expansion work

Also note that the equation given above is used for irreversible processes.
by Alex Nechaev 1I
Tue Jan 23, 2018 10:58 pm
Forum: Calculating Work of Expansion
Topic: reversible and irreversible
Replies: 2
Views: 110

Re: reversible and irreversible

The equations used to calculate work also vary depending on whether the process is reversible or irreversible. Reversible processes are isothermal, with the equation w=-nRT(ln(vf/vd)). Work for irreversible processes can be calculated using w=-Pext+Δv.
by Alex Nechaev 1I
Tue Jan 23, 2018 10:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Potential energy comparison
Replies: 1
Views: 73

Re: Potential energy comparison

I would say that potential energy is highest before combustion, as it will all be converted to kinetic energy during the reaction.
by Alex Nechaev 1I
Tue Jan 23, 2018 10:46 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy factors [ENDORSED]
Replies: 2
Views: 119

Re: Entropy factors [ENDORSED]

If you add energy to a solid, it can become a liquid. Liquids have more energy and entropy than solids. Any chemical reaction that increases the number of gas molecules also increases entropy. A chemical reaction that increases the number of gas molecules would be a reaction that pours energy into a...
by Alex Nechaev 1I
Tue Jan 23, 2018 10:43 pm
Forum: Phase Changes & Related Calculations
Topic: Steam
Replies: 7
Views: 625

Re: Steam

Steam causes more severe burns than boiling water does because the temperature required to convert water to steam is much higher than the temperature required to bring water to a boil. Steam quickly transfers the heat of vaporization to whatever it comes in contact with, which will result in severe ...
by Alex Nechaev 1I
Sat Jan 20, 2018 1:02 pm
Forum: Phase Changes & Related Calculations
Topic: Heat Capacity
Replies: 6
Views: 273

Re: Heat Capacity

I don't think it really matters whether you leave your final answer in kJ or Joules, but it's probably more likely that you'll see values in kJ, especially larger values of heat energy.
by Alex Nechaev 1I
Sun Dec 10, 2017 12:35 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Direction of the equilibrium
Replies: 2
Views: 250

Re: Direction of the equilibrium

It's always best to find Q to check the direction of the reaction. This way you just eliminate any chances of making mistakes at the beginning and know for sure that you're calculating correctly.
by Alex Nechaev 1I
Sun Dec 10, 2017 12:11 am
Forum: Significant Figures
Topic: Rounding: when and where?
Replies: 10
Views: 471

Re: Rounding: when and where?

It wouldn't be wrong to round up, since I'm pretty sure the rounding rules still apply to sig figs. Both would probably be acceptable.
by Alex Nechaev 1I
Tue Dec 05, 2017 5:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Pi and sigma bonds [ENDORSED]
Replies: 7
Views: 338

Re: Pi and sigma bonds [ENDORSED]

If there's a resonance structure, the pi bonds will be delocalized. Sigma bonds don't become delocalized, so resonance has no effect on them.
by Alex Nechaev 1I
Tue Dec 05, 2017 5:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Monodentate vs Bidentate etc. [ENDORSED]
Replies: 7
Views: 1454

Re: Monodentate vs Bidentate etc. [ENDORSED]

At the TA review session on Monday, they mentioned that the best way to determine whether a ligand is a polydentate is to try to draw the Lewis structure. This way, you can actually see the bonding sites in order to know.
by Alex Nechaev 1I
Tue Nov 28, 2017 2:04 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Help understanding polydentate
Replies: 4
Views: 290

Re: Help understanding polydentate

^What process do we need to use to determine this though? Is there a way to see without drawing the Lewis structures?
by Alex Nechaev 1I
Tue Nov 28, 2017 1:58 pm
Forum: Naming
Topic: why chloro instead of monochloro
Replies: 3
Views: 183

Re: why chloro instead of monochloro

Haocheng Zhang 1C wrote:Also, how to identify a polydentate ligand?
A polydentate ligand can be recognized by having more than 2 lewis base sites, such as multiple lone pair donating sites used to bond to a central atom or ion.
by Alex Nechaev 1I
Mon Nov 20, 2017 5:54 pm
Forum: Hybridization
Topic: Hybridization in General
Replies: 3
Views: 477

Re: Hybridization in General

The way that we determine hybridization is generally by drawing the Lewis Structure of the given compound and counting the number of regions of electron density that the compound has. If we have COF2, which has three regions of electron density, the number of orbitals filled when they merge together...
by Alex Nechaev 1I
Mon Nov 20, 2017 5:43 pm
Forum: Hybridization
Topic: General Hybridization
Replies: 3
Views: 215

Re: General Hybridization

This chart is also really helpful when it comes to VSEPR and hybridization: http://web.gccaz.edu/~chriy68124/VSEPR%20handout.pdf It depicts the lewis structures of many examples, which allows you to see the regions of electron density, and then includes a column with the hybridization of each exampl...
by Alex Nechaev 1I
Wed Nov 15, 2017 12:54 pm
Forum: Sigma & Pi Bonds
Topic: Sigma and pi
Replies: 12
Views: 648

Re: Sigma and pi

Yes. A single bond such as (C-H) has one sigma bond whereas a double (C=C) and triple (C≡C) bond has one sigma bond with remaining being pi bonds.
by Alex Nechaev 1I
Wed Nov 15, 2017 12:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Regions of electron density
Replies: 4
Views: 238

Re: Regions of electron density

Lone pairs and bonding pairs both count as regions of electron density. Lone pairs help determine the shape when you take electron repulsion into account and will also enable you to calculate the bond angles.
by Alex Nechaev 1I
Thu Nov 09, 2017 12:24 am
Forum: Sigma & Pi Bonds
Topic: Bonding
Replies: 2
Views: 216

Re: Bonding

This website has a really good description of the differences and includes diagrams: http://www.majordifferences.com/2014/10/difference-between-sigma-and-pi-bond.html#.WgQO1ROPLfY Basically, a sigma bond is formed by end to end overlapping while a pi bond is formed laterally, with the two p orbitals...
by Alex Nechaev 1I
Thu Nov 09, 2017 12:13 am
Forum: Trends in The Periodic Table
Topic: Noble Gases
Replies: 3
Views: 257

Re: Noble Gases

Even though the periodic trends indicate that elements closest to the noble gases have higher ionization energy and electron affinity, the noble gases themselves are exceptions to this trend. They have full octets, therefore they are stable, which means they are less reactive and do not need to have...
by Alex Nechaev 1I
Thu Nov 02, 2017 1:07 pm
Forum: Trends in The Periodic Table
Topic: Noble Gas Electron Affinity
Replies: 3
Views: 540

Re: Noble Gas Electron Affinity

I read in another discussion topic that the trends don't really apply to the noble gases because they are stable, therefore they are much less reactive than the atoms in other groups and don't need to follow the same trends.
by Alex Nechaev 1I
Thu Nov 02, 2017 12:51 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 4
Views: 293

Re: Electron Affinity

#67 in Chapter 2 asks which element has the higher electron affinity. Part b asks you to compare nitrogen and carbon. I thought the answer would be nitrogen because nitrogen is more towards the right of the periodic table (I believe that electron affinity is higher towards the top right of the peri...
by Alex Nechaev 1I
Sun Oct 29, 2017 12:46 pm
Forum: Quantum Numbers and The H-Atom
Topic: Abbreviating e- configurations [ENDORSED]
Replies: 7
Views: 458

Re: Abbreviating e- configurations [ENDORSED]

Another notation style includes listing each sub-orbital (i.e. px, py, pz) with the number of electrons in that orbital (i.e. 2px1). That's also just a convention, and it's fine to just write p instead of separating it into 3 sub-orbitals. It's alright if we don't write the notations with the as px...
by Alex Nechaev 1I
Sun Oct 29, 2017 12:27 pm
Forum: Trends in The Periodic Table
Topic: 2.60 [ENDORSED]
Replies: 1
Views: 185

2.60 [ENDORSED]

We went over this question in one of the Peer Learning Sessions, and I just need some clarification. The question reads: Which ion of the following pairs has the larger radius: a) Ca^2+ , Ba^2+ b) As^3- , Se^2- c) Sn^2+ , Sn^4+ ? What effect do the charges of these ions have on their atomic radius? ...
by Alex Nechaev 1I
Thu Oct 19, 2017 10:31 pm
Forum: Properties of Electrons
Topic: Atomic Spectra and Energy Levels
Replies: 3
Views: 229

Atomic Spectra and Energy Levels

When electrons jump from one energy level to the next (n=1 to n=2, for example), how do we know when the energy exerted or used will be a negative value? If it goes down an energy level, will that finding of the energy from that jump be negative? Or is it the opposite?
by Alex Nechaev 1I
Thu Oct 19, 2017 10:26 pm
Forum: Properties of Light
Topic: Wave Properties of Light Post assessment#31
Replies: 3
Views: 227

Re: Wave Properties of Light Post assessment#31

To add on to the first response, we are generally unable to observe wave-like behaviors in large objects like baseballs. Because electrons are so small, we can measure wavelength and frequency, but not enough wave-like properties are visible in a larger object to actually make a difference. They are...
by Alex Nechaev 1I
Thu Oct 12, 2017 11:02 pm
Forum: Properties of Light
Topic: 1.15
Replies: 4
Views: 207

Re: 1.15

The first thing I did was use v=c/λ to find the frequency of the wave. The value you get here can then be used to evaluate for n(final) in Rydberg's formula, since you know that n(initial) is 1 (because hydrogen starts at n=1). After plugging in all of your calculated values, all you have to do is s...
by Alex Nechaev 1I
Thu Oct 12, 2017 10:50 pm
Forum: Properties of Light
Topic: Planck Constant [ENDORSED]
Replies: 8
Views: 440

Re: Planck Constant [ENDORSED]

I would definitely use 6.626*10^-34 when doing calculations since it is more precise. If you're concerned about sig figs, just remember that they don't matter so much during the process as they do in your final answer. Use the least number of sig figs in the given values to determine how many you in...
by Alex Nechaev 1I
Wed Oct 04, 2017 11:14 pm
Forum: Balancing Chemical Reactions
Topic: Help on HW question H1
Replies: 5
Views: 269

Re: Help on HW question H1

The reason that you can't simply add another O to the reaction is because matter can neither be created nor destroyed. Therefore, you cannot end up with more than what you started with if it was not involved in the reaction in the first place. Adding more atoms to the product than there were in the ...
by Alex Nechaev 1I
Wed Oct 04, 2017 11:06 pm
Forum: Significant Figures
Topic: Calculating Significant Figures
Replies: 3
Views: 581

Re: Calculating Significant Figures

When working with significant figures in a problem, say, calculating the mass % of an element in a sample, always stick with the LEAST number of sig figs in the problem. For example, if an 8.00 g sample of Vitamin C contains 3.27 g of Carbon, 0.3661 g of Hydrogen, and 4.36 g of Oxygen, the least num...

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