Search found 50 matches
- 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: 699
Re: Cell Diagrams- Line Notation
Yes, and the electrodes should go on either side as well.
- 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: 737
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.
- 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: 1151
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.
- Tue Mar 06, 2018 10:46 pm
- Forum: General Rate Laws
- Topic: 15.3
- Replies: 4
- Views: 603
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.
- Tue Mar 06, 2018 10:42 pm
- Forum: General Rate Laws
- Topic: Coefficients affecting order & molecularity
- Replies: 2
- Views: 393
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.
- Tue Mar 06, 2018 10:40 pm
- Forum: General Rate Laws
- Topic: Coefficients
- Replies: 6
- Views: 999
Re: Coefficients
Coefficients do affect unique rates, but not the general rate law or determining formation or consumption of products or reactants.
- Tue Mar 06, 2018 10:38 pm
- Forum: General Rate Laws
- Topic: 15.5
- Replies: 2
- Views: 361
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.
- Tue Mar 06, 2018 10:34 pm
- Forum: General Rate Laws
- Topic: Specification of Reactant/Product
- Replies: 3
- Views: 379
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.
- Tue Mar 06, 2018 10:32 pm
- Forum: First Order Reactions
- Topic: k
- Replies: 16
- Views: 1655
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.
- Wed Feb 21, 2018 10:32 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: cell diagram [ENDORSED]
- Replies: 2
- Views: 327
Re: cell diagram [ENDORSED]
Here's the general layout of a cell diagram
- Wed Feb 21, 2018 10:28 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell diagrams
- Replies: 2
- Views: 312
Re: Cell diagrams
The electrodes are also included on either side of the cell diagram as the first and last elements.
- Wed Feb 21, 2018 10:26 am
- Forum: Balancing Redox Reactions
- Topic: Determining acidic or basic solution
- Replies: 3
- Views: 536
Re: Determining acidic or basic solution
The problem will usually tell you whether the solution is acidic or basic.
- Wed Feb 21, 2018 10:13 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: redox
- Replies: 7
- Views: 1226
Re: redox
Just remember opposites. The element being oxidized is the reducing agent and the element being reduced is the oxidizing agent.
- Wed Feb 21, 2018 10:10 am
- Forum: Balancing Redox Reactions
- Topic: redox agent
- Replies: 5
- Views: 695
Re: redox agent
Just remember opposites. The oxidizing agent is being reduced, and the reducing agent is being oxidized.
- Wed Feb 21, 2018 10:06 am
- Forum: Balancing Redox Reactions
- Topic: 3A Determining reduction vs oxidation
- Replies: 4
- Views: 607
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.
- Mon Feb 12, 2018 4:16 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: closed vs isolated
- Replies: 11
- Views: 1380
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.
- Mon Feb 12, 2018 4:13 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: When to use + sign
- Replies: 11
- Views: 1065
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.
- Mon Feb 12, 2018 4:08 pm
- Forum: Phase Changes & Related Calculations
- Topic: Origins of Internal Energy
- Replies: 2
- Views: 330
Origins of Internal Energy
Are we going to need to know the difference between translational, rotational, and vibrational energy?
- Mon Feb 05, 2018 2:17 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: negative entropy [ENDORSED]
- Replies: 10
- Views: 5773
Re: negative entropy [ENDORSED]
Negative entropy simply means that there is a decrease in disorder, or rather an increase in order of the system.
- 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: 2949
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.
- Mon Feb 05, 2018 2:02 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Clausius Inequality
- Replies: 1
- Views: 245
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.
- 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: 893
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...
- Tue Jan 23, 2018 10:59 pm
- Forum: Calculating Work of Expansion
- Topic: expansion work
- Replies: 2
- Views: 343
Re: expansion work
Also note that the equation given above is used for irreversible processes.
- Tue Jan 23, 2018 10:58 pm
- Forum: Calculating Work of Expansion
- Topic: reversible and irreversible
- Replies: 2
- Views: 333
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.
- Tue Jan 23, 2018 10:50 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Potential energy comparison
- Replies: 1
- Views: 297
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.
- Tue Jan 23, 2018 10:46 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy factors [ENDORSED]
- Replies: 2
- Views: 399
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...
- Tue Jan 23, 2018 10:43 pm
- Forum: Phase Changes & Related Calculations
- Topic: Steam
- Replies: 7
- Views: 1233
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 ...
- Sat Jan 20, 2018 1:02 pm
- Forum: Phase Changes & Related Calculations
- Topic: Heat Capacity
- Replies: 6
- Views: 778
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.
- Sun Dec 10, 2017 12:35 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Direction of the equilibrium
- Replies: 2
- Views: 498
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.
- Sun Dec 10, 2017 12:11 am
- Forum: Significant Figures
- Topic: Rounding: when and where?
- Replies: 10
- Views: 893
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.
- Tue Dec 05, 2017 5:21 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Pi and sigma bonds [ENDORSED]
- Replies: 7
- Views: 780
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.
- Tue Dec 05, 2017 5:13 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Monodentate vs Bidentate etc. [ENDORSED]
- Replies: 7
- Views: 5970
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.
- Tue Nov 28, 2017 2:04 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Help understanding polydentate
- Replies: 4
- Views: 781
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?
- Tue Nov 28, 2017 1:58 pm
- Forum: Naming
- Topic: why chloro instead of monochloro
- Replies: 3
- Views: 465
Re: why chloro instead of monochloro
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.Haocheng Zhang 1C wrote:Also, how to identify a polydentate ligand?
- Mon Nov 20, 2017 5:54 pm
- Forum: Hybridization
- Topic: Hybridization in General
- Replies: 3
- Views: 1893
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...
- Mon Nov 20, 2017 5:43 pm
- Forum: Hybridization
- Topic: General Hybridization
- Replies: 3
- Views: 703
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...
- Wed Nov 15, 2017 12:54 pm
- Forum: Sigma & Pi Bonds
- Topic: Sigma and pi
- Replies: 12
- Views: 1609
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.
- Wed Nov 15, 2017 12:52 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Regions of electron density
- Replies: 4
- Views: 529
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.
- Thu Nov 09, 2017 12:24 am
- Forum: Sigma & Pi Bonds
- Topic: Bonding
- Replies: 2
- Views: 644
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...
- Thu Nov 09, 2017 12:13 am
- Forum: Trends in The Periodic Table
- Topic: Noble Gases
- Replies: 3
- Views: 1664
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...
- Thu Nov 02, 2017 1:07 pm
- Forum: Trends in The Periodic Table
- Topic: Noble Gas Electron Affinity
- Replies: 3
- Views: 1808
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.
- Thu Nov 02, 2017 12:51 pm
- Forum: Trends in The Periodic Table
- Topic: Electron Affinity
- Replies: 4
- Views: 648
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...
- Sun Oct 29, 2017 12:46 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Abbreviating e- configurations [ENDORSED]
- Replies: 7
- Views: 1017
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...
- Sun Oct 29, 2017 12:27 pm
- Forum: Trends in The Periodic Table
- Topic: 2.60 [ENDORSED]
- Replies: 1
- Views: 427
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? ...
- Thu Oct 19, 2017 10:31 pm
- Forum: Properties of Electrons
- Topic: Atomic Spectra and Energy Levels
- Replies: 3
- Views: 437
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?
- Thu Oct 19, 2017 10:26 pm
- Forum: Properties of Light
- Topic: Wave Properties of Light Post assessment#31
- Replies: 3
- Views: 576
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...
- Thu Oct 12, 2017 11:02 pm
- Forum: Properties of Light
- Topic: 1.15
- Replies: 4
- Views: 553
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...
- Thu Oct 12, 2017 10:50 pm
- Forum: Properties of Light
- Topic: Planck Constant [ENDORSED]
- Replies: 8
- Views: 1495
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...
- Wed Oct 04, 2017 11:14 pm
- Forum: Balancing Chemical Reactions
- Topic: Help on HW question H1
- Replies: 5
- Views: 828
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 ...
- Wed Oct 04, 2017 11:06 pm
- Forum: Significant Figures
- Topic: Calculating Significant Figures
- Replies: 3
- Views: 1286
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...