Search found 53 matches
- Fri Mar 16, 2018 10:28 am
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 2988828
Re: Post All Chemistry Jokes Here
Did you know that you can cool yourself to -273.15˚C and still be 0k?
- Sun Mar 11, 2018 1:41 pm
- Forum: First Order Reactions
- Topic: Log vs ln
- Replies: 9
- Views: 1198
Re: Log vs ln
There wouldn't be any cases where you would need to use log. It's usually easiest to go by the given equation.
- Sun Mar 11, 2018 1:40 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Delta G at Boiling Point
- Replies: 3
- Views: 3385
Re: Delta G at Boiling Point
At boiling point, temperature and pressure are constant. Therefore, the change in enthalpy would be zero.
- Sun Mar 11, 2018 1:31 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Elements Acting as Electrodes
- Replies: 2
- Views: 437
Re: Elements Acting as Electrodes
The oxidation number for an atom in its elemental form is always zero. It is not always a solid.
- Wed Mar 07, 2018 11:51 am
- Forum: First Order Reactions
- Topic: 15.37(B) homework
- Replies: 3
- Views: 469
Re: 15.37(B) homework
For problems like this that give % of the initial like 10%, it would be ln(1/0.1) which ends up being ln(10). For 15%, it would be ln(1/0.15) since its ln of [A]/[Ao]
- Wed Mar 07, 2018 11:48 am
- Forum: General Rate Laws
- Topic: Problem 15.37
- Replies: 3
- Views: 539
Re: Problem 15.37
You would do ln(1/0.1) which is the same as ln(10).
- Wed Mar 07, 2018 11:46 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Initial Rate and Concentrations
- Replies: 2
- Views: 411
Re: Initial Rate and Concentrations
The change in concentration is proportional to the rate because the rate is dependent upon the concentration. This is why we can use the proportionality to figure out the order.
- Wed Mar 07, 2018 11:45 am
- Forum: First Order Reactions
- Topic: Example 15.3
- Replies: 2
- Views: 462
Re: Example 15.3
Make sure to look at the correct temperature in the table. Generally on tests though, I assume the k will be given but you should still know how to find it based on a table.
- Thu Mar 01, 2018 1:35 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetically Stable Vs. Thermodynamically Stable
- Replies: 4
- Views: 2110
Re: Kinetically Stable Vs. Thermodynamically Stable
Simply put, kinetics deals with the rate of a reaction and thermodynamics deals with favorability of the reaction.
- Thu Mar 01, 2018 1:28 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Units for Concentration
- Replies: 4
- Views: 543
Re: Units for Concentration
Just make sure all your units match but other than that, I don't think the answer has a preferred unit.
- Thu Mar 01, 2018 1:25 pm
- Forum: General Rate Laws
- Topic: Negative Signs [ENDORSED]
- Replies: 6
- Views: 1000
Re: Negative Signs [ENDORSED]
We want to work with positive numbers so you should make sure the rate is positive.
- Wed Feb 21, 2018 8:51 pm
- Forum: Balancing Redox Reactions
- Topic: OH/H20
- Replies: 4
- Views: 451
Re: OH/H20
The tests should be clear with whether it is acidic or basic.
- Wed Feb 21, 2018 8:48 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: When to include Pt in cell diagram
- Replies: 2
- Views: 470
Re: When to include Pt in cell diagram
Mostly, Pt is used when there is no conducting metal in the reaction.
- Wed Feb 21, 2018 8:41 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electrochem Exam
- Replies: 3
- Views: 424
Re: Electrochem Exam
The tests would explicitly say what you need to find and will be really clear.
- Wed Feb 21, 2018 8:33 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: K sig figs
- Replies: 4
- Views: 533
Re: K sig figs
I believe sig figs should not matter too much this quarter but just use the smallest number given in the problem.
- Wed Feb 21, 2018 8:32 pm
- Forum: Balancing Redox Reactions
- Topic: Acidic or basic?
- Replies: 2
- Views: 368
Re: Acidic or basic?
Most likely, it will be given so you don't need to worry about it. However, it can be determined by looking at the equation and whether it has H+ or OH- in it.
- Wed Feb 07, 2018 5:38 pm
- Forum: Calculating Work of Expansion
- Topic: Irreversible expansion
- Replies: 4
- Views: 630
Re: Irreversible expansion
Simply put, it matters when P and T are constant. Based on that, certain equations are used.
- Wed Feb 07, 2018 5:37 pm
- Forum: Calculating Work of Expansion
- Topic: Integral [ENDORSED]
- Replies: 4
- Views: 857
Re: Integral [ENDORSED]
You do not need to know integrals and how to derive the functions. It is helpful to understand as a way to change equations around and understand it. Rather than memorizing different equations, you could calculate it yourself.
- Wed Feb 07, 2018 5:36 pm
- Forum: Calculating Work of Expansion
- Topic: Work Equations [ENDORSED]
- Replies: 9
- Views: 1385
Re: Work Equations [ENDORSED]
It's easiest to choose equations based on the problem. You can tell by what they give what equation to use. Also, as mentioned, it depends on whether it is reversible or irreversible.
- Mon Feb 05, 2018 12:49 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Intermolecular Forces
- Replies: 2
- Views: 508
Re: Intermolecular Forces
Gibbs free energy of a solid changes more slowly with respect to a temperature change, which means its entropy is lower than the entropy of the liquid. This is related back to the strength of the intermolecular forces and the correspondence with the rigidity of the substance overall.
- Mon Feb 05, 2018 12:39 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: negative entropy [ENDORSED]
- Replies: 10
- Views: 5664
Re: negative entropy [ENDORSED]
Look at the signs in entropy as a change rather than positive and negative entropy.
- Mon Feb 05, 2018 12:38 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta S vs Delta U [ENDORSED]
- Replies: 5
- Views: 2884
Re: Delta S vs Delta U [ENDORSED]
For entropy, delta S is basically a measure of the change in order/disorder of the reaction. Increasing order gives us a negative delta S value, and decreasing order gives a positive delta S value. ΔU is the change in internal energy U of the system.
- Fri Jan 26, 2018 3:25 pm
- Forum: Phase Changes & Related Calculations
- Topic: When to use Kelvin or Celsius
- Replies: 10
- Views: 6778
Re: When to use Kelvin or Celsius
For many cases, Kelvin is used but it really just depends on the problem and the units given.
- Wed Jan 24, 2018 1:25 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed vs. Isolated
- Replies: 8
- Views: 1060
Re: Closed vs. Isolated
If the system allows neither energy or matter transfer, then it is an isolated system. However, if it allows only energy transfer, it is a closed system.
- Wed Jan 24, 2018 1:23 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Exothermic
- Replies: 7
- Views: 852
Re: Exothermic
https://www.youtube.com/watch?v=eJXL0IrbtqE
This video gives a good, simple explanation of endothermic and exothermic reactions.
This video gives a good, simple explanation of endothermic and exothermic reactions.
- Wed Jan 24, 2018 1:21 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Heat vs. Temp
- Replies: 9
- Views: 882
Re: Heat vs. Temp
The heat of an object is the total energy of all the molecular motion inside that object. Temperature, on the other hand, is a measure of the average heat or thermal energy of the molecules in a substance.
- Sun Jan 21, 2018 11:39 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: closed sysytem
- Replies: 3
- Views: 409
Re: closed sysytem
A mercury thermometer is a closed system because matter cannot enter or leave it.
- Sun Jan 21, 2018 11:37 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: the sign of q
- Replies: 5
- Views: 451
Re: the sign of q
Simply put, Q is positive if heat is added to the system, and negative if heat is removed.
- Sun Jan 21, 2018 11:35 pm
- Forum: Phase Changes & Related Calculations
- Topic: ΔU vs. ΔH
- Replies: 10
- Views: 3573
- Sat Jan 13, 2018 4:28 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat vs thermal energy
- Replies: 2
- Views: 267
Re: Heat vs thermal energy
Heat is the flow of thermal energy between two objects of different temperature whereas the thermal energy tells about how much is the transfer of energy due to temperature difference between two bodies. Hence thermal energy in transit gives heat.
- Sat Jan 13, 2018 4:02 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase Changes
- Replies: 13
- Views: 1499
Re: Phase Changes
It would be best to know the enthalpy of fusion and the enthalpy of vaporization as it is used in calculations.
- Sat Jan 13, 2018 3:56 pm
- Forum: Phase Changes & Related Calculations
- Topic: Physical Change vs Chemical Change
- Replies: 2
- Views: 1536
Re: Physical Change vs Chemical Change
Graphite and diamond are both large molecules made of carbon, but have different connectivity. The carbon in graphite are bonded to 3 other carbon neighbors, but in diamond carbon bonds with 4 neighbors. Therefore, it would be a chemical change.
- Sun Dec 03, 2017 12:51 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH and pOH
- Replies: 10
- Views: 1369
Re: pH and pOH
Dr. Lavelle's lecture went over pH and pOH but additionally watching this video may help. It gives a clear explanation.
https://www.youtube.com/watch?v=eoM1nzYFy8k
https://www.youtube.com/watch?v=eoM1nzYFy8k
- Sun Dec 03, 2017 12:49 pm
- Forum: Lewis Acids & Bases
- Topic: Lewis Acid & Base vs. Bronsted Acid & Base [ENDORSED]
- Replies: 2
- Views: 341
Re: Lewis Acid & Base vs. Bronsted Acid & Base [ENDORSED]
An example of this would be BF3 + F- ---> BF4-
BF3 is a lewis acid
F- is a lewis base
Neither are Bronsted acid/bases because there is no transfer of protons.
Also, all Bronsted acid/bases are Lewis acid/bases.
BF3 is a lewis acid
F- is a lewis base
Neither are Bronsted acid/bases because there is no transfer of protons.
Also, all Bronsted acid/bases are Lewis acid/bases.
- Wed Nov 29, 2017 6:12 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Module Question [ENDORSED]
- Replies: 1
- Views: 345
Module Question [ENDORSED]
I was confused about this problem from the module.
13. For the unbalanced reaction, CO (g) + H2 (g) ⇌ CH3OH (g), the equilibrium concentrations are [CO] = 0.0911 M, [H2 ] = 0.0822 M, [CH3OH] = 0.00892 M. What is the value of the equilibrium constant? Does the equilibrium favor reactants or products?
13. For the unbalanced reaction, CO (g) + H2 (g) ⇌ CH3OH (g), the equilibrium concentrations are [CO] = 0.0911 M, [H2 ] = 0.0822 M, [CH3OH] = 0.00892 M. What is the value of the equilibrium constant? Does the equilibrium favor reactants or products?
- Sun Nov 19, 2017 3:03 pm
- Forum: Naming
- Topic: writing chemical formula based on name
- Replies: 4
- Views: 320
Re: writing chemical formula based on name
First, there are two types of bonds: ionic and covalent. Based on the type of bond, chemical formulas are written differently. I put a link below that explains how to name the compounds in depth and would highly recommend watching it.
https://www.youtube.com/watch?v=mQpNjm7xB30
https://www.youtube.com/watch?v=mQpNjm7xB30
- Sun Nov 19, 2017 3:01 pm
- Forum: Naming
- Topic: Terminology
- Replies: 4
- Views: 402
Re: Terminology
If you are confused with topics, I would highly recommend watching videos in order to clarify things. The link below clearly explains what ligands are and you may find it very useful. Hope that helps!
https://www.youtube.com/watch?v=011Bj5USal8
https://www.youtube.com/watch?v=011Bj5USal8
- Fri Nov 10, 2017 3:04 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: More Polarizable/Polarizing Power
- Replies: 6
- Views: 791
Re: More Polarizable/Polarizing Power
High polarizing power is based on size and charge so Group 2 would have a higher polarizing power compared to Group 1. Also as you go up, polarizing power increases due to a smaller size. As for being the most polarizable, larger anions are more polarizing. It increases as you go up the group.
- Fri Nov 10, 2017 2:59 pm
- Forum: Dipole Moments
- Topic: Dipole moments
- Replies: 6
- Views: 1095
Re: Dipole moments
A dipole moment is a measurement of the separation of two opposite electrical charges.
Watching a video might help explain it better:
https://www.khanacademy.org/science/che ... ole-moment
Watching a video might help explain it better:
https://www.khanacademy.org/science/che ... ole-moment
- Sun Nov 05, 2017 11:17 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 3-D Lewis Structure Drawing
- Replies: 2
- Views: 732
Re: 3-D Lewis Structure Drawing
2-D representations show the atoms in the molecule and the connections between them but leave out other important factors. In order to draw a 3-D structure, first you must understand the different symbols such as normal bonds, dashed bonds, and wedged bonds. Dashed bonds are used to represent bonds ...
- Sun Nov 05, 2017 11:04 am
- Forum: Electronegativity
- Topic: Comparing Electronegativity of Elements
- Replies: 5
- Views: 1501
Re: Comparing Electronegativity of Elements
There are some common elements such as H, C, N, and O that we are expected to know electronegativity for in order to determine polarity. Other than that, we can base it off trends since we know electronegativity increases as we go higher up and to the right.
- Sat Oct 28, 2017 10:15 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: electron spin quantum number (ms) [ENDORSED]
- Replies: 4
- Views: 1772
Re: electron spin quantum number (ms) [ENDORSED]
Michael Cheng 1B wrote:How do you know if an electron will be spin up of spin down?
After determining the number of electrons and drawing the electron configuration, you would distribute the electrons using up and down arrows in order to show spin.
To see it visually:
http://www.graylark.com/eve/c-configs.svg
- Thu Oct 26, 2017 12:54 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Quantum number ml
- Replies: 2
- Views: 466
Re: Quantum number ml
Quantum number ml is the magnetic quantum number. It determines the number of orbitals and their orientation within a subshell. In the s orbital, there is only one possible orientation which is 0. For example in the p orbital, it would be 1 0 -1. Based on the electron, it would be one of those integ...
- Thu Oct 26, 2017 12:49 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Units [ENDORSED]
- Replies: 4
- Views: 530
Re: Units [ENDORSED]
I think it would be okay to leave it in meters but changing it to picometers would just be better to understand.
- Sun Oct 22, 2017 2:15 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: quantum numbers [ENDORSED]
- Replies: 5
- Views: 1066
Re: quantum numbers [ENDORSED]
Elements of the same period share the same principal quantum number. Atoms do not change principal quantum numbers as you move from left to right across the periodic table.
- Wed Oct 18, 2017 3:50 pm
- Forum: DeBroglie Equation
- Topic: Homework 1.13/ Rydberg
- Replies: 3
- Views: 321
Homework 1.13/ Rydberg
In 1.13, it states that the transition is from n=4 to n=2 so wouldn't that make n1=4 and n2=2? However, the solutions manual switches it around. Does anyone understand why?
- Tue Oct 17, 2017 3:57 pm
- Forum: Properties of Electrons
- Topic: Rydberg's formula
- Replies: 6
- Views: 1043
Rydberg's formula
I don't really understand what Rydberg's formula is about and the meaning of the different levels. Also, will the series we are starting from and jumping to be given?
- Tue Oct 17, 2017 3:52 pm
- Forum: Trends in The Periodic Table
- Topic: List of all trends?
- Replies: 5
- Views: 1016
Re: List of all trends?
I like to watch videos sometimes in order to understand and remember concepts. This video helped me and may be useful for you too. I also included a diagram with arrows that clearly show all the trends. Hope this helps! https://www.youtube.com/watch?v=XK-WTYncldA https://sciencenotes.org/periodic-ta...
- Fri Oct 13, 2017 1:17 pm
- Forum: Photoelectric Effect
- Topic: Confused about photoelectric effect! [ENDORSED]
- Replies: 6
- Views: 938
Re: Confused about photoelectric effect! [ENDORSED]
When light shines on a metal, electrons can be emitted from the surface of the metal. This is what is known as the photoelectric effect. From experiments, we have learned that intensity of the light does not affect the energies of the emitted electrons.
- Fri Oct 13, 2017 1:10 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Quantized Energy
- Replies: 5
- Views: 1020
Re: Quantized Energy
Energy is "quantized" because light comes in packets of energy defined by its frequency and planck's constant. Quantization has to do with it only being able to have discrete values.
- Tue Oct 03, 2017 4:09 pm
- Forum: SI Units, Unit Conversions
- Topic: Molecules [ENDORSED]
- Replies: 10
- Views: 1343
Re: Molecules [ENDORSED]
A mole would be 6.022 x 10^23 molecules. So, a mole is a unit quantity that is used to measure the quantity of molecules. A molecule is just 2 or more atoms combined by a chemical bond.
- Tue Oct 03, 2017 1:23 am
- Forum: Balancing Chemical Reactions
- Topic: Balancing Process
- Replies: 11
- Views: 1186
Re: Balancing Process
I assume it would just be be based on what would be easier to balance first. I think it's just a strategy, not really a rule.
- Tue Oct 03, 2017 1:17 am
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Fundamentals E Question 35 [ENDORSED]
- Replies: 2
- Views: 896
Re: Fundamentals E Question 35 [ENDORSED]
The reason you may be getting the wrong answer is because the molar mass you calculated is wrong. The molar mass of Ca5(PO4)3F is 504.3, which is what you got, but the molar mass of Ca5(PO4)3OH is actually 502.31. Now if you subtract 502.31 from 504.3 and divide that overall by 504.3, you will get 0...