## Search found 53 matches

Fri Mar 16, 2018 10:28 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7951
Views: 1178582

### 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: 570

### 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: 1793

### 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: 176

### 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: 191

### 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: 198

### 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: 183

### 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: 184

### 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: 905

### 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: 232

### 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: 381

### 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: 173

### 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: 173

### 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: 154

### 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: 233

### 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: 148

### 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: 204

### 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: 307

### 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: 538

### 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: 147

### 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: 775

### 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: 736

### 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: 1291

### 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: 492

### 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: 269

### Re: Exothermic

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: 379

### 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: 184

### 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: 192

### 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: 853

### Re: ΔU vs. ΔH

This is a really helpful video that explains ΔU and ΔH.
Sat Jan 13, 2018 4:28 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat vs thermal energy
Replies: 2
Views: 118

### 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: 694

### 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: 163

### 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: 586

### 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.

Sun Dec 03, 2017 12:49 pm
Forum: Lewis Acids & Bases
Topic: Lewis Acid & Base vs. Bronsted Acid & Base [ENDORSED]
Replies: 2
Views: 200

### 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.
Wed Nov 29, 2017 6:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Module Question [ENDORSED]
Replies: 1
Views: 154

### Module Question[ENDORSED]

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: 195

### 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.

Sun Nov 19, 2017 3:01 pm
Forum: Naming
Topic: Terminology
Replies: 4
Views: 246

### 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!

Fri Nov 10, 2017 3:04 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: More Polarizable/Polarizing Power
Replies: 6
Views: 406

### 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: 452

### 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:
Sun Nov 05, 2017 11:17 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 3-D Lewis Structure Drawing
Replies: 2
Views: 159

### 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: 664

### 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: 395

### 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: 251

### 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: 299

### 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: 394

### 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: 214

### 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: 630

### 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: 498

### 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: 470

### 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: 543

### 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: 641

### 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: 606

### 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: 350

### 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...