Search found 50 matches
- Mon Mar 12, 2018 8:33 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: What phase is water in in a combustion reaction?
- Replies: 2
- Views: 863
Re: What phase is water in in a combustion reaction?
It depends. Combustion reactions vary because the definition is vague "hydrocarbons react with O2 to form water and carbon dioxide". I believe often, however, the reactants are all gaseous.
- Mon Mar 12, 2018 8:28 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagram
- Replies: 3
- Views: 444
Re: Cell Diagram
If there is no conducting solids on one side of the diagram.
- Mon Mar 12, 2018 8:09 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Given information
- Replies: 5
- Views: 582
Re: Given information
It depends on the question. For some questions we will be told which is fast and which is slow. For most of the questions we have done in class and in the book, we are told the intermediate because we are given all the steps of the reaction.
- Tue Mar 06, 2018 2:54 pm
- Forum: General Rate Laws
- Topic: 15.17
- Replies: 4
- Views: 570
Re: 15.17
compare the reaction rates when all other reactants remain constant except for C. The reaction rate doesn't change even though C does, meaning it isn't in the rate law because it is a zero order reactant.
- Tue Mar 06, 2018 2:50 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: infinitesimal change
- Replies: 3
- Views: 2295
Re: infinitesimal change
Its the same as taking the derivative in calculus. We used it in thermodynamics to see what the effect of changing pressure or temperature would have on the system
- Tue Mar 06, 2018 2:48 pm
- Forum: General Rate Laws
- Topic: Proper units
- Replies: 7
- Views: 822
Re: Proper units
Unless the question specifies which unit it wants in the answer, it doesn't matter. However, make sure the units match up with constants in the formula sheet and with K
- Fri Mar 02, 2018 7:18 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Rate Constant [ENDORSED]
- Replies: 3
- Views: 633
Re: Rate Constant [ENDORSED]
Its a proportionality constant for the concentration of a reactant to the rate of reaction
- Fri Mar 02, 2018 7:13 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Intermediates [ENDORSED]
- Replies: 2
- Views: 368
Re: Intermediates [ENDORSED]
today we talked in class about how when reactions are coupled, one of the steps may go so much faster than the other step that the overall reaction speed is determined by the slower step. The intermediate's concentration in this case wouldn't affect the overall reaction
- Fri Mar 02, 2018 7:11 pm
- Forum: First Order Reactions
- Topic: First Order Reactions [ENDORSED]
- Replies: 2
- Views: 4012
Re: First Order Reactions [ENDORSED]
It depends on the reaction and the amount of concentration available. Its too general to say all of one is faster than another
- Tue Feb 20, 2018 11:37 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Pt in Cell diagrams
- Replies: 4
- Views: 669
Re: Pt in Cell diagrams
The inert electrode is necessary to make the electrons flow. You need this when the ions are aqueous or gaseous. You don't need it if there is a conducting solid.
- Tue Feb 20, 2018 11:35 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Homework Problem 14.55b [ENDORSED]
- Replies: 2
- Views: 1910
Re: Homework Problem 14.55b [ENDORSED]
In electrolysis, an electric current is passed through the substance. It is different than the chemical reaction that occurs in an galvanic cell. That is why you focus on the most positive standard reduction potentials
- Tue Feb 20, 2018 11:32 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 14.23a
- Replies: 2
- Views: 365
Re: 14.23a
First, the inert electrode has to be placed in the cell diagram because the electrodes are made of aqueous solutions (meaning there are no conducting solids). The platinum tends to go on the right side of the cell diagram (cathode-reduction) because it only transfers electrons. It does not exchange ...
- Sat Feb 17, 2018 12:00 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing Redox Reactions
- Replies: 1
- Views: 336
Re: Balancing Redox Reactions
In class he referred to the hydronium ion as the standard, so i would use that.
- Sat Feb 17, 2018 11:59 am
- Forum: Balancing Redox Reactions
- Topic: 14.1
- Replies: 3
- Views: 396
Re: 14.1
when balancing redox reactions, the charges on both sides SHOULD add up to be equal to eachother.
- Sat Feb 17, 2018 11:58 am
- Forum: Balancing Redox Reactions
- Topic: 9.3b
- Replies: 1
- Views: 237
Re: 9.3b
that is usually how you do it.
- Wed Feb 07, 2018 3:35 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 9.45
- Replies: 3
- Views: 490
Re: 9.45
yes, you can use that equation as long as temperature is constant.
- Wed Feb 07, 2018 3:31 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Half Reactions
- Replies: 6
- Views: 671
Re: Half Reactions
don't write both half reactions as reductions. Make sure to write the complete oxidation and reduction reactions, and as the person above me said, labeling is good for that too.
- Wed Feb 07, 2018 3:30 pm
- Forum: Balancing Redox Reactions
- Topic: oxidation
- Replies: 4
- Views: 522
Re: oxidation
If the element you are trying to find the oxidation number for is a transition metal, the oxidation number depends on the other elements in the compound. If its an ion, subtract the net oxidation numbers of the other elements in the compound (oxygen is almost always -2) from the total charge of the ...
- Wed Jan 31, 2018 6:24 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 9.43
- Replies: 5
- Views: 452
Re: 9.43
It is on0 the sheet of constants and formula's we are given at the start of every test. (Cp(water) = 75.3 J. K-1mol-1)
- Wed Jan 31, 2018 6:22 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Degeneracy and Entropy
- Replies: 3
- Views: 551
Re: Degeneracy and Entropy
Degeneracy is a property that is extremely difficult to measure in a lab, so often the CHANGE in degeneracy is measured. it can be increased moles of a substance or volume of a gas
- Wed Jan 31, 2018 6:17 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy and Temperature
- Replies: 3
- Views: 409
Re: Entropy and Temperature
Also, we used this equation in class to find the change in entropy when temperature is constant (as ice melts for example). If you want to find the change in entropy when temperature is not constant, use the equation delta S=n*C*ln(t2/t1)
- Wed Jan 24, 2018 4:00 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Boltzmann's Equation in relation to temperature
- Replies: 4
- Views: 474
Re: Boltzmann's Equation in relation to temperature
Boltzmann's equation works when the change in internal energy of the system is 0. So, if you were to change temperature, that would change the internal energy. What is possible though to find the entropy at two different energies and subtract them from eachother
- Wed Jan 24, 2018 3:57 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Assuming Temperature
- Replies: 3
- Views: 307
Re: Assuming Temperature
On tests and quizzes, I was told that if we need to assume standard conditions it will be explicitly stated in the problem
- Wed Jan 24, 2018 3:55 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess's Law [ENDORSED]
- Replies: 7
- Views: 882
Re: Hess's Law [ENDORSED]
From what I've seen, we will be given a few steps or reactions and their enthalpy's and the final reaction. Then the question will ask us for the enthalpy change of the final reation.
- Mon Jan 22, 2018 12:20 am
- Forum: General Science Questions
- Topic: Sig Figs
- Replies: 3
- Views: 770
Re: Sig Figs
I remember last quarter the rule was minus one on a test, and minus .5 on a quiz.
- Mon Jan 22, 2018 12:18 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: heat capacity
- Replies: 2
- Views: 375
Re: heat capacity
Molar heat capacity is the "heat required to raise the temp of 1 mole of a substance by one degree kelvin". Specific heat capacity is the "heat required to raise the temperature of 1 gram of a substance by one degree kelvin.
- Mon Jan 22, 2018 12:15 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Positive/Negative Signs in Entropy calculations
- Replies: 1
- Views: 176
Re: Positive/Negative Signs in Entropy calculations
Just to edit what you wrote, Q is positive when the system absorbs energy. The change in entropy depends on whether heat is released or not. Sometimes its best to use your intuition on whether its negative or not. For example, the heat of vaporization (or the change in entropy from liquid to gas) of...
- Tue Jan 16, 2018 11:26 am
- Forum: Phase Changes & Related Calculations
- Topic: enthalpy definition
- Replies: 3
- Views: 587
Re: enthalpy definition
In class, it was defined as "the amount of heat released or absorbed at a constant pressure (qp=delta H). Its also a state property, meaning its value is determined by its current state.
- Tue Jan 16, 2018 11:22 am
- Forum: Phase Changes & Related Calculations
- Topic: Types of Systems
- Replies: 10
- Views: 1449
Re: Types of Systems
an Isolated system can not exchange heat with its surroundings, but a closed system can. Neither system can exchange matter with its surroundings
- Tue Jan 16, 2018 11:20 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Equations and formulas
- Replies: 2
- Views: 216
Re: Equations and formulas
I think there will be much more constants needed in 14B, so he may only post equations
- Tue Dec 05, 2017 10:02 pm
- Forum: Bronsted Acids & Bases
- Topic: When is does a compound act as an acid or base?
- Replies: 1
- Views: 229
Re: When is does a compound act as an acid or base?
H2CO3 is the formula for carbonic acid. It's Ka is higher than 10^-7 so it will act as an acid in water. Its conjugate base is HCO3-, which acts as a base in water. If your not sure whether or not a compound will act as a base or acid, check its Ka/Kb values or determine whether its the conjugate ba...
- Tue Dec 05, 2017 9:56 pm
- Forum: Biological Examples
- Topic: Chemotheraphy Examples [ENDORSED]
- Replies: 3
- Views: 745
Re: Chemotheraphy Examples [ENDORSED]
This was lectured on in class. The chemotherapy drug he referred to was Cisplatin. The long name for this drug is Cis-diamminedichloroplatinum (II), which contrasts with trans-diamminedicholoplatinum because of where the ammine or chloride groups are placed (next to or opposite of one another). Cisp...
- Sun Dec 03, 2017 3:08 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: strength
- Replies: 2
- Views: 407
Re: strength
There are a few ways to tell. Strong acids and bases have extremely high K values for the chemical reaction of their disassociation in water. There are patterns too related to these higher K values (meaning very little product was left behind). Metal hydroxides tend to be strong bases (metal +hydrox...
- Sun Dec 03, 2017 3:02 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Dipole Moments
- Replies: 2
- Views: 392
Re: Dipole Moments
If the difference in electronegativity is greater, the dipole moment will be stronger.
- Mon Nov 27, 2017 7:31 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Reaction constant
- Replies: 4
- Views: 764
Re: Reaction constant
the problem will usually call it just K, and depending on what other values they give you in the problem, those will determine whether it is referring to Kc and Kp. The importance i think is to know the difference between the two.
- Mon Nov 27, 2017 7:29 am
- Forum: Hybridization
- Topic: Do pi bonds only form with double/triple bonds?
- Replies: 5
- Views: 712
Re: Do pi bonds only form with double/triple bonds?
yes, make sure to know that a triple bond has two pi bonds but a double bond only has one.
- Mon Nov 20, 2017 1:32 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Why do lone pairs take up more space than bonds?
- Replies: 5
- Views: 11722
Re: Why do lone pairs take up more space than bonds?
protons are positively charged and attract electrons, but electrons are negatively charged and repulse other electrons. A lone pair causes an area of high electron density and causes distortions due to the electron-electron distortion. They don't take up more space, they just have a stronger negativ...
- Mon Nov 20, 2017 1:28 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Number of Ligands
- Replies: 2
- Views: 350
Re: Number of Ligands
Count the functional groups (ions or molecules) attached to the central atom. This is the number of ligands you have
- Sun Nov 12, 2017 11:27 pm
- Forum: Lewis Structures
- Topic: Atomic Structure of HOCO
- Replies: 2
- Views: 398
Re: Atomic Structure of HOCO
It was a radical. If you added up the valence electrons it had an odd number. HOCO does not have a charge so all the formal charges had to add up to zero. The way to make this happen is to have the carbon double bond to one oxygen, and single bond to another (this oxygen is bonded to the hydrogen). ...
- Sun Nov 12, 2017 11:16 pm
- Forum: Octet Exceptions
- Topic: Expanded Octet
- Replies: 4
- Views: 628
Re: Expanded Octet
First you need to check if the element can have an expanded octet. It should be in period three or higher (P, S, Cl, etc). If expanding the octet allows all the formal charges to become zero/ it forms a more stable molecule, than do it. Sometimes its obvious to do if there are 6 peripheral atoms and...
- Sun Nov 05, 2017 4:48 pm
- Forum: Lewis Structures
- Topic: Taking into Account Shape and Structure
- Replies: 2
- Views: 480
Re: Taking into Account Shape and Structure
You need to understand resonance but I dont think new material from the most recent lecture will be on the midterm.
- Sun Nov 05, 2017 4:42 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg Post-Module #18 [ENDORSED]
- Replies: 2
- Views: 608
Re: Heisenberg Post-Module #18 [ENDORSED]
Normally, the problem will give you an atomic radius and you have to multiply by two to get the diameter (which becomes the uncertainty in position). But, this problem directly tells you that the uncertainty is just 1 % the radius, so there is no need to multiply by two and use the diameter. Try mul...
- Tue Oct 24, 2017 11:50 am
- Forum: Einstein Equation
- Topic: Comparing E=pc and E=.5mv^2
- Replies: 3
- Views: 614
Re: Comparing E=pc and E=.5mv^2
E=0.5mv^2 is the generic physics equation for kinetic energy. It really depends on what variables you are already given when you decide which formula to use. When discussing the photoelectric effect, it is more common to use the Kinetic energy equation.
- Tue Oct 24, 2017 11:28 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: p-orbitals
- Replies: 3
- Views: 421
Re: p-orbitals
We did that to the P orbital to demonstrate Hunds rule. Simply writing a superscript (3) after the P doesn't really show that each electron occupies its own orbital
- Tue Oct 24, 2017 11:26 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: 3d and 4s
- Replies: 5
- Views: 1404
Re: 3d and 4s
The only two exceptions where the d orbital will first (that we know of in class up to this point) are chromium and copper. Other than those exceptions, the 4s will fill first than the 3d orbital.
- Tue Oct 24, 2017 11:23 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: f-block
- Replies: 3
- Views: 524
Re: f-block
The f block is a series of elements that would enter between group three and group four. The reason these elements are in the f block is because one or more of their outermost electrons is in the f orbital. If you were add the f block elements to the periodic table, it would expand in width.
- Sun Oct 15, 2017 3:33 pm
- Forum: Properties of Light
- Topic: Problem 1.55 part A
- Replies: 1
- Views: 427
Re: Problem 1.55 part A
the method you used to solve the problem works too, the problem is difficult because concerting cm^-1 to m^-1 is tricky. you have to multiply the 3600 cm^-1 by (100 cm/1 m) so that the centimeters cancel and you are left with meters in the denominator. This should give you the answer in the solution...
- Sun Oct 15, 2017 3:21 pm
- Forum: Properties of Light
- Topic: 1.21- understanding how light acts as a wave
- Replies: 2
- Views: 414
Re: 1.21- understanding how light acts as a wave
The photoelectric effect shows that light has properties of particles. In the experiment, they would shoot photons at certain pieces of metal, but if the photon did not reach the threshold energy, than no electron was ejected. They tested that same light (with the same frequency/wavelength), but the...
- Fri Oct 06, 2017 11:20 pm
- Forum: Balancing Chemical Reactions
- Topic: What’s the quickest way to approaching writing a balanced equation with only one given compound?
- Replies: 3
- Views: 440
Re: What’s the quickest way to approaching writing a balanced equation with only one given compound?
When balancing a combustion equation, try to start by balancing the carbon and hydrogen on the product side to match the reactants. Since its a combustion, you can always add more to the O2 (reactant) to balance it.
- Fri Oct 06, 2017 11:15 pm
- Forum: Balancing Chemical Reactions
- Topic: Net Moles Produced [ENDORSED]
- Replies: 5
- Views: 872
Re: Net Moles Produced [ENDORSED]
A trick to problems like these is to add the coefficients of the reactants and subtract that value from the sum of the coefficients of products. Make sure to balance the chemical equation first