Search found 60 matches
- Sun Mar 10, 2019 11:12 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: 15.13 b) Doubling H2 concentration
- Replies: 1
- Views: 245
Re: 15.13 b) Doubling H2 concentration
Yes, the rate will increase by a factor of 2 if the concentration of H2 is doubled because the reaction is first order to both of the reactants, meaning they are directly proportional.
- Sun Mar 10, 2019 11:10 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Units of k
- Replies: 7
- Views: 1015
Re: Units of k
Since rate=k*(concentration)^power of reaction, and we know that the units of rate are always mol.L-1.s-1, and that sometimes the concentration is to the zero, first, or second power depending on the order of the reaction, then the units of k must change.
- Sun Mar 10, 2019 11:08 pm
- Forum: First Order Reactions
- Topic: pseudo vs 2nd order
- Replies: 4
- Views: 637
Re: pseudo vs 2nd order
It is appropriate to use pseudo-first order rate law when all reactant concentrations are changing, making the reaction very difficult to study. In this case, we make one reactant concentration small and the others large so that the reaction rate is dependent on only one reactant.
- Tue Mar 05, 2019 2:51 pm
- Forum: First Order Reactions
- Topic: First order graph
- Replies: 7
- Views: 845
First order graph
When graphing a first order reaction, with time on the x-axis and ln(A) on the y-axis, the y-intercept is the natural log of the initial concentration of the reactant, but what does the x-intercept of this graph represent?
- Tue Mar 05, 2019 2:48 pm
- Forum: First Order Reactions
- Topic: Rate constant and half life
- Replies: 3
- Views: 430
Rate constant and half life
Why does a higher rate constant mean a shorter half life?
- Tue Mar 05, 2019 2:45 pm
- Forum: First Order Reactions
- Topic: Radioactive Decay
- Replies: 3
- Views: 335
Radioactive Decay
How do we know that radioactive decay is a first order reaction?
- Tue Feb 26, 2019 11:37 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy Vs. Other energies
- Replies: 1
- Views: 161
Gibbs Free Energy Vs. Other energies
How does Gibb's free energy compare to other energies like potential energy, internal energy, or kinetic energy? Can it be any of these types of energies or does it differ in some way?
- Tue Feb 26, 2019 11:32 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Stoichiometric Coefficients in Cell Diagrams
- Replies: 2
- Views: 222
Re: Stoichiometric Coefficients in Cell Diagrams
No, just the elements or molecules are included in the cell diagrams to keep them easy to read.
- Tue Feb 26, 2019 11:31 pm
- Forum: Balancing Redox Reactions
- Topic: basic/acidic solutions
- Replies: 5
- Views: 538
Re: basic/acidic solutions
Usually, the problem will say that the reaction occurs in an acidic or basic solution if no H+ or OH- is already in the equation.
- Fri Feb 22, 2019 1:00 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Equations of delta G
- Replies: 4
- Views: 507
Re: Equations of delta G
It is also important to note that you might get slightly different answers when using the two different methods due to rounding differences since you are using a table of information for one and information given in the problem for the other.
- Fri Feb 22, 2019 12:58 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: 4J.7) 7th edition of the textbook
- Replies: 2
- Views: 325
Re: 4J.7) 7th edition of the textbook
It makes sense that you do not include elements like F2 and O2 in the enthalpy of formation equation because these diatomic molecules are already in their most stable form so it does not take any energy to get them into their most stable form.
- Fri Feb 22, 2019 12:56 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: 6th Ed. 9.65
- Replies: 1
- Views: 223
Re: 6th Ed. 9.65
To solve using Gibb's free energy, you find the Gibb's energy of formation for each molecule. If the energy is positive, then that means the elements are unstable and if the energy is negative, then that means the elements are stable.
- Thu Feb 14, 2019 9:11 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Isothermal and Free Expansion
- Replies: 2
- Views: 369
Re: Isothermal and Free Expansion
Isothermal is when the temperature stays constant and free expansion is when a gas is allowed to expand without any constraints.
- Thu Feb 14, 2019 9:04 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: ΔU = 0?
- Replies: 4
- Views: 979
Re: ΔU = 0?
Yes, since deltaU is equal to 3/2nRT, if deltaU is zero then T must be zero and the pathway is isothermal.
- Thu Feb 14, 2019 9:00 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kp equilibrium constant
- Replies: 6
- Views: 1604
Kp equilibrium constant
When calculating the equilibrium constant using pressure, do you have to convert to atmosphere or do units not matter?
- Wed Feb 06, 2019 11:07 pm
- Forum: Calculating Work of Expansion
- Topic: Temperature in Work Equations
- Replies: 3
- Views: 449
Temperature in Work Equations
For the equation W=-nRTlnV2/V1, if the temperature stays constant, why is it included in the equation but for the other work equation W=-PdeltaV if the temperature changes along the pathway, why is temperature not included in the equation?
- Wed Feb 06, 2019 11:03 pm
- Forum: Phase Changes & Related Calculations
- Topic: Problem 4B.1) 7th edition
- Replies: 2
- Views: 292
Re: Problem 4B.1) 7th edition
Yes, the work is positive because work is being done on the system and not by the system, so the system gains energy.
- Wed Feb 06, 2019 11:01 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: w=-PdeltaV
- Replies: 6
- Views: 580
Re: w=-PdeltaV
Use the equation W=-PdeltaV for a sudden irreversible expansion when work is done against a constant external pressure and temperature changes - less work is done for this pathway. Ue the other work equation for a reversible expansion, when temperature is constant, external pressure is not constant,...
- Thu Jan 31, 2019 10:33 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Change in internal energy equation
- Replies: 2
- Views: 353
Change in internal energy equation
When calculating the change in internal energy of a system, I know you can use the equation q=C*deltaT. Why is mass or moles not included in this equation? Are there other equations that can be used?
- Thu Jan 31, 2019 10:27 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard enthalpy
- Replies: 1
- Views: 225
Re: Standard enthalpy
The standard enthalpy of formation of an element in its most stable form is zero because the definition of standard enthalpy of formation is how much energy it takes to form a given molecule under standard conditions. If an element already exists in its most stable form, nothing has to form, so stan...
- Thu Jan 31, 2019 10:16 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase change and temperature
- Replies: 3
- Views: 372
Re: Phase change and temperature
All of the energy used in a phase change is used to break or form the bonds, and none of it to speed up the kinetic energy of the molecules or increase the temperature.
- Tue Jan 22, 2019 10:33 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kp
- Replies: 3
- Views: 358
Re: Kp
I have noticed that most answers tend to be in bar. Since Kp is a ratio, the units do not matter, but just make sure all the numbers in the calculation are in the same units.
- Tue Jan 22, 2019 10:30 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: ice chart
- Replies: 7
- Views: 863
Re: ice chart
I think the main reason for using an ice chart would be that you are given a weak acid. If you are given a strong acid, there is no need to use one because we can assume that the acid completely dissociates. For a weak acid, on the other hand, it only partially dissociates, which is where an ice cha...
- Tue Jan 22, 2019 10:16 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Weak vs Strong Acid and Bases
- Replies: 2
- Views: 222
Re: Weak vs Strong Acid and Bases
When calculating the pH of a strong acid, you assume all of it dissociates, so however many moles of acid you have is the amount of moles of H30+ is. You would use the log equation to find pH from there. If you are given a weak base, all of it does not dissociate, so you would have to use an ice tab...
- Wed Jan 16, 2019 11:44 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Question 5I.13 part b
- Replies: 1
- Views: 246
Question 5I.13 part b
For the question 5I.13 part b in the 7th edition, it asks, if 2.0 mmol F2 was placed into the reaction vessel instead of chlorine, what would its equilibrium composition at 1000. K? I am assuming you use an ICE table to solve for the concentrations, yet I keep getting an answer that is slightly off ...
- Wed Jan 16, 2019 11:39 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Le Chatelier's Principle
- Replies: 11
- Views: 1508
Re: Le Chatelier's Principle
I also think it is important to consider the fact that your solution depends on if pressure is increased by decreasing the volume of the container, or adding an inert gas.
- Wed Jan 16, 2019 11:35 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Question 11.35 6th edition
- Replies: 2
- Views: 321
Re: Question 11.35 6th edition
I'm pretty sure you would find Ka by doing 10^-2.12, which would give you 0.0076, a reasonable value.
- Thu Jan 10, 2019 9:46 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Clarification from lecture 1 - Jan 7th
- Replies: 3
- Views: 265
Re: Clarification from lecture 1 - Jan 7th
When you are finding the equilibrium constant of the reverse reaction, you simply take the inverse of the equilibrium constant for the forward reaction.
- Thu Jan 10, 2019 9:30 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Definition of equilibrium
- Replies: 4
- Views: 203
Re: Definition of equilibrium
In addition to this, a system reaches equilibrium when the forward and reverse reaction rates are equal.
- Thu Jan 10, 2019 9:27 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Liquids and Solids in Equilibrium Constants
- Replies: 5
- Views: 351
Liquids and Solids in Equilibrium Constants
I know that we do not include solids and liquids when calculating the equilibrium constant because they do not have concentrations, but even if they do not have concentrations, don't they still affect the equilibrium?
- Wed Dec 05, 2018 8:41 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Focus 9C.3 Part d
- Replies: 3
- Views: 417
Re: Focus 9C.3 Part d
I was confused by this too. I think the alphabetical rule only applies when you are naming the complex, not writing its formula, so I think the ligand can be in any order. In terms of the parentheses, I am not completely sure - maybe to make the complex name easier to read?
- Wed Dec 05, 2018 8:38 pm
- Forum: Conjugate Acids & Bases
- Topic: Neutralization Reactions
- Replies: 6
- Views: 946
Re: Neutralization Reactions
I think you are referring to problem 7 in Fundamentals J. A neutralization reaction is an acid and base reacting to form a salt and water. If we are given the salt and know that water is always produced, we just have to find the two reactants. For part A, for instance, we are given the salt KBr and ...
- Wed Dec 05, 2018 8:32 pm
- Forum: Bronsted Acids & Bases
- Topic: Bronsted Versus Lewis
- Replies: 4
- Views: 467
Bronsted Versus Lewis
I remember Professor Lavelle mentioning that either Bronsted or Lewis is a more general classification meaning that all acids and bases are one thing but not necessarily the other. Which term is more general, Bronsted or Lewis?
- Mon Nov 26, 2018 8:13 pm
- Forum: Sigma & Pi Bonds
- Topic: Homework 2F.3 7th Edition Part B
- Replies: 1
- Views: 165
Homework 2F.3 7th Edition Part B
For Homework problem 2F.3 7th Edition Part B we were asked to state the number of sigma and pi bonds for the molecule SO2. The answer I got was that there should be 2 sigma and 2 pi bonds. However, the first answer in the book is 2 sigma bonds and 1 pi bond. I do not understand how this would be pos...
- Mon Nov 26, 2018 8:05 pm
- Forum: Sigma & Pi Bonds
- Topic: the orbitals
- Replies: 1
- Views: 242
Re: the orbitals
A sigma bond is formed by two orbitals, each with one electron that interacts end to end. A pi bond on the other hand, is also formed by two orbitals, each with one electron that overlap side-by-side. Therefore the difference between a sigma and pi bond is that a sigma aligns end to end, while a pi ...
- Mon Nov 26, 2018 7:42 pm
- Forum: Hybridization
- Topic: s-character and bond angle, question 2F15 7th edition
- Replies: 1
- Views: 353
s-character and bond angle, question 2F15 7th edition
Question 2F15 in the 7th edition asks: do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased? The answer is: as the s-character of hybrid orbital increases, the bond angle increases. I do not know how to approach this question...
- Sun Nov 25, 2018 10:16 pm
- Forum: Sigma & Pi Bonds
- Topic: sigma and pi bond diagrams
- Replies: 1
- Views: 220
sigma and pi bond diagrams
In class we were shown a diagram of s-s orbital overlap, s-p orbital overlap, and p-p orbital overlap. I am wondering if these visuals are simply conceptual to try to get us to understand the concept or if this is actually the configuration in an atom?
- Sun Nov 25, 2018 10:12 pm
- Forum: Hybridization
- Topic: pi bond breaking
- Replies: 1
- Views: 130
pi bond breaking
I am aware that a pi bond, unlike a sigma bond, cannot rotate and if a pi bond does try to rotate the bond breaks. What are the biological implications of a pi bond breaking in our bodies?
- Sun Nov 25, 2018 10:10 pm
- Forum: Hybridization
- Topic: regions of electron density and double bonds
- Replies: 2
- Views: 270
regions of electron density and double bonds
When finding the regions of electron density in order to determine the hybridization why do both single and double bonds count as one region of electron density? Wouldn't the single versus double bond alter the hybridization?
- Mon Nov 12, 2018 11:27 pm
- Forum: Bond Lengths & Energies
- Topic: Induced dipole interation
- Replies: 2
- Views: 327
Re: Induced dipole interation
Also it is important to note that there can be dipole induced-dipole interactions and induced dipole-induced dipole interactions. Dipole induced-dipole interactions require a dipole to be present and an induced dipole-induced dipole are always present because atoms will always have electrons that ca...
- Mon Nov 12, 2018 11:19 pm
- Forum: Bond Lengths & Energies
- Topic: Covalent radii
- Replies: 2
- Views: 361
Covalent radii
Covalent radii, to my understanding, is the covalent bond length which is the sum of the two atom's radii. Isn't this assuming that there is no space between the atoms in the bond or is it just that the space is negligible?
- Mon Nov 12, 2018 10:51 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Tetrahedral versus Trigonal Pyramidal
- Replies: 3
- Views: 371
Tetrahedral versus Trigonal Pyramidal
Why does a tetrahedral have bond angles of 109.5 degrees while a trigonal pyramidal have bond angles of less than 109.5 degrees. Is it because the lone pair on the trigonal pyramidal is closer to the central atom and pushes the other atoms closer together?
- Fri Nov 09, 2018 11:38 am
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Hydrogen Bonding versus other Intermolecular forces
- Replies: 2
- Views: 306
Hydrogen Bonding versus other Intermolecular forces
How does the attractive force related to hydrogen bonding compare to that of other intermolecular forces (ion-ion, ion-dipole, dipole-dipole, dipole induced dipole) and why?
- Fri Nov 09, 2018 11:29 am
- Forum: Dipole Moments
- Topic: Attractive Force
- Replies: 3
- Views: 189
Re: Attractive Force
Although I agree with the point mentioned above, it is also important to think about the size of the atom. The larger the atom or the more energy levels it has, the farther the atom will be from the atom it is bonded to. Since the distance between the two atoms will be larger, the bond will be weaker.
- Fri Nov 09, 2018 11:23 am
- Forum: Ionic & Covalent Bonds
- Topic: Polarizability
- Replies: 9
- Views: 842
Re: Polarizability
In addition to this, I believe that the more polarizable an atom is, the stronger the bond it will form with another atom.
- Thu Nov 01, 2018 9:03 pm
- Forum: Bond Lengths & Energies
- Topic: 2.25 Homework Problem
- Replies: 4
- Views: 896
2.25 Homework Problem
The question is: Which bond is longer: the NF bond in NF3 or the PF bond in PF3? The PF bond is longer, but why? Is it because P has a larger atomic radius?
- Thu Nov 01, 2018 8:57 pm
- Forum: Student Social/Study Group
- Topic: Bond Length
- Replies: 1
- Views: 210
Re: Bond Length
I believe that to find the bond length you add the atomic radii of each atom that is part of the bond. The atomic radii will usually be provided to you.
- Thu Nov 01, 2018 8:56 pm
- Forum: Lewis Structures
- Topic: 7th edition 2b9
- Replies: 3
- Views: 285
Re: 7th edition 2b9
To find the formal charge of an element, you use the equation V - (L+S/2) where V is the valence electrons, L is the lone electrons, and S is shared electrons.
- Wed Oct 24, 2018 8:37 pm
- Forum: Photoelectric Effect
- Topic: ejecting electrons in quantized energy levels
- Replies: 2
- Views: 371
Re: ejecting electrons in quantized energy levels
I think when you reference quantized energy you are thinking about energy levels in an atom. When the electron absorbs the energy of a photon, it can only jump up to an integer amount of energy levels. If the electron absorbs enough energy to be ejected from the atom, the left over energy (photon en...
- Wed Oct 24, 2018 7:59 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Electron Spin
- Replies: 3
- Views: 246
Re: Electron Spin
I do not think we are required to know whether an electron spin is up or down. I think the only thing to note here is that if two electrons are paired, they have opposite spin. If two electrons are parallel, on the other hand, they have the same spin.
- Wed Oct 24, 2018 7:43 pm
- Forum: *Shrodinger Equation
- Topic: Schrodinger's wave function
- Replies: 2
- Views: 585
Schrodinger's wave function
I am aware that Schrondinger's equation is used to precisely describe the location of an electron within an atom, but why is a wave function used to do this?
- Thu Oct 18, 2018 11:01 pm
- Forum: *Black Body Radiation
- Topic: Black Body [ENDORSED]
- Replies: 4
- Views: 1051
Re: Black Body [ENDORSED]
Black body objects are simply theoretical-in other words, in the real world there does not exist an object that is truly a black body, or absorbs all wavelengths of light.
- Thu Oct 18, 2018 10:29 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Rydberg equation
- Replies: 2
- Views: 305
Re: Rydberg equation
This is simply a convention. A free electron or one that is no longer attracted to the nucleus of an atom can be said to have zero energy. As an electron goes down in energy levels, the energy becomes more negative. That is why there is a negative sign in the Rydberg equation.
- Thu Oct 18, 2018 10:25 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Homework 1E.25
- Replies: 2
- Views: 168
Homework 1E.25
The question is : Give the notation for the valence shell configuration (including the outermost d-electrons) of (a) alkali metals (b) group 15 elements (c) group 5 transition metals (d) the coinage metals (Cu, Ag, Au). I do not understand the format they used for the answers. The answers are: ns^1,...
- Thu Oct 11, 2018 4:28 pm
- Forum: Properties of Electrons
- Topic: bound electrons
- Replies: 2
- Views: 2522
Re: bound electrons
A bound electron is one that is still considered part of the atom and is attracted to the nucleus whereas a free electron is one that absorbed enough energy from photons to completely leave the atom.
- Thu Oct 11, 2018 4:27 pm
- Forum: Photoelectric Effect
- Topic: Empirical Equation
- Replies: 4
- Views: 392
Re: Empirical Equation
The threshold energy differs with each metal used. So for different problems using the same metal, the work function or threshold energy would remain the same.
- Thu Oct 11, 2018 4:25 pm
- Forum: *Black Body Radiation
- Topic: The Importance of Black Body Radiation (?)
- Replies: 5
- Views: 815
Re: The Importance of Black Body Radiation (?)
Although I do not think we need to know much detail on black body radiation, I think it is helpful to know that it is an object that absorbs all wavelengths of light. This is a conceptual idea, and I do not think there actually exists an object that can absorb all wavelengths, just the majority.
- Wed Oct 03, 2018 6:10 pm
- Forum: Empirical & Molecular Formulas
- Topic: Problem F5 (7th Edition)
- Replies: 3
- Views: 2046
Re: Problem F5 (7th Edition)
Yes, that would be your final answer! When finding mass composition of a compound the main steps are to: 1. find the molar mass of the entire compound 2. find the molar mass of each element within the compound 3. divide the molar mass of each element you found in step 2 by the molar mass you found i...
- Wed Oct 03, 2018 6:01 pm
- Forum: Balancing Chemical Reactions
- Topic: Molecules present after Dilution
- Replies: 2
- Views: 343
Re: Molecules present after Dilution
This is how I approached the problem: 1. You are given the molarity (0.10 mol/L) and the starting volume (0.010 L). You can also find the ending volume by using a doubling equation. For this equation you do: 0.010(2^90) which equals 1.24 x 10^25. 2. Now, we can use the equation MV=MV that we used in...
- Wed Oct 03, 2018 5:50 pm
- Forum: Significant Figures
- Topic: Significant Figures
- Replies: 3
- Views: 224
Re: Significant Figures
Also keep in mind the rules for significant figures are different for adding and subtracting versus multiplying and dividing. When you are adding and subtracting, you use the value with the least amount of decimal places (so if you have 14.23+2.9 the answer would have one decimal place). For multipl...