Search found 52 matches
- Thu Mar 15, 2018 4:56 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: isolated system after time
- Replies: 2
- Views: 483
Re: isolated system after time
The change in internal energy (delta U) for an isolated system is always 0 because no work is done on/by the system and no heat leaves/enters the system.
- Thu Mar 15, 2018 4:50 pm
- Forum: *Enzyme Kinetics
- Topic: Catalysts and Intermediates
- Replies: 5
- Views: 1169
Re: Catalysts and Intermediates
Catalysts are usually part of the original reactants. They are not formed in one of the reactions, like intermediates are.
- Thu Mar 15, 2018 4:45 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: 15.49
- Replies: 4
- Views: 651
Re: 15.49
The rate law for each individual step is just the rate constant times the reactant concentrations for the reactants (including intermediates) in that particular equation.
- Fri Mar 09, 2018 1:53 pm
- Forum: Second Order Reactions
- Topic: Units [ENDORSED]
- Replies: 5
- Views: 820
Re: Units [ENDORSED]
The units for the rate constant changes depending on the order of reaction, but the rate itself is always in mol/(L*s).
- Fri Mar 09, 2018 1:52 pm
- Forum: General Rate Laws
- Topic: 15.13
- Replies: 4
- Views: 631
Re: 15.13
Both gases are distributed throughout the 0.75 L container, so you use that volume for both H2 and I2.
- Fri Mar 09, 2018 1:50 pm
- Forum: First Order Reactions
- Topic: Help on 15.3
- Replies: 7
- Views: 1027
Re: Help on 15.3
Rate is expressed as change in concentration over time, so the units are mol/(L*s).
- Thu Mar 01, 2018 1:57 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: 15.9
- Replies: 3
- Views: 535
Re: 15.9
Rate is always expressed in mol/(L*s), so k changes units depending on the order of the reaction.
- Thu Mar 01, 2018 1:52 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Overall order
- Replies: 4
- Views: 773
Re: Overall order
The overall order of a reaction can be different from the order of the individual reactants. For example, a reaction may be first order with respect to X and first order with respect to Y. Even though the reactions are first order with respect to individual reactants, the overall order is second ord...
- Thu Feb 22, 2018 6:33 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Galvanic vs. Electrolytic Cell
- Replies: 3
- Views: 484
Re: Galvanic vs. Electrolytic Cell
Galvanic cells have spontaneous reactions, while electrolytic cells have nonspontaneous reactions.
- Thu Feb 22, 2018 6:24 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: What other elements could be used besides Pt?
- Replies: 5
- Views: 697
Re: What other elements could be used besides Pt?
Carbon in graphite form can be used as well.
- Thu Feb 22, 2018 6:21 pm
- Forum: Balancing Redox Reactions
- Topic: Half Reaction Order
- Replies: 9
- Views: 2817
Re: Half Reaction Order
The placement of the arrow indicates whether oxidation or reduction occurs, so it is important. If it is Zn2+ + 2e- --> Zn, it is reduction since the zinc cation gains electrons. If it is Zn --> Zn2+ + 2e-, it is oxidation since zinc loses electrons.
- Fri Feb 16, 2018 2:26 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Magnitude
- Replies: 2
- Views: 409
Re: Magnitude
Magnitude would refer to the distance from zero. For example, -5 and 5 are the same magnitude. However, -6 is a greater distance from 0 than +4, so the magnitude is greater.
- Fri Feb 16, 2018 2:24 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Water in cell diagram
- Replies: 3
- Views: 436
Re: Water in cell diagram
It is assumed that the cations and anions involved in the half reactions are in aqueous solution, so water doesn't need to be explicitly written.
- Fri Feb 16, 2018 2:12 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing redox rxns [ENDORSED]
- Replies: 7
- Views: 930
Re: Balancing redox rxns [ENDORSED]
You just need to balance it so that the electrons that are transferred cancel out between the two half reactions.
- Thu Feb 08, 2018 10:26 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Temperature and Spontaneity
- Replies: 2
- Views: 388
Re: Temperature and Spontaneity
If both delta H and delta S are negative, the reaction is only spontaneous at low temperatures since the T delta S part of the equation will be overall positive. In order for a reaction to be spontaneous, then, the negative delta H needs to be of larger magnitude than the positive T delta S so that ...
- Thu Feb 08, 2018 9:58 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: delta G formation
- Replies: 2
- Views: 433
Re: delta G formation
Since the hydrogen gas is still the same substance, the entropy will not change.
- Thu Feb 08, 2018 9:55 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: delta G=0
- Replies: 6
- Views: 1484
Re: delta G=0
Either delta H and delta S are 0, indicating that no reaction occurred, or delta H = T delta S and they cancel out.
- Thu Feb 01, 2018 2:58 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Entropy Change factors
- Replies: 6
- Views: 780
Re: Entropy Change factors
More complex molecules can occupy more microstates so the entropy values are higher.
- Thu Feb 01, 2018 2:56 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: DeltaS= q(rev)/T
- Replies: 1
- Views: 223
Re: DeltaS= q(rev)/T
Most biological processes are irreversible. In thermodynamics, though, systems are often approximated as reversible and the assumption that the pressure inside and outside the system is the same is made.
- Thu Feb 01, 2018 2:47 pm
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: 9.23 Determining what has higher entropy state
- Replies: 4
- Views: 640
Re: 9.23 Determining what has higher entropy state
Because COF2 has more microstates, its degeneracy is higher. The different atoms in COF2 can take more positions than the identical atoms in BF3 so it is at a higher entropy state.
- Thu Jan 25, 2018 2:51 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Formation of a Cation from an Atom
- Replies: 3
- Views: 1204
Re: Formation of a Cation from an Atom
It is endothermic because it takes energy to break bonds and remove electrons from the atom. Forming cations is always endothermic.
- Thu Jan 25, 2018 2:45 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Confusion about entropy formula
- Replies: 6
- Views: 579
Re: Confusion about entropy formula
Reversible reactions occur when a system is in thermodynamic equilibrium with its surroundings, while this is not true for irreversible reactions.
- Thu Jan 25, 2018 2:40 pm
- Forum: Calculating Work of Expansion
- Topic: Irreversible Expansion
- Replies: 3
- Views: 537
Re: Irreversible Expansion
Irreversible expansion is irreversible because pressure is reduced much more quickly than in a reversible reaction, where the pressure changes very slowly and maximum work is done. In irreversible processes, the system is not in thermodynamic equilibrium the entire time while in reversible processes...
- Fri Jan 19, 2018 1:39 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: q and delta H interchangeable in calculations?
- Replies: 4
- Views: 2415
Re: q and delta H interchangeable in calculations?
They are equivalent only under certain conditions, in this case at constant pressure.
- Fri Jan 19, 2018 1:37 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Internal Energy
- Replies: 4
- Views: 525
Re: Internal Energy
However, when no expansion work is done, the change in internal energy is equal to the change in enthalpy.
- Fri Jan 19, 2018 1:27 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: W=-(Pex)(deltaV)
- Replies: 5
- Views: 1524
Re: W=-(Pex)(deltaV)
As the volume increases and the system expands, energy is lost as work so there is a negative sign.
- Fri Jan 12, 2018 3:00 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: 8.25
- Replies: 1
- Views: 179
8.25
A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q =3.50 kJ), resulting in a temperature rise of 7.32 'C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(aq) were mi...
- Fri Jan 12, 2018 2:55 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Question 8.3
- Replies: 2
- Views: 250
Re: Question 8.3
Since the question noted that there was an inner diameter, you can assume that it is referring to a cylinder.
- Sat Dec 09, 2017 8:41 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: 12.23 [ENDORSED]
- Replies: 7
- Views: 1195
Re: 12.23 [ENDORSED]
The equilibrium constant K changes with temperature so Kw is 10^-14 only at 25 degrees Celsius.
- Sat Dec 09, 2017 8:00 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Relationship between pH, protanation and molarity
- Replies: 5
- Views: 824
Re: Relationship between pH, protanation and molarity
You use the molarity of H30+ and OH- to find the pH and pOH by taking the -log of each.
-log[H30+]=pH
-log[OH-]=pOH
-log[H30+]=pH
-log[OH-]=pOH
- Sat Dec 09, 2017 7:56 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Direction of the equilibrium
- Replies: 2
- Views: 490
Re: Direction of the equilibrium
Usually only the reactants have concentrations since none of the products have been formed yet (Q=0) so the reaction proceeds to the products. If the initial product concentrations are also given, it's not a bad idea to check Q to see which direction the reaction proceeds.
- Sun Dec 03, 2017 10:28 pm
- Forum: Bronsted Acids & Bases
- Topic: Acid and base reactions in water
- Replies: 1
- Views: 330
Re: Acid and base reactions in water
Yes, because a Bronsted acid is a proton donor so water gains a proton.
- Fri Dec 01, 2017 10:23 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Table 11.2 [ENDORSED]
- Replies: 1
- Views: 341
Table 11.2 [ENDORSED]
In Table 11.2, it lists values of K and Kc for various chemical equilibrium reactions. For top half of the table, the values of K and Kc are the same for each reaction (ex: K=4.0x10^31 and Kc=4.0x10^31), but for the second half of the table, K and Kc are different for each reaction (ex: K=3.0x10^-11...
- Sun Nov 26, 2017 11:30 pm
- Forum: Ideal Gases
- Topic: 11.7 Part C
- Replies: 2
- Views: 433
Re: 11.7 Part C
They only gave the overall pressure of the flask so in order to determine the partial pressures of X2 and X, you need to figure out the percentage of the total pressure for X2 and X. This is done by counting the number of molecules of X2 and X. Out of the 17 molecules in the flask, 12 were X and 5 w...
- Sun Nov 26, 2017 11:26 pm
- Forum: Naming
- Topic: Oxidation Numbers
- Replies: 2
- Views: 359
Re: Oxidation Numbers
The oxidation number refers to the charge of the ion. You determine the oxidation number by comparing the overall charge of the compound to the charges of anions within the compound in order to determine the charge on the transition metal cation.
Q. 37C
With the help of Table 17.4, determine the coordination
number of the metal ion in each of the following complexes:
[PtCl2(en)2]2+
How do we know that en (ethylenediamine) is bidentate?
number of the metal ion in each of the following complexes:
[PtCl2(en)2]2+
How do we know that en (ethylenediamine) is bidentate?
Re: Naming
It is named ferrate because it is an anion within a coordination compound.
- Sun Nov 19, 2017 8:31 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 180degrees and lone pairs?
- Replies: 4
- Views: 597
Re: 180degrees and lone pairs?
It could be trigonal bipyramidal with 3 lone pairs and a 180 degree bond angle.
- Tue Nov 07, 2017 9:00 pm
- Forum: Resonance Structures
- Topic: Delocalized electrons
- Replies: 4
- Views: 630
Re: Delocalized electrons
Delocalization occurs when there is resonance. For example, if there are two resonance structures--one with a single bond between 2 atoms and one with a double bond between two atoms, there won't be exactly 2 or 4 electrons bonded in that area. The electrons aren't specifically associated with these...
- Tue Nov 07, 2017 8:26 pm
- Forum: Lewis Structures
- Topic: 3.97
- Replies: 2
- Views: 331
Re: 3.97
It has to be drawn this way since there is a tetrahedral structure to the molecule. Each phosphorus atom is connected to all 3 of the other phosphorus atoms, but this is hard to convey using a 2D Lewis structure.
- Sat Nov 04, 2017 11:02 am
- Forum: Octet Exceptions
- Topic: Exercise 3.59 - Question on Radicals
- Replies: 3
- Views: 532
Re: Exercise 3.59 - Question on Radicals
It would make sense for the unpaired electron to be on the atom with lower electronegativity since the atom with higher electronegativity has a stronger pull on the electrons and is more likely to fulfill its octet.
- Sat Nov 04, 2017 10:56 am
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Sigma and Pi Bonds
- Replies: 3
- Views: 613
Re: Sigma and Pi Bonds
Sigma bonds are the first covalent bonds that atoms can make. Since it is a covalent bond, the electrons are shared. If two atoms have a single covalent bond, it's a sigma bond. When they have double bonds, there is a sigma and a pi bond, and both types of bonds share electrons between the atoms.
- Sun Oct 29, 2017 7:53 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ionization Energy [ENDORSED]
- Replies: 5
- Views: 752
Re: Ionization Energy [ENDORSED]
The second ionization energy is also higher than the first because there is less shielding.
- Sun Oct 29, 2017 7:50 pm
- Forum: Coordinate Covalent Bonds
- Topic: Chapter 3 Question 51
- Replies: 1
- Views: 522
Chapter 3 Question 51
Hypochlorous acid, HClO, is found in white blood cells, where it helps to destroy bacteria. Write two Lewis structures with different atom arrangements for HClO and select the most likely structure by identifying the structure with formal charges closest to zero. Consider only structures with single...
- Sun Oct 22, 2017 7:28 pm
- Forum: Ionic & Covalent Bonds
- Topic: Chemical formula?
- Replies: 5
- Views: 689
Re: Chemical formula?
The Roman numerals refer to the charge on that atom. In this case, chromium has a +3 charge so you know how to write the formula for a neutral molecule.
- Sun Oct 22, 2017 7:16 pm
- Forum: Ionic & Covalent Bonds
- Topic: covalent bond
- Replies: 7
- Views: 1079
Re: covalent bond
Yes, one bond can only involve two atoms. However, one atom can have more than two bonds.
- Fri Oct 13, 2017 5:31 pm
- Forum: Properties of Light
- Topic: Velocity [ENDORSED]
- Replies: 13
- Views: 1550
Re: Velocity [ENDORSED]
I went to Dr. Lavelle's office hours today and learned that De Broglie's equation cannot be applied to light or electromagnetic radiation. It can only be applied to particles with rest mass, like electrons, so you can't use the speed of light in De Broglie's equation.
- Fri Oct 13, 2017 5:08 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Example Shown During Lecture
- Replies: 2
- Views: 447
Re: Example Shown During Lecture
You're allowed to use the Rydberg equation if you know how it works. Like Tess said, he showed us the other method because it is more easily explainable.
- Sun Oct 08, 2017 6:34 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Spectra Post-Assessment Q. 29 [ENDORSED]
- Replies: 2
- Views: 455
Atomic Spectra Post-Assessment Q. 29 [ENDORSED]
In 1.0 s, a 60 W bulb emits 11 J of energy in the form of infrared radiation (heat) of wavelength 1850 nm. What is the energy per photon of light emitted? How many photons of infrared radiation does the lamp generate in 1.0 s? I understand how to find the energy per photon (1.074 x 10-19 J), but how...
- Sun Oct 08, 2017 6:25 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Spectra Post-Module Assessment Q. 20 [ENDORSED]
- Replies: 2
- Views: 403
Re: Atomic Spectra Post-Module Assessment Q. 20 [ENDORSED]
Each photon excites an electron to a higher level, so 1 million photons excites 1 million electrons (there is more than one hydrogen atom in the sample).
- Thu Oct 05, 2017 11:25 am
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: E.29 part b HELP
- Replies: 3
- Views: 452
Re: E.29 part b HELP
The number of moles of Cl- ions is different than the moles of CuCl2, so you use a stoichiometric ratio (2 mol Cl-/1 mol CuCl2) to get the correct moles of Cl- ions.
- Tue Oct 03, 2017 11:17 pm
- Forum: Balancing Chemical Reactions
- Topic: Nitrogen
- Replies: 5
- Views: 716
Nitrogen
When a problem states that nitrogen is formed, can we always assume that the product is gaseous nitrogen (N2)?