Search found 30 matches
- Wed Mar 09, 2016 2:50 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode Sign
- Replies: 1
- Views: 564
Re: Anode Sign
If you want to add both reactions rather than subtract, then yes you flip the anode sign. This is because you are using reduction potentials, but oxidation is occurring at the anode, which is the reverse reaction of reduction. Therefore, you would have to flip the sign for the reaction occurring at ...
- Wed Mar 09, 2016 2:44 am
- Forum: *Alkenes
- Topic: Bonds As functional groups
- Replies: 2
- Views: 699
Re: Bonds As functional groups
Double and triple bonds are considered functional groups because just like any other functional group, they would get priority in naming (for example, if the numbers 1 and 2 were to be assigned to a double bond and a methyl substituent, then the 1 would be assigned to the double bond because it has ...
- Fri Mar 04, 2016 10:12 am
- Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
- Topic: Cyclohexane problem
- Replies: 1
- Views: 499
Re: Cyclohexane problem
The first thing to look at is which option will give the lowest numbers. In this case, you have two options: you can either use 1,1,2 or 1,2,2. Since it is better to use two 1s rather than two 2s, we go with the first option. The only time you put the lower number with the substituent that comes fir...
- Thu Mar 03, 2016 1:23 am
- Forum: *Organic Reaction Mechanisms in General
- Topic: The position of nucleophile and elctrophile
- Replies: 1
- Views: 498
Re: The position of nucleophile and elctrophile
In this case, yes. The Br must attach to the carbon in the center because it is bound to more carbons, so it is more stable than the carbons on the sides.
- Tue Feb 23, 2016 1:29 pm
- Forum: *Alkanes
- Topic: Naming Clarification
- Replies: 3
- Views: 832
Re: Naming Clarification
The rule that we must use the lowest number to specify which carbon the substituent is attached to is to ensure that there is a uniform way to specify which carbon we are referring to, but the substituents should always be in alphabetical order, regardless of the numbers or prefixes in front of the ...
- Tue Feb 16, 2016 9:56 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Catalyst
- Replies: 1
- Views: 511
Re: Catalyst
A catalyst is a substance that increases the rate of a reaction by lowering the activation energy of a reaction. It does this by binding to the reactants and making it easier for the product to form (by bringing reactants together, orienting the reactants in the correct position to react, or providi...
- Tue Feb 09, 2016 1:04 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Q 14.21
- Replies: 1
- Views: 520
Re: Q 14.21
The first half reaction should be reversed because the Cu^(2+) is being reduced to Cu, and Cr^(2+) should be oxidized to Cr^(3+), which has a reduction potential of -0.41 V (this value can be found in the table). Subtracting the reduction potential of the anode from that of the anode gives 0.34 v -(...
- Thu Feb 04, 2016 8:52 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing Redox Reactions with e-
- Replies: 1
- Views: 418
Re: Balancing Redox Reactions with e-
After you add all the H2O (and H+ or OH-), find the charge on both sides of the reaction. For example, consider the reaction Cl2 + 2H2O --> 2HClO + 2H+ The reactant side has a total charge of 0 (because the Cl2 and H2O are neutral) while the product side has an overall charge of +2 (because of the 2...
- Tue Feb 02, 2016 1:55 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Ecell calculations
- Replies: 2
- Views: 586
Re: Ecell calculations
Changing the stoichiometric coefficients would not change the value for Ecellstandard because it is an intensive property, so it doesn't depend on the amount of substance present. However, if you reverse the chemical equation, then you would have to reverse the sign for Ecellstandard.
- Tue Jan 26, 2016 9:44 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Isothermal and delta U
- Replies: 3
- Views: 931
Re: Isothermal and delta U
Since the temperature does not change, delta T is 0, which makes delta U also equal to 0. This is because if the temperature does not change, the kinetic energy of the molecules doesn't change, so there is no change in internal energy.
- Fri Jan 22, 2016 1:04 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Definition of degeneracy and relationship to entropy
- Replies: 6
- Views: 4415
Re: Definition of degeneracy and relationship to entropy
The equation S=klnW is used to calculate statistical entropy (the entropy associated with large numbers of atoms and molecules). The equation delta S=q/T is used to calculate the thermodynamic entropy. In both cases, increasing the temperature or volume causes an increase in entropy because it would...
- Wed Jan 20, 2016 10:31 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy Equations
- Replies: 2
- Views: 586
Re: Entropy Equations
\Delta S=nRln(V_{2}/V_{1}) is the equation that should be used when there is a change in volume. When there is a change in temperature, use the equation \Delta S=nRln(T_{2}/T_{1}) . The equation \Delta S=q/T should be used when you know the q (or can calculate it) for a reversible p...
- Thu Jan 14, 2016 10:12 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Work
- Replies: 4
- Views: 1016
Re: Work
The negative sign in -PdeltaV must always be used when calculating work (even when work is done on the system). When work is done on the system, the gas will be compressed. This means that the final volume will be less than the initial volume, so the change in volume will be negative. A negative val...
- Fri Jan 08, 2016 12:46 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Using Bond Enthalpies in Calculations
- Replies: 3
- Views: 908
Re: Using Bond Enthalpies in Calculations
The process for calculating the enthalpy change of a reaction using bond enthalpies should not be thought of as enthalpy of reactants - enthalpy of products. Rather, it is the enthalpy needed to break the bonds in the reactants (a positive value) plus the enthalpy released when new bonds are formed ...
- Sat Dec 05, 2015 1:19 am
- Forum: Calculating the pH of Salt Solutions
- Topic: Why is H-H Equation an approximation
- Replies: 2
- Views: 1404
Re: Why is H-H Equation an approximation
When we use the Henderson-Hasselach equation, we assume that the concentration of the acid, [HA] is the initial acid concentration. This is an approximation because a small percentage of the acid is converted to its conjugate base in the reaction HA + H2O --> A- + H3O+. Since we do not use the conce...
- Sun Nov 29, 2015 11:14 pm
- Forum: Properties & Structures of Inorganic & Organic Bases
- Topic: Inductive Effect
- Replies: 2
- Views: 1218
Re: Inductive Effect
The inductive effect can be useful in determining relative acid strength because if there are acids in which the same type of bond is broken when donating the H atom, then the acid that results in the most stable anion is the strongest acid. For example, when comparing CLOH and IOH, the O-H bond is ...
- Tue Nov 24, 2015 11:41 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Why is trichloroacetic acid stronger than acetic acid?
- Replies: 1
- Views: 13413
Re: Why is trichloroacetic acid stronger than acetic acid?
Since the Cl atoms in CCl4COOH are more electronegative than H atoms (in CH3COOH), they pull electron density away from the central carbon atom. This causes the carbon atom to pull electron density from the oxygen in the O-H bond, which weakens the O-H bond. Because the O-H bond is weaker in trichlo...
- Mon Nov 16, 2015 6:02 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homework 11.89 balanced equation
- Replies: 1
- Views: 490
Re: Homework 11.89 balanced equation
If you look at the changes in the partial pressures of A, B, and C, then you can see that A and C changed by 10 kPa while B changed by 5 kPa, so the molar ratio of A:B:C is 2:1:2.
- Mon Nov 16, 2015 5:54 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: stability of atoms/molecules at equilibrium
- Replies: 1
- Views: 475
Re: stability of atoms/molecules at equilibrium
Decomposition reactions that have a small equilibrium constant have reactants that are more thermodynamically stable as compared to molecules with a higher K value for their decomposition reaction. This is because a small K value means that reactants are favored over the products, so it is difficult...
- Sun Nov 15, 2015 12:57 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: #10 from Quiz 3 Prep Fall 2014
- Replies: 1
- Views: 524
Re: #10 from Quiz 3 Prep Fall 2014
Since you are given Kp rather than Kc, you need to find the initial partial pressure of H2O. Use the number of moles of H2O (0.100 mol) and the volume (4.00 L) to solve for the partial pressure of H2O by using the equation PV=nRT. When you do this, the partial pressure of H2O is 2.05 atm, which is a...
- Sun Nov 15, 2015 11:45 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium Constant for Partial Pressure
- Replies: 1
- Views: 535
Re: Equilibrium Constant for Partial Pressure
The partial pressures given in the problem are in kPa. When finding the equilibrium constant, the partial pressures should be in bar. To convert from kPa to bar, you have to divide the partial pressures by 100.
- Thu Nov 12, 2015 5:01 pm
- Forum: Naming
- Topic: Writing formulas from compounds with "bis"
- Replies: 1
- Views: 557
Re: Writing formulas from compounds with "bis"
The prefixes di, tri, tetra, etc. are used to indicate how many molecules of a specific compound is in the coordinate compound. For example, diamine would mean there are two NH3 molecules present. However, alternate prefixes are used when the molecule already has a prefix (such as in ethylenediamine...
- Thu Nov 12, 2015 11:52 am
- Forum: Naming
- Topic: Naming of Oxalate
- Replies: 1
- Views: 1410
Re: Naming of Oxalate
The alternative prefixes must also be used for polydentate ligands. Since oxalato can form a bond with the metal in two places (the two oxygen atoms with the negative formal charges), it is a bidentate and uses the alternative prefixes.
- Sat Nov 07, 2015 4:01 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Difference between Q and K
- Replies: 3
- Views: 1064
Re: Difference between Q and K
If Q is less than K, then the ratio of the molar concentration of products to that of reactants is less than what it is at equilibrium, so the reaction will proceed in the forward reaction in order to increase the molar concentration of products to approach the value of K. If Q is greater than K, th...
- Wed Nov 04, 2015 1:52 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Uncertainty in position
- Replies: 5
- Views: 1392
Re: Uncertainty in position
The electron confined to an atom with a radius greater than 150 pm would have a larger uncertainty in position, and, because of this, it would have a lower uncertainty in velocity. Therefore, the velocity of the electron in the atom with a larger radius could be more precisely known as compared to t...
- Tue Oct 27, 2015 11:48 am
- Forum: Octet Exceptions
- Topic: How to draw Lewis Structures for incomplete octets?
- Replies: 1
- Views: 1687
Re: How to draw Lewis Structures for incomplete octets?
H, Li, and Be are exceptions to the octet rule because they do not have complete octets. In the case of BF3, B is also an exception because it has 6 valence electrons rather than 8 (it will eventually form a coordinate covalent bond with another atom or molecule that has a lone pair in order to acqu...
- Thu Oct 22, 2015 1:45 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Sigma bonds and Pi Bonds
- Replies: 8
- Views: 2599
Re: Sigma bonds and Pi Bonds
No, there can only be one sigma bond between two atoms because when the orbitals from two atoms overlap end-to-end (in a sigma bond), in order to form another bond to share more electrons, it is only possible for their orbitals to overlap side-to-side (which forms a pi bond). This is why double bond...
- Fri Oct 16, 2015 1:32 am
- Forum: Octet Exceptions
- Topic: Radical Octets
- Replies: 1
- Views: 543
Re: Radical Octets
Radicals are atoms with an unpaired electron. They are highly reactive because they are most stable when they gain an electron from another atom. Any element in the p-block starting with the third row of the periodic table can have an expanded octet. This is because atoms with orbitals in the n=3 le...
- Thu Oct 08, 2015 11:23 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron Configuration for Chromium
- Replies: 1
- Views: 844
Re: Electron Configuration for Chromium
If Cr were to form a bond with another atom, then yes, it would be best to remove an electron from the 4s orbital so that the configuration would be 3d^5. However, when the Cr atom is not bonding, there is no way for it to just "lose" an electron, so it has to have the electron in an orbit...
- Fri Oct 02, 2015 4:09 pm
- Forum: Photoelectric Effect
- Topic: Wavelengths of photons
- Replies: 3
- Views: 604
Re: Wavelengths of photons
In the photoelectric effect, the photons released by the atom were not measured; the detector only detected the ejected electrons. The wavelengths of the electromagnetic radiation emitted by atoms to form the emission spectrum depends on the element because the atoms release different wavelengths of...