Search found 60 matches
- Tue Mar 12, 2019 5:25 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slow or Fast Step
- Replies: 3
- Views: 427
Re: Slow or Fast Step
Most often the slow step will be given to you. If it is not, you can look at the overall rate law, which usually represents the rate determining step (slow step).
- Tue Mar 12, 2019 5:16 pm
- Forum: First Order Reactions
- Topic: Rate dependency
- Replies: 5
- Views: 515
Re: Rate dependency
Also remember to look at the order of the reactants. If there rate order of a reactant is zero, then it is not dependent on the concentration, but rather k.
- Tue Mar 12, 2019 5:13 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: molecularity
- Replies: 3
- Views: 445
Re: molecularity
You can find the molecularity of a reaction by looking at the rate determining step, or slow step. The overall rate law if the rate law of the slow step, since this step determine the rate of the reaction. If there are two molecules reacting, then it is bimolecular. If there is three, then it is ter...
- Tue Mar 12, 2019 5:10 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: order of a cell diagram
- Replies: 4
- Views: 487
Re: order of a cell diagram
If there are coefficients in the half reactions, you do not need to include them. Just remember to separate the phases with a bar and the two half reactions with a double bar.
- Tue Mar 12, 2019 5:04 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slow vs Fast Step
- Replies: 4
- Views: 422
Re: Slow vs Fast Step
If the slow step is the not first step and contains and intermediate, you can assume the first step is at equilibrium and use the pre-equilibrium approach.
- Fri Mar 08, 2019 3:36 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Rate Order Graphs
- Replies: 3
- Views: 436
Re: Rate Order Graphs
If you are only given the reactant concentrations and their respective times, you can use graphs to determine the order of each reactant. For example, if the graph of ln[A] vs. time is linear, it is first order. In addition, if [A] vs. time is linear, then it is zero order.
- Fri Mar 08, 2019 3:32 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slow step
- Replies: 4
- Views: 468
Re: Slow step
The addition, the slow step should not contain an intermediate as one of its reactants since it cannot appear in the rate law.
- Mon Mar 04, 2019 11:39 am
- Forum: Balancing Redox Reactions
- Topic: Cell diagrams
- Replies: 8
- Views: 756
Re: Cell diagrams
That is correct. The only exception for liquids is mercury liquid, which is a good conductor of electricity. Therefore, if mercury liquid is present, you do not need to add Pt.
- Mon Mar 04, 2019 11:37 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Study Advice
- Replies: 73
- Views: 6563
Re: Study Advice
Try doing all of the homework practice questions. I found doing this to be very helpful. By doing this, you can gauge your strengths and weaknesses and subsequently attend office hours or workshops to clarify any questions you may have.
- Mon Mar 04, 2019 11:34 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Nernst Equation
- Replies: 4
- Views: 387
Re: Nernst Equation
Use the information that you have to solve for a certain desired variable. Because many of the values in the Nernst equation are constants, you usually only need to find one or two more values.
- Mon Mar 04, 2019 11:29 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: van't hoff equation
- Replies: 6
- Views: 695
Re: van't hoff equation
Use the base e and raise it to the value on the right hand side of the equation (-delta H/R*(1/T2-1/T1)). Then isolate the variable K2 to determine the value.
- Mon Mar 04, 2019 11:25 am
- Forum: Van't Hoff Equation
- Topic: K value- Temp
- Replies: 6
- Views: 970
Re: K value- Temp
In addition, in order to use the equation stated above, you must assume that delta H and delta S are constant. This equation allows us to determine K at different temperatures is these values (delta H and delta S) are known.
- Sun Feb 17, 2019 4:59 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Temperature
- Replies: 2
- Views: 251
Re: Temperature
More information must be given in order to determine whether a process will proceed in the forward or reverse direction. The change in enthalpy by the reaction is particularly important as you can determine whether the reaction is endothermic or exothermic.
- Sun Feb 17, 2019 4:54 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: DeltaS= nCln(T2/T1)
- Replies: 4
- Views: 1226
Re: DeltaS= nCln(T2/T1)
Always look at the context of the question. If you are having trouble determining which one is constant, go back to the basics. Like stated above, sometimes you may have to split the entropy change into several steps, which works since entropy is a state function.
- Sun Feb 17, 2019 4:46 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpies
- Replies: 8
- Views: 809
Re: Bond Enthalpies
In addition, this method is the least accurate because we are calculating the average bond enthalpies of each bond from different molecules. Therefore, there will always be some error in the final value.
- Sun Feb 17, 2019 4:41 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Reversible v irreversible
- Replies: 4
- Views: 750
Re: Reversible v irreversible
To add, reversible reactions always result in more work because of the infinitesimally pressure differences.
- Sun Feb 17, 2019 4:37 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy Definition
- Replies: 4
- Views: 403
Re: Gibbs Free Energy Definition
Gibbs free is energy is energy available to do work. You can think of it as enthalpy being the total amount of energy and T times delta S (TΔS) being the energy that is lost to entropy. Thus, change in Gibbs free energy is equal to change in enthalpy minus TΔS (ΔG = ΔH – TΔS).
- Sun Feb 17, 2019 4:33 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Positive Gibbs Free Energy
- Replies: 3
- Views: 359
Re: Positive Gibbs Free Energy
Reactions with a positive Gibbs free energy are usually carried out with accompaniment of another reaction. This is called a coupled reaction, and it allows the overall process to occur. An example is ATP hydrolysis, in which ATP is used to carry out the main reaction.
- Sun Feb 03, 2019 4:40 pm
- Forum: Calculating Work of Expansion
- Topic: internal vs. external pressure
- Replies: 3
- Views: 5817
Re: internal vs. external pressure
Internal pressure is how much change in energy a system undergoes when it expands or contracts. External pressure is the amount of energy that is applied from the outside. At equilibrium, these two are equal
- Sun Feb 03, 2019 4:30 pm
- Forum: Calculating Work of Expansion
- Topic: What is Work?
- Replies: 5
- Views: 482
Re: What is Work?
Work is the transfer of mechanical energy between two systems and is measured in Joules. In other words, it is the energy transferred by a system to its surroundings.
- Sat Feb 02, 2019 5:46 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: bond enthalpy equations
- Replies: 6
- Views: 581
Re: bond enthalpy equations
Bond enthalpy is defined as the amount of energy required to break a bond. You can calculate bond enthalpy of a reaction by subtracting the total bond enthalpies of products from the total bond enthalpies of reactants.
- Sat Jan 26, 2019 11:27 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: heat capacity
- Replies: 7
- Views: 731
Re: heat capacity
Heat capacity allows us to quantify a substance's ability to absorb heat energy. It is also important to note the difference between heat capacity and specific heat, as specific heat focuses solely on one unit of mass.
- Sat Jan 26, 2019 11:20 am
- Forum: Phase Changes & Related Calculations
- Topic: Severe burn from steam clarification
- Replies: 5
- Views: 1926
Re: Severe burn from steam clarification
To add, steam is a lot more severe than boiling water because it has more heat energy than water. An immense amount of energy is released when steam hits your skin and condenses into a liquid.
- Fri Jan 25, 2019 3:44 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: What not to count
- Replies: 9
- Views: 846
Re: What not to count
If you are talking about salt solutions, then you must disregard ions that fully dissociate because they do not affect the pH of the solution. For example, cations of strong bases do not affect pH because they fully dissociate. The same applies to anions of strong acids.
- Thu Jan 17, 2019 9:54 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: when is x negligible
- Replies: 7
- Views: 6516
Re: when is x negligible
[OH-] is equal to [H30+] when the pH of the solution is neutral. Kw is always 1 x 10^-14 at 25 C.
- Thu Jan 17, 2019 9:45 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Quadratic equation and ICE box
- Replies: 3
- Views: 280
Re: Quadratic equation and ICE box
If you are given a K value that is less than 10^-3 and end up with x variables that are cubed (or higher), you can use the approximation that was shown in class. Although you can use approximations for quadratic equations as well, it is safer to use the quadratic formula to obtain a more accurate an...
- Thu Jan 17, 2019 9:39 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE box
- Replies: 2
- Views: 308
Re: ICE box
Yes, that is correct. Try to use what is given to you in the question. If there is no product, assume that the reaction will shift to the right.
- Sun Jan 13, 2019 1:44 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kc and Kp
- Replies: 5
- Views: 269
Re: Kc and Kp
You use Kc or Kp based on the information that is given and what the question is asking for. For example, if you are given gases and their molar concentrations, you can use Kc. However, if the question requires you to calculate Kp, use the Ideal Gas Law to convert Kc to Kp.
- Sun Jan 13, 2019 1:38 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: (aq) in calculating K
- Replies: 9
- Views: 1209
Re: (aq) in calculating K
When calculating K, we do not consider pure liquids and solids because we are only interested in things that are changing. Pure solids remain constant and liquids like water are too excessive to consider.
- Sun Jan 13, 2019 1:33 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equations
- Replies: 6
- Views: 463
Re: Equations
When you are given equilibrium concentrations, you must use Kc to calculate the equilibrium constant. This can apply to both aqueous solutions and gases. In contrast, Kp can only be used to calculate the equilibrium constant of partial pressures. Kp cannot be applied to aqueous solutions since they ...
- Fri Dec 07, 2018 1:32 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Are all pH calculations done to 2 decimal places or do we use sig figs in pH calculations? [ENDORSED]
- Replies: 2
- Views: 1319
Re: Are all pH calculations done to 2 decimal places or do we use sig figs in pH calculations? [ENDORSED]
For pH calculations, the sig figs are only accounted for after the decimal point. In this case, since there are two sig figs in 0.0092 M Ba(OH)2, the final answer should present two digits after the decimal point. Thus, 12.96 is correct.
- Fri Dec 07, 2018 1:29 am
- Forum: Lewis Structures
- Topic: Valence electrons
- Replies: 2
- Views: 269
Re: Valence electrons
The valence electrons are the electrons in the outermost energy level. In this case, the elements in the d block will have valence electrons in the s block. For example, the element Mn will have its valence electron in the 4s orbital.
- Fri Dec 07, 2018 1:20 am
- Forum: Amphoteric Compounds
- Topic: Amphiprotic vs. amphoteric
- Replies: 3
- Views: 463
Re: Amphiprotic vs. amphoteric
Amphoteric compounds are essentially any compound that can act as an acid or base. Amphiprotic compounds are also amphoteric compounds, but more specially refer to compounds having the ability to either donate or accept a proton.
- Fri Dec 07, 2018 1:12 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: H-bonds
- Replies: 4
- Views: 436
Re: H-bonds
Hydrogen bonds are strong dipole-dipole forces that result from polar bonds within a molecule. When an N, O, or F atom is bonded to H, the molecule becomes extremely polar due to the high electronegativity difference.
- Fri Dec 07, 2018 1:01 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Coordination Complexes
- Replies: 2
- Views: 165
Coordination Complexes
What is the difference between a tetrahedral complex and a square planar complex?
- Sun Dec 02, 2018 4:33 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Final pH
- Replies: 3
- Views: 324
Re: Final pH
You can use the formula pH + pOH = 14 for any aqueous solution. The "p" essentially means to take the negative logarithm of a value. To solve for either pH or pOH, plug in the given values to obtain a certain variable.
- Sun Dec 02, 2018 4:20 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Chemical Bonds of Nonmetals
- Replies: 2
- Views: 460
Re: Chemical Bonds of Nonmetals
Nonmetals rarely lose electrons and therefore it is common for them to gain electrons and form anions, as their electronegativities are very high.
- Sun Nov 25, 2018 7:46 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Dipole-Dipole forces
- Replies: 3
- Views: 383
Re: Dipole-Dipole forces
This is not the only way. Nonpolar molecules can have dipole-dipole forces as well, only the dipoles cancel each other out. Therefore, it is important to look at the overall structure of the molecule and their respective dipole moments.
- Sun Nov 25, 2018 7:42 pm
- Forum: Properties of Light
- Topic: Speed of light
- Replies: 13
- Views: 3803
Re: Speed of light
Just to be safe, you should use the constant given on the formula sheet. Otherwise, ask your TA for their preference.
- Sun Nov 25, 2018 7:40 pm
- Forum: Lewis Acids & Bases
- Topic: How do we know something is a lewis acid or base?
- Replies: 4
- Views: 683
Re: How do we know something is a lewis acid or base?
It is helpful to draw the Lewis structure of the molecule when determining whether something is a Lewis base or acid. For example, if there is a lone pair on a central atom in a molecule, the molecule is mostly likely a Lewis base because it can donate those electrons to an acid.
- Thu Nov 15, 2018 11:07 pm
- Forum: Ionic & Covalent Bonds
- Topic: H bonds and melting points
- Replies: 4
- Views: 581
Re: H bonds and melting points
In addition, hydrogen bonds are so strong because of the intermolecular forces between polar molecules. These forces are especially stronger due to the bonds between hydrogen and atoms with high electronegativity (i.e. N, O, and F).
- Thu Nov 15, 2018 10:55 pm
- Forum: Ionic & Covalent Bonds
- Topic: Polar/non polar molecules
- Replies: 5
- Views: 605
Re: Polar/non polar molecules
You can determine if a molecule is polar or nonpolar based on its shape. For example, if the shape of the molecule is symmetric and it presents an even distribution of electron densities, then it is most likely nonpolar (and vice versa).
- Sun Nov 11, 2018 5:39 pm
- Forum: Lewis Structures
- Topic: Exceptions to Octet Rule
- Replies: 5
- Views: 999
Re: Exceptions to Octet Rule
Although elements in period 3 and beyond have an expanded octet (due to their ability to access their d orbital), it does not necessarily mean that they don't obey the octet rule. It is always best to assign each element an octet when drawing Lewis structures and to determine the best and most stabl...
- Sun Nov 11, 2018 5:35 pm
- Forum: Bond Lengths & Energies
- Topic: bond energy
- Replies: 4
- Views: 379
Re: bond energy
The bond energy between atoms is usually given in the problem. You can therefore use the information given to isolate a certain variable and determine its bond energy. However, it is good to know that double and triple bonds have significantly greater bond energies than single bonds.
- Sun Nov 11, 2018 5:31 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Intermolecular Forces
- Replies: 4
- Views: 394
Re: Intermolecular Forces
Yes, Van der Waals forces and London dispersion forces are used interchangeably and are therefore the same strength. They are the weakest intermolecular forces between molecules.
- Thu Nov 01, 2018 10:57 pm
- Forum: Ionic & Covalent Bonds
- Topic: Copper Ions
- Replies: 3
- Views: 330
Re: Copper Ions
As anions, copper II loses one more electron than copper I since their forms are Cu2+ and Cu1+, respectively.
- Thu Nov 01, 2018 10:52 pm
- Forum: Ionic & Covalent Bonds
- Topic: Electron Configuration
- Replies: 3
- Views: 311
Re: Electron Configuration
A more conventional way to write the electron configuration of Br is [Ar] 4s2 3d10 4p5 since the 4s subshell is filled first. However, either is correct.
- Thu Nov 01, 2018 10:31 pm
- Forum: Lewis Structures
- Topic: d orbitals in valence shell that accommodate additional e-
- Replies: 2
- Views: 151
Re: d orbitals in valence shell that accommodate additional e-
Only elements with orbitals higher than p can have more than the octet because of the additional space. The s and p orbitals can only hold 8 electrons in total.
- Fri Oct 26, 2018 9:10 pm
- Forum: Ionic & Covalent Bonds
- Topic: Valence Electrons
- Replies: 3
- Views: 316
Re: Valence Electrons
The elements are held together by electrostatic attractions. In the case of ionic bonds, the atoms are attracted to one another due to their opposite charges.
- Thu Oct 25, 2018 9:31 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Ionization Energy
- Replies: 3
- Views: 379
Re: Ionization Energy
Yes, that is correct. The same concept can be applied to halogens, which require one more electron to complete an octet.
- Thu Oct 25, 2018 2:24 pm
- Forum: Einstein Equation
- Topic: E=hv [ENDORSED]
- Replies: 52
- Views: 17757
Re: E=hv [ENDORSED]
The value E represents the energy of the photon. However, you can use the equation E=hv to calculate the energy required to remove an electron after taking into account the kinetic energy. This works because the energy of the photon must be greater than or equal to the energy required to remove the ...
- Thu Oct 18, 2018 3:44 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Bohr condition explaining lines
- Replies: 2
- Views: 1700
Re: Bohr condition explaining lines
Bohr's model shows that electrons move from one orbit to another based on whether or not the energy of the photons is equivalent to the energy difference between the orbits. Thus, the spectral line is essentially a representation of this condition.
- Thu Oct 18, 2018 3:35 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Spectroscopy vs Molecular Spectroscopy
- Replies: 2
- Views: 366
Re: Atomic Spectroscopy vs Molecular Spectroscopy
Atomic spectroscopy studies how electromagnetic energy is absorbed or emitted by atoms. Molecular spectroscopy studies the interactions of both atoms and molecules. Therefore, molecular spectroscopy is much more comprehensive as it provides more information about certain characteristics.
- Thu Oct 18, 2018 3:18 pm
- Forum: Trends in The Periodic Table
- Topic: Period Table 'blocks'
- Replies: 5
- Views: 452
Re: Period Table 'blocks'
Blocks are essentially a simple way to categorize elements into their respective orbital. These categories are determined by the highest energy electrons.
- Thu Oct 11, 2018 12:26 pm
- Forum: Trends in The Periodic Table
- Topic: Types of Radii
- Replies: 2
- Views: 492
Re: Types of Radii
The radius of an atom is the distance from the center of the nucleus to the edge of the farthest electron cloud. A covalent radius is formed when two of the same elements are covalently bonded to one another. This radius can be determined using half of the distance between the two nuclei. Lastly, an...
- Thu Oct 11, 2018 12:15 pm
- Forum: SI Units, Unit Conversions
- Topic: Atoms and Molecules
- Replies: 5
- Views: 368
Re: Atoms and Molecules
It really depends on the context of the problem. If the question is asking you to find the number of atoms or ions in a specific molecule, remember to multiply the number of moles appropriately.
- Thu Oct 11, 2018 12:11 am
- Forum: SI Units, Unit Conversions
- Topic: Should Significant Figures be affected by constants?
- Replies: 10
- Views: 877
Re: Should Significant Figures be affected by constants?
The significant figures in your final answer should not be affected by the number of sig figs in your constants. Simply put, apply the sig figs rules based on the number of sig figs of the variable given to you in the problem. In your case, your final answer should be 5.86957 x 10^-7 m since 6 sig f...
- Thu Oct 04, 2018 4:08 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Problem G5
- Replies: 8
- Views: 693
Re: Problem G5
Yes, in this case we are using the M1V1=M2V2 formula. M1V1 is equal to the number of moles of Na2CO3, which is 1.08 x 10^-3 mol. You then set this equal to M2V2. M2 can be calculated using the given number of grams of Na2CO3 (2.111g) and volume (250.0mL). With this information, you set the equations...
- Thu Oct 04, 2018 3:01 pm
- Forum: SI Units, Unit Conversions
- Topic: mol vs. mmol
- Replies: 12
- Views: 2533
mol vs. mmol
What is a mmol? In some of the practice questions in G we are given the unit mmol.
- Thu Oct 04, 2018 2:45 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Molecules vs Formula Units? E21
- Replies: 2
- Views: 188
Re: Molecules vs Formula Units? E21
There is essentially no difference when calculating for molecules and formula units. Formula units are used for ionic compounds and molecules are used for covalent bonds.