Search found 60 matches
- Thu Mar 14, 2019 4:39 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Calculating A
- Replies: 1
- Views: 280
Re: Calculating A
Yes, Dr. Lavelle said we are supposed to assume A is 1 unless another value of A is given. We did not cover how to calculate A in lecture so I don't think we have to worry about any questions that would ask us to do so.
- Thu Mar 14, 2019 4:36 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Intermediate vs catalyst
- Replies: 8
- Views: 859
Re: Intermediate vs catalyst
A catalyst doesn't get used up in a reaction, so even if it is used up in one of the steps, it'll be regenerated in another step. Intermediates are the products of one step that are then used as reactants in a following step.
- Thu Mar 14, 2019 4:35 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Rate laws
- Replies: 2
- Views: 319
Re: Rate laws
They are not included, since only reactants are included in the rate law.
- Sun Mar 10, 2019 5:06 pm
- Forum: Van't Hoff Equation
- Topic: Equilibrium
- Replies: 6
- Views: 769
Re: Equilibrium
The K used in the Van't Hoff equation is the equilibrium constant. It is useful for finding the equilibrium constant at different temperatures.
- Sun Mar 10, 2019 5:04 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slowest step
- Replies: 4
- Views: 560
Re: Slowest step
The fast steps, in comparison to the slow step, are negligible because they occur so quickly. The time that the slow step takes is more representative of how long the entire reaction takes.
- Sun Mar 10, 2019 4:59 pm
- Forum: General Rate Laws
- Topic: Rate Laws
- Replies: 8
- Views: 726
Re: Rate Laws
The integrated rate laws are given on the formula sheet, but I think you should still have a general idea about how to integrate to get them.
- Sat Mar 02, 2019 2:09 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: E
- Replies: 4
- Views: 480
Re: E
I think it's ok to add them in redox reactions because the half reactions are still parts of the same overall redox reaction, as opposed to adding together the E values of two completely separate reactions.
- Sat Mar 02, 2019 2:07 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Cell Potential Spontaneity
- Replies: 7
- Views: 870
Re: Cell Potential Spontaneity
It is spontaneous when E is positive, which means Gibbs free energy would be negative because when E is positive in delta G=-nFE, delta G will be negative, which once again shows that the reaction is spontaneous.
- Wed Feb 27, 2019 7:30 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: delta G naught when K<1
- Replies: 3
- Views: 3149
delta G naught when K<1
Why is delta G naught positive when K<1? Wouldn't the forward reaction be favored and therefore spontaneous, making it negative?
- Thu Feb 21, 2019 9:43 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Units for Gibbs
- Replies: 8
- Views: 950
Re: Units for Gibbs
Either J or kJ should be fine for the final answer, as long as you're consistent with units while you're doing the calculation so that the number ends up being correct.
- Thu Feb 21, 2019 9:41 pm
- Forum: Balancing Redox Reactions
- Topic: Week 7 Homework
- Replies: 15
- Views: 1266
Re: Week 7 Homework
I did mostly Gibbs free energy questions and a few of the electrochemistry questions from the beginning of outline 5.
- Thu Feb 21, 2019 9:38 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Gibbs
- Replies: 3
- Views: 496
Re: Gibbs
It is the energy available to do work, which determines spontaneity of a reaction because a negative value of delta G means the reaction is spontaneous, while a positive value means it is not spontaneous.
- Sun Feb 17, 2019 8:07 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: calculating delta G
- Replies: 4
- Views: 451
Re: calculating delta G
Yes, it would be 298K because T is in Kelvin in the Gibbs free energy equation.
- Sun Feb 17, 2019 8:05 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Non-spontaneous and spontaneous processes
- Replies: 2
- Views: 333
Re: Non-spontaneous and spontaneous processes
Changing the temperature can make a reaction spontaneous, since increasing temperature will increase entropy. At a certain temperature, the value for Gibbs free energy will become negative and the reaction will be spontaneous.
- Sun Feb 17, 2019 8:04 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy?
- Replies: 2
- Views: 313
Re: Gibbs free energy?
It uses enthalpy, temperature, and entropy to determine whether or not a reaction will be spontaneous.
- Sat Feb 09, 2019 6:30 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: constant volume
- Replies: 3
- Views: 378
Re: constant volume
Since work is the force applied on the object multiplied the distance it has moved, if volume is constant, the distance is zero, which means no work is done.
- Sat Feb 09, 2019 6:25 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: formulas given on midterm
- Replies: 4
- Views: 442
Re: formulas given on midterm
There is a link on the Chem 14B website called "Constants and Equations" that has the formula sheet.
- Sat Feb 09, 2019 6:21 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Closed, Open, and Isolated Systems
- Replies: 5
- Views: 561
Re: Closed, Open, and Isolated Systems
Matter and energy can be exchanged in an open system, like a reaction in an open beaker. Only energy, but not matter, can be exchanged with the surroundings in a closed system, like when there is a piston. No matter or energy is exchanged with the surroundings in an isolated system, like in a closed...
- Sat Feb 02, 2019 10:07 pm
- Forum: Calculating Work of Expansion
- Topic: SI unit for P
- Replies: 6
- Views: 700
Re: SI unit for P
I think we are supposed to use atm for pressure, and since there's a very small difference between atm and bars, the value with either of these units will be pretty much the same.
- Sat Feb 02, 2019 10:00 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Angles
- Replies: 5
- Views: 549
Re: Bond Angles
Forming bonds releases energy, so the negative sign represents the loss of energy from the system.
- Sat Feb 02, 2019 9:59 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: delta H vs q
- Replies: 9
- Views: 948
Re: delta H vs q
Delta H is the change in enthalpy, while q is just heat, so it doesn't represent a change.
- Sat Jan 26, 2019 1:35 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Delta H
- Replies: 4
- Views: 445
Re: Delta H
The reaction is endothermic, since a positive value of delta H means that the heat of the products is greater than the heat of the reactants, which means the reaction required the absorption of heat.
- Sat Jan 26, 2019 1:32 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: State properties
- Replies: 3
- Views: 362
Re: State properties
Enthalpy of a reaction with multiple steps can be found by adding the enthalpy of each step together because it is a state function, while the same can not be done with heat.
- Sat Jan 26, 2019 1:30 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Changing sign of enthalpy
- Replies: 3
- Views: 422
Re: Changing sign of enthalpy
Since the positive and negative indicates whether energy is being absorbed or released for the reaction to take place, if the reaction absorbs heat in one direction, the reverse reaction will release heat since the bonds that were initially being broken are now being formed and vice versa.
- Sun Jan 20, 2019 2:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sig figs in pH
- Replies: 7
- Views: 842
Re: Sig figs in pH
The number of sig figs in the H3O+ concentration is the how many numbers there should be after the decimal place in the pH value.
- Sun Jan 20, 2019 2:27 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: When x is small
- Replies: 4
- Views: 508
Re: When x is small
x needs to be smaller than 10^(-3) to be ignored. This means it's small enough to be insignificant, which connects to the approximation being valid if it's within 5% because it means the x was small enough.
- Sun Jan 20, 2019 2:19 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Given Kw
- Replies: 2
- Views: 216
Re: Given Kw
Since water is neutral, the concentration of H3O+ ions and OH- ions has to be equal, and since water is neutral at any temperature, Kw has to be the same.
- Sun Jan 13, 2019 12:04 am
- Forum: Ideal Gases
- Topic: Q
- Replies: 5
- Views: 501
Re: Q
K is calculated with the concentrations of the products and reactants when the reaction is at equilibrium, while Q can be calculated at any point in the reaction, which means the concentrations of the products and reactants can vary at different times in the reaction. Q is compared to K to determine...
- Sun Jan 13, 2019 12:01 am
- Forum: Ideal Gases
- Topic: Homework Week 2
- Replies: 10
- Views: 1052
Re: Homework Week 2
Yes, the homework is due in discussion so it'll be due on Tuesday for you.
- Sat Jan 12, 2019 11:57 pm
- Forum: Ideal Gases
- Topic: K and Q
- Replies: 7
- Views: 519
Re: K and Q
K is calculated with the concentrations of the reactants and products when the reaction is at equilibrium, which means K will always be constant as long as it is the same reaction at the same temperature. Q can be calculated at any point in the reaction, so there will be different concentrations of ...
- Sat Dec 08, 2018 10:15 pm
- Forum: Bronsted Acids & Bases
- Topic: Lewis vs Bronsted
- Replies: 10
- Views: 1592
Re: Lewis vs Bronsted
Lewis acids accept lone pairs and Lewis bases donate lone pairs. Bronsted acids donate protons and Bronsted bases accept protons.
- Sat Dec 08, 2018 10:11 pm
- Forum: Lewis Acids & Bases
- Topic: Lewis Acid
- Replies: 6
- Views: 648
Re: Lewis Acid
HBr has a greater bond length because Br has a greater atomic radius than F, which means it is easier for HBr to donate a proton, so it is a stronger acid.
- Sat Dec 08, 2018 10:10 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: polarity
- Replies: 2
- Views: 361
Re: polarity
Polarity is determined by the unequal sharing of electrons, so a molecule would be polar if the atoms that it is made of do not have the same electronegativity and do not cancel each other out with dipoles in opposite directions.
- Fri Nov 30, 2018 1:23 pm
- Forum: Biological Examples
- Topic: acids
- Replies: 5
- Views: 428
Re: acids
Not all parts of the body can handle low pH levels the same way, which is why it hurts to get vinegar in a cut that is more sensitive to the acidity.
- Fri Nov 30, 2018 1:21 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Cis and Trans
- Replies: 10
- Views: 1016
Re: Cis and Trans
It depends on what the molecule is being used for, because cis will usually be polar and trans will usually be nonpolar.
- Fri Nov 30, 2018 1:19 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Oxidation number
- Replies: 9
- Views: 861
Re: Oxidation number
You would find the oxidation number by figuring out how many electrons it would lose or gain.
- Sat Nov 24, 2018 2:38 pm
- Forum: Hybridization
- Topic: reason for hybridization
- Replies: 9
- Views: 10265
Re: reason for hybridization
Hybridization occurs because hybridized orbitals have lower energy than when they are unhybridized, so the compounds that they form are more stable.
- Sat Nov 24, 2018 2:32 pm
- Forum: Hybridization
- Topic: double bonds
- Replies: 14
- Views: 1262
Re: double bonds
A single bond is a sigma bond, a double bond is one sigma and one pi bond, and a triple bond is one sigma bond and two pi bonds.
- Sat Nov 24, 2018 2:29 pm
- Forum: Hybridization
- Topic: Writing out Hybridization
- Replies: 8
- Views: 613
Re: Writing out Hybridization
Dr. Lavelle said he writes it as sp^3d, but the textbook writes it as dsp^3, so either is fine.
- Sat Nov 17, 2018 2:24 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: VSEPR- Polar vs Nonpolar
- Replies: 5
- Views: 284
Re: VSEPR- Polar vs Nonpolar
A molecule is nonpolar if its atoms have the same electronegativity or if the dipole moments cancel each other out, and it is polar when the dipole moments do not cancel out.
- Sat Nov 17, 2018 2:23 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Sigma and Pi Bonds
- Replies: 2
- Views: 278
Sigma and Pi Bonds
How would you be able to tell whether a bond is a sigma or a pi bond?
- Sat Nov 17, 2018 2:21 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: cis and trans prefix's to molecules
- Replies: 2
- Views: 174
Re: cis and trans prefix's to molecules
Cis is when atoms of the same element are on the same side of the molecule and trans is when atoms of the same element are on opposite sides of the molecule.
- Sat Nov 10, 2018 5:55 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Lone Pairs
- Replies: 4
- Views: 373
Re: Lone Pairs
The repulsion strength between lone pairs is greater than the repulsion between a lone pair and a bonding pair, and a lone pair and bonding pair have a greater repulsion than two bonding pairs. As repulsion increases, the size of the bond angle increases.
- Sat Nov 10, 2018 5:48 pm
- Forum: Resonance Structures
- Topic: Bond Lengths
- Replies: 6
- Views: 929
Re: Bond Lengths
We also need to know that the dissociation energy for longer bonds is lower than the dissociation energy of shorter bonds because they are easier to break.
- Sat Nov 10, 2018 5:41 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Shapes
- Replies: 5
- Views: 1550
Re: Shapes
They are tetrahedral when there are four areas of electron density because the atoms will spread out as far apart from each other as possible.
- Sat Nov 03, 2018 7:33 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Nodes and Nodal Planes
- Replies: 1
- Views: 447
Re: Nodes and Nodal Planes
Nodal planes are where there are no electrons in an atom. Because s-orbitals are spherical, they have no nodal planes. P-orbitals have 1, d-orbitals have 2, and so on.
- Sat Nov 03, 2018 7:30 pm
- Forum: Resonance Structures
- Topic: ????
- Replies: 2
- Views: 274
Re: ????
The first part is explaining how a combination of all the resonance structures is a more accurate representation of the bond lengths than each individual resonance structure on its own.
- Sat Nov 03, 2018 7:28 pm
- Forum: Lewis Structures
- Topic: Lewis Structure of SO4^2- and Formal Charge
- Replies: 1
- Views: 478
Re: Lewis Structure of SO4^2- and Formal Charge
We are supposed to calculate formal charge when drawing every Lewis structure and try to minimize it as much as possible. I don't think you have to draw multiple resonance structures unless the question specifically asks for them.
- Fri Oct 26, 2018 4:14 pm
- Forum: Lewis Structures
- Topic: writing the structure
- Replies: 5
- Views: 584
Re: writing the structure
It doesn't matter which side the electrons are drawn on, but they are usually spread around the atom evenly, so they don't start pairing until there is at least one electron on each side.
- Fri Oct 26, 2018 4:08 pm
- Forum: Ionic & Covalent Bonds
- Topic: Bonding Between Cations and Anions
- Replies: 3
- Views: 265
Re: Bonding Between Cations and Anions
When he drew the Lewis structure of the entire molecule, he drew the SO4 molecule between the NH4 molecules, without including any of the lines that indicate bonding.
- Fri Oct 26, 2018 4:03 pm
- Forum: Ionic & Covalent Bonds
- Topic: Calculating number of valence electrons in bonds
- Replies: 5
- Views: 2744
Re: Calculating number of valence electrons in bonds
Also, if the molecule is charged, you need to account for those electrons. For example, if the molecule has a charge of +1, you need to subtract one electron, or if the molecule has a charge of -2, you need to add two electrons.
- Fri Oct 19, 2018 1:24 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg Uncertainty Equation
- Replies: 3
- Views: 298
Re: Heisenberg Uncertainty Equation
Problems will sometimes give the indeterminacy in position (delta x) and mass of the object and ask you to solve for delta v. This can be done because (delta p)=(delta v)*mass, so you can use the information you are given to calculate delta v.
- Fri Oct 19, 2018 1:09 pm
- Forum: Properties of Light
- Topic: Intensity vs. Amplitude
- Replies: 5
- Views: 382
Re: Intensity vs. Amplitude
The intensity of light in the wave model is associated with the amplitude of a wave because a higher amplitude correlates with higher intensity light. When thinking about light as a particle, the intensity of the light is based on the number of photons.
- Fri Oct 19, 2018 1:06 pm
- Forum: Properties of Light
- Topic: Friday 10/5 Lecture
- Replies: 7
- Views: 679
Re: Friday 10/5 Lecture
The greek letter nu is the curly v that represents frequency (in Hertz or s^-1), while the regular v represents velocity (in m/s or m*s^-1).
- Sat Oct 13, 2018 2:12 pm
- Forum: DeBroglie Equation
- Topic: De Broglie Equation Dividing J*s by kg*m/s
- Replies: 2
- Views: 1089
Re: De Broglie Equation Dividing J*s by kg*m/s
During Friday's lecture, Professor Lavelle said that 1 J= 1 kg.m^2.s^(-2). In the equation, the units are (J.s)/(kg.m/s), so if you plug in the units for J, all the units except for m will cancel out, which gives wavelength in meters.
- Sat Oct 13, 2018 2:03 pm
- Forum: *Black Body Radiation
- Topic: Importance of Black Bodies?
- Replies: 3
- Views: 695
Re: Importance of Black Bodies?
We don't need to worry about knowing their significance in this course because they are only for hypothetical situations.
- Sat Oct 13, 2018 1:58 pm
- Forum: Einstein Equation
- Topic: calculating kinetic energy
- Replies: 5
- Views: 358
Re: calculating kinetic energy
We would use kg in the equation because it is the standard SI unit. Most equations will use base SI units.
- Sat Oct 06, 2018 9:34 pm
- Forum: Empirical & Molecular Formulas
- Topic: Empirical formula set up
- Replies: 9
- Views: 678
Re: Empirical formula set up
Any number of grams can technically be used to find the empirical formula, but because percentages are given as parts of 100, it makes it easier to assume that it is a 100 gram sample.
- Sat Oct 06, 2018 9:06 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Percision and Accuracy
- Replies: 5
- Views: 713
Re: Percision and Accuracy
Another example is if you are measuring the temperature of a substance and consistently get 39 degrees Celsius during 5 separate trials, but the substance is actually 35 degrees Celsius. This would mean that the measurements are precise, since you repeatedly get the same result, but they are not acc...
- Sat Oct 06, 2018 5:10 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: MOLARITY
- Replies: 17
- Views: 2167
Re: MOLARITY
Molarity is also important for dilution problems because it can be used in the equation (Minitial)(Vinitial)=(Mfinal)(Vfinal) to determine concentrations, volumes, or moles of the solute before or after the solution has been diluted.