## Search found 60 matches

Thu Mar 14, 2019 4:39 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Calculating A
Replies: 1
Views: 76

### 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: 273

### 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: 103

### 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: 371

### 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: 199

### 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: 225

### 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: 178

### 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: 272

### 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: 675

### 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: 328

### 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: 469

### 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: 158

### 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: 134

### 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: 127

### 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: 97

### 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: 104

### 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: 150

### 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: 200

### 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: 222

### 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: 164

### 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: 274

### 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: 140

### 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: 121

### 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: 109

### 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: 155

### 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: 144

### 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: 60

### 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: 186

### 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: 396

### 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: 274

### 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: 807

### 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: 232

### 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: 172

### 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: 178

### 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: 372

### 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: 290

### 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: 2179

### 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: 406

### 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: 252

### 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: 107

### 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: 101

### 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: 49

### 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: 186

### 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: 584

### 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: 234

### 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: 269

### 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: 162

### 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: 227

### 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: 211

### 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: 67

### 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: 665

### 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: 147

### 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: 115

### 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: 302

### 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: 108

### 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: 480

### 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: 113

### 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: 329

### 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: 307

### 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: 1035

### 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.

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