## Search found 50 matches

Mon Mar 12, 2018 8:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: What phase is water in in a combustion reaction?
Replies: 2
Views: 178

### Re: What phase is water in in a combustion reaction?

It depends. Combustion reactions vary because the definition is vague "hydrocarbons react with O2 to form water and carbon dioxide". I believe often, however, the reactants are all gaseous.
Mon Mar 12, 2018 8:28 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 3
Views: 208

### Re: Cell Diagram

If there is no conducting solids on one side of the diagram.
Mon Mar 12, 2018 8:09 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Given information
Replies: 5
Views: 269

### Re: Given information

It depends on the question. For some questions we will be told which is fast and which is slow. For most of the questions we have done in class and in the book, we are told the intermediate because we are given all the steps of the reaction.
Tue Mar 06, 2018 2:54 pm
Forum: General Rate Laws
Topic: 15.17
Replies: 4
Views: 255

### Re: 15.17

compare the reaction rates when all other reactants remain constant except for C. The reaction rate doesn't change even though C does, meaning it isn't in the rate law because it is a zero order reactant.
Tue Mar 06, 2018 2:50 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: infinitesimal change
Replies: 3
Views: 492

### Re: infinitesimal change

Its the same as taking the derivative in calculus. We used it in thermodynamics to see what the effect of changing pressure or temperature would have on the system
Tue Mar 06, 2018 2:48 pm
Forum: General Rate Laws
Topic: Proper units
Replies: 7
Views: 364

### Re: Proper units

Unless the question specifies which unit it wants in the answer, it doesn't matter. However, make sure the units match up with constants in the formula sheet and with K
Fri Mar 02, 2018 7:18 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate Constant [ENDORSED]
Replies: 3
Views: 216

### Re: Rate Constant[ENDORSED]

Its a proportionality constant for the concentration of a reactant to the rate of reaction
Fri Mar 02, 2018 7:13 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates [ENDORSED]
Replies: 2
Views: 167

### Re: Intermediates[ENDORSED]

today we talked in class about how when reactions are coupled, one of the steps may go so much faster than the other step that the overall reaction speed is determined by the slower step. The intermediate's concentration in this case wouldn't affect the overall reaction
Fri Mar 02, 2018 7:11 pm
Forum: First Order Reactions
Topic: First Order Reactions [ENDORSED]
Replies: 2
Views: 1617

### Re: First Order Reactions[ENDORSED]

It depends on the reaction and the amount of concentration available. Its too general to say all of one is faster than another
Tue Feb 20, 2018 11:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt in Cell diagrams
Replies: 4
Views: 276

### Re: Pt in Cell diagrams

The inert electrode is necessary to make the electrons flow. You need this when the ions are aqueous or gaseous. You don't need it if there is a conducting solid.
Tue Feb 20, 2018 11:35 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Homework Problem 14.55b [ENDORSED]
Replies: 2
Views: 557

### Re: Homework Problem 14.55b[ENDORSED]

In electrolysis, an electric current is passed through the substance. It is different than the chemical reaction that occurs in an galvanic cell. That is why you focus on the most positive standard reduction potentials
Tue Feb 20, 2018 11:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.23a
Replies: 2
Views: 111

### Re: 14.23a

First, the inert electrode has to be placed in the cell diagram because the electrodes are made of aqueous solutions (meaning there are no conducting solids). The platinum tends to go on the right side of the cell diagram (cathode-reduction) because it only transfers electrons. It does not exchange ...
Sat Feb 17, 2018 12:00 pm
Forum: Balancing Redox Reactions
Topic: Balancing Redox Reactions
Replies: 1
Views: 140

### Re: Balancing Redox Reactions

In class he referred to the hydronium ion as the standard, so i would use that.
Sat Feb 17, 2018 11:59 am
Forum: Balancing Redox Reactions
Topic: 14.1
Replies: 3
Views: 180

### Re: 14.1

when balancing redox reactions, the charges on both sides SHOULD add up to be equal to eachother.
Sat Feb 17, 2018 11:58 am
Forum: Balancing Redox Reactions
Topic: 9.3b
Replies: 1
Views: 89

### Re: 9.3b

that is usually how you do it.
Wed Feb 07, 2018 3:35 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.45
Replies: 3
Views: 197

### Re: 9.45

yes, you can use that equation as long as temperature is constant.
Wed Feb 07, 2018 3:31 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half Reactions
Replies: 6
Views: 285

### Re: Half Reactions

don't write both half reactions as reductions. Make sure to write the complete oxidation and reduction reactions, and as the person above me said, labeling is good for that too.
Wed Feb 07, 2018 3:30 pm
Forum: Balancing Redox Reactions
Topic: oxidation
Replies: 4
Views: 231

### Re: oxidation

If the element you are trying to find the oxidation number for is a transition metal, the oxidation number depends on the other elements in the compound. If its an ion, subtract the net oxidation numbers of the other elements in the compound (oxygen is almost always -2) from the total charge of the ...
Wed Jan 31, 2018 6:24 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.43
Replies: 5
Views: 166

### Re: 9.43

It is on0 the sheet of constants and formula's we are given at the start of every test. (Cp(water) = 75.3 J. K-1mol-1)
Wed Jan 31, 2018 6:22 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Degeneracy and Entropy
Replies: 3
Views: 231

### Re: Degeneracy and Entropy

Degeneracy is a property that is extremely difficult to measure in a lab, so often the CHANGE in degeneracy is measured. it can be increased moles of a substance or volume of a gas
Wed Jan 31, 2018 6:17 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy and Temperature
Replies: 3
Views: 180

### Re: Entropy and Temperature

Also, we used this equation in class to find the change in entropy when temperature is constant (as ice melts for example). If you want to find the change in entropy when temperature is not constant, use the equation delta S=n*C*ln(t2/t1)
Wed Jan 24, 2018 4:00 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Boltzmann's Equation in relation to temperature
Replies: 4
Views: 199

### Re: Boltzmann's Equation in relation to temperature

Boltzmann's equation works when the change in internal energy of the system is 0. So, if you were to change temperature, that would change the internal energy. What is possible though to find the entropy at two different energies and subtract them from eachother
Wed Jan 24, 2018 3:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Assuming Temperature
Replies: 3
Views: 157

### Re: Assuming Temperature

On tests and quizzes, I was told that if we need to assume standard conditions it will be explicitly stated in the problem
Wed Jan 24, 2018 3:55 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law [ENDORSED]
Replies: 7
Views: 380

### Re: Hess's Law[ENDORSED]

From what I've seen, we will be given a few steps or reactions and their enthalpy's and the final reaction. Then the question will ask us for the enthalpy change of the final reation.
Mon Jan 22, 2018 12:20 am
Forum: General Science Questions
Topic: Sig Figs
Replies: 3
Views: 444

### Re: Sig Figs

I remember last quarter the rule was minus one on a test, and minus .5 on a quiz.
Mon Jan 22, 2018 12:18 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: heat capacity
Replies: 2
Views: 151

### Re: heat capacity

Molar heat capacity is the "heat required to raise the temp of 1 mole of a substance by one degree kelvin". Specific heat capacity is the "heat required to raise the temperature of 1 gram of a substance by one degree kelvin.
Mon Jan 22, 2018 12:15 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Positive/Negative Signs in Entropy calculations
Replies: 1
Views: 101

### Re: Positive/Negative Signs in Entropy calculations

Just to edit what you wrote, Q is positive when the system absorbs energy. The change in entropy depends on whether heat is released or not. Sometimes its best to use your intuition on whether its negative or not. For example, the heat of vaporization (or the change in entropy from liquid to gas) of...
Tue Jan 16, 2018 11:26 am
Forum: Phase Changes & Related Calculations
Topic: enthalpy definition
Replies: 3
Views: 263

### Re: enthalpy definition

In class, it was defined as "the amount of heat released or absorbed at a constant pressure (qp=delta H). Its also a state property, meaning its value is determined by its current state.
Tue Jan 16, 2018 11:22 am
Forum: Phase Changes & Related Calculations
Topic: Types of Systems
Replies: 10
Views: 643

### Re: Types of Systems

an Isolated system can not exchange heat with its surroundings, but a closed system can. Neither system can exchange matter with its surroundings
Tue Jan 16, 2018 11:20 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Equations and formulas
Replies: 2
Views: 159

### Re: Equations and formulas

I think there will be much more constants needed in 14B, so he may only post equations
Tue Dec 05, 2017 10:02 pm
Forum: Bronsted Acids & Bases
Topic: When is does a compound act as an acid or base?
Replies: 1
Views: 135

### Re: When is does a compound act as an acid or base?

H2CO3 is the formula for carbonic acid. It's Ka is higher than 10^-7 so it will act as an acid in water. Its conjugate base is HCO3-, which acts as a base in water. If your not sure whether or not a compound will act as a base or acid, check its Ka/Kb values or determine whether its the conjugate ba...
Tue Dec 05, 2017 9:56 pm
Forum: Biological Examples
Topic: Chemotheraphy Examples [ENDORSED]
Replies: 3
Views: 442

### Re: Chemotheraphy Examples[ENDORSED]

This was lectured on in class. The chemotherapy drug he referred to was Cisplatin. The long name for this drug is Cis-diamminedichloroplatinum (II), which contrasts with trans-diamminedicholoplatinum because of where the ammine or chloride groups are placed (next to or opposite of one another). Cisp...
Sun Dec 03, 2017 3:08 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: strength
Replies: 2
Views: 220

### Re: strength

There are a few ways to tell. Strong acids and bases have extremely high K values for the chemical reaction of their disassociation in water. There are patterns too related to these higher K values (meaning very little product was left behind). Metal hydroxides tend to be strong bases (metal +hydrox...
Sun Dec 03, 2017 3:02 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Dipole Moments
Replies: 2
Views: 208

### Re: Dipole Moments

If the difference in electronegativity is greater, the dipole moment will be stronger.
Mon Nov 27, 2017 7:31 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Reaction constant
Replies: 4
Views: 383

### Re: Reaction constant

the problem will usually call it just K, and depending on what other values they give you in the problem, those will determine whether it is referring to Kc and Kp. The importance i think is to know the difference between the two.
Mon Nov 27, 2017 7:29 am
Forum: Hybridization
Topic: Do pi bonds only form with double/triple bonds?
Replies: 5
Views: 386

### Re: Do pi bonds only form with double/triple bonds?

yes, make sure to know that a triple bond has two pi bonds but a double bond only has one.
Mon Nov 20, 2017 1:32 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Why do lone pairs take up more space than bonds?
Replies: 5
Views: 3242

### Re: Why do lone pairs take up more space than bonds?

protons are positively charged and attract electrons, but electrons are negatively charged and repulse other electrons. A lone pair causes an area of high electron density and causes distortions due to the electron-electron distortion. They don't take up more space, they just have a stronger negativ...
Mon Nov 20, 2017 1:28 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Number of Ligands
Replies: 2
Views: 209

### Re: Number of Ligands

Count the functional groups (ions or molecules) attached to the central atom. This is the number of ligands you have
Sun Nov 12, 2017 11:27 pm
Forum: Lewis Structures
Topic: Atomic Structure of HOCO
Replies: 2
Views: 221

### Re: Atomic Structure of HOCO

It was a radical. If you added up the valence electrons it had an odd number. HOCO does not have a charge so all the formal charges had to add up to zero. The way to make this happen is to have the carbon double bond to one oxygen, and single bond to another (this oxygen is bonded to the hydrogen). ...
Sun Nov 12, 2017 11:16 pm
Forum: Octet Exceptions
Topic: Expanded Octet
Replies: 4
Views: 326

### Re: Expanded Octet

First you need to check if the element can have an expanded octet. It should be in period three or higher (P, S, Cl, etc). If expanding the octet allows all the formal charges to become zero/ it forms a more stable molecule, than do it. Sometimes its obvious to do if there are 6 peripheral atoms and...
Sun Nov 05, 2017 4:48 pm
Forum: Lewis Structures
Topic: Taking into Account Shape and Structure
Replies: 2
Views: 204

### Re: Taking into Account Shape and Structure

You need to understand resonance but I dont think new material from the most recent lecture will be on the midterm.
Sun Nov 05, 2017 4:42 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Post-Module #18 [ENDORSED]
Replies: 2
Views: 324

### Re: Heisenberg Post-Module #18[ENDORSED]

Normally, the problem will give you an atomic radius and you have to multiply by two to get the diameter (which becomes the uncertainty in position). But, this problem directly tells you that the uncertainty is just 1 % the radius, so there is no need to multiply by two and use the diameter. Try mul...
Tue Oct 24, 2017 11:50 am
Forum: Einstein Equation
Topic: Comparing E=pc and E=.5mv^2
Replies: 3
Views: 360

### Re: Comparing E=pc and E=.5mv^2

E=0.5mv^2 is the generic physics equation for kinetic energy. It really depends on what variables you are already given when you decide which formula to use. When discussing the photoelectric effect, it is more common to use the Kinetic energy equation.
Tue Oct 24, 2017 11:28 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: p-orbitals
Replies: 3
Views: 235

### Re: p-orbitals

We did that to the P orbital to demonstrate Hunds rule. Simply writing a superscript (3) after the P doesn't really show that each electron occupies its own orbital
Tue Oct 24, 2017 11:26 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 3d and 4s
Replies: 5
Views: 420

### Re: 3d and 4s

The only two exceptions where the d orbital will first (that we know of in class up to this point) are chromium and copper. Other than those exceptions, the 4s will fill first than the 3d orbital.
Tue Oct 24, 2017 11:23 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: f-block
Replies: 3
Views: 264

### Re: f-block

The f block is a series of elements that would enter between group three and group four. The reason these elements are in the f block is because one or more of their outermost electrons is in the f orbital. If you were add the f block elements to the periodic table, it would expand in width.
Sun Oct 15, 2017 3:33 pm
Forum: Properties of Light
Topic: Problem 1.55 part A
Replies: 1
Views: 237

### Re: Problem 1.55 part A

the method you used to solve the problem works too, the problem is difficult because concerting cm^-1 to m^-1 is tricky. you have to multiply the 3600 cm^-1 by (100 cm/1 m) so that the centimeters cancel and you are left with meters in the denominator. This should give you the answer in the solution...
Sun Oct 15, 2017 3:21 pm
Forum: Properties of Light
Topic: 1.21- understanding how light acts as a wave
Replies: 2
Views: 236

### Re: 1.21- understanding how light acts as a wave

The photoelectric effect shows that light has properties of particles. In the experiment, they would shoot photons at certain pieces of metal, but if the photon did not reach the threshold energy, than no electron was ejected. They tested that same light (with the same frequency/wavelength), but the...
Fri Oct 06, 2017 11:20 pm
Forum: Balancing Chemical Reactions
Topic: What’s the quickest way to approaching writing a balanced equation with only one given compound?
Replies: 3
Views: 259

### Re: What’s the quickest way to approaching writing a balanced equation with only one given compound?

When balancing a combustion equation, try to start by balancing the carbon and hydrogen on the product side to match the reactants. Since its a combustion, you can always add more to the O2 (reactant) to balance it.
Fri Oct 06, 2017 11:15 pm
Forum: Balancing Chemical Reactions
Topic: Net Moles Produced [ENDORSED]
Replies: 5
Views: 564

### Re: Net Moles Produced[ENDORSED]

A trick to problems like these is to add the coefficients of the reactants and subtract that value from the sum of the coefficients of products. Make sure to balance the chemical equation first