## Search found 50 matches

Mon Mar 12, 2018 2:53 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediate
Replies: 6
Views: 361

### Re: Intermediate

Catalysts are involved in the first step of the equation on the reactants side and then reformed in another elementary step as products. Intermediates are formed during an elementary step first as products and then re-used as reactants later in another elementary step. Both do not show up in the ove...
Mon Mar 12, 2018 2:46 pm
Forum: *Alcohols
Topic: Functional Groups on Final? [ENDORSED]
Replies: 5
Views: 913

### Re: Functional Groups on Final?[ENDORSED]

The functional groups we learned today are part of the 14B syllabus and so I would expect that they are fair to be tested upon for the final
Mon Mar 12, 2018 2:46 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Replies: 3
Views: 197

Heterogeneous catalysts are usually only available in the solid state and therefore mainly function through adsorption, homogeneous catalysts are available in all states and therefore can but no do not have to function through adsorption.
Thu Mar 08, 2018 5:39 pm
Forum: General Rate Laws
Topic: 15.17 type problems
Replies: 4
Views: 311

### Re: 15.17 type problems

You can show your work by writing the ratio of concentration in exp 1 over concentration in exp 2 raised to some power equals the ratio of rate in exp 1 over rate in exp 2. This would be written as (conc1/conc2)^n=(rate1/rate2) where n is the order.
Thu Mar 08, 2018 5:36 pm
Forum: General Rate Laws
Topic: integrated rate law to determine order
Replies: 2
Views: 202

### Re: integrated rate law to determine order

For second order integrated rate law = k is positive, reciprocal of concentration is taken
For first order integrated rate law = ln/e will be involved, k is negative
For 0 order integrated rate law = k is negative, concentration is left as is
Thu Mar 08, 2018 5:31 pm
Forum: Experimental Details
Topic: 15.19c
Replies: 2
Views: 563

### Re: 15.19c

Rate is given in units of mol/(Ls), and as such when doing calculations involving the rate law, all your values should be in moles.
Tue Feb 27, 2018 11:25 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19
Replies: 3
Views: 244

### Re: 15.19

You do, as the orders of all reactants factor into the overall order of the reaction
Tue Feb 27, 2018 11:21 am
Forum: General Rate Laws
Topic: Order of reactions?
Replies: 3
Views: 204

### Re: Order of reactions?

Zero - rate of reaction is equal to rate constant k
1st order - depends on only ONE reactant concentration
2nd order - depends on two different reactants or one reactant squared
Tue Feb 27, 2018 11:18 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Midterm 6A (Multiple Choice)
Replies: 4
Views: 427

### Re: Midterm 6A (Multiple Choice)

When determining the molar entropy of molecules, the phase of the molecule takes priority over size. That is, only if both molecules are in the same phase does size matter. Otherwise, the entropy of gases >> liquids > solids
Thu Feb 22, 2018 11:16 am
Forum: Balancing Redox Reactions
Topic: Writing and Balancing Half Reactions
Replies: 6
Views: 445

### Re: Writing and Balancing Half Reactions

1. Identify the key element that undergoes an oxidation state change. 2. Balance the number of atoms of the key element on both sides. 3. Add the appropriate number of electrons to compensate for the change of oxidation state. 4. Add H+ (in acid medium), or OH- (in basic medium), to balance the char...
Thu Feb 22, 2018 11:15 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt(s) in a cell diagram
Replies: 1
Views: 143

### Re: Pt(s) in a cell diagram

For either the cathode or anode, if there is no conducting solid, then Pt(s) will be placed there. For example, if the reaction at the anode consists of Fe+2(aq) -> Fe+3 + e-, then Pt(s) will be placed on that side.
Thu Feb 22, 2018 11:13 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic vs. Electrolytic Cell
Replies: 3
Views: 226

### Re: Galvanic vs. Electrolytic Cell

A Galvanic cell converts chemical energy into electrical energy. An electrolytic cell converts electrical energy into chemical energy. Electrolysis is used to drive an oxidation-reduction reaction in a direction in which it does not occur spontaneously.
Thu Feb 15, 2018 8:47 pm
Forum: Balancing Redox Reactions
Topic: Splitting Redox Reactions
Replies: 3
Views: 265

### Re: Splitting Redox Reactions

The other molecules whose oxidation states remain the same throughout the reaction are spectators and don't have to be written in the final reaction.
Thu Feb 15, 2018 8:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Standard ∆G for a system at equilibrium
Replies: 3
Views: 270

### Re: Standard ∆G for a system at equilibrium

Standard change in free energy of a system at equilibrium is not 0, but rather related to the equilibrium constant K at that temperature. If K is >1, then standard change in free energy will be -, and if K<1, then standard change in free energy is +. It is delta g or change in energy that is 0 for a...
Thu Feb 15, 2018 8:38 pm
Forum: Student Social/Study Group
Topic: Sections on Test 2
Replies: 3
Views: 327

### Re: Sections on Test 2

I'm assuming that Test 2 will be on electrochemistry, which according to the electrochemistry outline spans from chapter 14.1 to 14.11.
Thu Feb 08, 2018 11:05 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Hydrogen Electrode
Replies: 1
Views: 111

### Re: Standard Hydrogen Electrode

I think we need to understand that we get the standard reduction potential of elements from galvanic cells that involve the element in question and hydrogen. A cell that involves a standard hydrogen electrode is a considered a galvanic cell.
Thu Feb 08, 2018 11:01 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: interpretation of galvanic cell diagram
Replies: 2
Views: 128

### Re: interpretation of galvanic cell diagram

For this cell diagram, on the left silver loses an electron to become Ag+ and subsequently reacts with iodine to form AgI. The electron passes to the cathode where chlorine ions, silver chloride, and silver are all interacting with each other.
Thu Feb 08, 2018 10:57 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Extensive Property?
Replies: 3
Views: 233

### Re: Extensive Property?

To build on this, intensive properties would be like density and melting/boiling point of an element, which remain the same despite the amount of matter present in a sample.
Thu Feb 01, 2018 7:00 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Negative delta s value
Replies: 4
Views: 4171

### Re: Negative delta s value

Negative delta s does not by itself correspond to a spontaneous process, but rather the product of T and delta S should be less than delta H, which has to be negative. Negative delta S actually means that either temperature has decreased, pressure has increased, or volume has decreased.
Thu Feb 01, 2018 6:55 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: units conversion for entropy
Replies: 6
Views: 339

### Re: units conversion for entropy

The only case where this would matter would be in a problem and some values are in j/k and kj/k. Here, you would convert all units to either j/k or kj/k.
Thu Feb 01, 2018 6:51 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible vs. Irreversible reactions
Replies: 2
Views: 181

### Re: Reversible vs. Irreversible reactions

If temperature remains constant throughout the reaction, then it is said to be isothermal. In a reversible reaction, the external pressure equals the internal pressure of the container, and the external pressure is increased or decreased in small increments. In a irreversible reaction, there is a no...
Fri Jan 26, 2018 4:19 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reversible and Irreversible
Replies: 3
Views: 206

### Re: Reversible and Irreversible

For a reversible process, pressure inside and outside of the system will be equal. For an irreversible process, there will be a significant difference between the pressure inside and outside of the system.
Fri Jan 26, 2018 4:18 pm
Forum: Phase Changes & Related Calculations
Topic: When to use Kelvin or Celsius
Replies: 10
Views: 1971

### Re: When to use Kelvin or Celsius

It depends on the units of the constants in the problem. For example, in a problem that gives molar heat capacity, you would use kelvin, whereas in a problem that gives specific heat capacity, you would use celsius. If no preference is stated, than either or is fine.
Fri Jan 26, 2018 4:16 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Question [ENDORSED]
Replies: 3
Views: 183

### Re: Entropy Question[ENDORSED]

Take for example water vapor compared to water as a liquid. In water vapor, the molecules are able to move much more freely and therefore contain a larger number of states than the molecules in the liquid, which are much more constrained and limited in their movements.
Sun Jan 21, 2018 4:14 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: state property
Replies: 3
Views: 215

### Re: state property

Heat is not an intrinsic property of a system, as it only occurs when there is a temperature difference between two objects. Intrinsic properties would be like pressure or volume.
Sun Jan 21, 2018 4:12 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: self test 8.7B
Replies: 2
Views: 186

### Re: self test 8.7B

part a is -30 because the reaction is exothermic, part b is +40 because work is being done on the system, so the internal energy is 40-30=10kJ
Sun Jan 21, 2018 4:06 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Homework Problem 8.41
Replies: 2
Views: 145

### Re: Homework Problem 8.41

In this case, the water gives off the heat and the ice absorbs it, but yes, we always take into account the energy needed to undergo a phase change in heat equilibrium problems.
Thu Jan 11, 2018 11:37 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Chapter 8
Replies: 6
Views: 299

### Re: Chapter 8

We are starting from section 8.8 in the book, as everything before that deals with work and internal energy, not heat and enthalpy. Number 29 is the first question that deals with enthalpy in the book.
Thu Jan 11, 2018 11:34 am
Forum: Phase Changes & Related Calculations
Topic: Why steam burns are worse explained
Replies: 5
Views: 285

### Re: Why steam burns are worse explained

When steam hits your hand, it first condenses, and because ∆H for the vaporization of water is extremely high, a lot of heat is released upon contact with your body. When water hits your hand, it does not require this phase change, and the heat transferred to your body is therefore much less.
Thu Jan 11, 2018 11:31 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Equations
Replies: 6
Views: 359

### Re: Equations

To find the heat needed for a temperature change, the formula is q = mC∆t, where m is mass and C is the specific heat of the substance in J/(g)(c).
To find the heat needed for a phase change, the formula is q = n∆H, where n is the number of moles and ∆H is given in kJ/mol.
Fri Dec 08, 2017 4:24 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 25 degrees C
Replies: 2
Views: 227

### Re: 25 degrees C

Ka is affected by temperature and therefore would change if it not at 25 degrees Celsius. If this is the case, I would assume the question would provide the new Ka for the specified temperature.
Fri Dec 08, 2017 4:17 pm
Forum: Bronsted Acids & Bases
Topic: 12.9 d)
Replies: 1
Views: 195

### Re: 12.9 d)

First, you have to figure out the oxidation states of each species in each compound for the reactants and products. For the reactants, in NH4I: NH4 is +1 and I is -1 and in KNH2: K is +1 and NH2 is -1. For the products, in KI: K is +1 and I is -1, and NH3 is netural. Because K and I did not change o...
Tue Nov 28, 2017 11:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Square planar vs Tetrahedral
Replies: 2
Views: 245

### Re: Square planar vs Tetrahedral

A square planar shape has six areas of electron density, 2 of which are lone pairs, whereas a tetrahedal shape has four areas of electron density and no lone pairs.
Tue Nov 28, 2017 11:31 pm
Forum: Naming
Topic: Iron v ferrate in coordination compound naming
Replies: 8
Views: 2081

### Re: Iron v ferrate in coordination compound naming

I think we always use ferrate for coordination compounds.
Mon Nov 27, 2017 3:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T_shaped Molecules
Replies: 2
Views: 219

### Re: T_shaped Molecules

An example of a T-shaped molecule would be BF3 or ClF3.
Mon Nov 27, 2017 2:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Double and Triple Bonds
Replies: 1
Views: 198

### Re: Double and Triple Bonds

No, in the VSEPR model single, double, and triple bonds all count as one area of electron density.
Sun Nov 19, 2017 8:14 pm
Forum: Biological Examples
Topic: TM Concept Clarification
Replies: 2
Views: 240

### Re: TM Concept Clarification

Up to 6 ligands, which are also Lewis bases, donate their pair of electrons to a transition metal to form the cage-like molecule
Wed Nov 15, 2017 7:11 pm
Forum: Octet Exceptions
Topic: Why do octets expand?
Replies: 4
Views: 383

### Re: Why do octets expand?

According to the principal quantum number (n) of period 3, the angular momentum number (l) can be 2, 1, or 0. Therefore, elements in the third period have empty d shells even though they come before elements with electrons in them already on the periodic table
Wed Nov 15, 2017 7:07 pm
Forum: Sigma & Pi Bonds
Topic: When looking at at molecule how can I determine when they will form sigma and pi bonds?
Replies: 3
Views: 252

### Re: When looking at at molecule how can I determine when they will form sigma and pi bonds?

The first bond that atoms form is always a sigma bond, any bond after that is a pi bond, so CO has 1 sigma bond and 2 pi bonds
Wed Nov 15, 2017 7:06 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Understanding sigma and pi bonds?
Replies: 8
Views: 430

### Re: Understanding sigma and pi bonds?

And because molecules with pi bonds are unable to rotate, all of the atoms within the molecule are located in the same plane
Wed Nov 15, 2017 7:02 pm
Forum: Administrative Questions and Class Announcements
Replies: 2
Views: 251

You should email your TA, telling him where you think you deserved more points. On past midterms, one point was deducted for incorrect units or sig figs.
Wed Nov 15, 2017 7:00 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determing Molecular Shape
Replies: 2
Views: 232

### Re: Determing Molecular Shape

We are expected to know the bond angles for every structure that we have learned, this includes

Linear (180 degrees)
Trigonal planar (120)
Tetrahedral (109)
Trigonal Pyramidal (<109)
Bent (<109)
Trigonal Bipyramidal (120 and 90)
Seesaw (<120 and <90)
Octahedral (90)
Square Planar (90)
Tue Nov 07, 2017 9:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Beryllium Octet Rule
Replies: 6
Views: 3227

### Re: Beryllium Octet Rule

The first four elements of the periodic table up to boron never obtain an octet of electrons
Tue Nov 07, 2017 9:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Midterm
Replies: 2
Views: 289

### Re: Midterm

Yes, everything up to vsper models is on the midterm
Thu Nov 02, 2017 1:09 am
Forum: Electronegativity
Topic: oxygen and nitrogen
Replies: 3
Views: 444

### Re: oxygen and nitrogen

The ionization energy of oxygen is higher than that of nitrogen because nitrogen has half asymmetry in its p shell while oxygen has a full first orbital. The higher electron affinity of oxygen compared to nitrogen compensates for this deficiency when talking about electronegativity.
Thu Nov 02, 2017 1:00 am
Forum: Trends in The Periodic Table
Topic: Problem 2.61 Part C
Replies: 2
Views: 247

### Re: Problem 2.61 Part C

Yes, ionization energy generally increases from left to right across a period because the electrons are closer to the nucleus from the added protons and higher positive charge
Wed Oct 25, 2017 10:11 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Exceptions to Electron Configuration [ENDORSED]
Replies: 5
Views: 1105

### Re: Exceptions to Electron Configuration[ENDORSED]

A quick google search turned out that molybdenum has the same valence electron configuration as chromium but tungsten does not, while both silver and gold have the same valence electron configuration as copper.
Wed Oct 25, 2017 10:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 2.1 part d
Replies: 4
Views: 235

### Re: 2.1 part d

Yes, the electron moves from a lower energy state to a higher energy state, which is a greater distance from the nucleus. In this case, it moves from the first shell to the second shell.
Sun Oct 15, 2017 9:32 pm
Forum: Properties of Electrons
Topic: Atomic Spectra [ENDORSED]
Replies: 4
Views: 363

### Re: Atomic Spectra[ENDORSED]

^ yes, things in nature will always go to their lowest state of energy, and in this case that state is n=1
Sun Oct 15, 2017 9:30 pm
Forum: Photoelectric Effect
Topic: Photoelectric effect [ENDORSED]
Replies: 4
Views: 328

### Re: Photoelectric effect[ENDORSED]

To build on what Andrea said, raising the intensity of light just increased the number of photons, and without sufficient frequency these photons were still unable to eject electrons.