## Search found 22 matches

Wed Mar 09, 2016 9:57 am
Forum: General Rate Laws
Topic: Pseudo rate constant
Replies: 2
Views: 487

### Re: Pseudo rate constant

Since it is the first-order pseudo reaction, then look at the plot of ln[A] vs Time. It should be a straight line and the slope of that line is -k.
Sun Mar 06, 2016 4:41 pm
Forum: Second Order Reactions
Topic: Determining order of a reaction
Replies: 2
Views: 445

### Re: Determining order of a reaction

That is when you are looking at the reaction mechanisms. So for reaction mechanisms, you are looking at each step that leads to the total reaction. The order of each reactant of each step is the coefficient.
Sun Mar 06, 2016 4:39 pm
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: Cis or trans in long chains
Replies: 2
Views: 446

### Re: Cis or trans in long chains

The 3,6-Dimethyl-3-Octene is trans. So look at the double bond, that is the middle. So the two branches from the first carbon of the double bond is CH 2 CH 3 and CH 3 . The two branches of the second carbon is H and CH 2 CHCH 3 CH 2 CH 3 . So we know that for cis, the priority groups are on the same...
Sun Feb 28, 2016 9:38 pm
Forum: *Alkanes
Topic: 4-ethyl-2,2-dimethyl-hexane
Replies: 1
Views: 332

### Re: 4-ethyl-2,2-dimethyl-hexane

The reason why it is 4,2,2 and not 3,5,5 is because the numbers are lower overall. For the rule that says that the first named substituent gets the lower number is only when the numbers are the same. For example if you start count from the right, the numbers are 3,5 and if you start counting from th...
Wed Feb 17, 2016 8:27 pm
Forum: General Rate Laws
Topic: Rate law
Replies: 1
Views: 312

### Re: Rate law

No, the exponent--order--does not always equal the stoichoimetric coefficient. For 2A->B, the rate=k[A]^n where n=2 because rate=k[A][A]. It is not because there are two moles of A but because there are two reactants that happen to be the same.
Mon Feb 15, 2016 5:05 pm
Forum: First Order Reactions
Topic: The dependancy on initial concentration
Replies: 1
Views: 473

### Re: The dependancy on initial concentration

The equation for half-life of a 1st order reaction is t (1/2) =0.693/k, the equation for half-life of a 2nd order reaction is t (1/2) =1/(k*[A] 0 ) and the equation for half-life of a zero order reaction is t (1/2) =[A] 0 /2*k. The key point here is that the equation for half...
Tue Feb 02, 2016 12:38 am
Forum: Balancing Redox Reactions
Topic: Half Reactions: Balancing
Replies: 1
Views: 302

### Re: Half Reactions: Balancing

The standard reduction potential (E^o) is an intensive property, so that means that the size or amount of something in the system will not change its value. An example that Dr. Lavelle used in lecture was the density of water. At 20 degrees celsius, the density of water if 0.9982g/cm^3 whether you h...
Thu Jan 28, 2016 5:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 1
Views: 379

### Re: Bond Enthalpies

Do you remember the molecular geometry based on VSEPR? Well that is linked to the mean bond enthalpy in a way. For example, CH4, every hydrogen broken off affects the remaining C-H bond. So every C-H requires a slightly different energy to be broken. That is why you use the mean bond enthalpies. Whi...
Sun Jan 24, 2016 11:29 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.15
Replies: 1
Views: 308

### Re: 9.15

Entropy is the measure of disorder. So " Low entropy means little disorder; high entropy means great disorder " (page 319 of the textbook). In part (a), you are asked to calculate the entropy change for freezing. When you freeze something, you are going from great disorder to little disord...
Tue Jan 19, 2016 1:56 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H vs. q
Replies: 1
Views: 388

### Re: Delta H vs. q

H is enthalpy and q is heat. But enthalpy, H, equals qP, or heat of the system when pressure is constant.
Sun Jan 10, 2016 5:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question regarding Enthalpy
Replies: 2
Views: 376

### Re: Question regarding Enthalpy

Yes. The delta H for the forward reaction is negative of the delta H of the reverse reaction. It is easier to think of it the other way though. delta H of the reverse reaction=-(delta H of forward reaction) because the forward reaction is what is given so if you reverse the reaction, you are essenti...
Sat Dec 05, 2015 3:44 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Fall 2011 Final Exam Q7A
Replies: 1
Views: 403

### Re: Fall 2011 Final Exam Q7A

Yes, you should be able to solve the problem by finding out which pOH is closest to pKB. In our course reader, on page 156, it says, "OPTIMUM BUFFERING CAPACITY OIF A WEAK ACID OCCURS WHEN [ACID]=[CONJUGATE CASE] OR FOR WEAK BASE WHEN [BASE]=[CONJUGATE ACID]...pH=pKA (pOH=pKB)"
Wed Nov 25, 2015 11:21 am
Forum: Biological Examples
Topic: Which direction would the reaction proceed if:
Replies: 2
Views: 488

### Re: Which direction would the reaction proceed if:

The reaction stays the same and does not favor a side because if you double each of the two reactants it is the same as quadrupling the concentration of reactants so if you quadruple the concentration of the products, there is an equivalent increase on both side resulting is no change in equilibrium.
Thu Nov 19, 2015 9:50 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Carbonic acid classificiation
Replies: 1
Views: 1438

### Re: Carbonic acid classificiation

Carbonic acid is considered an inorganic acid because of the structure of the molecule. Usually organic compounds contains carbons and hydrogens but at least one hydrogen is bonded to a carbon. For carbonic acid, none of the hydrogen bonds to the central carbon thus carbonic acid is an inorganic com...
Sun Nov 15, 2015 12:45 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Square-Planar/Tetrahedral Complex
Replies: 1
Views: 372

### Re: Square-Planar/Tetrahedral Complex

A complex with a coordination number of 4 would most likely have a tetrahedral shape because the ligands would be as far apart from each other as possible. A complex with a coordination number of 4 could have a square-planar shape, but there are specific requirements for that. Usually for a complex ...
Thu Nov 05, 2015 12:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angle of square pyramidal
Replies: 5
Views: 3340

### Re: Bond angle of square pyramidal

All the bond to bond angles should be 90 degrees because the lone pair to bond angle repulsion is stronger than the bond to bond repulsion. So the lone pair should repeal all the bond electrons away more stronger, resulting in all the bond to bond angles decreasing to less than 90.
Sun Nov 01, 2015 4:59 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Molecular Orbitals
Replies: 1
Views: 224

### Re: Molecular Orbitals

You use the diagram where the sigma pz bond is below the pi px and pi py bonds when Z (atomic number)>8. You use the diagram where the sigma pz bond is above the pi px and pi py bonds when Z (atomic number)<8.
Sun Nov 01, 2015 4:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR Practice
Replies: 31
Views: 7581

### Re: VSEPR Practice

I was wondering why the HClO4 molecule and the XeOF4 molecule are both polar. There are 4 Oxygen atoms attached directly to the Cl in the HClO4 molecule, so I thought they would have the same pull on the electrons. Or is it because of the extra H that theres a polarity? And is this the same explana...
Wed Oct 21, 2015 12:33 pm
Forum: Ionic & Covalent Bonds
Topic: Oxygen Double Bond
Replies: 2
Views: 3647

### Re: Oxygen Double Bond

Oxygen tend to form double bonds because of the formal charge. A molecule is more stable when the atoms in the molecules have formal charges of zero. The formal charge for oxygen is zero when it has a double bond because the formal charge equals the valence minus the sum of the lone electrons and th...
Tue Oct 13, 2015 5:50 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Shells & Orbitals
Replies: 3
Views: 602

### Re: Shells & Orbitals

Shells and orbitals are different and should not be used interchangeably. Shells are the energy levels while orbitals are in subshells. So shells have subshells -- s, p, d, f. Within these subshells there are orbitals. So in the p subshell, there are three orbitals -- px, py, pz. Then each orbital h...
Sun Oct 11, 2015 3:27 pm
Forum: Lewis Structures
Topic: Xe Lewis Dot Structure
Replies: 2
Views: 3097

### Re: Xe Lewis Dot Structure

The reason why Xenon can bond to 6 Fluorines is because it is an exception to the octet rule. Some elements in period 3 or high can hold more than an octet due to the 3d orbitals that are available for electrons to be added. These elements that are exceptions can have up to 10, 12, or 14 electrons i...
Sun Oct 04, 2015 7:10 pm
Forum: Significant Figures
Topic: All students read this sig fig post [ENDORSED]
Replies: 116
Views: 11781

### Re: All students read this sig fig post[ENDORSED]

When trying to figure out the sig. fig. of the final answer, do we take into account the sig. fig. of constants? I vaguely remember that my teacher for AP Chemistry said that we do not need to consider the sig. fig of constants (like Avogadro's number or speed of light) when we are determining the s...