## Search found 24 matches

Mon Mar 13, 2017 8:40 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 2013 Final Exam #2
Replies: 3
Views: 456

### Re: 2013 Final Exam #2

Part A From the problem, we are given that the generation of ATP from ADP is nonspontaneous and must be coupled to a spontaneous reaction, which is 3 NADH + 3/2 O2 + 3 H+ --> 3 H2O +3 NAD+ for 3 moles of NADH, ΔGr = -660.3kJ We know that the ΔGr of generation of ATP4- is +30.5kJ. For every 3 moles o...
Thu Mar 09, 2017 3:20 pm
Forum: *Alkanes
Topic: Naming Help
Replies: 7
Views: 724

### Re: Naming Help

It should be alphabetical with lowest number.
Also, the order of substituents should be taken into account (priority)
Thu Mar 02, 2017 10:03 am
Forum: *Free Energy of Activation vs Activation Energy
Topic: Chapter 4
Replies: 1
Views: 210

### Re: Chapter 4

Hi! The diagrams of #4.40 is explained on page 164 of Ch. 4.4 of Figure 4.7 Diagram 1 shows a fast reaction because ΔG‡ is small. Since ΔGr is negative, we know that the reaction is spontaneous (favorable) and exergonic. This is likely to occur at room temperature. Diagram 2 shows a slow reaction si...
Tue Feb 21, 2017 8:13 am
Forum: General Rate Laws
Topic: Units of K
Replies: 4
Views: 1392

### Re: Units of K

Memorizing the k units helps. You can also set up the rate equations to find the k units For example: a 2nd order rate equation is rate = k [R]^2 The unit of rate is mol/Ls and each [R] has the unit of mol/L Then, mol/Ls = k (mol/L)(mol/L) k must cancel out 1 L in denominator and 1 mole in numerator...
Mon Feb 13, 2017 5:56 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Winter 2013 Midterm
Replies: 2
Views: 361

### Re: Winter 2013 Midterm

You can convert the temperature from Celsius to Kelvin but since we want ΔT, 273K added to both final and initial temperature will be canceled so it's pointless to actually add 273
Hope this helps :)
Mon Feb 06, 2017 5:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: ∆G = -nFE
Replies: 4
Views: 327

### Re: ∆G = -nFE

You should look at the number of e- for n In the example 14.9a: 2Ce^4+ + 3I- --> 3Ce^3+ + I3- We need to identify which is oxidized and which is reduced 1) We are given that 2Ce^4+ --> 2 Ce3+ Then, that means in order to balance the charge on reactant and product sides, 2 e- must be added to the rea...
Wed Feb 01, 2017 5:59 pm
Forum: Calculating Work of Expansion
Topic: Sign of Work
Replies: 4
Views: 535

### Re: Sign of Work

Hi there! To figure out the sign of work, we should refer to... If we define work as W= -PΔV, we can figure out the sign of W to plug intp ΔU = Q + W If the piston moves out, then there is an increase in volume. Thus, W = -PΔV and ΔV is positive. W is negative. The energy of the system has decreased...
Mon Jan 23, 2017 5:47 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Ideal Gas
Replies: 2
Views: 381

### Re: Ideal Gas

You use different C for ΔS = nC ln (T2/T1)
When it's given constant volume, you use 3/2R. Under constant pressure, you use 5/2R
This can be found in "Constants and Equations Used in Chem, Biochem, and Physics" section of the laminated periodic table.
Sun Jan 22, 2017 9:48 pm
Forum: Student Social/Study Group
Topic: Study Group Chem 14B
Replies: 5
Views: 610

### Re: Study Group Chem 14B

Hey! I live in Courtside C4. It'll be great to have a study group. :D
Mon Jan 16, 2017 11:47 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: By or On the System? [ENDORSED]
Replies: 4
Views: 456

### Re: By or On the System?[ENDORSED]

"Do work on the system (compress a piston) or let the system do work on the surroundings (piston moves out)" This means that if we define work as W= -PΔV, we can figure out the sign of W to plug intp ΔU = Q + W If the piston moves out, then there is an increase in volume. Thus, W = -PΔV an...
Wed Jan 11, 2017 6:09 pm
Forum: Phase Changes & Related Calculations
Topic: Calculating work
Replies: 1
Views: 284

### Re: Calculating work

The question is Air in a bicycle pump is compressed by pushing in the handle. If the inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm, how much work is done in the compression? First, we need to know that work is W= -P delta V (or - pressure x change ...
Mon Nov 28, 2016 11:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp and Kc Same?
Replies: 4
Views: 527

### Re: Kp and Kc Same?

Kp is used for pressure and Kc is used for concentration
Mon Nov 21, 2016 9:59 pm
Forum: Bronsted Acids & Bases
Topic: J Section Question 1
Replies: 2
Views: 480

### Re: J Section Question 1

Usually, it's easy to tell the differences between Brønsted acid and Brønsted base
Acids have H+ and bases have OH-
One exception to the examples above is the NH3
You need to know Ammonia is a base
Tue Nov 15, 2016 8:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Quiz 3 Prep Fall 2014 #10
Replies: 2
Views: 443

### Re: Quiz 3 Prep Fall 2014 #10

Solve for pressure from PV=nRT first since you are given Kp (not Kc)!
When you use the ICE BOX, you should use it on partial pressure of the reactants and products.
Tue Nov 08, 2016 9:30 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Homework 17.33
Replies: 7
Views: 614

### Re: Homework 17.33

The answer to this homework question is a) HN(CH2CH2NH2)2, the 3 Nitrogen atoms have lone pairs to bond with a metal center atom, thus is polydentate b) CO3^2- can bond with a metal atom with one or two Oxygen atoms c) H2O is monodentate d) C2O4^2- can bond with a metal atom with 2 Oxygen atoms You ...
Wed Nov 02, 2016 9:05 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Which Diagram to draw in a bond with both elements Z<8 and Z>8 [ENDORSED]
Replies: 8
Views: 838

### Re: Which Diagram to draw in a bond with both elements Z<8 and Z>8[ENDORSED]

For heteronuclear diatomic molecules (one element has Z<8 and other has Z>8), see the BO molecule example provided by this page:http://www.nyu.edu/classes/tuckerman/adv.chem/lectures/lecture_15/node1.html The energy level of orbitals of element Z>8 will be lower than those of element Z<8 and pi 2px ...
Tue Oct 25, 2016 4:00 pm
Forum: Lewis Structures
Topic: Acids and Bases
Replies: 1
Views: 294

### Re: Acids and Bases

Lewis Acid accepts electron pair
Lewis Base donates electron pair
For example, we can view H2O as H+ and OH- forming H2O. OH- donates an electron pair and H+ accepts e- pair. The bond between O and H (H+ and O of OH-) is from the electron pair of O of OH-
Tue Oct 18, 2016 1:20 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Chapter 3 HW #23
Replies: 1
Views: 324

### Re: Chapter 3 HW #23

Positive: Cl +7, have 7 electrons. Can give 7e-
[Ne] with a full octet
Negative: Cl -1, can accept 1 more e- to obtain a full octet
[Ar] with a full octet
Both have noble gas configurations
Wed Oct 12, 2016 10:34 am
Forum: Balancing Chemical Reactions
Topic: Balancing Chemical Equations
Replies: 6
Views: 1279

### Re: Balancing Chemical Equations

A trick you can use when balancing chemical equations is to balance one element (for example Carbon) first, balance another element, and lastly oxygen especially when it is in the form of O2 Given the chemical equation CH3OH + O2 --> CO2 + H2O Personally, I would balance Carbon first. Both sides hav...
Wed Oct 05, 2016 9:03 am
Forum: Properties of Light
Topic: Threshold Potential
Replies: 1
Views: 325

### Re: Threshold Potential

The work function/threshold is determined experimentally
Here is a list of work functions: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/photoelec.html#c1
Tue Oct 04, 2016 2:04 pm
Forum: Properties of Electrons
Topic: 1.15....Where did I go wrong? [ENDORSED]
Replies: 3
Views: 668

### Re: 1.15....Where did I go wrong?[ENDORSED]

ΔE= Ef - Ei is the correct approach to this problem. However, ΔE is negative when electron is moving down in energy level, meaning n final < n initial.
Tue Sep 27, 2016 10:51 am
Forum: Significant Figures
Topic: Sig Figs Throughout Problems
Replies: 12
Views: 2662

### Re: Sig Figs Throughout Problems

Number of sig figs vary with problems. For example, a dilution problem may ask you to dilute 5.00 mL of some 1.0M solution to 1.00 mL of unknown concentration. In this case, you use M1V1=M2V2 and multiplication in sig fig rule states to use least number of sig fig. Therefore, you will have 2 sig fig...
Tue Sep 27, 2016 10:45 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: The Number of Moles in 2Na+2H2O--> 2NaOH+H2?
Replies: 3
Views: 10258

### Re: The Number of Moles in 2Na+2H2O--> 2NaOH+H2?

Atoms do not equal to mole. 1 mole has 6.022x10^23 atoms/molecules. The reaction above states that 2 mol of Sodium Na reacts with 2 mol of water H2O to form 2 mol of Sodium Hydroxide NaOH and 1 mol of Hydrogen gas H2. It is not referring to 2 atoms of sodium, 2 molecules of water, etc. You can view ...
Tue Sep 27, 2016 10:38 am
Forum: Significant Figures
Topic: Sig Figs Throughout Problems
Replies: 12
Views: 2662

### Re: Sig Figs Throughout Problems

Other than using sig figs of the previous calculation, another useful method to determine the number of sig figs that the final answer should have is by looking at the sig figs of the provided numbers in the original problem. But overall, according to my AP chemistry teacher, you should definitely k...