## Search found 51 matches

Thu Mar 15, 2018 6:31 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Midterm #2b
Replies: 1
Views: 264

### Midterm #2b

I'm a little confused on how you get this answer...

C6H12O6 (s) + 6 O2(g) → 6 CO2(g) + 6 H2O(l) ∆H°rxn=-2805 kJ.mol-1
Explain why ∆S°rxn for the above reaction should be positive or negative

the answer is that: 1 mol of solid → 6 mols of liquid ∆S°rxn for the above reaction is positive
Tue Mar 13, 2018 2:59 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.65 c
Replies: 2
Views: 183

### Re: 15.65 c

K=k/k' so if k is bigger the equilibrium constant will increase.
Tue Mar 13, 2018 2:58 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: question 15.47
Replies: 4
Views: 249

### Re: question 15.47

I believe that it's not included in the overall reaction because it cancels with the Cl from step 1
Mon Mar 12, 2018 6:47 pm
Forum: General Rate Laws
Topic: Decomposition of Ozone
Replies: 1
Views: 112

### Decomposition of Ozone

For the reaction 2O3(g)->3O2(g) why would the rate law be k[O3]^2/[O2]?
Sun Mar 11, 2018 3:52 pm
Forum: Zero Order Reactions
Topic: Slope From
Replies: 5
Views: 408

### Re: Slope From

Sun Mar 11, 2018 3:38 pm
Forum: General Rate Laws
Topic: Units
Replies: 11
Views: 786

### Re: Units

The most important thing is to make sure that all of your units are consistent, and to see if the problem asks you for specific units.
Sun Mar 11, 2018 3:36 pm
Forum: General Rate Laws
Topic: Integrated Rate Laws
Replies: 6
Views: 373

### Re: Integrated Rate Laws

It would be helpful to know and understand it but you shouldn't be expected to derive it on a test
Wed Mar 07, 2018 9:24 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19c
Replies: 6
Views: 356

### Re: 15.19c

Yeah it looks like they just converted everything to mol, I also got 2.85 for c because I didnt convert to mol
Wed Mar 07, 2018 4:23 pm
Forum: First Order Reactions
Topic: 15.37(B) homework
Replies: 3
Views: 222

### Re: 15.37(B) homework

So then it wouldn't matter whether you had the actual initial concentration?
Fri Mar 02, 2018 3:20 pm
Forum: Zero Order Reactions
Topic: slope
Replies: 9
Views: 1324

### Re: slope

Reactant concentration is decreasing so the slope will be negative so therefore k must be negative.
Second order reactions of 1/[A] has a positive slope so k is positive
Fri Mar 02, 2018 3:11 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E = E^o - (RT/nF) ln Q [ENDORSED]
Replies: 4
Views: 314

### Re: E = E^o - (RT/nF) ln Q[ENDORSED]

T will usually be a given temperature and R is a constant on the formula sheet.
R= 8.314JK^-1mol^-1
Fri Mar 02, 2018 2:56 pm
Forum: Zero Order Reactions
Topic: Units of k [ENDORSED]
Replies: 13
Views: 667

### Re: Units of k[ENDORSED]

An easy way of rememberin gthis is to to take (M^1-x)/s where s is the order of the reaction.
For example, for a 1st order reaction 1-1=0 and M^0=1 so the unit for k will be 1/s for 1st order rxn.
Tue Feb 20, 2018 11:53 pm
Forum: Balancing Redox Reactions
Topic: Reversing anode half-reactions
Replies: 1
Views: 193

### Reversing anode half-reactions

I'm having trouble understanding when and why we need to reverse the anode reactions... any help would be appreciated!
Tue Feb 20, 2018 11:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.11 d
Replies: 2
Views: 121

### Re: 14.11 d

That makes a lot of sense thank you!!
Tue Feb 20, 2018 9:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.11 d
Replies: 2
Views: 121

### 14.11 d

For 14.11 d the question is about writing the half-reactions and balanced equations for the cell reaction of galvanic cells. On part D, why is does the half reaction of the anode have H+ on the left side instead of the right?
Sat Feb 17, 2018 1:28 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: First Law
Replies: 5
Views: 659

### Re: First Law

q is zero when there is no heat lost or gained. In the isothermal system q is equal to -w
Sat Feb 17, 2018 1:24 pm
Forum: Balancing Redox Reactions
Topic: 14.1
Replies: 3
Views: 221

### Re: 14.1

The charges on either side should equal each other and if their not they it needs to be balanced
Wed Feb 14, 2018 11:42 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: delta U [ENDORSED]
Replies: 10
Views: 634

### Re: delta U[ENDORSED]

I know that delta U is 0 for isothermal reactions but I'm not sure why that is
Tue Feb 13, 2018 10:56 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 3
Views: 206

### Delta G

In a sample of 1 mol of gas initially at 1atm and 298K thats heated at constant pressure to 350K, and is then compressed isothermally it its initial volume and finally cooled to 298K at constant volume, why is Delta G 0?
Sat Feb 10, 2018 3:36 pm
Forum: Van't Hoff Equation
Topic: How to calculate K [ENDORSED]
Replies: 3
Views: 392

### Re: How to calculate K[ENDORSED]

From lnK=ΔG°/-RT you take e^x of both sides so the ln will cancel and you will have e^whatever ΔG°/-RT is
Wed Feb 07, 2018 12:19 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: ideal cooler [ENDORSED]
Replies: 5
Views: 346

### Re: ideal cooler[ENDORSED]

The "ideal" cooler does not exchange heat or matter with the surroundings and system.
Wed Feb 07, 2018 12:15 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated
Replies: 9
Views: 558

### Re: Isolated

Heat can be generated inside the system which causes the change in temperature
Thu Jan 25, 2018 9:59 pm
Forum: Phase Changes & Related Calculations
Topic: Heat and Work relation
Replies: 6
Views: 395

### Re: Heat and Work relation

Not necessarily for this equation.
Thu Jan 25, 2018 9:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Hmwk Q 8.31
Replies: 2
Views: 228

### Re: Hmwk Q 8.31

It's given that C at constant Pressure equals=5/2R the C at constant volume is given to be 3/2R
R is a given constant that equals R = 8.314 J·K-1·mol-1
Thu Jan 25, 2018 9:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Internal Energy
Replies: 5
Views: 273

### Re: Internal Energy

A change in pressure(delta P) does not necessarily mean that pressure is 0 it just means that the pressure is constant. The equation for work uses the actual pressure not the change in the pressure.
Fri Jan 19, 2018 3:12 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.19b
Replies: 1
Views: 99

### 8.19b

In question 8.19 part b it asks what percentage of the heat calculated in part a, which was 1.4x10^2 kj, is used to raise the temperature of the water? the answer is ((1.3x10^5J)/(1.45x10^5J))x100=90% but I'm not sure where these numbers come from
Thu Jan 18, 2018 8:53 pm
Forum: Phase Changes & Related Calculations
Topic: 8.5
Replies: 5
Views: 242

### Re: 8.5

Change in internal energy is the sum of the energy terms so it is equal to q + w so you just add 524kJ and 340kJ
Thu Jan 18, 2018 8:49 pm
Forum: Phase Changes & Related Calculations
Topic: 8.17
Replies: 3
Views: 232

### Re: 8.17

When there is a phase change, such as when going from a solid to a liquid (melting), heat is required although the temperature does not change. Melting is an endothermic reaction so q will be positive and work is done by the system because it's losing energy so w is negative. Condensation work is po...
Sat Jan 13, 2018 4:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Difference between delta H and delta U
Replies: 2
Views: 20259

### Re: Difference between delta H and delta U

Delta H is the change in enthalpy which is equal to change in U +P*change in V and the delta U is the change in internal energy of the system.
q is the heat of the system.
Thu Jan 11, 2018 10:38 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy is a state property
Replies: 13
Views: 743

### Re: Enthalpy is a state property

Enthalpy is determined by the current state of the system and and is therefore independent of how the state was prepared. It is not reliant on the path of the system.
Thu Jan 11, 2018 10:32 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Sublimation
Replies: 4
Views: 280

### Re: Sublimation

Sublimation is a type of phase transition of a substance from solid to vapor without going through the liquid phase.
Sat Dec 09, 2017 4:33 pm
Forum: DeBroglie Equation
Topic: Difference between DeBrogile and Light
Replies: 3
Views: 258

### Re: Difference between DeBrogile and Light

The De broglie equation is wavelength=h/p where p=mv with the v relating to velocity of a particle not the frequency. If you were given the frequency and asked to find the wavelength you would use c=wavelength times frequency. So basically you use De broglie when comparing wavelength to its mass and...
Sat Dec 09, 2017 1:26 pm
Forum: Properties of Electrons
Topic: Velocity of Ejected electron
Replies: 4
Views: 5377

### Re: Velocity of Ejected electron

Work functions are used when you are trying to find the kinetic energy of an ejected electron in which case you would take the energy supplied by the photon minus the work function.
Sat Dec 09, 2017 1:25 pm
Forum: Properties of Electrons
Topic: Velocity of Ejected electron
Replies: 4
Views: 5377

### Re: Velocity of Ejected electron

To find the velocity of the ejected electron you use the kineticE=(1/2)mv^2 equation. You then plug in energy of the ejected electron given to you in part a and set it equal to 1/2 times the mass of an electron times v^2. You do not need to use the work function.
Fri Dec 08, 2017 9:18 pm
Forum: Naming
Topic: Order of Ligands
Replies: 8
Views: 500

### Re: Order of Ligands

They must be in alphabetical order without the prefixes.
Fri Dec 08, 2017 8:25 pm
Forum: Conjugate Acids & Bases
Topic: basicity strength
Replies: 3
Views: 360

### basicity strength

When comparing bases, what do you look at to determine which base is stronger?
Fri Dec 08, 2017 8:14 pm
Forum: Sigma & Pi Bonds
Topic: Sigma Bonds
Replies: 4
Views: 362

### Re: Sigma Bonds

Sigma bonds refer to one single bond. In a double bond you can think of the first bond as being a sigma bond and the rest of the bonds being pi bonds. So a double bond will have one sigma bond and one pi bond and a triple bond will have one sigma bond and two pi bonds.
Wed Dec 06, 2017 7:38 pm
Forum: Bronsted Acids & Bases
Topic: Strong vs. Weak
Replies: 5
Views: 304

### Re: Strong vs. Weak

Okay thank you!
Wed Dec 06, 2017 6:34 pm
Forum: Bronsted Acids & Bases
Topic: Strong vs. Weak
Replies: 5
Views: 304

### Strong vs. Weak

How can you tell the difference between a strong and a weak acid and strong and weak base by looking at the reaction equation?
Wed Nov 29, 2017 7:25 pm
Forum: Sigma & Pi Bonds
Topic: Pi bonds
Replies: 6
Views: 929

### Re: Pi bonds

Pi bonds can only overlap side by side with electron densities on each side of the internuclear axis so if it rotated the bond would be broken.
Wed Nov 29, 2017 7:09 pm
Forum: Sigma & Pi Bonds
Topic: Sigma and pi
Replies: 12
Views: 891

### Re: Sigma and pi

Sigma bonds are always the first bonds to form and are single bonds and the remaining bonds are pi bonds. In an example of N2, the 2 pi bonds will appear to surround the single sigma bond when the electron densities of the pi bonds combine.
Sun Nov 19, 2017 8:36 pm
Forum: Ionic & Covalent Bonds
Topic: different types of bonds
Replies: 6
Views: 453

### Re: different types of bonds

A non-polar bond has equal sharing of the bonding electron pair and usually takes place between nonmetals so the dipoles cancel and ha a dipole moment of zero. A polar bond has unequal sharing of the electron pair so there is a nonzero dipole moment. Ionic bonds have a difference in electronegativit...
Sun Nov 19, 2017 6:24 pm
Forum: Hybridization
Topic: Hybridization
Replies: 6
Views: 351

### Re: Hybridization

Hybridization is the merging of two different orbitals to form a new atomic orbital which can change the bonding properties.
Sun Nov 19, 2017 6:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Triple vs. double bonds
Replies: 2
Views: 283

### Triple vs. double bonds

On a homework problem for writing the lewis structure for ClCN, why would Carbon form a triple bond with nitrogen and a single bond with chlorine instead of a double bond with both Nitrogen and chlorine?
Thu Oct 26, 2017 3:56 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Units [ENDORSED]
Replies: 4
Views: 349

### Re: Units[ENDORSED]

Either way is probably fine, just check to make sure it doesn't specify for a specific one in the problem.
Thu Oct 26, 2017 3:55 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Test 3 [ENDORSED]
Replies: 7
Views: 2481

### Re: Test 3[ENDORSED]

My TA told us that the test will cover 1.6 through CH 2
Sun Oct 22, 2017 10:21 pm
Forum: *Shrodinger Equation
Topic: What is a node?
Replies: 5
Views: 463

### Re: What is a node?

Yes, a node is where the wave function passes through zero
Sun Oct 22, 2017 10:20 pm
Forum: Photoelectric Effect
Topic: Work Function [ENDORSED]
Replies: 5
Views: 409

### Re: Work Function[ENDORSED]

Yes, if a photon has energy of the photon is greater than or equal to the work function the electron will be removed
Sun Oct 15, 2017 12:52 pm
Forum: Properties of Light
Topic: Speed of Light Constant
Replies: 18
Views: 970

### Re: Speed of Light Constant

I would use 2.9988x10^8 just because it is more accurate; however, if 3.00x10^8 was the number given in the problem then I would use that one instead.
Fri Oct 06, 2017 12:22 am
Forum: Balancing Chemical Reactions
Topic: Combustion [ENDORSED]
Replies: 6
Views: 590

### Re: Combustion[ENDORSED]

Yes, because there was a reaction with oxygen leading to the production of carbon dioxide and water!
Thu Oct 05, 2017 9:35 pm
Forum: SI Units, Unit Conversions
Topic: Do we need to memorize unit conversions? [ENDORSED]
Replies: 9
Views: 2286

### Re: Do we need to memorize unit conversions?[ENDORSED]

Some temperature conversions that are good to know:
When going from Celsius to Kelvin you add 273.15 to the temperature in Celsius (and subtract 273.15 going from kelvin to celsius)
Celsius= (Fahrenheit-32)x(5/9)