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
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: 417
- Tue Mar 13, 2018 2:59 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: 15.65 c
- Replies: 2
- Views: 400
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: 467
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: 283
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: 762
Re: Slope From
It can help you to identify the rate constant.
- Sun Mar 11, 2018 3:38 pm
- Forum: General Rate Laws
- Topic: Units
- Replies: 11
- Views: 1488
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: 825
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: 773
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: 491
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: 4823
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
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: 661
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
R= 8.314JK^-1mol^-1
- Fri Mar 02, 2018 2:56 pm
- Forum: Zero Order Reactions
- Topic: Units of k [ENDORSED]
- Replies: 13
- Views: 1555
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.
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: 427
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: 286
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: 286
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: 996
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: 413
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: 3055
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: 446
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: 879
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: 625
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: 1110
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: 736
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: 325
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
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: 525
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: 152
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: 489
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: 1154
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: 40275
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.
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: 1894
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: 548
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: 513
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: 14675
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: 14675
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: 865
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: 631
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: 608
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: 598
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: 598
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: 1945
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: 1611
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: 891
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: 655
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: 655
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: 560
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: 2815
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: 746
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: 692
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: 1784
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: 1010
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: 4779
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)
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)