Search found 51 matches
- Wed Mar 11, 2020 12:30 am
- Forum: Environment, Ozone, CFCs
- Topic: stoichiometric coefficients
- Replies: 19
- Views: 1417
Re: stoichiometric coefficients
Either way is correct, but if you wanted to answer a question with one mol of O3, then you can use the reaction with 3/2 to make it simpler.
- Wed Mar 11, 2020 12:23 am
- Forum: Administrative Questions and Class Announcements
- Topic: What is the plan for the final?
- Replies: 16
- Views: 1001
Re: What is the plan for the final?
Adriana_4F wrote:It's worth 180 points now.. I hope it won't be worth less now that it's open book :/
He just sent an update saying it will still be worth 180 points.
- Wed Mar 11, 2020 12:21 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: 7E.1
- Replies: 3
- Views: 246
Re: 7E.1
A catalyst will increase the reaction rate of both directions, because it lowers the activation energy. Delta H is not changed because that is in relation to thermodynamics, and therefore will not affect the reaction rates.
- Wed Mar 11, 2020 12:14 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Rate Constant K
- Replies: 4
- Views: 379
Re: Rate Constant K
k is the rate constant of the forward reaction, while k' is the rate constant of the reverse reaction. K is the equilibrium value.
- Wed Mar 11, 2020 12:12 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Difference between catalyst and intermediate
- Replies: 9
- Views: 625
Re: Difference between catalyst and intermediate
A catalyst will be present at the beginning and the end of a set of reactions. An intermediate will be produced, but then be a reactant in a later reaction.
- Thu Mar 05, 2020 8:58 pm
- Forum: General Science Questions
- Topic: Reducing Math Errors
- Replies: 7
- Views: 642
Re: Reducing Math Errors
One way I usually have some problems is with parentheses. It helps to practice how you type the equations into the calculator and figure out how it should be typed before you put it in. If you have enough time during your test, I will also check my answer by using it to find a constant given in the ...
- Thu Mar 05, 2020 8:55 pm
- Forum: Balancing Redox Reactions
- Topic: Strength of Reducing/Oxidizing Agents
- Replies: 4
- Views: 328
Re: Strength of Reducing/Oxidizing Agents
You can determine if the metal is a stronger reducing agent based on the value of the reduction potential. The more negative standard reduction potential, the better reducing agent it is, and the more likely it is to oxidize.
- Thu Mar 05, 2020 8:48 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: 6.61
- Replies: 2
- Views: 287
Re: 6.61
You can assume that the E naught of the cell is equal to zero because this occurs in a concentration cell, which is when the two half cells have the same electrode but have different concentrations. Since the anode and cathode half reactions are the same, their total reduction potentials will be the...
- Thu Mar 05, 2020 8:45 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: max work and cell potential
- Replies: 3
- Views: 247
Re: max work and cell potential
The maximum work will be equivalent to Gibbs free energy. When Ecell is positive, the work value and gibbs free energy will be negative, meaning that it is spontaneous and work is being done by the system.
- Thu Mar 05, 2020 8:38 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Question 6M.11
- Replies: 2
- Views: 253
Re: Question 6M.11
You can determine which one will oxidize and reduce by looking at the reduction potentials of each. The more positive reduction potential will be the reduction half reaction, and the other half reaction will be oxidation. In this example, Co2+ is reduced and Ti2+ is oxidized.
- Wed Feb 26, 2020 1:27 pm
- Forum: Balancing Redox Reactions
- Topic: 6L.9
- Replies: 2
- Views: 211
Re: 6L.9
It is also helpful to remove the spectator ions so you can see the charge on the ions for the redox half reactions. For example, instead of NaCl, you could write Na+.
- Wed Feb 26, 2020 1:25 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: G(not) and G
- Replies: 15
- Views: 700
Re: G(not) and G
Gnaught will be under standard conditions, which are 1.0M, 1atm, and 25C.
- Wed Feb 26, 2020 1:22 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Strength of a reducing agent
- Replies: 3
- Views: 257
Re: Strength of a reducing agent
A reducing agent should be increase in strength with its decrease in electronegativity. If it is more likely to lose an electron and be oxidized, it will be a better reducing agent.
- Wed Feb 26, 2020 1:21 pm
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: Porous Disk and Salt Bridge
- Replies: 13
- Views: 1164
Re: Porous Disk and Salt Bridge
They have the same function, so one will not be more efficient than the other.
- Wed Feb 26, 2020 1:13 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: log or ln
- Replies: 6
- Views: 475
Re: log or ln
You can use either but the log one is more useful when you have to solve for pH or have the pH given in the question, because you are then able to leave it in log[H+] form.
- Sat Feb 22, 2020 1:50 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: n in -nFE
- Replies: 12
- Views: 826
Re: n in -nFE
n represents the moles of electrons. In each balanced half reaction, the number of moles of electrons should be the same, but on different sides of the reaction.
- Sat Feb 22, 2020 1:44 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 5
- Views: 523
Re: Salt Bridge
Negative ions in the salt bridge (ex. NO3- or Cl-) will travel to the anode to maintain the charge, while positively charged ions (ex. K+ or Na+) will travel to the cathode.
- Sat Feb 22, 2020 1:37 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Midterm 6D
- Replies: 5
- Views: 431
Re: Midterm 6D
Both A and C involve changing the phase change to one with more entropy. However, the answer is A because that change is associated with a larger increase in entropy then the phase change from solid to liquid.
- Sat Feb 22, 2020 1:36 pm
- Forum: Student Social/Study Group
- Topic: Midterm 3C
- Replies: 1
- Views: 152
Re: Midterm 3C
NH4Cl will be able to dissociate, making NH4+ and Cl-. This will make it more acidic because NH4+ will be able to donate protons.
- Sat Feb 22, 2020 1:34 pm
- Forum: Phase Changes & Related Calculations
- Topic: delta G0 versus delta G
- Replies: 15
- Views: 2495
Re: delta G0 versus delta G
Delta G naught (and any other thing with this symbol) shows free energy at standard conditions, while delta G will be at given conditions.
- Fri Feb 14, 2020 10:27 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: PV=nRT
- Replies: 5
- Views: 275
Re: PV=nRT
It can sometimes be tricky to know when to use PV=nRT, but I generally try to figure out what equations could be used to solve a problem. Then, if I am missing a variable, I check to see if PV=nRT is applicable. Delta should only be used when you know that there is a change in the system. For exampl...
- Fri Feb 14, 2020 10:22 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free energy concept
- Replies: 16
- Views: 787
Re: Gibbs Free energy concept
It shows how much energy is available to do work. It is really important in determining if the reaction is spontaneous (ΔG-). A reaction could be spontaneous if it becomes more disordered, if energy is released, or both. The negative value shows that product formation will be favored.
- Fri Feb 14, 2020 10:16 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Delta G
- Replies: 6
- Views: 347
Re: Delta G
It means that it is under standard conditions. In calculating ΔG, if you wanted to calculate the standard form, you would have to use other values that are also in their standard form.
- Fri Feb 14, 2020 10:14 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Why is delta U = 0 for isothermal reactions?
- Replies: 11
- Views: 4214
Re: Why is delta U = 0 for isothermal reactions?
The temperature is constant, and no energy will enter or leave the system. Therefore, ΔU=0.
- Fri Feb 14, 2020 10:12 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Delta S
- Replies: 4
- Views: 379
Re: Delta S
In a reversible process, the ΔSuniverse is equal to 0, so the ΔSsys=-ΔSsurr. In a irreversible process, ΔSsurr=0, so ΔSuni=ΔSsys.
- Sat Feb 08, 2020 10:34 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Delta H and qp
- Replies: 8
- Views: 161
Re: Delta H and qp
LBacker_2E wrote:You said you can make assumptions about delta H when pressure is constant, so can you make assumptions about internal energy when volume is constant? If so, what would they be?
If the volume is constant, then work will be equal to 0. The internal energy equation will then be ΔU= q.
- Sat Feb 08, 2020 10:29 am
- Forum: Phase Changes & Related Calculations
- Topic: Enthalpy of a combustion reaction?
- Replies: 7
- Views: 396
Re: Enthalpy of a combustion reaction?
Since combustion reactions release a lot of heat, their ΔH will be negative.
- Sat Feb 08, 2020 10:26 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Spontaneous vs Nonspontaneous
- Replies: 4
- Views: 171
Re: Spontaneous vs Nonspontaneous
In class, we talked about the gibbs free energy equation (ΔG= ΔH - TΔS). When this equation is divided by -T, it produces -ΔG/T= ΔS(sys) +ΔS(surr)= ΔS(uni). Since -ΔG/T=ΔS(uni), we then know that a spontaneous reaction will have a -ΔG and a +ΔS(uni).
- Sat Feb 08, 2020 10:21 am
- Forum: Phase Changes & Related Calculations
- Topic: phase changes, temperature constant?
- Replies: 11
- Views: 577
Re: phase changes, temperature constant?
The temperature remains constant because the energy is going towards the phase change itself, and will therefore not heat the system.
- Sat Feb 08, 2020 10:20 am
- Forum: Phase Changes & Related Calculations
- Topic: General Phase Change Calculations
- Replies: 6
- Views: 320
Re: General Phase Change Calculations
These calculations frequently have to be divided into two parts because the phase change will occur at a constant temp (so you use things like Hvap) while the second part might deal with an increase or decrease in temperature.
- Sun Feb 02, 2020 10:56 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated system
- Replies: 10
- Views: 1262
Re: Isolated system
Wait, but I assumed that heat would still technically be able to escape from a hydroflask to the surroundings. Are there any other examples that would be an isolated system? Heat isn’t supposed to be able to leave a hydroflask unless the lid is off. Another example of an isolated system is the univ...
- Fri Jan 31, 2020 11:03 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy Unit
- Replies: 6
- Views: 164
Re: Enthalpy Unit
We frequently use kJ, as opposed to J, because the values produced are very large and therefore make more sense when written in kJ.
- Fri Jan 31, 2020 11:01 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess' Law
- Replies: 7
- Views: 221
Re: Hess' Law
Since it is a state property, only the final and initial state will matter. This allows us to add and subtract the values of enthalpy.
- Fri Jan 31, 2020 10:59 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: state property
- Replies: 8
- Views: 262
Re: state property
A state property is a quantity of the substance. It does not rely upon how the substance is made.
- Fri Jan 31, 2020 10:57 am
- Forum: Calculating Work of Expansion
- Topic: 4A.3
- Replies: 8
- Views: 395
Re: 4A.3
I did this problem yet I keep getting my final answer as 28.6, which would round up to 29. The answer says it' supposed to be 28. Has anyone else been getting the same thing? I also got 29. 28 is the product of using sig figs early, then rounding down. I think either answer would be correct, but my...
- Fri Jan 31, 2020 10:55 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpies
- Replies: 5
- Views: 203
Re: Bond Enthalpies
Bond enthalpies are average, whereas in other methods they are more specific.
- Thu Jan 23, 2020 7:01 pm
- Forum: Ideal Gases
- Topic: Kc vs Kp
- Replies: 109
- Views: 4382
Re: Kc vs Kp
Kp can be used when all the concentrations are in pressure, and Kc when they are concentrations. Pressure can be converted to concentration by using PV=nRT (and vice versa), but all the species must be in the gas phase to use Kp.
- Thu Jan 23, 2020 6:56 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 6A.21
- Replies: 2
- Views: 89
Re: 6A.21
The correct values for a and b will be the same, because water is neutral (pH 7). The amount of H+ and OH- will be equivalent, so Ka=Kb and Kw=Ka*Kb.
- Thu Jan 23, 2020 6:52 pm
- Forum: Ideal Gases
- Topic: Acid and Bases
- Replies: 16
- Views: 499
Re: Acid and Bases
A pH lower than 7 will be acidic and higher than 7 it will be basic. Some very strong acids and bases can fall outside of this range, above 14 or into the negative numbers.
- Thu Jan 23, 2020 6:46 pm
- Forum: Phase Changes & Related Calculations
- Topic: Autoprotolysis
- Replies: 15
- Views: 738
Re: Autoprotolysis
Maya Pakulski 1D wrote:Emily Lo 1J wrote:It is the transfer of a proton between the same type of molecule. An example of it would be 2H2O H3O + OH
What are some other common examples of autoprotolysis besides water?
Ammonia and acetic acid can also both undergo autoprolysis.
- Thu Jan 23, 2020 6:40 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Value of Ka, Kw, Kb
- Replies: 5
- Views: 141
Re: Value of Ka, Kw, Kb
Kw has a specific value at 25 degrees C (1.0x10^-14). Kw relates to Kb and Ka by Kw=Ka*Kb.
- Thu Jan 16, 2020 4:20 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Endothermic and exothermic
- Replies: 5
- Views: 196
Re: Endothermic and exothermic
Another way to tell if a reaction is exothermic or endothermic is to see if bonds are breaking or being formed. Bond breaking is an endothermic process, because it requires energy, while bond making is an exothermic process.
- Thu Jan 16, 2020 12:45 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Inert Gas
- Replies: 5
- Views: 139
Re: Inert Gas
An inert gas will not participate in the reaction. Once added, it will not shift the equilibrium or change the value of K.
- Thu Jan 16, 2020 12:38 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Kw
- Replies: 16
- Views: 366
Re: Kw
In lecture Lavelle said that Kw is a constant, 1.0 x 10^-14. I'm looking at a homework problem, and it gives kw as 2.1 x 10^-14, could someone clarify the meaning of the value of Kw? The homework question im referring to is 6A.21 In that problem, the Kw is different because it was found at a differ...
- Thu Jan 16, 2020 12:32 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Units in ICE Table
- Replies: 8
- Views: 214
Re: Units in ICE Table
All values in the ICE table must use mol/L, because data from this table will be used to calculate K.
- Thu Jan 16, 2020 12:19 pm
- Forum: Ideal Gases
- Topic: Kp given instead of Kc
- Replies: 8
- Views: 451
Re: Kp given instead of Kc
You can convert to pressure by using the ideal gas equation (PV=nRT).
- Sat Jan 11, 2020 2:15 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Partial Pressure
- Replies: 3
- Views: 191
Re: Partial Pressure
Dalton's law says that the partial pressure (the pressure exerted by each gas) of all of the gases summed will be equivalent to the total pressure.
- Sat Jan 11, 2020 2:12 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: When to use Le Chatelier's
- Replies: 4
- Views: 183
Re: When to use Le Chatelier's
The only time we have covered that we don't use Le Chatelier's is when an inert gas is added, because this does not cause a change in the equilibrium.
- Sat Jan 11, 2020 2:10 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Table Calculations
- Replies: 4
- Views: 92
Re: ICE Table Calculations
When there is a cubic equation we will be able to assume that x is very small, so that we do not have to solve a cubic equation, which would be done by graphing. Otherwise, the general rule is that you can assume that x is insignificant when K.
- Sat Jan 11, 2020 2:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K vs. Q
- Replies: 10
- Views: 504
Re: K vs. Q
The difference in K and Q is because K is taken when the reaction is at equilibrium and Q is taken at another point to determine if the reaction has reached equilibrium. The values of Q and K also help to determine which way the reaction will move from the point where Q was taken. This can also help...
- Tue Jan 07, 2020 2:54 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Writing expression for K
- Replies: 5
- Views: 196
Re: Writing expression for K
You can use partial pressures when all the reactants and products of a reaction are in the gas phase and when the units are in the gas phase (bar, atm, mmHg, Torr, etc). You normally use concentrations when other phases other than the gas phase are involved in the reaction, and you can use PV=nRT t...