## Search found 51 matches

Wed Mar 11, 2020 12:30 am
Forum: Environment, Ozone, CFCs
Topic: stoichiometric coefficients
Replies: 9
Views: 129

### 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: 307

### 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: 51

### 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: 68

### 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: 110

### 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: 178

### 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: 79

### 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: 86

### 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: 73

### 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: 39

### 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: 64

### 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: 173

### 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: 60

### 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: 524

### 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: 61

### 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: 123

### 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: 39

### 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: 150

### 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: 47

### 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: 436

### 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: 56

### 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: 237

### 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: 62

### 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: 251

### 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: 61

### 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: 55

### 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: 71

### 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: 46

### 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: 136

### 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: 51

### 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: 176

### 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: 40

### 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: 62

### 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: 59

### 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: 114

### 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: 53

### 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: 43
Views: 572

### 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: 14

### 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: 158

### 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: 176

### 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 $\rightleftharpoons$ 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: 46

### 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: 69

### 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: 65

### 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: 135

### 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: 94

### 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: 132

### 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: 45

### 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: 47

### 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: 31

### 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$< 10^-5$.
Sat Jan 11, 2020 2:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K vs. Q
Replies: 10
Views: 107

### 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: 84

### 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...