Search found 31 matches
- Mon Mar 11, 2019 11:49 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Le Chatelier's Principle
- Replies: 3
- Views: 387
Re: Le Chatelier's Principle
Le Chatelier's Pronciple says that chemical reactions adjust so as to minimize the effect od changes in concentration of molecules involved, changes in pressure, and changes in temperature. It indicates how ththe reaction will respond.
- Mon Mar 11, 2019 11:39 am
- Forum: General Rate Laws
- Topic: Are coefficients in rate laws?
- Replies: 2
- Views: 282
Re: Are coefficients in rate laws?
We raise each molecule's concentration to the power of the coefficient of that molecule in the balanced chemical equation. Therefore, it changes the value of the rate constant k in the rate law.
- Mon Mar 11, 2019 11:35 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Pre-Equilibrium vs Steady-State Approach
- Replies: 2
- Views: 318
Pre-Equilibrium vs Steady-State Approach
As Professir Lavelle said in lecture, the pre-equilibrium approach is less flexible than the steady-state approach. Why is this true?
- Tue Mar 05, 2019 1:43 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: 6th edition 14.47
- Replies: 4
- Views: 640
Re: 6th edition 14.47
I got 2.68 * 10^6 as well using ln, but why would we get just 10^6 (a completely different answer) by using log instead ln?
- Tue Mar 05, 2019 1:41 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: difference between galvanic and voltaic
- Replies: 4
- Views: 3041
Re: difference between galvanic and voltaic
A voltaic cell refers to a galvanic cell and vice versa. A voltaic, aka a galvanic, cell is an electrochemical cell that derives electrical energy from the redox reactions within the cell.
- Tue Mar 05, 2019 1:32 pm
- Forum: General Rate Laws
- Topic: Unique Rate
- Replies: 4
- Views: 418
Re: Unique Rate
The unique rate refers to the unique average rate of reaction.
- Mon Feb 25, 2019 9:18 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Reducing agent/oxidizing agent
- Replies: 5
- Views: 558
Re: Reducing agent/oxidizing agent
The reducing agent is the substance that undergoes oxidation (losing electrons) and thus corresponds to the anode.
- Mon Feb 25, 2019 9:15 pm
- Forum: Balancing Redox Reactions
- Topic: about redox reaction
- Replies: 5
- Views: 790
Re: about redox reaction
Redox reactions do not always include oxygen. For example, look at #13 from Chapter 14 in the 6th Edition. Not one of the cell reactions for the galvanic cells given, all of which are redox reactions, include oxygen.
- Mon Feb 25, 2019 9:11 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 6th Edition 14.13
- Replies: 1
- Views: 232
Re: 6th Edition 14.13
The anode corresponds to the oxidation half-reaction, and the cathode corresponds to the reduction half-reaction. In oxidation, the oxidation number of the element increases, and in reduction, the oxidation number of the element decreases. From Cl2(g)+H2(g) --> HCl(aq), Cl goes from a charge of 0 to...
- Mon Feb 25, 2019 9:01 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 2
- Views: 328
Re: Salt Bridge
Yes, galvanic cells must have a salt bridge or a porous disk for the reason provided by the previous reply. The electron transfer from one reaction beaker to another will stop due to charge buildup, but the salt bridge or the porous disk will allow for ions to transfer and for the two solutions to r...
- Wed Feb 20, 2019 4:24 pm
- Forum: Van't Hoff Equation
- Topic: when to use
- Replies: 4
- Views: 478
Re: when to use
The van't Hoff equation describes the temperature dependence of K. It also relates the change in K to the change in temperature given the standard deltaH.
- Wed Feb 20, 2019 4:18 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode v. Cathode
- Replies: 9
- Views: 986
Re: Anode v. Cathode
The anode is where electrical current flows in from outside and is the site of the oxidation half-reaction. The cathode where electrical current flows out and is the site of the reduction half-reaction.
- Wed Feb 20, 2019 4:13 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 5
- Views: 561
Re: Salt Bridge
Without a salt bridge or a porous disk to allow ion transfer and to keep the two solutions neutral, electron transfer from one reaction beaker to the other will stop due to charge buildup.
- Mon Feb 11, 2019 9:23 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: q and w = 0
- Replies: 3
- Views: 420
Re: q and w = 0
If no heat was exchanged in the system, q = 0 and deltaU = w.
If no work was being done in the system, w = 0 and deltaU = q.
For an ideal gas in an isothermal system, deltaU = 0 = q + w. In this situation, q = nRTln(V2/V1).
If no work was being done in the system, w = 0 and deltaU = q.
For an ideal gas in an isothermal system, deltaU = 0 = q + w. In this situation, q = nRTln(V2/V1).
- Mon Feb 11, 2019 8:29 pm
- Forum: Student Social/Study Group
- Topic: Missed monday review session: Lavelle's past exam questions
- Replies: 2
- Views: 345
Re: Missed monday review session: Lavelle's past exam questions
These are the problems covered during lecture 1.
- Mon Feb 11, 2019 5:51 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Question 8.19
- Replies: 2
- Views: 302
Re: Question 8.19
Again, adding the approach of adding the q of water and the q of copper together is correct. For the q of water, mcdeltaT=(400g)(4.18J/gK)(78K)=130.416kJ. For the q of copper, mcdeltaT=(500g)(0.385J/gK)(78K)=15.015kJ. We then add these two values together and, keeping in mind sig figs, we get 1.4*10...
- Tue Feb 05, 2019 12:40 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Important Thermochemistry Equations
- Replies: 3
- Views: 430
Re: Important Thermochemistry Equations
All of these equations will be given on a test, midterm, or final on the equation sheet, but it is also good to know how to derive some of these equations by knowing one or two of them.
- Tue Feb 05, 2019 12:07 pm
- Forum: Calculating Work of Expansion
- Topic: Work vs Degeneracy
- Replies: 2
- Views: 347
Re: Work vs Degeneracy
Degeneracy and work are two different concepts. As we learned in lecture, degeneracy is the number of ways of achieving a given energy state for particles like electrons. Work has to do with how energy enters or leaves a system. They simply share the letter that denotes them, though degeneracy is a ...
- Tue Feb 05, 2019 11:57 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Q change and temperature
- Replies: 2
- Views: 295
Re: Q change and temperature
To phrase the previous answer slightly differently: Say the system in a piston undergoes expansion, which indicates that you are adding energy in the form of heat to the system and the system does work. There is no change in internal energy and, therefore, no change in temperature. Heat can be conve...
- Sun Feb 03, 2019 1:31 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Why Bond Enthalpies are the least accurate
- Replies: 3
- Views: 1742
Re: Why Bond Enthalpies are the least accurate
A bond enthalpy is considered an estimate of the energy needed to break the average bond. Bonds can be either weakened or strengthened depending on the other atoms in the molecule associated with the bond and would need either less or more energy to break. Therefore, the bond enthalpy can be slightl...
- Sun Feb 03, 2019 1:21 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Negative or Positive Work
- Replies: 3
- Views: 367
Re: Negative or Positive Work
Another way to think about this is when work is being done by the system (or works on the surroundings), work is negative. The system's energy also decreases. When the surroundings do work on the system, it's positive.
- Sun Feb 03, 2019 1:14 pm
- Forum: Phase Changes & Related Calculations
- Topic: State Function
- Replies: 10
- Views: 895
Re: State Function
A state property is one whose value is determined by its current state. It is not dependent on the path taken to obtain that state. Work does depend on the path taken and is related to the change in energy when a system moves from one state to another. Therefore, work is not a state property.
- Mon Jan 21, 2019 6:39 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH of weak acid and its salt
- Replies: 2
- Views: 333
Re: pH of weak acid and its salt
I believe Professor Lavelle mentioned that, if we wanted, we could include and write out the potassium as K+ on both sides of the equation. Nitrous acid stays as one molecule when in water, but potassium nitrite, as a salt, dissociates in water to form NO2- and K+. That NO2- is included in the HNO2 ...
- Mon Jan 21, 2019 6:12 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: 7th Edition 6B.9
- Replies: 2
- Views: 271
Re: 7th Edition 6B.9
Yes, very strong acids can have negative pH values.
- Mon Jan 21, 2019 6:11 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Post Assessment
- Replies: 1
- Views: 227
Re: Post Assessment
Whether or not a reaction is exothermic depends on the delta H. If the delta H is positive, then the reaction is endothermic. If the delta H is negative, then the reaction is exothermic. For an endothermic reaction, if the temperature is increased, the forward reaction is favored and the equation wi...
- Tue Jan 15, 2019 8:35 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Polyprotic Acids
- Replies: 2
- Views: 123
Re: Polyprotic Acids
Any acid that contains more than one H+ per molecule is a polyprotic acid. Therefore, any acid that contains more than one H+ per molecule will donate its H+. I believe that the number of protonations will not be specified because it is assumed that the reaction will go to completion and all of the ...
- Tue Jan 15, 2019 1:39 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: question from module
- Replies: 4
- Views: 414
Re: question from module
When the volume of a system is compressed, the effect on the system depends on how many moles are on each side of the equation. If the moles of the reactants equal the moles of the products, like in this situation, the change in volume has an equal effect on the reactants and the products. Thus, the...
- Tue Jan 15, 2019 1:22 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Calculate pOH
- Replies: 3
- Views: 180
Re: Calculate pOH
To put it simply, yes.
The chemical equation of the dissociation of Ba(OH)2 is Ba(OH)2 -> 2OH- + Ba2+
This indicates that in the dissociation of Ba(OH)2, 2 hydroxide ions form.
The chemical equation of the dissociation of Ba(OH)2 is Ba(OH)2 -> 2OH- + Ba2+
This indicates that in the dissociation of Ba(OH)2, 2 hydroxide ions form.
- Fri Jan 11, 2019 4:41 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Le Chatelier's Principle [ENDORSED]
- Replies: 3
- Views: 318
Re: Le Chatelier's Principle [ENDORSED]
When we increase the concentration of a substance like we did with the N2 and the NH3, the reaction moves to the right (the products) and to the left (the reactants), respectively. When we increase N2, the reaction produces more of the NH3 to use up that excess N2. When we increase NH3, the reaction...
- Fri Jan 11, 2019 12:35 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Quadratic Equations
- Replies: 3
- Views: 323
Re: Quadratic Equations
There will only ever be one plausible answer to the quadratic equation because there cannot be two concentrations of a substance at a given temperature and with the given molar concentrations of the other substance.
- Tue Jan 08, 2019 4:36 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: 11.13c (6th Edition)
- Replies: 2
- Views: 208
11.13c (6th Edition)
Hey! I was hoping someone could clarify 11.13 part c for me. CO_{3}^{2-} (aq) + 2H_{3}O^{+} (aq)\rightarrow CO_{2} (g) + 3H_{2}O (l) Because there are aqueous and gaseous reactants and products, my approach to this question was to use molar concentrations, not partial...