## Search found 29 matches

Sun Mar 18, 2018 2:01 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 2
Views: 203

### Re: Concentration Cells

The anode would have the solution with a lower concentration and the cathode would have the solution with a higher concentration. If you want an explanation as to why, this Khan Academy video offers a great one! https://www.khanacademy.org/science/chemistry/oxidation-reduction/cell-potentials-under-...
Sun Mar 18, 2018 1:36 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Value of “k” in Kinetics
Replies: 5
Views: 304

### Re: Value of “k” in Kinetics

In kinetics, k usually refers to rate constant k. I'm pretty sure that k should always be positive or >1 because rates of reactions are always positive values. This includes rates that occur in the reverse direction.
Sun Mar 18, 2018 1:32 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic vs. Voltaic
Replies: 2
Views: 183

### Re: Galvanic vs. Voltaic

Galvanic cells and voltaic cells are the same thing, and both derive energy from spontaneous redox reactions that occur within the cell. The cell (and its half-reactions) should be setup so that standard E is positive, though this may not always be the case (i.e. in number 5 of Lyndon's Practice Fin...
Sun Mar 18, 2018 1:09 am
Forum: Calculating Work of Expansion
Topic: Work done on or by system
Replies: 2
Views: 209

### Re: Work done on or by system

For irreversible expansions, keep the equation w=-PΔV in mind. If there is an increase in volume (+ΔV), work will be negative, meaning work was done by the system. If there is a decrease in volume (-ΔV), work will be positive, meaning work was done on the system.
Sun Mar 18, 2018 1:02 am
Forum: *Enzyme Kinetics
Topic: Catalyst and equilibrium constant
Replies: 3
Views: 521

### Re: Catalyst and equilibrium constant

A catalyst won't affect the equilibrium constant k , which is the ratio of products to reactants when a reversible chemical reaction reaches equilibrium at a given temperature. However, because catalysts increase the rate of a reaction, it can affect rate constant k . Be cognizant of which k constan...
Sun Mar 18, 2018 12:56 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Inert Electrodes
Replies: 2
Views: 209

### Re: Inert Electrodes

In this class, Pt(s) seems to be chosen as the inert electrode more than C(gr), though either can be used.
Sun Mar 18, 2018 12:52 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic/Voltaic Cells
Replies: 2
Views: 224

### Re: Galvanic/Voltaic Cells

A galvanic or voltaic cell is a cell that derives electrical energy from spontaneous redox reactions taking place within the cell. The anode is constantly passing electrons to the cathode, usually via an electrical wire, while a porous disk or salt bridge maintains the charges of the aqueous solutio...
Sun Mar 18, 2018 12:35 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated systems
Replies: 3
Views: 271

### Re: Isolated systems

Usually in a bomb calorimeter, there is some mass of water and some sample (let's say octane) burning. The system we are concerned with would be the octane, and its surroundings would be the water. While burning, the octane would release heat and the water would absorb it. So, within the bomb calori...
Sun Mar 18, 2018 12:22 am
Forum: General Rate Laws
Topic: Coefficients and Exponents
Replies: 2
Views: 299

### Re: Coefficients and Exponents

The exponent, or order, of individual species in a rate law can only be determined by reaction mechanisms or experimental values. In a multi-step kinetics mechanism, when deriving the substitution for an intermediate, you have to find the equilibrium constant for the fast reaction that the intermedi...
Sun Mar 18, 2018 12:16 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: sign of k
Replies: 3
Views: 416

### Re: sign of k

Rate constants can never be negative because the rate of a reaction is always positive.
Sat Mar 17, 2018 5:56 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Writing Cell Diagrams
Replies: 3
Views: 227

### Writing Cell Diagrams

I'm confused on how to write half reactions and construct cell diagrams for redox reactions that have only one product. Can someone explain how to write the half-reactions for a redox reaction like 2Ag(s) + Br2(g) --> 2AgBr(s)?
Sat Mar 17, 2018 3:42 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Drawing Reaction Profiles
Replies: 1
Views: 81

### Drawing Reaction Profiles

Question 15.89 asks you to sketch a reaction profile. I know that you're supposed to take into account whether the reaction is endothermic/exothermic and that each step in a reaction correlates to one "hill". How do you know how large to draw each peak and where the position of substrates ...
Sat Mar 17, 2018 1:13 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation
Replies: 2
Views: 172

### Nernst Equation

Are the Nernst equations (one involving log Q and the other involving ln Q) supposed to be interchangeable, and yield similar if not the same answers? If not, under what conditions are we supposed to use each equation?
Sat Mar 17, 2018 12:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge vs. Porous Disk
Replies: 2
Views: 171

### Salt Bridge vs. Porous Disk

When are salt bridges used as opposed to porous disks? Are salt bridges only used if the solutions are in two separate beakers whereas the porous disk is used if the solutions are in the same beaker and merely separated by the disk? Or are they used for certain solutions?
Sat Mar 17, 2018 12:28 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Q7b Lyndon's Review
Replies: 6
Views: 205

### Re: Q7b Lyndon's Review

Also in this problem, I still don't understand the difference between Lyndon's little k and big k. Is one supposed to represent the rate constant while the other represents the equilibrium constant? And if so, which is which?
Thu Mar 15, 2018 8:16 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius equation and order of rxn
Replies: 3
Views: 131

### Re: Arrhenius equation and order of rxn

The Arrhenius equation can essentially be used for all orders of reactions because order isn't a piece of information needed for the equation.
Thu Mar 15, 2018 8:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 #7
Replies: 5
Views: 250

### Re: Test #2 #7

Another way to do this problem is by plugging in the values of E°=1.33 V and E°=-0.74 V into the equation ΔG°= -nFE° to solve for their respective ΔG° values. You add these values together to get the total ΔG°, then plug that value back into the ΔG°= -nFE° equation again and solve E° this time to ge...
Thu Mar 15, 2018 7:52 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity of Water
Replies: 4
Views: 273

### Heat Capacity of Water

Can someone explain why the heat capacity of water is so high? Is it because it takes more energy to break H20's hydrogen bonds?
Thu Mar 15, 2018 7:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: State Functions
Replies: 4
Views: 289

### State Functions

Can someone remind me which properties are state functions? I know enthalpy, Gibb's free energy, and entropy are definitely state functions, and work and heat are not state functions. Which other ones am I missing?
Thu Mar 15, 2018 7:47 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics
Replies: 5
Views: 254

### Re: kinetics

Another example of how kinetics and thermodynamics connect is if you add heat (one aspect of thermodynamics) to a reaction, its rate will increase due to an increase of kinetic energy.
Sun Mar 11, 2018 11:10 pm
Forum: General Rate Laws
Topic: Determining Orders
Replies: 2
Views: 121

### Determining Orders

I recognize that you can't assume that a substance's order correlates to its coefficient in a given chemical equation. Unless it is given in a problem, can you only determine the order of a substance in a general rate law when given a chart of concentrations and initial rates?
Sun Mar 11, 2018 11:00 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 6
Views: 175

### Intermediates

Does a substance have to be a product of the first step in a series of reactions and a reactant of the final step of series in order to be an intermediate? For example, in homework question 15.46, C4H9+ is a product in Step 1 and a reactant in Step 2. However, it does not appear in Step 3. Would it ...
Sun Mar 11, 2018 10:39 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal Processes
Replies: 2
Views: 218

### Isothermal Processes

Why does an isothermal reversible process have 0 change in internal energy? I know that isothermal processes have no change in temperature.
Sun Mar 04, 2018 10:17 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 883169

### Re: Post All Chemistry Jokes Here

"I would tell another chemistry joke, but all of my good ones argon."

"That's sodium funny! I slapped my neon that one!"
Sun Mar 04, 2018 10:16 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 883169

### Re: Post All Chemistry Jokes Here

Do you remember what happens when metal and oxygen react? My memory is a little rusty.
Sun Mar 04, 2018 10:15 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 883169

### Re: Post All Chemistry Jokes Here

What do you do with a sick chemist?

Well, if you can't curium, and you can't helium, you might as well barium.
Tue Feb 20, 2018 10:59 pm
Forum: Balancing Redox Reactions
Topic: Homework Question 14.5
Replies: 2
Views: 135

### Re: Homework Question 14.5

Since O3 and O4 both have neutral charges, how do we know whether the half reaction gains electrons or loses electrons? Usually the electrons are used to balance out the charges, but the charges of O3 and O4 are already balanced.
Tue Feb 20, 2018 10:52 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Calculating lnQ in Homework 14.37 and 14.41
Replies: 1
Views: 76

### Calculating lnQ in Homework 14.37 and 14.41

When calculating lnQ, the solutions manual neglects to convert pressure to M and vice versa. What is the reasoning behind this?
Tue Feb 20, 2018 7:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Potential and Spontanaeity
Replies: 2
Views: 108

### Cell Potential and Spontanaeity

I know that a process is spontaneous when delta G is negative. Is a process spontaneous or non-spontaneous when cell potential is negative?