Search found 30 matches

Wed Mar 13, 2019 2:07 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Adding Pt in 6L5 b)
Replies: 2
Views: 137

Re: Adding Pt in 6L5 b)

You need Pt in the cell diagram if there is no solid present, so it can act as an electrode to transfer electrons.
Wed Mar 13, 2019 2:03 pm
Forum: First Order Reactions
Topic: 0 Order vs Independent Rate?
Replies: 1
Views: 82

Re: 0 Order vs Independent Rate?

I'm not positive, but I think they're the same thing. When a reaction is 0 order, the rate = k[A]^0, and since [A]^0 is equal to 1, the rate will just be rate = k. Since the rate is always the same regardless of the reactant concentration, the rate is independent of the concentration.
Wed Mar 13, 2019 1:56 pm
Forum: General Rate Laws
Topic: Rate equations to know
Replies: 5
Views: 218

Re: Rate equations to know

The reference sheet we will be given is posted on ccle, but it looks like we will be given most of the equations and just have to remember which integrated rate law and half life goes with which reaction order
Tue Mar 05, 2019 3:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Ecell
Replies: 13
Views: 453

Re: Ecell

When you do that, make sure you don't negate the E value because that would change it into the standard oxidizing potential. Use the E values exactly as they are given
Tue Mar 05, 2019 2:54 pm
Forum: First Order Reactions
Topic: First order graph
Replies: 7
Views: 320

Re: First order graph

time
Tue Mar 05, 2019 2:53 pm
Forum: First Order Reactions
Topic: Rate constant and half life
Replies: 3
Views: 171

Re: Rate constant and half life

It goes through the reaction faster, so it will go down to half it's original concentration at a faster speed, making it take a shorter amount of time to do so
Mon Feb 25, 2019 2:13 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Voltage
Replies: 2
Views: 135

Re: Voltage

Log base 10 makes it easier when you are working with acid-base solutions because pH is found using log base 10, so it's easier to find the concentration if they're both using the same form of a log
Mon Feb 25, 2019 2:08 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 2
Views: 106

Re: Cell Diagrams

When they are in an aqueous solution together, they are separated by a comma. When one is a solid and the other is in an aqueous solution, they are separated by a line.
Mon Feb 25, 2019 2:05 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Moles in -nFEcell
Replies: 5
Views: 247

Re: Moles in -nFEcell

n represents the number of electrons transferred in a balanced redox reaction
Wed Feb 20, 2019 4:36 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 2
Replies: 2
Views: 142

Re: Test 2

My TA said that they will most likely give us values for enthalpy and entropy because making us calculate everything would be a lot of work for only one problem. That being said, it is still possible that they could make us calculate it to be used in the gibbs free energy equation, so I would look o...
Wed Feb 20, 2019 4:29 pm
Forum: General Science Questions
Topic: Midterm
Replies: 5
Views: 484

Re: Midterm

Ka2 is the Ka for taking away the second hydrogen in H3PO4

the reaction would be

H2PO4(-) + H2O = HPO4(2-) + H3O(+)

and Ka2 would be

(HPO4(2-)*H3O(+))/H2PO4(-)
Wed Feb 20, 2019 4:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode v. Cathode
Replies: 9
Views: 355

Re: Anode v. Cathode

Dhwani Krishnan 1G wrote:what is the difference between an anode and cathode?

An anode is negatively charged and contains the oxidation part of a reaction, and electrons flow away from it
A cathode is positively charged and contains the reduction part of the reaction, and electrons flow towards it
Wed Feb 13, 2019 12:32 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: state function
Replies: 4
Views: 158

Re: state function

No- both work and heat are not state functions
Wed Feb 13, 2019 12:30 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 3/2R vs 5/2R
Replies: 8
Views: 442

Re: 3/2R vs 5/2R

3/2R is used when it is at constant volume for a monoatomic ideal gas
5/2R is used when it is at constant pressure for a monoatomic ideal gas
Wed Feb 13, 2019 12:27 am
Forum: Administrative Questions and Class Announcements
Topic: Lyndon's HOTDOG MIDTERM REVIEW SESSION!! FINALLY!
Replies: 49
Views: 3924

Re: Lyndon's HOTDOG MIDTERM REVIEW SESSION!! FINALLY!

Help with question 2c)? I understand that since we're cooling it kc will also drop because it's dependent on temperature, but what is the detailed explanation? Since the reaction is breaking bonds, we know that it will be endothermic. When we learned how temperature affects a system, we learned tha...
Wed Feb 06, 2019 9:43 pm
Forum: Calculating Work of Expansion
Topic: Integral Expression for Work
Replies: 4
Views: 191

Re: Integral Expression for Work

My TA said that the only equations we will have to use for work are w=-PΔV (for a system with constant pressure) and w=-nRT(ln(V2/V1)) (for a reaction that is isothermal reversible). The integral is more for understanding than actual needing to use the equation to solve it for this class (I think)
Wed Feb 06, 2019 9:22 pm
Forum: Phase Changes & Related Calculations
Topic: Symbol inquiry
Replies: 4
Views: 187

Re: Symbol inquiry

Internal energy is represented by "U", and change of internal energy is represented by "ΔU"
the delta symbol (Δ) always represents a change in something
Wed Feb 06, 2019 4:18 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: S equation
Replies: 2
Views: 104

Re: S equation

-KB is equal to R/Na, where Na is avagadros constant of 6.022 x 10^23, which is how many particles are in 1 mole
-Capital W represents degeneracy, the number of ways of achieving a given energy state
-KB is the boltzman constant, which is equal to 1.381 x 10^-23 J/K
Wed Jan 30, 2019 2:36 pm
Forum: Phase Changes & Related Calculations
Topic: Week 4 Homework
Replies: 12
Views: 553

Re: Week 4 Homework

I believe you can do any problem from the thermodynamics set, but most of the stuff that we've covered in class is in parts 4D and 4C because he has been going out of the order of the textbook, so those will probably be easier and more helpful because we've learned them already.
Wed Jan 30, 2019 2:32 pm
Forum: Calculating Work of Expansion
Topic: Units for Work
Replies: 6
Views: 284

Re: Units for Work

To convert L⋅atm to Joules, you need to use the conversion factor of 101.325 J/1 L*atm, so basically just multiply your answer found using volume and pressure by 101.325 to get the actual answer in joules.
Wed Jan 30, 2019 2:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 4
Views: 210

Re: Hess's Law

I find that it's easiest to start off with the thing that only exists in one place. For example, in my discussion we did problem 4D.19: find the reaction enthalpy for the reaction [H2 + Br2 -> 2HBr] given: NH3 + HBr -> Nh4Br N2 + 3H2 -> 2NH3 N2 + 4H2 + Br2 -> 2NH4Br We know that we need 2HBr for the...
Wed Jan 23, 2019 5:43 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Strength of acids based on Ka and pKa
Replies: 4
Views: 567

Re: Strength of acids based on Ka and pKa

pKa and pKb work on the same scale as pH and pOH, respectively. A low pKa indicates a stronger weak acid, whereas a high pKa indicates a weaker acid. In the same way, a low pKb indicates a stronger weak base, whereas a high pKb indicates a weaker base. You can look at the Ka and Kb to compare, but I...
Wed Jan 23, 2019 5:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating pH of Weak Acids and Bases
Replies: 2
Views: 107

Re: Calculating pH of Weak Acids and Bases

Basically, the reason for this is that with such a low Ka, subtracting x won't have that much of an affect on the original concentration. If you were to subtract 1x10^-5 from .1, you would end up with .09999, which is still essentially .1 (especially when you would eventually round for sig figs). La...
Wed Jan 23, 2019 5:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating Equilibrium Constants
Replies: 2
Views: 98

Re: Calculating Equilibrium Constants

Yes- in an ice table, the number of x's you put for the change is the same as the amount in the equation. For example, in the equation "N2 + 3H2 = 2NH3", you would subtract 1x from N2, 3x from H2, and add 2x to NH3. Logically, this makes sense because in a reaction, 1 molecule of N2 will c...
Mon Jan 14, 2019 2:51 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient Value
Replies: 5
Views: 119

Re: Reaction Quotient Value

If Q is equal to K, that means that the concentrations at the time we are evaluating are equal to the concentrations found when the reaction is in equilibrium. This means that the reaction is in equilibrium, so neither reaction is favored because at equilibrium, the forward and reverse reactions occ...
Mon Jan 14, 2019 2:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th edition 5I.35
Replies: 1
Views: 120

Re: 7th edition 5I.35

The entire problem is essentially an ice table with the variable "p" substituted in for the change. The First thing you want to do is balance the equation, then find the equilibrium concentrations in terms of "p" and substitute it into the K equation. 2NO <--> N2 + O2 I / 1 bar /...
Mon Jan 14, 2019 2:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Forward vs. Reverse Reactions
Replies: 4
Views: 266

Re: Forward vs. Reverse Reactions

Kc and Kp both find the equilibrium constant for the reaction, while Qc and Qp can be calculated at any time during a reaction in order to determine which direction the reaction will proceed in. If Q < K, that means that there are more reactants (denominator) than products (numerator) at that time t...
Thu Jan 10, 2019 1:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: how to write the formula for K
Replies: 6
Views: 190

Re: how to write the formula for K

When it's written as a subscript of P, that means that it is using partial pressures instead of concentrations. If you are using concentrations, it's okay to write the brackets around it because that indicates that the unit is mol/L. Just double check to make sure which method you are actually using...
Thu Jan 10, 2019 1:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: The relationship between Kc and K
Replies: 2
Views: 115

Re: The relationship between Kc and K

Kc is used to calculate the equilibrium constant using the concentration of the products and reactants at equilibrium. Kc is essentially a more specific way of saying K, because it specifies that you are calculating it using concentration, whereas Kp is calculated using partial pressure. Q, the reac...
Thu Jan 10, 2019 1:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc and Qc
Replies: 4
Views: 11630

Re: Kc and Qc

Kc and Kp both find the equilibrium constant for the reaction, with Kc being calculated using equilibrium concentration and Kp being calculated using equilibrium partial pressures. Qc and Qp can be calculated at any time during a reaction in order to determine which direction the reaction will proce...