Search found 31 matches
- Mon Mar 11, 2019 5:57 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Rate Law
- Replies: 2
- Views: 312
Re: Rate Law
With an overall reaction, we have no idea what steps go behind it. It could happen just as it is written, or there could be a number of elementary steps occurring in the background that are not obvious. For this reason, when we are given an overall reaction, we must examine its reaction mechanism (s...
- Mon Mar 11, 2019 5:55 pm
- Forum: Ideal Gases
- Topic: Cell Diagram/Ecell
- Replies: 8
- Views: 944
Re: Cell Diagram/Ecell
Anode side is the one that gets oxidized. Cathode side is the one that gets reduced. In a galvanic cell, the E nought cell should be positive, so flip your half reactions such that the sum of the E values gives you a positive value. If both flipped combinations of the reactions give you a positive E...
- Mon Mar 11, 2019 5:53 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation number?
- Replies: 12
- Views: 7528
Re: Oxidation number?
It's basically the idea that the group that an element is found can give clues as to what its oxidation number if. Note, that this doesn't work for transition metals. Example: elements in group 1 have an oxidation number of +1 and elements in group 2 have an oxidation number of +2. Elements in the s...
- Mon Mar 04, 2019 8:27 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Pt
- Replies: 14
- Views: 1364
Re: Pt
I agree with the above. Platinum is only used in an electrode when you have nonconducting solids, or aqueous/gaseous substances in one half of your electrochemical cell (that is, in the absence of conducting metal/solid). This is because in every electrochemical cell you need some current conducting...
- Mon Mar 04, 2019 8:23 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: E cell spontaneity
- Replies: 5
- Views: 605
Re: E cell spontaneity
Yes it would be valid to say that. E cell > 0 (when we input it into -nFE) gives us a negative delta G meaning the forward reaction is spontaneous. When E cell < 0, the same equation will give us a positive delta G, meaning the forward reaction is not favored, but the reverse reaction is (the forwar...
- Mon Mar 04, 2019 8:20 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Endergonic vs. Endothermic
- Replies: 6
- Views: 1933
Re: Endergonic vs. Endothermic
I agree with the above answers. Endergonic refers to the consumption of Gibb's free energy (delta G > 0) by the system. Endothermic refers to the consumption of enthalpy (heat under constant pressure conditions) by the system (delta H > 0).
- Mon Feb 25, 2019 9:27 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt bridge
- Replies: 2
- Views: 343
Re: Salt bridge
Electrons travel from the anode to the cathode. So eventually, there will be to many electrons in the cathode, and there will be resistance to electron flow (because electrons don't like moving toward negative charge). This is when the salt bridge comes into action. The salt bridge will release posi...
- Mon Feb 25, 2019 9:18 pm
- Forum: Balancing Redox Reactions
- Topic: about redox reaction
- Replies: 5
- Views: 790
Re: about redox reaction
Redox reactions do not always involve oxygen. Redox reactions always involve the reduction and oxidation of some compound. So one compound loses electrons and another compound gains these lost electrons. Whether Oxygen is present or not has nothing to do with a redox reaction.
- Mon Feb 25, 2019 9:16 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Value of K in Gibbs free energy equation
- Replies: 3
- Views: 693
Re: Value of K in Gibbs free energy equation
Standard conditions for Gibbs free energy are some fixed temperature (usually 25 degrees celsius), pure liquid/solid, gases are 1 atm/bar, aqueous are 1 M. Also all compounds are at their standard states (so oxygen wouldn't be O in these conditions, it would be O2).
- Mon Feb 18, 2019 2:55 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Polyprotic Acids
- Replies: 5
- Views: 531
Re: Polyprotic Acids
For polyprotics you have multiple Ka values depending on the number of hydrogens. Each ka after the initial one is smaller (because its hard to separate a H+ from a negatively charged ion). Sulfuric acid is a strong acid during its initial deprotonation. Afterwards, its a weak acid. Other acids (unl...
- Mon Feb 18, 2019 2:52 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy Problems
- Replies: 3
- Views: 352
Re: Gibbs Free Energy Problems
We will be given all standard enthalpies/entropies that we need to solve the problem. Don't worry about memorizing any specific values.
- Mon Feb 18, 2019 2:48 pm
- Forum: Van't Hoff Equation
- Topic: Temperature Dependence of K
- Replies: 5
- Views: 577
Re: Temperature Dependence of K
I agree with the above answers. We learned in the equilibrium chapter how K changes based on whether a reaction is endothermic or exothermic. The Van T' Hoff equation just quantifies the conceptual understanding that we gained in the past. With it, we can calculate the actual change in K value for c...
- Mon Feb 18, 2019 2:45 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Change in free energy for a reaction at equilibrium
- Replies: 3
- Views: 309
Re: Change in free energy for a reaction at equilibrium
The change in Gibbs free energy for a reaction at equilibrium is 0. When delta G is zero, it means neither the forward reaction nor the reverse reaction is more spontaneous or more favored than the other. That is, both directions are equally favored. This matches with the definition of equilibrium (...
- Mon Feb 11, 2019 8:59 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Difference between delta U and delta H?
- Replies: 3
- Views: 445
Re: Difference between delta U and delta H?
I agree with above post. delta U = q + w in that it includes changes in heat (or enthalpy depending on whether its a constant pressure environment). Delta U can change for the following reasons: (1) matter is being added or removed (2) change in work (3) change in heat. Enthalpy, is exclusively the ...
- Mon Feb 11, 2019 8:55 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: state functions
- Replies: 2
- Views: 344
Re: state functions
I agree with the above. Heat is like work in that it isn't state function. Its only a state function when there is constant pressure, and heat = enthalpy. Further, heat given off/absorbed by the system is dependent on the pathway taken. See the example in the book on reversible and irreversible isot...
- Mon Feb 11, 2019 8:51 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Isothermal
- Replies: 1
- Views: 257
Re: Isothermal
That is correct. In isothermal reactions delta T = 0. Since the temperature doesn't change, the kinetic energy of the molecules of an ideal gas don't change either. Due to this delta U = 0. Because delta U = 0, 0 = q+ w, and w = -q.
- Mon Feb 04, 2019 10:52 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard / Formation / Reaction
- Replies: 1
- Views: 439
Re: Standard / Formation / Reaction
Standard = the enthalpy value has a nought (o) as a superscript. It means that the reactants are all in their standard states. Reaction = the enthalpy value associated with some reaction. Formation = enthalpy value associated with the formation of one mole of a particular substance from its substitu...
- Mon Feb 04, 2019 10:48 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Work Formula
- Replies: 5
- Views: 607
Re: Work Formula
Area * distance is equal to the volume. You can think of it in terms of units. Area is m^2 and distance in m. So multiply them together and you get m^3, which is volume. Think of the areas as being slices with very small width and being stacked one on top of each other to form a 3D shape.
- Mon Feb 04, 2019 9:38 am
- Forum: Calculating Work of Expansion
- Topic: Integral calculations
- Replies: 4
- Views: 522
Re: Integral calculations
I don't think we will have to take an integral. Dr. Lavelle was only deriving the formula for work done by reversible expansion. We will get to this formula in class later, I believe.
- Mon Jan 28, 2019 8:42 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Units of Kp
- Replies: 9
- Views: 3678
Re: Units of Kp
The partial pressure can be in any units, but remember to use the same units for all of your gases. Also, the Kp value itself will change based on what units you use for the partial pressure of the gases. Its important to use the appropriate kp value in your calculations (based on what units the pro...
- Mon Jan 28, 2019 8:39 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Question 12.61 (Sixth Edition)
- Replies: 2
- Views: 1538
Re: Question 12.61 (Sixth Edition)
Set up an ICE table, but this fill in the equilibrium concentration of H+ ions (do 10 ^ -pH). Write the reaction, and it should be evident that the concentration of H+ is the same as that of the equilibrium concentration of conjugate. Then, if we suppose that we start with some x amount of initial a...
- Mon Jan 28, 2019 8:34 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Exothermic vs. Endothermic
- Replies: 10
- Views: 3190
Re: Exothermic vs. Endothermic
Exothermic is a reaction that releases heat. Its delta H is negative, < 0. Endothermic is a reaction that absorbs heat from its environment. Its delta H is positive, > 0.
- Mon Jan 21, 2019 2:39 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pKa confusion
- Replies: 2
- Views: 259
Re: pKa confusion
Ka < 10^-3 is a weak acid. pKa = -log(Ka). So the higher Ka, stronger acid, lower pKa. Its like how if you have a really strong acid, the pH is super small. Same logic for pKb. Also the scale is 0 to 14 just like pH and pOH.
- Mon Jan 21, 2019 2:36 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Aluminum Conjugate
- Replies: 1
- Views: 288
Re: Aluminum Conjugate
So, the AlCl3 becomes Al3+ and 3Cl-. The Cl- is obviously unreactive. But, the Al3+ forms coordinate covalent bonds (I believe) with water. The number of waters can't be logically determined. The same thing happens for Fe3+. So we have: (Al(H2O))3+. But, what can happen is that another water molecul...
- Mon Jan 21, 2019 2:31 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Partial pressure vs pressure
- Replies: 2
- Views: 232
Re: Partial pressure vs pressure
I agree with the above. Partial pressure changes can be treated the same as changes in the concentration of a specific reactant. However, changes in the overall pressure of the system (due to a change in the volume), is a little different. You have to determine the direction of the reaction that is ...
- Mon Jan 14, 2019 8:49 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Weak Acid/Base Calculations
- Replies: 2
- Views: 327
Re: Weak Acid/Base Calculations
I agree with the above. Weak acids and bases only dissociate partially. If the Ka or Kb is incredibly small, x (amount dissociated) is very very small. For a Weak acid: HA <--> H+ + A- I C E The equilibrium value for H+ can be used to then calculate the pH of the solution. Hope that was helpful.
- Mon Jan 14, 2019 8:46 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Maintaining relation between [H3O+] and [OH-]
- Replies: 2
- Views: 492
Re: Maintaining relation between [H3O+] and [OH-]
The reaction or process is 2H2O (l) <---> H3O+ (aq) + OH- (aq)
The Kc value for such a reaction at some temperature is Kc = H3O+ * OH-
Since the Kc is the same for some temperature, for the K value to be constant, H3O and OH vary inversely.
The Kc value for such a reaction at some temperature is Kc = H3O+ * OH-
Since the Kc is the same for some temperature, for the K value to be constant, H3O and OH vary inversely.
- Mon Jan 14, 2019 8:43 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Temperature and the equilibrium constant
- Replies: 2
- Views: 302
Re: Temperature and the equilibrium constant
I believe temperature is the only factor that can change the K-value. A change in temperature will cause an endothermic reaction to shift to the right. It will then reach a new equilibrium at this new temperature, in which products are higher in concentration than before and reactants are smaller in...
- Thu Jan 10, 2019 6:27 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Pure solids and liquids in eq. constants [ENDORSED]
- Replies: 4
- Views: 1943
Re: Pure solids and liquids in eq. constants [ENDORSED]
Solids don't have a concentration, so they are not placed in the equation. Additionally, the concentration of a liquid doesn't change throughout the reaction, so its like placing a [H2O] on the top and bottom of the Ka equation, and having them cancel out, I believe.
- Thu Jan 10, 2019 6:23 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Table Units
- Replies: 4
- Views: 576
Re: ICE Table Units
I've seen ICE tables use moles on a Khan Academy video on acid base titrations. Personally, if they give you a volume, its probably a hint to use molarity. Dr. Lavelle's future lectures on acids and bases may shed more light on this.
- Thu Jan 10, 2019 6:20 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Partial Pressures Definition
- Replies: 2
- Views: 236
Re: Partial Pressures Definition
Suppose we have a mixture of gases in a box. The total pressure of the mixture agains the walls of the box is equal to the pressure exerted by each individual gas. The pressure exerted by each individual gas is the partial pressure. We use partial pressures for gases because I think because the part...