Search found 31 matches

by Jayasuriya Senthilvelan 4I
Mon Mar 11, 2019 5:57 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Law
Replies: 2
Views: 32

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...
by Jayasuriya Senthilvelan 4I
Mon Mar 11, 2019 5:55 pm
Forum: Ideal Gases
Topic: Cell Diagram/Ecell
Replies: 8
Views: 193

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...
by Jayasuriya Senthilvelan 4I
Mon Mar 11, 2019 5:53 pm
Forum: Balancing Redox Reactions
Topic: Oxidation number?
Replies: 12
Views: 179

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...
by Jayasuriya Senthilvelan 4I
Mon Mar 04, 2019 8:27 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt
Replies: 14
Views: 208

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...
by Jayasuriya Senthilvelan 4I
Mon Mar 04, 2019 8:23 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: E cell spontaneity
Replies: 5
Views: 83

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...
by Jayasuriya Senthilvelan 4I
Mon Mar 04, 2019 8:20 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Endergonic vs. Endothermic
Replies: 6
Views: 172

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).
by Jayasuriya Senthilvelan 4I
Mon Feb 25, 2019 9:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt bridge
Replies: 2
Views: 42

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...
by Jayasuriya Senthilvelan 4I
Mon Feb 25, 2019 9:18 pm
Forum: Balancing Redox Reactions
Topic: about redox reaction
Replies: 5
Views: 78

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.
by Jayasuriya Senthilvelan 4I
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: 60

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).
by Jayasuriya Senthilvelan 4I
Mon Feb 18, 2019 2:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Polyprotic Acids
Replies: 5
Views: 94

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...
by Jayasuriya Senthilvelan 4I
Mon Feb 18, 2019 2:52 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy Problems
Replies: 3
Views: 59

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.
by Jayasuriya Senthilvelan 4I
Mon Feb 18, 2019 2:48 pm
Forum: Van't Hoff Equation
Topic: Temperature Dependence of K
Replies: 5
Views: 80

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...
by Jayasuriya Senthilvelan 4I
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: 41

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 (...
by Jayasuriya Senthilvelan 4I
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: 78

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 ...
by Jayasuriya Senthilvelan 4I
Mon Feb 11, 2019 8:55 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: state functions
Replies: 2
Views: 63

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...
by Jayasuriya Senthilvelan 4I
Mon Feb 11, 2019 8:51 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal
Replies: 1
Views: 48

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.
by Jayasuriya Senthilvelan 4I
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: 29

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...
by Jayasuriya Senthilvelan 4I
Mon Feb 04, 2019 10:48 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Work Formula
Replies: 5
Views: 81

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.
by Jayasuriya Senthilvelan 4I
Mon Feb 04, 2019 9:38 am
Forum: Calculating Work of Expansion
Topic: Integral calculations
Replies: 4
Views: 79

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.
by Jayasuriya Senthilvelan 4I
Mon Jan 28, 2019 8:42 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Units of Kp
Replies: 9
Views: 295

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...
by Jayasuriya Senthilvelan 4I
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: 153

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...
by Jayasuriya Senthilvelan 4I
Mon Jan 28, 2019 8:34 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Exothermic vs. Endothermic
Replies: 10
Views: 136

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.
by Jayasuriya Senthilvelan 4I
Mon Jan 21, 2019 2:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pKa confusion
Replies: 2
Views: 58

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.
by Jayasuriya Senthilvelan 4I
Mon Jan 21, 2019 2:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Aluminum Conjugate
Replies: 1
Views: 54

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...
by Jayasuriya Senthilvelan 4I
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: 45

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 ...
by Jayasuriya Senthilvelan 4I
Mon Jan 14, 2019 8:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Weak Acid/Base Calculations
Replies: 2
Views: 38

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.
by Jayasuriya Senthilvelan 4I
Mon Jan 14, 2019 8:46 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Maintaining relation between [H3O+] and [OH-]
Replies: 2
Views: 57

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.
by Jayasuriya Senthilvelan 4I
Mon Jan 14, 2019 8:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Temperature and the equilibrium constant
Replies: 2
Views: 46

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...
by Jayasuriya Senthilvelan 4I
Thu Jan 10, 2019 6:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pure solids and liquids in eq. constants [ENDORSED]
Replies: 4
Views: 81

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.
by Jayasuriya Senthilvelan 4I
Thu Jan 10, 2019 6:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Table Units
Replies: 4
Views: 64

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.
by Jayasuriya Senthilvelan 4I
Thu Jan 10, 2019 6:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Partial Pressures Definition
Replies: 2
Views: 39

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...

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