CHEMISTRY COMMUNITY

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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).

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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).

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

We will be given all standard enthalpies/entropies that we need to solve the problem. Don't worry about memorizing any specific values.

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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 (...

Jayasuriya Senthilvelan 4I

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 ...

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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 ...

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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...

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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.

Jayasuriya Senthilvelan 4I

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...

CHEMISTRY COMMUNITY

Search found 31 matches

Re: Rate Law

Re: Cell Diagram/Ecell

Re: Oxidation number?

Re: Pt

Re: E cell spontaneity

Re: Endergonic vs. Endothermic

Re: Salt bridge

Re: about redox reaction

Re: Value of K in Gibbs free energy equation

Re: Polyprotic Acids

Re: Gibbs Free Energy Problems

Re: Temperature Dependence of K

Re: Change in free energy for a reaction at equilibrium

Re: Difference between delta U and delta H?

Re: state functions

Re: Isothermal

Re: Standard / Formation / Reaction

Re: Work Formula

Re: Integral calculations

Re: Units of Kp

Re: Question 12.61 (Sixth Edition)

Re: Exothermic vs. Endothermic

Re: pKa confusion

Re: Aluminum Conjugate

Re: Partial pressure vs pressure

Re: Weak Acid/Base Calculations

Re: Maintaining relation between [H3O+] and [OH-]

Re: Temperature and the equilibrium constant

Re: Pure solids and liquids in eq. constants [ENDORSED]

Re: ICE Table Units

Re: Partial Pressures Definition