CHEMISTRY COMMUNITY

Emily Lo 1J

If your K value is less than 1.0*10^-3, then you can assume that the x value will not greatly effect the values in your equation. So if the K value is that small, you can assume that the x value in the denominator is 0.

Emily Lo 1J

The Kw is the equilibrium constant for water (the autoprotolysis of water). So the w in Kw is water.

Emily Lo 1J

State functions only depend on the initial and final products. Examples are entropy, enthalpy, and gibbs free energy.

Emily Lo 1J

You don't include water into your ice table because it's a liquid and when writing the equilibrium constants out, you disregard the liquids.

Emily Lo 1J

Cooper Baddley 1F wrote:The Mn is actually being reduced because it is going from a charge of +7 to +2 so that would be your cathode.

Oh that makes more sense! Thank you!!

Emily Lo 1J

As long as you have the anode on the left side and the cathode on the right side, it should be fine. Usually, you can determine what is losing the electron or gaining the electron when you're writing the half reactions if you know which are the anode and the cathode.

Emily Lo 1J

If the anode has a larger value than the cathode, does the reaction favor the products? Does it have to be the cathode that is a larger value for the reaction to favor the products? And is this something we should know?

Emily Lo 1J

SO the problem is asking: Identify the reactions with K > 1 in the following list and, for each such reaction, identify the oxidizing agent and calculate the standard cell potential. MnO4−(aq) + 8 H+(aq) + 5 Ce3+(aq)→5 Ce4+(aq) + Mn2+(aq) + 4 H2O(l) Both MnO4- and Ce3+ are losing electrons, does any...

Emily Lo 1J

Alicia Lin 2F wrote:The cathode is always written on the right side and the anode is always written on the left.

And does the flow of electrons go from the anode to the cathode?

Emily Lo 1J

When we're given a cell diagram, how do we distinguish which side is the anode and which side is the cathode? I'm trying to find examples where we would figure out which one is which. Like would we be given elements and we just figure it out from that? (There might be an obvious answer to this and I...

Emily Lo 1J

I don't think it matters in what order you write them as long as you place a comma in between because of the similar phases.

Emily Lo 1J

A line is used to separate elements of different phases and a comma is used for elements of the same phase. So if you had Cu(s) and Cu2+(aq), there would be a line between them.

Emily Lo 1J

So a concentration cell is just the same element with different concentrations? With the Ag and Ag+ example will the elements always have one that has a positive charge?

Emily Lo 1J

On Outline 5, one of the bulletins says to "understand what is meant by the electrochemical series". Did we go over this in class? I'm not sure what it is.

Emily Lo 1J

How do you derive the Nernst equation? Where do you start?

Emily Lo 1J

Is the reducing agent what is losing electrons? What exactly is the reducing agent? I never really grasped the concept of the reducing and oxidation agents.

Emily Lo 1J

Are there different equations regarding isothermal reversible and irreversible free expansions?

Emily Lo 1J

On Q6B, how do you determine which process will have delta H and delta g be similar?

Emily Lo 1J

You have to think about how Ka=[A][H+]/[CB] (CB being conjugate base). By rearranging the equation, you can get Ka/[H+] = [A]/[CB], which is a ratio. Were we given this equation anywhere? I mean like the original, not manipulated, equation? And I don't recall using it before the midterm but I may b...

Emily Lo 1J

On Q3D on the midterm, it asked for the net charge given the pH and pKa and I did not know how to find the charge. Does anyone know how to find the charge given the pH? Do we use the pH to calculate it or the pH?

Emily Lo 1J

Someone correct me if I'm wrong but I think all ideal gasses have an enthalpy of 0. I think the elements have to be in their standard state.

Emily Lo 1J

Usually, you'll be given a couple or more equations that are related to the main one given and then you'll want to algebraically solve to get the main equation through the other ones. Whatever changes made on those equations you make onto the delta H's. Then you add them up to get the net change in ...

Emily Lo 1J

You just have to make sure that you have the right units with the R value. For the most part in thermochemistry we used 8.314 but like in an instance of using PV=nRT, we would use the other R values.

Emily Lo 1J

Reactions will usually want to go towards a state that they are, in a sense, "comfortable" in, so they want to go towards favorable reactions. Usually, these reactions release heat. And I think an easy way to think about spontaneous reactions is that they can happen randomly (spontaneously...

Emily Lo 1J

Can someone help explain why and how the equation for 3b includes (1/2)(m)(delta H of fusion)? I get what you would isolate to get the answer but I'm not sure how they got that part of the equation.

Emily Lo 1J

We're able to use Hess' Law because enthalpy is a state function. Since it's a state function, we're able to just add the enthalpies together.

Emily Lo 1J

For an isolated system, nothing can come in or out of the system. In a closed system, heat can come in and out of the system. Both can't have matter come in or out but the main difference between isolated and closed is that nothing can come inside an isolated system. It's like an insulated bottle, h...

Emily Lo 1J

It can decrease in entropy when the system decreases in disorder, which could be thought of as molecules. When the temperature decreases, the disorder decreases because the movement of molecules slows down. Someone correct me if I'm wrong though.

Emily Lo 1J

In the equation delta S equals q rev over temperature, what exactly is q rev?

Emily Lo 1J

Yes, a negative is exothermic so then a positive would be endothermic. A way to remember it would be that exothermic is like "exit" and if something is exiting then it is leaving or losing something.

Emily Lo 1J

It makes more energy to change from liquid water to water vapor. And as Matthew said, there is a longer flat line from liquid to vapor than from solid to liquid, which basically means that more energy is required to get to that vapor temperature.

Emily Lo 1J

It's mainly used to find the unknown value of a concentration. It's also based on what values you're given but you'll mainly be given the concentrations of the reactant and want to solve for the products.

Emily Lo 1J

What is the difference between a calorimeter and a bomb calorimeter? Are there different uses for both of them?

Emily Lo 1J

The universe is a system that has no surroundings to which heat or matter for that fact can be exchanged. This exactly the properties that make a system isolated. So the universe is isolated because heat or matter can't be exchanged? SO an isolated system means that heat can't be transferred to the...

Emily Lo 1J

How can you change the energy in a closed system? And does it differ with isolated systems?

Emily Lo 1J

Organic Chemistry Tutor is a really good one! I used it in 14a and it helped a lot!!

Emily Lo 1J

The equation is [H3O^+][OH^-] = Kw. Generally, it would be [1.0x10^-7][1.0x10^-7] = 1.0x10^-14. This is when Kw is at 25 C., otherwise I think the Kw value would be different at different temperatures.

Emily Lo 1J

If you got a negative number inside the square root, I would re-check the calculations inside of the square root. You shouldn't be getting a negative because that would result in an imaginary number.

Emily Lo 1J

Did Professor Lavelle say if there was a method preferred over another? And how would we know which one to use?

Emily Lo 1J

Is there a relationship between the standard reaction enthalpy and the standard enthalpy of formation?

Emily Lo 1J

You can use ICE tables for acids and bases but you mainly use them when you have weak acids and weak bases.

Emily Lo 1J

Kb is for bases while Ka is for acids.

Emily Lo 1J

They're the same. You can disregard the X in the denominator when K < 10^-3 which essentially allows you to solve for X without the quadratic formula. It also means that X is small enough to be excluded in the equation.

Emily Lo 1J

What is the conjugate seesaw?

Emily Lo 1J

It is the transfer of a proton between the same type of molecule. An example of it would be 2H2O $\rightleftharpoons$ H3O $^{+}$ + OH $^{-}$

Emily Lo 1J

If the Q value is less than K, then there is more reactant than there is product in the reaction, and the direction which the reaction favors it forward. If the Q value is greater than K, then there is more product than there is reactant in the reaction, and the direction which the reaction favors i...

Emily Lo 1J

Yes it can apply to both! They are both calculated the same way. Just the only difference between the two is that K is at equilibrium while Q can be calculated at anytime in the reaction.

Emily Lo 1J

K can only be calculated when the reaction has reached equilibrium. Q can be calculated at any point in a reaction.

Emily Lo 1J

It tells us whether there is more reactant or product during the reaction. And with that, it can determine whether a forward or reverse reaction is favored. So if Q is smaller than K, then there is more reactant than product, resulting in favoring a forward reaction. If K is smaller than Q, then the...

Emily Lo 1J

It's a way to help you track your steps but you don't have to use the table.

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