CHEMISTRY COMMUNITY

Sophie Krylova 2J

When do we add the platinum/graphite electrodes? (besides the hydrogen reaction) And if you add it, do you always add it to both sides of the cell diagram?

Sophie Krylova 2J

In example 14.10 it says that to find Q you need to divide left side by the right side concentration. Why isn’t it the other way around - like products over reactants and hence right over left?

Sophie Krylova 2J

Is total entropy change for an isothermal reversible expansion always zero? Why?

Sophie Krylova 2J

The second law states that the total entropy of an isolated system always increases. At the same time we talk about how if total entropy is negative, the reaction is not spontaneous or if it's zero, the rxn is at equilibrium. How are these two scenarios possible in the light of the second law, stati...

Sophie Krylova 2J

How much work do we need to show for this kind of problem? Because sometimes you can just look at the data and estimate the orders for the reactants.

Sophie Krylova 2J

Why are the initial rates proportional to concentrations and is it true always?

Sophie Krylova 2J

Yes, that's right. Mechanisms will not be on the test and those are the right chapter sections

Sophie Krylova 2J

I believe you will be told which one is the slowest, or you'll see it bc it will match the rate.

Sophie Krylova 2J

One application is nuclear reactions; the substances decay and their amount approaches 0 as an asymptote, so it doesn't make sense to talk about the time when it actually reaches 0.

Sophie Krylova 2J

From the general formula R=k[X]^n you can see that the rate units are fixed and so are the concentration units. Therefore, k units will change depending on what power the concentration is raised to.

Sophie Krylova 2J

To find the half life you simply plug in 0.5 for the final concentration and 1 for initial for the formula for the equations of any rate orders.

Sophie Krylova 2J

I don't think it has to be, because you can always multiply and divide all the coefficients by the same number to go from fractions to whole numbers and vice versa and the reaction won't change.

Sophie Krylova 2J

For example in part a) there are only two elements on each side of the double lines, but for the rest it's three. What does that mean then?

Sophie Krylova 2J

In the context of a problem if you're, for instance, given the rate, and d[]/dt of reactant/product X and at least one other d[]/dt and asked to find a in aX, you can multiply d[]/dt by its coefficient and then divide by d[]/dt of X to find a. (But that's an unlikely scenario)

Sophie Krylova 2J

I understand how to interpret the cell diagrams with two different reactions/compounds, but can somebody explain how to work with the ones where there are 3 reactions going on? (all the parts except of a)

Sophie Krylova 2J

How do you calculate moles of electrons? Do you need to go through the whole balancing process to find that?

Sophie Krylova 2J

So you could apply Hess' law for gibbs free energy too, since it's a state property?

Sophie Krylova 2J

In what context do we talk about Entropy vs change in entropy?

Sophie Krylova 2J

If it says that an exothermic reaction has occurred, do we automatically assume the temperature of the system decreases due to release of heat? (and vice versa with endothermic)

Sophie Krylova 2J

When we do calculations with the ICE table, do we use moles or molarities?

Sophie Krylova 2J

Yeah, but I guess my question was how can you tell if the product is water vapor vs liquid water

Sophie Krylova 2J

To calculate delta n in the reaction we need to subtract the number of moles of reactants from products. In order to do that we need to know if the water as the product of combustion is in gas or liquid state. How can you usually tell? (I remember it almost always being gas, but in the case it was a...

Sophie Krylova 2J

In the formula dS= q/T temperature is in the denominator, so with higher temperature dS is less. But isn't there more entropy with higher temperature?..

Sophie Krylova 2J

Heat of vaporization line os longer, because heat required for the process is represented by the x axis and vaporization requires more heat than fusion (the bonds between the molecules are completely broken). I believe the steepness is determined by the specific enthalpy values, but I am not 100% su...

Sophie Krylova 2J

In class we talked about how the reaction proceeds when the change in entropy is positive. Is it referring to the system or the surroundings?

Sophie Krylova 2J

So whenever we are told that pressure or volume is constant, do we automatically assume that the other isn't?

Sophie Krylova 2J

For calorimeter problems, is the water, the calorimeter, or the air (outside of the calorimeter) the surroundings?

Sophie Krylova 2J

Usually you would give the answer in the same units as the data given.

Sophie Krylova 2J

How do we take the phase change into account for calculating standard rxn enthalpy through enthalpies of formation?

Sophie Krylova 2J

I haven't looked at the problem specifically, but dU is not just work. dU = w + q (q is heat)

Sophie Krylova 2J

If enthalpy in the forward reaction is positive, it means it will be negative in the reverse rxn. Negative enthalpy means releasing heat; therefore, the reverse reaction will be exothermic.

Sophie Krylova 2J

You can add and cancel out products and reactants; multiply, divide and reverse the equations.

Sophie Krylova 2J

For H2 enthalpy of formation is zero, because it already is the most elementary form. In the problem, however, it's talking about hear of combustion, which is different -- Hydrogen does release heat.

Sophie Krylova 2J

Internal energy (U) is the same thing as enthalpy under the condition of constant pressure. Cp also implies the pressure is constant, unlike Cu. So for our purposes (of calculating enthalpy), U can be substituted for H for Cp, but not Cv.

Sophie Krylova 2J

If Q is greater than K and we are asked to find the equilibrium concentrations, are the products now considered as the reactants? So, do we put the on the denominator and use 1/K?

Sophie Krylova 2J

If for the ice box problem you are given initial concentrations and not asked to find Q, can you assume that the reaction will proceed to the products side, or do we always need to find Q first to make sure of the direction?

Sophie Krylova 2J

If for the ice box problem you are given initial concentrations and not asked to find Q, can you assume that the reaction will proceed to the products side, or do we always need to find Q first to make sure of the direction?

Sophie Krylova 2J

But what if individual ligands have charge, like CN- or SO4-2? So when you draw the lewis structure of what is inside the brackets, would you add the charges on those ligands?

Sophie Krylova 2J

So it's similar to the idea that donating electrons provides for a stronger bond than sharing?

Sophie Krylova 2J

When we draw a coordination compound, in which the ligand is charged, do we indicate the charge on the ligand in the lewis structure?

Sophie Krylova 2J

In the formula in the textbook aqua goes before oxalato, even though C is before O. Is this right or no?

Sophie Krylova 2J

Why in some HW problems the cation is simply "cobalt" but in others "cobaltate?"

Sophie Krylova 2J

Why will adding NH3 or KCl etc replace H20 in the TM complex?

Sophie Krylova 2J

Why will adding NH3 or KCl etc replace H20 in the TM complex?

Sophie Krylova 2J

Can somebody explain what the question is asking?

Sophie Krylova 2J

In the solution of part a) there is a single bond between O and Sb, rather than a double. I understand that O is more electronegative and more likely to pull electrons to itself, rather than share, but based on the formal charge calculation double bond would be more stable. Same thing with S and O i...

Sophie Krylova 2J

The solution squared is zero, that means there is zero probability of an electron being there. But what does the solution by itself represent?

Sophie Krylova 2J

So technically we don't know if a certain electron has positive or negative spin?

Sophie Krylova 2J

If n=5, then is it the row of the periodic table or the actual shell? (bc for d and f orbitals the two would be different)

Sophie Krylova 2J

How would you approach a formula like this to draw a lewis structure? H2C(NH2)COOH

Sophie Krylova 2J

How does the ability to "penetrate" the nucleus account for higher Zeff?

Sophie Krylova 2J

So is 3 d higher or lower in energy than 4 s?

Sophie Krylova 2J

In the textbook in some part of the explanation it says that s orbitals "penetrate" the nucleus. What does that mean?

Sophie Krylova 2J

Sometimes in questions about this quantum number the answer would be n-1; other times it's just n.. Can somebody explain that please I'm confused..

Sophie Krylova 2J

Are we expected to know the material in the textbook not covered in the lectures for the test? For ex, section 1.1 of the textbook, where the experiments leading to the current atomic model are described?

Sophie Krylova 2J

Adding on, this equation can help you figure out the wavelength of light (photons), but not the wavelength of electrons, because c (the speed of *light*) is directly involved with this equation. For wavelength of electrons or any bodies that have mass (mass of photons isn't really discussed) use de ...

Sophie Krylova 2J

When the electrons receive some amount of energy they "jump" to an exited state, and when they go back to their ground state they emit energy in the form of light. Why can't they just stay in the exited state if they have enough energy for it?

Sophie Krylova 2J

I understand the concept of what it is and vaguely how I am supposed to find it, but can somebody show the actual calculations?

Sophie Krylova 2J

This might be confusing, but in case you like to solve it using dimensional analysis:)

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