CHEMISTRY COMMUNITY

Lourick Bustamante 1B

Activation energy cannot be negative because it is the minimum amount of energy that a reaction requires to undergo a specific reaction, making it positive. So if the activation energy were to be negative, then that would mean there is a release of energy.

Lourick Bustamante 1B

In isothermal processes, ΔU will be 0.

Lourick Bustamante 1B

I think changing the temperature does cause a change in pressure/volume. Because for a gas, for example, when heated, the particles move more rapidly and this causes them to expand ?

Lourick Bustamante 1B

The problem is asking you to calculate ΔU, the change in the internal energy. It is given that it is a constant-volume calorimeter, so you know that there is no ΔV therefore, w=0. That being said, we know that ΔU=q. Use the equation -q cal =CΔT to solve for C---you should get the value -478.1 J. We ...

Lourick Bustamante 1B

To measure the rate of a reaction, you can use the differential rate law which is k[Reactancts] n with n being the amount of moles; the differential rate law is rate as a function of concentration of reactants. On the other hand, you can also use the integrated rate law which is [A] t = -kt + [A] 0 ...

Lourick Bustamante 1B

You use the value of 1.40 g CO because you know the change in temperature caused by this amount of CO, and so you can then set a ratio to get the change in temperature for one mole of CO (28 g CO). That being said, you could take 1.40 g CO/.686°C = 28.0 g CO/ΔT and cross-multiply to solve for ΔT to ...

Lourick Bustamante 1B

Half lives depend on the initial concentration of A. If the initial concentration of A is larger, it will take a longer time for half of it to decay than if the initial concentration was smaller.

Lourick Bustamante 1B

Q is the the reaction quotient and K is the equilibrium constant. Both Q and K are calculated the same way (by using pressures or concentrations) but they are applied differently depending on the equation that you are using. Because they are calculated the same, it shouldn't make too much of a diffe...

Lourick Bustamante 1B

Also, going off of finding the half-life, remember that you can also find the "one-third" life or "one-fourth" life, etc.

Lourick Bustamante 1B

Given the metal and the solution that you are observing, you form a balanced chemical equation using the half-reactions and their E° values. Once you calculate the E° value for the balance chemical equation, you get a value that is either positive or negative. If E° is negative, then ΔG is positive,...

Lourick Bustamante 1B

E° = standard reduction potential
When comparing the values of E°, you can use the rules:
- most easily reduced element/best oxidizing agent = higher E°
- most easily oxidized element/best reducing agent = lower E°

Lourick Bustamante 1B

The two equations are equal to each other; therefore, you can use either one. The equation k[R]^n is just the other reaction rate equation reexpressed after doing experiments to observe d[R]/dt. The equation k[R]^n is in terms of the rate constant, k, the concentration of reactant, [R], and the orde...

Lourick Bustamante 1B

Residual entropy is the measure of how many different arrangements a molecule can have. Molar entropy is a measure of a molecule's chaos. Both of your statements above are true, and they don't oppose one another. You can compare two molecules, and have one molecule have higher residual entropy AND a...

Lourick Bustamante 1B

E is referring to the cell potential. (We are currently learning about this in electrochemistry.)

Lourick Bustamante 1B

How did you know that the amount of heat released when H2O goes from a gas to a liquid was -44 kj/mol?

Lourick Bustamante 1B

Yes, hydrogen atoms barely have any mass compared to fluorine atoms. Therefore, since the molecules being compared are made up of only carbon, fluorine, and hydrogen, the molecules with the a higher ratio of fluorine to hydrogen would have the greater molar entropies.

Lourick Bustamante 1B

If a reaction has a higher chance of occurring more spontaneously, then it would be considered less stable because less stable particles are more likely to react.

Lourick Bustamante 1B

I'm pretty sure it can be calculated using either pressures or concentrations, but I'm not 100% sure. I know that Q can be calculated using both pressures and concentrations, though. So I think the same applies to K.

Lourick Bustamante 1B

Yes, I'm not sure if G can have a lowest value, but if I'm remembering correctly, Lavelle said that measuring G alone is very difficult, therefore we always measure the change in G. If you meant to ask about DeltaG, DeltaG can't have a lowest value, and if it does, then it definitely wouldn't be 0! ...

Lourick Bustamante 1B

This is a really helpful explanation! The analogy that Lavelle really helps to provide an example as to why the Second Law of Thermodynamics proves to be true. Compared to the universe, the entropy observed in a system will always be too small to have any notable effect on the universe's entropy, an...

Lourick Bustamante 1B

Yes, I agree with what is said above! DeltaS of the system added to the DeltaS of the surroundings are equal to the DeltaS total/universe. Some other points to remember are that if the calculated DeltaS total value is greater than 0, then the reaction being observed is spontaneous, and oppositely, i...

Lourick Bustamante 1B

I know Prof. Lavelle stated that degeneracy is the number of ways of achieving a given energy state, and then connects it to the entropy through the Boltzman Equation which is S = klnW. So is that how we find it? If we use entropy to find degeneracy?

Lourick Bustamante 1B

A vacuum is a volume that encloses little or no matter. In other words, it is a region that has a gaseous pressure much lower than that of atmospheric pressure---so that's what it represents in the system with the ideal gas that we were shown in class!

Lourick Bustamante 1B

He said, "The magnitude of deltaS depends on temperature at which heat is transferred. Therefore, deltaH [or q] plays an important/bigger role at a lower temperature." (:

Lourick Bustamante 1B

I believe that they are equal, but q=CdeltaT is the general form of the equation, assuming that you are only reacting 1 gram or 1 mole of something. If the amount of whatever you are reacting is not 1, then the calculations need to be specific to the amount of whatever you are reacting. Therefore, i...

Lourick Bustamante 1B

It's a given! It's explained in Chapter 8.10 of the textbook! (:

Lourick Bustamante 1B

Example 8.3a) Calculate the heat necessary to increase the temperature of 100. g of water from 20 degrees Celsius to 100 degrees Celsius. In the worked out calculation, the delta T value used is 80. K. Why is the temperature change 80 K instead of 353.1 K? It seems that they just changed the units w...

Lourick Bustamante 1B

By definition according to Lavelle, standard enthalpy of a reaction occurs when all reactants and products are in their standard states at 1 ATM. It's also known as reaction enthalpy. Standard enthalpy of formation, on the other hand, is the standard reaction enthalpy for the formation of one mole o...

Lourick Bustamante 1B

Correct! The cutoff time for each week is Sunday at 11:59pm.

Lourick Bustamante 1B

Heat and work are not state functions. Work can't be a state function because it is proportional to the distance an object is moved, which depends on the path used to go from the initial to the final state. Same with heat. I hope this is helpful!

Lourick Bustamante 1B

Each element has the same amount of electrons, but the amount of protons is not changing. Therefore, the elements with more protons have a stronger pull on the electrons making the atomic radius decrease.

Lourick Bustamante 1B

Hi guys! Can someone please guide me through the steps of solving this problem. When asked for help during the review session, it was said that there was an issue with the kinetic energy relative to the energy of the photon. Here's the question: An electron was ejected from the surface of an unknown...

Lourick Bustamante 1B

How do you calculate the electronegativity for the atoms of a specific element?

Lourick Bustamante 1B

Are there other rules/tips/tricks that are useful for manipulating equilibrium constants?

Lourick Bustamante 1B

Can someone please explain to me why the answer to b) ends with cobalt compared to the answer to c) which ends in cobaltate? I need clarification on when to add the -ate at the end of the metal name.

Lourick Bustamante 1B

Did you know that you can cool yourself to -273.15˚C and still be 0k?

Lourick Bustamante 1B

I’d memorize them. The more tools you have in your toolbox, the better.

Lourick Bustamante 1B

Yea, we will be covering it. I believe it's in Chapter 4 if I'm not mistaking.

Lourick Bustamante 1B

I usually like to draw one bond between each of the atoms and then I assign the rest of the valence electrons!

Lourick Bustamante 1B

Bond angle determines if a molecule has lone pairs because lone pairs have strong repulsive factors that cause it to displace the other atoms, pushing other atoms closer together. This causes the bond angle between the other two atoms to decrease. Therefore, if there is a lone pair for part B, the s...

Lourick Bustamante 1B

All elements in period 3 and further have the ability to have more than 8 valence electrons.

Lourick Bustamante 1B

The minimum numbers for n and l are 0, but the minimum number for ml would depend on the value of l which can range from 0 all the way to infinity, theoretically. But if applying what we know about energy levels, as energy level n gets larger, the electrons in these energy levels become virtually un...

Lourick Bustamante 1B

The magnetic quantum number ml determines the number of orbitals and their orientation within a subshell. Its value depends on the orbital angular momentum quantum number l. Given a certain value for l, ml is an interval ranging from the negative value of l to the positive value of l, so it can be z...

Lourick Bustamante 1B

I agree with the post above. It's important to always keep the units consistent with the form of the unit in the final answer.

Lourick Bustamante 1B

The octet rule can be used for the some of the s- and p- block elements (with exception for the lighter elements in these blocks), and only applies to some of the elements in the d- block. General exceptions to the octet rule: (1) molecules whose atoms have fewer than 8 electrons (e.g., boron chlori...

Lourick Bustamante 1B

Why do certain orbitals get filled first even though the other orbitals have a smaller number? (for example, 4s fills before 3d)

Lourick Bustamante 1B

Why is it that we use E = h(c/λ) instead of just E = hv?

Lourick Bustamante 1B

I am having trouble on Question 1.13 on the homework and I'm thinking that it might be because I have Rydberg's formula or constant wrong. On Lavelle's Atomic Spectra video module it says that the Rydberg's constant is R = 3.29 x 10^15 s^-1, but online it is saying that R = 1.09 x 10^7 m^-1. Which o...

Lourick Bustamante 1B

^ I agree with both people. Lavelle said in lecture that it's okay to leave it in meters, but as stated above, it'll be easier to interpret and use the calculation if it were to be converted.

Lourick Bustamante 1B

The next test isn't until next week (:

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