CHEMISTRY COMMUNITY

Delaney Smith 1C

How can you determine the catalyst by looking at the reaction? For example in 7E.5, how do you know the catalyst in this reaction?

Delaney Smith 1C

I don't think you can tell by just the activation energy. In a endergonic reaction, the products are higher than the reactants. If it is a slow endergonic reaction the activation energy is going to be much larger. In a faster endergonic reaction, the activation energy will be much lower. The same th...

Delaney Smith 1C

A catalyst doesn't affect deltaH! Remember to not mix thermodynamics with kinetics. All catalysts do is lower the activation energy of the reaction which therefore increases the rate of the reaction, but not the enthalpy of the reaction!

Delaney Smith 1C

I don't understand why they subtracted 0.59, but I solved the problem without 0.59 being subtracted and got 2.7x10^10 which is what the solution manual got as well.

Delaney Smith 1C

I am confused on what we are suppose to solve for this question. How do you determine if the student's mechanism is valid? I looked at Dr. Lavelle's work but I was still confused on this concept.

Delaney Smith 1C

Since you have the initial concentration of A, [A]o, and you are given the number of moles for each reactant and product, you can solve to find [A]t which you can then plug into the equation ln[A]t=-kt+ln[A]o to solve for k. To find [A]t you would subtract the mole ratio of A to B times the concentr...

Delaney Smith 1C

Wait, how do you solve for k if you don't have [A]t?

Delaney Smith 1C

How do you solve for the rate of consumption?

Delaney Smith 1C

What is the importance of the Arrhenius equation? What are you trying to find using this equation?

Delaney Smith 1C

I am not sure whether you use integrated or differential rate laws, but to determine order you can either look at the units given for k(r) or the exponent's in the equation. Usually, the units for
zero order: mol/(L x s)
1st order: 1/s
2nd order: L/(mol x s)

Delaney Smith 1C

Hi! I am a little confused, when we are solving for first order problems, will we actually ever use the equation ln[A]=-kt+ln[A] or do you just use rate=k[A]?

Delaney Smith 1C

How does change in temperature affect K or Q?

Delaney Smith 1C

Hi! For some problems such as 6K.5, when I am adding the electrons to balance the charge, I am sometimes getting the wrong number of electrons. I know how to find the initial and final oxidation numbers, but why isn't the charge you add to the reactants or products always equal to the change in oxid...

Delaney Smith 1C

Why is the charge of MnO4- +7?

Delaney Smith 1C

K can be affected by cell potential. Cell potential depends on factors such as concentration, gas pressure, and temperature so all of these factors also affect K.

Delaney Smith 1C

t=0 usually is the start for most reactions so when you are wanting to observe initial rates you want to observe rates that are closest to zero. It can be initial rates right after time t=0 so it is easiest to measure.

Delaney Smith 1C

Hello! I was absent on Wednesday of week 8, I have the notes but I don't really understand what the notes mean. Can someone briefly explain the concept of Kinetics and the most important takeaway from that lecture? Thanks!

Delaney Smith 1C

Why do you use 2 for n in the equation DeltaG=-nFE in 6L.1 a?

Delaney Smith 1C

Hi! I'm really confused with 6K.1. I'm having a hard time identifying the elements undergoing oxidation and reduction, and writing and balancing the reactions. Can anyone help explain?

Delaney Smith 1C

Can someone explain what the reaction, I (reactant) and I2 (product), will look like graphically?

Delaney Smith 1C

Hi! I was absent Friday. Can someone explain what electrochemistry means and the importance of electrochemistry? Thanks!

Delaney Smith 1C

Yes, if you increase the partial pressure of a product gas, ΔG becomes more positive. If you increase the partial pressure of a reactant gas, ΔG becomes more negative because of the equation ΔG=ΔGo+RTlnQ where Q equals partial pressure of products over the partial pressure of reactants.

Delaney Smith 1C

If the reaction is at equilibrium, Q=K and ΔG=-RTlnK. If you increase the partial pressure of a product gas, ΔG becomes more positive. If you increase the partial pressure of a reactant gas, ΔG becomes more negative. Therefore, ΔG depends on pressure and K.

Delaney Smith 1C

According to the textbook, the cis compound has 12 different orientations while the trans compound only has three different orientations, decreasing the entropy due to the fact that there is less uncertainty in its orientations. In regards to entropy, residual entropy is the measure of how many dif...

Delaney Smith 1C

Like what Maia said above, in the review session today they said that they have almost never used Cp and only Cv. But when you are calculating, you can also check to see if the compound is a monatomic or diatomic compound. If it's monatomic then use 3/2, but if it's diatomic use 5/2.

Delaney Smith 1C

Monatomic compounds are composed of single atoms, and diatomic compounds are composed of molecules containing two atoms. what-are-the-seven-diatomic-elements-606623-v3-5b562dab46e0fb0037fee8c7.png Difference-Between-Monatomic-and-Diatomic-Comparison-Summary.png I don't know why the C s values are 3...

Delaney Smith 1C

nshahwan 1L wrote:Would we ever have to calculate/know the amount of that force? Thanks!!

I don't think we have to worry about solving for force as we haven't been given any equations that include force

Delaney Smith 1C

Internal energy equals the sum of heat and work. If internal energy is equal to zero than heat is equal to the opposite of what work is equal to.

Delaney Smith 1C

(a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its temperature from 20.0°C to the boiling point of water, 100.0°C. (b) What percentage of the heat is used to raise the temperature of the water? Can someone explain the concept of t...

Delaney Smith 1C

What does it mean to have a constant volume or constant pressure?

Delaney Smith 1C

If energy is going into the system that means something else is doing work on the system and the work on the system is positive. If energy is going out of the system, that means that the system is doing work on the surrounding environment and energy is being lost from the system and is negative.

Delaney Smith 1C

To go off of the idea that higher entropy means higher disorder, that means that gas has high entropy because it has many microstate while solids have the lowest entropy because it has the fewest microstates.

Delaney Smith 1C

Can someone explain the concept of extensive property? What are some examples of extensive property?

Delaney Smith 1C

The residual entropy of a system is the difference between the calculated and experimental entropy at a given temperature

Delaney Smith 1C

Patricia Cardenas wrote:
Delaney Smith 1C wrote:Hi guys! I wasn't able to make this past Friday's lecture (week 4). Could anyone share their notes with me? Thank you so much!

I can share my notes with you too, what's your email?

dmsmith14@g.ucla.edu

Thank you!

Delaney Smith 1C

Deena Doan 2F wrote:Yeah, I can! What's your email?

dmsmith14@g.ucla.edu

Thank you so much!

Delaney Smith 1C

Hi guys! I wasn't able to make this past Friday's lecture (week 4). Could anyone share their notes with me? Thank you so much!

Delaney Smith 1C

For method 3, how do you make sure everything is in standard state? Do you just divide by the number of moles for each substance so you have one mole?

Delaney Smith 1C

Can someone explain why DeltaHsub = DeltaHfus + DeltaHvap?

Delaney Smith 1C

It will most likely depend on the information given. You use: Hess's law (method 1) : If you have two equations that can be added together to get the wanted composite equation, you can add the deltaHRXN of each equation to get the net deltahHRXN Method 2: if you are given the bond enthalpies and can...

Delaney Smith 1C

The third method is referred to as the standard enthalpy of formation. The standard enthalpy of formation is the change in enthalpy of the products and reactants with each substance being in standard state (one mole).

Delaney Smith 1C

Can anyone briefly explain how to go about drawing lewis structures? I know it's useful to draw out for method 2, but I forgot. Thanks!

Delaney Smith 1C

What do you do again when you are calculating pOH? Also, how do you know if you are calculating for a base or for an acid?

Delaney Smith 1C

In 6A.23, how do you know how to write the reaction? I'm confused on how to know if OH- or H3O is in the reaction and if so which side it is on?

Delaney Smith 1C

Acids produce conjugate bases when they dissociate in aqueous solutions. On the other hand, bases produce conjugate acids when they dissociate in aqueous solutions. The conjugate seesaw basically just means that stronger acids produce weaker bases and stronger bases will produce weaker acids.

Delaney Smith 1C

How do you know in a problem whether the acid/base is strong or weak? Do you memorize them or is there an easier way to tell?

Delaney Smith 1C

For partial pressure, the composition will tend to change in a way that minimizes the resulting increase in pressure. The basic point is that the reaction will shift to whichever side that has less moles.

Delaney Smith 1C

Why are changes in solvent concentrations insignificant in a reaction?

Delaney Smith 1C

Yes, if the reaction is shifted to the left that means that the are more moles on the left side of the reaction which are the reactants. While if the reaction is shifted to the right that means there are more moles on the right side of the reaction which are the products.

Delaney Smith 1C

The reaction is still present and occurring even when the products are equal to the reactants. This just means that P/R ratio is the same so there won't be more products or reactants as the reaction is at equilibrium.

Delaney Smith 1C

How do you know if a reaction is at equilibrium or not at equilibrium? Will the question state specifically to solve for K or Q or do you have to know just by looking at the reaction whether you're solving a reaction at equilibrium or not at equilibrium?

Delaney Smith 1C

ICE is good to use when you are solving for the composition of reactants or products in a reaction. Otherwise you would be solving for K if the reaction is at equilibrium or Q if the reaction is not at equilibrium.

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