CHEMISTRY COMMUNITY

Jessica Helfond 2F

Why does the graph of time versus concentration need to be linear?

Jessica Helfond 2F

How do kinetics and thermodynamics interact to control reactions? How do they each impact a reaction differently?

Jessica Helfond 2F

How can you tell what the order of a reaction is?

Jessica Helfond 2F

If [A]₀ is the initial concentration of A, then what does [A] represent?

Jessica Helfond 2F

Could someone explain what the rate constant (k) actually represents within a reaction?

Jessica Helfond 2F

How do temperature and activation energy impact the rate constant?

Jessica Helfond 2F

How does the Van't Hoff equation relate to equilibrium?

Jessica Helfond 2F

How do you know what order to put the reactants and products in when constructing a cell diagram?

Jessica Helfond 2F

How do you find the number of electrons to balance a redox reaction?

Jessica Helfond 2F

Do salt bridges and porous disks both allow ion transfer in the same way? Or would we use one instead of the other in certain situations?

Jessica Helfond 2F

How does Gibbs free energy relate to the spontaneity of a reaction?

Jessica Helfond 2F

Could someone explain what Gibbs free energy actually is? And how does that relate to entropy and enthalpy?

Jessica Helfond 2F

Will we need to know how to derive formulas for the midterm? Or is it just something he showed us in class in order to provide background for the concept?

Jessica Helfond 2F

Will we be told is there is changed/constant volume or temperature? Or is it something we will have to figure out using PV=nRT?

Jessica Helfond 2F

In what circumstances will we use equations with the Boltzmann equation versus nrtln(v2/v1) or nrtln(t2/t1)?

Jessica Helfond 2F

Could someone explain conceptually why this equation works? I know what each of them means but I'm not sure why the internal energy is equal to the heat plus work.

Jessica Helfond 2F

I'm pretty sure we would be given any constant we need to convert between units of pressure and volume. That being said, I think 1L*atm=101.325J is just like any other constant on the constant sheet we're given, we don't need to know where it comes from.

Jessica Helfond 2F

A reversible reaction does more work than an irreversible reaction. This is because we change the volume infinitesimally, so we push against the force little by little to change the volume. This means a reversible reaction is slower, but more efficient. On the other hand, irreversible is fast but in...

Jessica Helfond 2F

How is thermodynamics different from enthalpy? I get that thermodynamics is heat transfer, but how does that differ from enthalpy, which is the heat absorbed or released?

Jessica Helfond 2F

What does calculating the infinitesimal change in volume mean? I get that it's when the volume is changing in very small steps, but what does that mean for the system in the big picture?

Jessica Helfond 2F

What is the difference between heat capacity and specific heat capacity? Why is one extensive and the other intensive?

Jessica Helfond 2F

To go from pH to concentration, you can do 10^-pH. You then use this concentration in the ICE box and solve for x to find Ka.

Jessica Helfond 2F

Protonation is the addition of a proton (H+). Conversely, deprotonation is the removal of a proton (H+). Protonation occurs for bases, while deprotonation occurs for acids. The percent protonated is the amount of base that gets a H+ in the process of the reaction. If it's strong, the percent will be...

Jessica Helfond 2F

I think we should be familiar with what strong acids/bases are going to be (for example, HCl/NaOH) so we can recognize them. Additionally, Lavelle said if the Ka is smaller than 10^-3, it means it's a weak acid. The same goes for bases I'm pretty sure.

Jessica Helfond 2F

How do you know if something is a salt? How do you know if it will create an acidic or basic solution?

Jessica Helfond 2F

I'm pretty sure Ka values will be given to us either in the problem or in a table with other Ka values. For this specific problem, it's probably given in a table somewhere in the textbook. Hope this helps!

Jessica Helfond 2F

How do we know if an acid is strong or weak? Similarly, how do we know if a base is strong or weak?

Jessica Helfond 2F

How do we know if a gas is ideal? Do we just assume it is in most scenarios?

Jessica Helfond 2F

In lecture, Lavelle's slides said for changes in pressure, K does not change, whereas for changes in temperature, K does change. Was this just an example or is this always the case? If it's always the case, why does K change for temperature and not pressure?

Jessica Helfond 2F

Will we always be given the numbers for the equilibrium constants of the products or reactants? Or will we have to find them ourselves?

Jessica Helfond 2F

I don't think we'll be given a chart. I think we're just supposed to generally know how to name ligands and coordination compounds.

Jessica Helfond 2F

How can you tell if an acid/base is strong or weak?

Jessica Helfond 2F

What does it mean if something is outside of the coordination sphere? How does that work structurally?

Jessica Helfond 2F

There are quite a few molecular shapes we need to know for the test. I think it makes the most sense to look at them in terms of how many regions of electron density there are within the molecule. For molecules that have two regions of electron density, the molecule is linear. If there are three reg...

Jessica Helfond 2F

Do we need to be able to use the equation m=q x d to calculate the dipole moment? We took notes on this in class but never did any calculations with it. Is it just a concept we need to be familiar with or will we have to calculate the dipole moment within molecules?

Jessica Helfond 2F

Could someone explain how we know how many sigma/pi bonds there are within a molecule?

Jessica Helfond 2F

It's not necessary for us to know the exact angle, I think it was just a specific example to show us the proof that the bond length was less. As long as you know it's less than 109.5, you should be good.

Jessica Helfond 2F

Could someone explain why in part b the solution says it's possible to have lone pairs? If the two atoms have a bond length of 180 degrees, wouldn't the lone pair push them closer together and then the bond length would be less than 180 degrees?

Jessica Helfond 2F

From what I understand, it shouldn't matter whether you draw it vertically or horizontally. The electron and bond positions would be the same, which is what is most important.

Jessica Helfond 2F

Additionally, as a general rule, triple bonds are going to be the shortest because they are the strongest. Double bonds are the next shortest and strongest, and single bonds are going to be the longest and therefore the weakest.

Jessica Helfond 2F

Are single/double/triple bonds the only scenario in which there is high electron density that we need to know in terms of VSEPR model?

Jessica Helfond 2F

Could someone explain the bond angles in the trigonal bypyramidal shape? Specifically, how/where there are 120 degree angles?

Jessica Helfond 2F

There's also a periodic table with the elements and their electronegativity numbers, but I'm pretty sure Lavelle said we don't have to memorize the exact values. If we needed to know the precise numbers, it would be given to us.

Jessica Helfond 2F

Could someone explain Lewis acids and bases? And how does it relate to coordinate covalent bonds?

Jessica Helfond 2F

In what context would there be a radical? If they're so unstable, how do they exist?

Jessica Helfond 2F

What does it mean by achieving "lowest energy" when bonding?

Jessica Helfond 2F

Could someone explain why we write the 3d block before the 4s block when 4s occurs first on the periodic table? Which would get removed first when bonding?

Jessica Helfond 2F

Could someone explain why removing the second ionization energy of an element is always higher than the first?

Jessica Helfond 2F

From what I understand, these are the five different ml numbers for a d orbital. Three of the ml numbers are similar to the way we've been writing them: d(xy), d(yz), and d(zx). Another is written as dx^2-dy^2. The final way is dz^2. I think the variances have to do with the different e- densities o...

Jessica Helfond 2F

From what I understand, in the magnetic quantum number (ml), for l=1, ml= -1,0,+1. Because the subscript goes px, py, pz, py is the middle term, just as 0 is the middle term. Thus, py=0. I believe px and pz would be interchangeable for -1 and +1. Hope this helped!

Jessica Helfond 2F

Could someone explain what the H in the Schrodinger equation represents? I can't seem to find it in my notes or the textbook.

Jessica Helfond 2F

Could someone explain why we have to account for the difference in position and momentum (why it's Δp and Δx instead of just p and x)? Why aren't we able to determine the precise value of the two?

Jessica Helfond 2F

Watts is equivalent to Joules per second. So in this problem, 32 W=32J/s. Then you can find the amount of photons the lamp generates, and then convert the photons to moles by using Avogadro's constant. Hope this helped!

Jessica Helfond 2F

In simple terms, resting mass is just when an object has mass when it's stationary. Hope this helped!

Jessica Helfond 2F

Could someone explain how wavelength and frequency are different? Or are they related?

Jessica Helfond 2F

Why was the photoelectric effect unexpected? What did they think would happen instead?

Jessica Helfond 2F

Could someone explain what the formula Ek=1/2 Me- * Ve-^2 represents?

Jessica Helfond 2F

A one step chemical reaction can only have one limiting reagent because (as long as the 2 reactants are present in different amounts and/or you need different amounts for the reaction) you will run out of one first. Therefore, the reaction will not be able to continue because you will be out of one ...

Jessica Helfond 2F

Could someone explain why we use significant figures? Wouldn't keeping more decimals be more precise in the answer, or should we just always go by how many sig figs are given in the question?

Jessica Helfond 2F

Can someone explain to me what an aqueous solution is? And why do we need to include the state of matter when we write and balance chemical reactions?

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