CHEMISTRY COMMUNITY

MorganYun1H

If by reaction profile you mean the graph/diagram of the reaction, then the intermediates would be the troughs in between each peak/step.

MorganYun1H

you can ignore it because a zero order reactant means that the rate of the reaction is not dependent on the change in concentration of that particular reactant. Therefore, you can ignore it.

MorganYun1H

catalysts lower activation energy therefore the forward and reverse rate will both increase.

MorganYun1H

But, one of the UAs told me that in this class we won't be getting fractional orders. Maybe someone could verify?

MorganYun1H

So then will we ever see a positive k value?

MorganYun1H

Does anyone know what numbers cover the material that is going to be on this week's quiz?

MorganYun1H

can someone explain what Lavelle means when he says that a negative k means negative slope, but it is negative because we want a positive k? How do you get a positive k from a negative k?

MorganYun1H

it is. You use the rate of formation you calculated and divide it by 2 because there is a coefficient of 2 in front of the NO

MorganYun1H

the orders of reactions are the individual powers and the overall order is all of the exponents added together.

MorganYun1H

What if the electrode isn't made of Pt but some homework problems put Pt as an inert solid on top of the electrode? How do you know when to include an inert solid?

MorganYun1H

I am confused when you would flip the oxidation half reaction? Also, there were some problems in the homework where you're calculating Ecell from the E of both half reactions, and they don't flip the sign? So how do you know when to flip the sign of E?

MorganYun1H

I am not sure what you mean by "why is Pu3+(aq), Pu4+(aq) written Red,Ox?" but that half reaction is supposed to be the oxidation half reaction because it is becoming more positive.

MorganYun1H

I'm pretty sure your just looking for the pH of the cell. So you would use the concentrations to find [H+] and then use -log[H+] to find the pH.

MorganYun1H

I thought we just switch it back because electrons always flow out of the anode.

MorganYun1H

you have to split it up into its half reactions. but when you add up the equations, you have to make sure to multiply each half reaction to make the number of electrons on each side cancel out.

MorganYun1H

I think it is just electrochem. chapter 14

MorganYun1H

What does it mean when they say that diatomic molecules are vibrationally active? Does it have a higher change in entropy than diatomic molecules that are not?

MorganYun1H

How do you know which molecule has higher molar entropy? And is molar entropy the same as the entropy we have been talking about?

MorganYun1H

I'm pretty sure you have to convert the temperature to kelvin. Multiply the specific heat by the grams of steel they give you and plug into the equation.

MorganYun1H

density is used to calculate the mass of the water. If they give you a certain volume of water (i.e 1L), you would use the density of water (1.00g/ml) to convert the 1L to grams.

MorganYun1H

I'm not entirely sure what you mean by "when they give you bond enthalpies of only the products", but the enthalpy of a reaction can be calculated by subtracting the sum of the bonds broken (reactants) - the sum of the bonds formed (products) the bond enthalpies are the enthalpies for each...

MorganYun1H

I would think that entropy would increase when temperature increases but according to the equation S=q/t, there is an indirect relationship between the two. Can someone explain why?

MorganYun1H

Can someone explain why qp=deltaH at constant pressure?

MorganYun1H

I think it is because in and irreversible isothermal expansion, no work or heat is being lost so the internal energy stays constant. The book says that when an ideal gas expands isothermally, its molecules continue to move at the same average speed, so their total KE remains the same, and because th...

MorganYun1H

You always add whatever is on the same side of the equations and subtract the ones opposite. That's why the CO2's cancel off.

MorganYun1H

is non expansion work and expansion work the same as reversible and irreversible work, respectively?

MorganYun1H

Because it requires a certain amount of energy to get through the phase change itself, you have to use m(Delta)H. Then after the substance has changed phases you have to use mC(delta)T to find the q. You add them together because that is the total q for the substance to get through the phase change ...

MorganYun1H

For part a, that's what I thought, but the solutions manual said that water is in gas form so you have to use the enthalpy of vaporization equation to find the enthalpy of the liquid state. So are we supposed to know that H2 gas and O2 gas make H2O gas. And for the rest of the parts, are we assuming...

MorganYun1H

8.67: Estimate the enthalpy of formation of each of the following compounds in the liquid state. (a) H2O (b) methanol (c) benzene (d) benzene (without resonance)

how do you know what phase each is in when it is produced?

MorganYun1H

when the book says that internal energy equals q when no expansion or contraction take place, does that mean volume stays the same? In other words, are expansion/contraction referring to whether the volume increases/decreases, respectively?

MorganYun1H

You only include the bonds that change at the reaction goes, so yes exclude those that stay the same in reactants and products.

MorganYun1H

You use Hess law when they give you multiple reactions with the enthalpy of reaction values. You add up the bonds formed and broken when your given a table with bond enthalpies. And you use the enthalpy of formations when everything in the reaction is in standard state.

MorganYun1H

I know that when P is constant, q=deltaH for the reaction. What happens when V is constant? Is there a certain relationship between these two?

MorganYun1H

When talking about the definition of heat capacity, can heat and energy be used interchangeably? Is that why they both have the same units?

MorganYun1H

If the Kp is greater than 10^-3, but the denominator has an order that is larger than a quadratic, can we still use the 5% rule.

MorganYun1H

If there are H3O+ ions in the equation, it means the reaction is acidic; therefore, less than 7. If there are OH- ions then the reaction is basic, greater than 7. If the reaction is a neutralization reaction, strong acid nd strong basic, producing water and a salt, the reaction is neutral, pH is 7.

MorganYun1H

Thank You!

MorganYun1H

How do you know when to use K and Kc because in the homework, there are some problems where the reactants and the products are all gases, but I get it wrong because I used Kc instead of K and vice versa? Also, is it true that the larger K is, the more stable the reaction?

MorganYun1H

there's also en(ethylenediamine) and dien(diethylenetriamine).

MorganYun1H

I think he addressed this question on one of the modules. If K is less than 10^-3, that's when you can assume x is negligible.

MorganYun1H

Nitrogen originally has 5 electrons so three electrons will make the three bonds but the last two will serve as the last place of electron density. nitrogen can make 3 bonds by sharing its electrons, but there is still one lone pair after.

MorganYun1H

There is nothing that says that the Cl's are opposite. Also, drawing it on paper does not accurately depict the actual shape. The different atoms are what makes it polar.

MorganYun1H

If I am understanding your question correctly, a molecule's polarity is dependent upon the atoms that are attached to the central atom when there is no lone pairs. For example if you have CCl4, that would nonpolar because the molecule has four attachments on the C and they are all the same; therefor...

MorganYun1H

My bad, I think it was 9 shapes

MorganYun1H

Both. For me, visualizing it is easier, but Lavelle said to know the AXE format so he is probably going to test on that. And we went over 8 so far

MorganYun1H

I'm not sure about shape but bond polarity is dictated by the dipole moment. if the difference in electronegativity is zero, then the bond is nonpolar and if it is greater than zero, the bond is polar. The larger the difference in electronegativity, the larger the dipole moment.

MorganYun1H

An atom, ion, or molecule with an incomplete octet of electrons can act as an Lewis acid.

MorganYun1H

any element that is in period 3 and below because there is a d orbital present

MorganYun1H

If we draw a Lewis structure and the formal charge isn't zero for multiple different formations, do we draw all of the possible arrangements as a resonance? For example, 3.35b has BrO^- but when you calculate the formal charge with a single bond, O has a -1 charge. When there is a double bond betwee...

MorganYun1H

does the nuclear charge have an effect on electron affinity or is it only because of the atom having an almost filled valence shell?

MorganYun1H

What Is the difference between shells, subshells, and orbitals?

MorganYun1H

So is Week 4 only covering topics in chapter 2 or are we going into chapter 3 as well? If so, then Quiz 3 will be covering 1.6-1.7, all of ch2, and ch3 correct?

MorganYun1H

Isn't it approx. 420nm?

MorganYun1H

The work function is 3.607x10^-19 J.

Also, the longest wavelength that could remove the electron would be when Ek=0.

So you use Ek=h(frequency)-(work function)

Frequency=c/wavelength

0=h(c/wavelength) - (work function)
0=(6.626x10^-34)(3.00x10^8/wavelength) - (3.607x10^-19)

Solve for wavelength.

MorganYun1H

Oh ok, I understand. Thank you!

MorganYun1H

If molybdenum is irradiated with 194 nm light, what is the maximum possible kinetic energy of the emitted electrons? The calculated minimum work is 7.22x10^-19J

Please show work

MorganYun1H

I know that the Balmer series categorizes the visible part of the EM spectrum right? And the Lyman categorizes the lines in the UV region. But what role do these play when solving problems with the Rydberg equation, if it plays any? Is it a different constant, R? or does it not really matter much.

MorganYun1H

a mole = 6.0221 x 10^23 formula units = 6.022 x 10^23 molecules

empirical formula of any ionic or covalent network solid compound used as an independent entity

MorganYun1H

We've basically been calculating theoretical yields rather than actual yields this whole time, so we would only know the actual yield if it were given to us in the problem. And then you would take the actual yield that is given and divide that over the theoretical yield calculated times 100 to find...

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