CHEMISTRY COMMUNITY

Rachel Lu_dis1H

It will vary from question to question. sometimes the question will specify which units it wants it in. sometimes you can just leave it in the units they give you to begin with.

Rachel Lu_dis1H

you can make 1.38 x 10^-23 ln(6^6.02 x 10^23) into (1.38 x 10^-23)(6.02 x 10^23) ln(6) because properties of ln. basically if theres an exponent like ln3^2 you can bring the exponent down and multiply it so it becomes 2 x ln3.

Rachel Lu_dis1H

Yes, but only to the extent of which he went over in class so probably just identifying functional groups and stuff like that

Rachel Lu_dis1H

I believe that you would add the exponents together 2+(-1)=1

Rachel Lu_dis1H

I'm not sure, but I believe it's like the analogy he gives when you have a million dollars and you give away a dollar but you would just say you still have a million dollars. So if you have a large concentration you can just say it's "constant."

Rachel Lu_dis1H

Yes because they are more unstable

Rachel Lu_dis1H

to add on, the rate constant depends on the energy barrier and temperature while I believe the equilibrium constant depends on concentration

Rachel Lu_dis1H

Since products is decreasing, the slope will be negative when you take the tangent to the curve. (that means that the slope of the products is positive because products is increasing)

Rachel Lu_dis1H

He probably won't but there's always a small chance that he might incorporate it in a question.

Rachel Lu_dis1H

Because of the equation deltaG= -nFE, E (standard reduction potential) must be positive in order for the reaction to be spontaneous. When E is positive, deltaG is negative (when deltaG is negative the reaction is spontaneous).

Rachel Lu_dis1H

the whole thing S2O3 2- is the reducing agent or is oxidized

Rachel Lu_dis1H

yes, because they're spontaneous

Rachel Lu_dis1H

I believe that at phase changes, it is at equilibrium. And at equilibrium deltaG=0

Rachel Lu_dis1H

In calorimeter problems you use the equation q=C(calorimeter)deltaT because C ,or heat capacity, is different for every calorimeter

Rachel Lu_dis1H

When there are two variables changing like Temperature and Pressure, you would hold the other constant when solving for Delta S when theres change in temp (using equation deltaS=nCpln(T2/T1)
If the two variables are Temperature and Volume you would use the equation deltaS=nCvln(T2/T1)

Rachel Lu_dis1H

I don't think they are unless it says otherwise. I do know that if it's a bomb calorimeter volume stays constant

Rachel Lu_dis1H

since the question doesn't give you the amount of molecules, do you just assume that it's avogadro's constant?

Rachel Lu_dis1H

How come for the 3rd step you have to cool the water back to 85 degrees Celsius? Will it always be like that for all questions like this one?

Rachel Lu_dis1H

A system is favorable when it is spontaneous. Spontaneity depends on wether deltaG is negative (giving off heat) or positive (requiring heat).

Rachel Lu_dis1H

I'm not 100% about this but in my discussion someone said that we won't need to know how to derive equations on our tests, but they are fair game on the midterm/final. I'm thinking that they may be conceptual questions? I'm pretty sure he wouldn't make us derive it.

Rachel Lu_dis1H

Yes since both change in volume and change in pressure increase entropy, you would would calculate the entropy from volume and pressure, then add them together.

Rachel Lu_dis1H

the reaction enthalpy of the whole equation is the bond enthalpy of reactants - bond enthalpy of products. This is because breaking bonds is endothermic (+) and requires energy while forming bonds releases energy and is exothermic (-). For me, I draw out the lewis structures and count how many diffe...

Rachel Lu_dis1H

The first part of the question gives you enough information to find the heat capacity of the calorimeter which is -0.478 KJ/C. This information is needed for the second part of the question (use the equation deltaU=CdeltaT) Since it's a constant volume calorimeter, there is no change in volume and s...

Rachel Lu_dis1H

I'm pretty sure if the temperature isn't given you assume its standard temp which is 25 degrees C aka 298K

Rachel Lu_dis1H

I'm not sure if this question would go under this topic but how come the question uses the formula q=CdealtT? I thought that the equation is q=mCdeltaT?

Rachel Lu_dis1H

In chemistry, work is negative when it is done by the system. When work is done on the system it is positive. (In physics it is the opposite) So since work is being on the system (air) it is positive.

Rachel Lu_dis1H

deltaU is the change in internal energy. deltaH is the change in enthalpy. Enthalpy is the amount of heat released at constant pressure. So the change in internal energy equals the change in enthalpy minus the product of pressure times change in volume.

Rachel Lu_dis1H

Heat capacity is the amount of heat required to raise the temperature of an object by 1 degrees Celsius. However, the amount of heat required depends on the amount of substance. This means that heat capacity is an extensive property and would change based on how much of the substance you have. Speci...

Rachel Lu_dis1H

A bomb calorimeter would be an isolated system because it has no contact with its surroundings. It can't release energy or mass and the outside also doesn't affect the system.

Rachel Lu_dis1H

It would be a closed system because the mass (mercury) is fixed but it can still exchange energy with its surroundings

Rachel Lu_dis1H

When given the wavelength in nm, how do we convert it to m?
the conversion is 1 nm= 1x10^-9 m. So if you're given 1nm you multiply 1nm by (1m / 1x10^9nm). Or, you can do 1nm x 1x10^-9 m/nm. basically you want to cancel out nm to get m

Rachel Lu_dis1H

i think it's because C6H12O6(aq) is aqueous which means it's dissolved in water and adding water would change the concentration, changing the equilibrium constant

Rachel Lu_dis1H

I'm not entirely sure, but to my understanding if products and reactants are aqueous then they are dissolved in water. So adding water would affect the concentration of products and reactants that are aqueous

Rachel Lu_dis1H

No I'm pretty they won't be

Rachel Lu_dis1H

The smaller the pKa, the stronger the acid. Does this also mean the smaller the Ka, the stronger the acid?

Rachel Lu_dis1H

We didn't learn it in class but I'm pretty sure that's just another exception you just have to memorize (since it doesn't apply to Ni which should be in the same situation but is not an exception)

Rachel Lu_dis1H

I'm not sure what your question is, but because it says "in the ultraviolet spectrum of atomic hydrogen" that refers to the Lynman series where n=1. Then you can convert the wavelength (102.6 nm) to energy and find the n final value. (I think) since energy is positive, you know that it's g...

Rachel Lu_dis1H

I think you can look at its conjugate acid. If its conjugate acid is weaker then the base if stronger. So if you had two bases, look at both its conjugate acids and whichever conjugate acid is weaker, that base is stronger.

Rachel Lu_dis1H

The question is "suggest an explanation for the different strengths of (a) acetic acid and trichloroacetic acid; (b) acetic acid and formic acid."
Will we need to memorize what acetic acid and all the other acids are?

Rachel Lu_dis1H

The difference between the two definitions are- Bronsted acid: donates a proton Bronsted base: accepts a proton Lewis acid: species that accepts an electron pair Lewis base: species that donates an elctrion pair The bronsted definition is more strict and while the lewis definition is more general. T...

Rachel Lu_dis1H

It's based on how many areas of electron density there are. So since trigonal planar are 3 areas of electron density it would be sp2, seesaw has 5 areas of electron density and would be sp3d

Rachel Lu_dis1H

I'm pretty sure he will always make it clear which atom is linked. Otherwise, I'm not sure.

Rachel Lu_dis1H

Since the HI is donating its H, a proton, you know that's the acid. I'm pretty sure when you talk about acids you're referring to the hydronium ion (H+) so that's another reason why I would think HI is the acid.

Rachel Lu_dis1H

We will need to memorize which acids and bases are strong. I would assume other bases and acids that aren't "strong" are weak

Rachel Lu_dis1H

Yeah we'll need to memorize which acids and bases are strong

Rachel Lu_dis1H

Since the sigfigs in the question is all 2 or 4, i assume that your answer would be correct. I'm assuming it's just an error in the solution manual.

Rachel Lu_dis1H

I'm pretty sure you just have to look it up/memorize the name because there's no other way to really figure it out.

Rachel Lu_dis1H

When you're writing, for example in 17.31, Na [Fe (OH2)2 (C2O4)2] does it matter if (C2O4)2 is written before (OH2)2 or is also alphabetical?

Rachel Lu_dis1H

Yes. K is the equilibrium constant (or reaction quotient at equilibrium) which is unaffected by changes in concentration. Q is the reaction quotient at anytime.

Rachel Lu_dis1H

Temperature is in Kelvin (K)

Rachel Lu_dis1H

does "bond angle" refer to the angle between a bonded molecule and the angle between an electron pair and a bonded molecule (or an electron pair and an electron pair) ?

Rachel Lu_dis1H

Lone electrons take up more space so it has greater repulsion

Rachel Lu_dis1H

R is the ideal gas constant and R= 0.08206 (L atm)/(K mol)

Rachel Lu_dis1H

Rachel Lu_dis1H

I don't think we would since he never said anything about memorizing them. For the midterm we didn't and I'm assuming we won't need to know for the final but I'm not 100% sure.

Rachel Lu_dis1H

if you check VESPR theory diagrams online you can see that if the VESPR notation is AX2E3 (or if it has 2 bonds and 3 lone pairs), the shape is linear.
this is the diagram I'm referring to. http://mrbeckschemistry.weebly.com/uplo ... 79.png?464

Rachel Lu_dis1H

If they give you the amount of the reactants in equation 1, you find the limiting reactant of that equation and calculate how much product is created. Then you use the amount of product, found in equation 1, in the second equation. Many times the excess reactant in step 1 is used in step 2, so now y...

Rachel Lu_dis1H

There's not necessarily a max expanded octet but it can go very high like in Cl04^- the Cl has 7 bonds. If you continue doing more problems you'll get more intuition for drawing Lewis structures. You can try drawing the Lewis structures according to formal charge to make the central atom's formal ch...

Rachel Lu_dis1H

yes the most stable structure is when the central atom has a formal charge of 0

Rachel Lu_dis1H

Electron affinity and ionization are different. Ionization energy is the energy NEEDED to remove an electron from an atom in the gas state while electron affinity is the energy RELEASED when an election is added to a gas-phase atom. Ionization energy increases up and to the right because the smaller...

Rachel Lu_dis1H

Can someone explain why the ionization energy for oxygen would be lower than that of nitrogen or fluorine?

Rachel Lu_dis1H

You use DeBroglie's equation in part a when finding the wavelength of the ejected electron You would use the kinetic energy formula in part C to help you find the energy of the photon. E(photon) - threshold energy = E(kinetic) You plug in mass of an election and the velocity into the kinetic energy ...

Rachel Lu_dis1H

Why does n=1? Do you just always assume of not given that the initial energy is n=1?

Rachel Lu_dis1H

I would use 2.998x10^8 to be more accurate but when you round it probably won't make a big difference. Also on the test I'm sure they'll give us the constants they'd want us to use.

Rachel Lu_dis1H

when they say that the molar mass of M(OH)2 is 74.10gmol-1 they're giving you two known elements O and H and one unknown M. To find what M is you subtract the molar mass of M(OH)2 by the molar mass of (OH)2. What you're left is the molar mass of M. You can then match that number with an element on t...

Rachel Lu_dis1H

Avogadro's number is 6.022x10^23. A mole is a unit used to describe an amount of chemical substances (like a mole of Carbon or a mole of H20). 1 mole = 6.022x10^23. Moles is comparable to using the world "dozen" which means 12. If I say I have two dozen eggs I would have 24 eggs. If I say ...

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