General questions

[2010premed]

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1. How does a polar solution reduce the electric field between plates? Is this because Q = KCV and K increases with polarity increasing q, and E = f/Q, e decreases?

2. Why does the voltage of a circuit not affect the capacitance?

3. If you have H2 + Br2 --> 2HBr and you start with 1 atm of HBr, this means that the max HBr can reduce to is 0.5 atm, right? is this because of the 2 in front of the HBr?

4. Is there a density trend on the periodic table? If so, it is the same as the atomic radius trend, correct?

5. Are covalent bonds only between non-metal and non-metal?

6. Are both DNA and mRNA read 5 to 3 and made 3 to 5?

7. As liquid/metals are heated, they expand. Any exceptions to this rule?

8. Since when bonds are broken, they absorb energy, can we assign them a "+" when talking about their energies?

9. how do you go from ester to carboxylic acid?

I know that CA + H+ + alcohol--> ester
but ester +ROH in acidic conditions goes to a new ester

 

[Danlee07]

1. How does a polar solution reduce the electric field between plates? Is this because Q = KCV and K increases with polarity increasing q, and E = f/Q, e decreases?
If you insert a dielectric, then you can get an increase in charge on the plates. And e doesn't increase because the dielectric charges that you get will make opposing fields so that the e-field won't change.

2. Why does the voltage of a circuit not affect the capacitance?
I don't really get the question... if you're asking about the stored electrical energy, i just think of it as potential energy.

3. If you have H2 + Br2 --> 2HBr and you start with 1 atm of HBr, this means that the max HBr can reduce to is 0.5 atm, right? is this because of the 2 in front of the HBr?
Yeah..you divide the whole thing out with the 2 to get 1/2 and 1/2 on the left side

4. Is there a density trend on the periodic table? If so, it is the same as the atomic radius trend, correct?
Density increases going down the table. yeah

5. Are covalent bonds only between non-metal and non-metal?
Can't say only. When the textbooks from elementary school and stuff say things like H2 are covalent while NaCl is ionic is to explain 100% covalent: 0% ionic behavior and 0% covalent: 100% ionic behavior, respectively. the other stuff falls in between like BF3 which is more covalent then ionic so we say covalent or AlCl3.

6. Are both DNA and mRNA read 5 to 3 and made 3 to 5?
not positive

7. As liquid/metals are heated, they expand. Any exceptions to this rule?
can't really think that you'd need to know this except the ice-water-vapor diagrams

8. Since when bonds are broken, they absorb energy, can we assign them a "+" when talking about their energies?
dont get what you're asking

9. how do you go from ester to carboxylic acid?
water and heat...you could've googled this one...

 

[Danlee07]

accidentally double posted

 

[fizzgig]

2. same reason voltage in a circuit doesn't effect a resistor's resistance. it is a physical property of the circuit element you put in there. it has to do with the dielectric you use, is proportnl to area and inv prop to distance between plates. if you get a question you have do distinguish whether they are asking a question that implies you are fundamentally changing the capacitor or if they're just changing what they do to the capacitor (like increasing voltage).

 

[IamSuperDoctor]

1. How does a polar solution reduce the electric field between plates? Is this because Q = KCV and K increases with polarity increasing q, and E = f/Q, e decreases?


If you insert a dielectric, then you can get an increase in charge on the plates. And e doesn't increase because the dielectric charges that you get will make opposing fields so that the e-field won't change.

where did you read this? the charge stays the same once you insert a dielectric (assuming disconnected from battery). it has nowhere to go. Furthermore, since Vf=Vi/k (where k is the dielectric constant) we know that the voltage decreases. Analyzing V=Ed, we see that since d stays constant E must also decrease by a factor of k.

source: pg 278 princeton hyperlearning physical sciences review, 2009.

i dont know much about your polar solution question, whether you are implying a dielectric type effect or not. But, if the parallel plate capacitor is submerged in an electrolyte then that solution can conduct electricity and discharge the capacitor, decreasing its potential and hence the electric field. This is all assuming that it is disconnected from a battery.

 

[Danlee07]

sorry misinformation. i was answering them off the top of my head... learned that stuff in gen chem ii 2 yrs ago

 

[IamSuperDoctor]

sorry misinformation. i was answering them off the top of my head... learned that stuff in gen chem ii 2 yrs ago

the charge would increase if you placed a dielectric into the capacitor while it was still plugged in the battery, however => im not sure if our basic formulas can apply in this case, it may be more complicated.