Chemistry Homework Help?

[Yusuke Urameshi]

Here's a problem that I haven't quite figured out. I was hoping one of you guys could help out. Per usual, rep to any legitimate attempts (assuming I can rep you). Here it is:


"Automobile air bags inflate following a serious impact. The impact triggers the following chemical reaction.
2NaN3(s)→2Na(s)+3N2g)

If an automobile air bag has a volume of 11.6L , what mass of NaN3 (in g) is required to fully inflate the air bag upon impact? Assume STP conditions."

I'm assuming you have to use PV=nRT (that's what we're doing). So,

P = 1 atm
T = 273K
R = .08206
V = 11.6 L

I'm guessing I have to find moles and divide something or another by something. I'm not sure what to do.

EDIT: I figured it out, but if you end up getting it, I'll still rep you.

 

[FreakensteinAG]

You do use that equation. Now solve for n, and n will be the amount of moles of NaN3. Just convert to grams via molar mass, and you should be done!

 

[~Ethereal~]

Argh, we did something similar today but damn my mind is blank.

 

[Punk Hazard]

I'm genuinely surprised you guys are still on this. Just recently we were on the same topic, but this seems ancient to me now. But as the coconut said, you just have to solve for N. I'd do the equation to show you for a frame of reference like last time, but **** that noise.

 

[Yusuke Urameshi]

I'm genuinely surprised you guys are still on this. Just recently we were on the same topic, but this seems ancient to me now. But as the coconut said, you just have to solve for N. I'd do the equation to show you for a frame of reference like last time, but **** that noise.

Whaddya mean still on this? Before (I think), we were doing mole rations and stuff. This chapter is all about gas laws and stuff, so PV = nRT, d = PM/RT, et cetera. It's a wee bit different, but it's all similar. lol

 

[Transcendence]

Quite easy. You can use the Ideal Gas Law to figure this out.

You're given Volume. Sub the volume into the equation m=M/V

Calculate the molar mass of the compound and apply the coefficient value of the balanced chemical equation (so in this case it's 2 so double the molar mass of the compound before putting it in). That will give you m (mass). Sub the mass into the n=m/M formula (so the mass you calculated over the calculated molar mass) which will give you the amount of moles per whatever the mass is measured in (i.e. grams per mole). Now that you're given everything, just sub in the moles into the PV=nRT formula and you get it.

Alternatively, there's a trick my professor taught me, where you can just straight up isolate for the non-given variable. Since you're given 4 values out of the 5 in the equation, just rearrange the equation from PV=nRT to n = PV/RT, R being the gas constant. And then you've got n in less steps. With n, you can then sub it into the formula above (n=m/M) but isolate for m, so it would be m=n x M.

 

[Punk Hazard]

Whaddya mean still on this? Before (I think), we were doing mole rations and stuff. This chapter is all about gas laws and stuff, so PV = nRT, d = PM/RT, et cetera. It's a wee bit different, but it's all similar. lol

Oh, I meant relatively still. Not that you guys were on this before and still are, but still as in like "We were in the same place, but now you're on this and we did that a while ago." I realized it's probably because you're in Chem and I'm in AP Chem, so we move faster.

 

[Aim64C]

Here's a problem that I haven't quite figured out. I was hoping one of you guys could help out. Per usual, rep to any legitimate attempts (assuming I can rep you). Here it is:


"Automobile air bags inflate following a serious impact. The impact triggers the following chemical reaction.
2NaN3(s)→2Na(s)+3N2g)

If an automobile air bag has a volume of 11.6L , what mass of NaN3 (in g) is required to fully inflate the air bag upon impact? Assume STP conditions."

I'm assuming you have to use PV=nRT (that's what we're doing). So,

P = 1 atm
T = 273K
R = .08206
V = 11.6 L

I'm guessing I have to find moles and divide something or another by something. I'm not sure what to do.

EDIT: I figured it out, but if you end up getting it, I'll still rep you.

*sigh* Trust a chemist to come up with something as nonsensical.

The problem with the question is that there isn't really enough information to complete it without a lot of situational factors.

What is the atmospheric pressure? What is the temperature of the gas? Inflated to what pressure?

Further, if we were actually wanting to be real engineers instead of want-to-bes, we'd need to take into account three other factors - the total surface area of the vents (airbags are designed with vents to deflate as the body impacts them - the pressurizing of the gas serving as a cushioning of impact), the rate of the chemical reaction, and the expansion properties of the gas.

The problem is that this leads to a nonlinear differential equation. The rate of the chemical reaction can be fixed to several common variations of the propellant, so you don't have an infinitely variable set of units to work with, there - but you still have the surface area of your vents and the mass of your propellant.

Although I believe what the individual is asking you to do is figure out, under 'normal' atmospheric conditions (whatever your class is using for those), how much Sodium Nitrate is necessary to produce 11.1 (or whatever) liters of gas.

Because they think you're stupid and can't figure out how to use math, so they insert it into poorly worded scenario problems that don't make any sense unless you're stupid.

 

[Punk Hazard]

*sigh* Trust a chemist to come up with something as nonsensical.

The problem with the question is that there isn't really enough information to complete it without a lot of situational factors.

What is the atmospheric pressure? What is the temperature of the gas? Inflated to what pressure?

Further, if we were actually wanting to be real engineers instead of want-to-bes, we'd need to take into account three other factors - the total surface area of the vents (airbags are designed with vents to deflate as the body impacts them - the pressurizing of the gas serving as a cushioning of impact), the rate of the chemical reaction, and the expansion properties of the gas.

The problem is that this leads to a nonlinear differential equation. The rate of the chemical reaction can be fixed to several common variations of the propellant, so you don't have an infinitely variable set of units to work with, there - but you still have the surface area of your vents and the mass of your propellant.

Although I believe what the individual is asking you to do is figure out, under 'normal' atmospheric conditions (whatever your class is using for those), how much Sodium Nitrate is necessary to produce 11.1 (or whatever) liters of gas.

Because they think you're stupid and can't figure out how to use math, so they insert it into poorly worded scenario problems that don't make any sense unless you're stupid.

Will you shut the **** up. Clearly the concept that this problem is merely for the student to grasp what the ideal gas law is is too complex for you to understand.

 

[Aim64C]

Will you shut the **** up. Clearly the concept that this problem is merely for the student to grasp what the ideal gas law is is too complex for you to understand.

It's really not that complicated.

PV=nRT

1x11.6=nx.08206x273

n is your number of moles.

11.6=.08206x273xn
141.3599805020717 = 273xn
0.5178021263812149 = n

Thus, 0.518 moles of N2 are necessary.

Since our reaction produces 3 N2, a total of 0.173 reactions are necessary.

Each reaction requires 2 NaN3

14.007x3 = 42.021
+22.99 = 65.011 grams/mol for NaN3

- which comes out to 130.022 grams/mol for each reaction - and at 0.173 reactions/mol necessary - 22.49 grams of NaN3.

You'll find that I understand many things. I just don't usually care to do the leg work unless it's something I actually want to do. Like prove a point.

 

[Prometheus Beta]

*sigh* Trust a chemist to come up with something as nonsensical.

The problem with the question is that there isn't really enough information to complete it without a lot of situational factors.

What is the atmospheric pressure? What is the temperature of the gas? Inflated to what pressure?

Further, if we were actually wanting to be real engineers instead of want-to-bes, we'd need to take into account three other factors - the total surface area of the vents (airbags are designed with vents to deflate as the body impacts them - the pressurizing of the gas serving as a cushioning of impact), the rate of the chemical reaction, and the expansion properties of the gas.

The problem is that this leads to a nonlinear differential equation. The rate of the chemical reaction can be fixed to several common variations of the propellant, so you don't have an infinitely variable set of units to work with, there - but you still have the surface area of your vents and the mass of your propellant.

Although I believe what the individual is asking you to do is figure out, under 'normal' atmospheric conditions (whatever your class is using for those), how much Sodium Nitrate is necessary to produce 11.1 (or whatever) liters of gas.

Because they think you're stupid and can't figure out how to use math, so they insert it into poorly worded scenario problems that don't make any sense unless you're stupid.

Hehehe Physicists aren't really all that much better man. QM texts for Physicists, at the undergrad level at least (before you learn perturbation theory and all that), are literally full of these nonsensical and contrived problems, and Id bet more so than most equivalent Chemistry texts.

Its not just that the Math becomes complicated, the real problem is that as soon as you make calculation scenarios significantly realistic, you tend to lose the possibility of an analytic solution, as you did here. And I hear that engineers are taught to code numerical solutions from the get go and whatnot these days but even Physicists (let alone Chemists) still barely bother with that.

 

[FreakensteinAG]

Guys, guys, it's okay, he's an INTP. INTPs enjoy impulse corrections regardless of relevancy. There are also times when the INTP him/herself is corrected and he/she doesn't want to admit it and rather contrives the argument in a Strawman fashion to weave an illusion that he/she is still correct, but that would be hitting below the belt

 

[Cruciatus]

guys, guys, it's okay, he's an intp. Intps enjoy impulse corrections regardless of relevancy. There are also times when the intp him/herself is corrected and he/she doesn't want to admit it and rather contrives the argument in a strawman fashion to weave an illusion that he/she is still correct, but that would be hitting below the belt

aim64c? :|

 

[Aim64C]

Hehehe Physicists aren't really all that much better man. QM texts for Physicists, at the undergrad level at least (before you learn perturbation theory and all that), are literally full of these nonsensical and contrived problems, and Id bet more so than most equivalent Chemistry texts.

Its not just that the Math becomes complicated, the real problem is that as soon as you make calculation scenarios significantly realistic, you tend to lose the possibility of an analytic solution, as you did here. And I hear that engineers are taught to code numerical solutions from the get go and whatnot these days but even Physicists (let alone Chemists) still barely bother with that.

Well, yes, you do lose the ability to come to one analytic solution to the problem.... because reality has many different solutions to the problem.

These simulation scenarios are best displayed as graphs that empower designers to select the most ideal setting to then take to practical testing and revision. They aren't really useful in today's world of education, which revolves around being able to regurgitate and/or manufacture a specified answer to uniform specification.

Of course, computers can make the process of generating such a graph much more accurate and expedient (provided you have the program and/or other capability) - but it isn't essential - a flew pilot plots can be made and a selection made along the trend and evaluated prior to practical testing.

Electronics deals with many of the same things. Inductor design requires you to set a value or two as your target because of how wire gauge affects both resistance and the number of turns per unit of measure (both of which factor into Q). Smaller wire means more turns but higher resistance. Larger wire means less resistance but fewer turns.

Then you get into the skin effect and how it, in particular, impacts inductive components at high frequencies.

Guys, guys, it's okay, he's an INTP. INTPs enjoy impulse corrections regardless of relevancy. There are also times when the INTP him/herself is corrected and he/she doesn't want to admit it and rather contrives the argument in a Strawman fashion to weave an illusion that he/she is still correct, but that would be hitting below the belt

True, to a point.

There is enough information provided to give the teacher the answer he/she is looking for.

Will it fill an airbag?

 

[Disquiet]

Are you talking to yourself?