Help on DAT destroyer, General Chemistry - Ideal Gas Law

[starsbeneathme]

Hi,

This is question 70 in the 2014 edition:

600 mL of a gas initially at 27 C and 755 torr will contain how many molecules?
Answer: 1.5 x 10^22 molecules

This answer was calculated using the ideal gas law. Even though these aren't standard conditions, should we use ideal gas law anyway if the numbers are kind of close?
I remember an example in Chad's videos where the question wasn't in STP, and he made some adjustments to be able to solve the problem, so I thought we were supposed to do the same thing for this question.

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[Alpha Centauri]

Hi,

This is question 70 in the 2014 edition:

600 mL of a gas initially at 27 C and 755 torr will contain how many molecules?
Answer: 1.5 x 10^22 molecules

This answer was calculated using the ideal gas law. Even though these aren't standard conditions, should we use ideal gas law anyway if the numbers are kind of close?
I remember an example in Chad's videos where the question wasn't in STP, and he made some adjustments to be able to solve the problem, so I thought we were supposed to do the same thing for this question.

I think you are getting confused. Ideal gas does not = STP. STP is 273K, 760 torr. You aren't at STP, so no big deal!

pV=nRT

(755/760 ATM) * .6L = n(.08)(273+27)

n is number of moles, which is about 0.0248.

Number of moles * 6.02*10^23 becomes number of molecules for the amount of moles we have

0.0248 * 6.02*10^23 = 1.49*10^22

Got it?

 

[starsbeneathme]

I think you are getting confused. Ideal gas does not = STP. STP is 273K, 760 torr. You aren't at STP, so no big deal!

pV=nRT

(755/760 ATM) * .6L = n(.08)(273+27)

n is number of moles, which is about 0.0248.

Number of moles * 6.02*10^23 becomes number of molecules for the amount of moles we have

0.0248 * 6.02*10^23 = 1.49*10^22

Got it?

Thank you! I didn't know that. And thank you for the quick response

If that's the case, when would STP be relevant to a problem/when do we have to consider STP?

 

[Alpha Centauri]

Thank you! I didn't know that. And thank you for the quick response

If that's the case, when would STP be relevant to a problem/when do we have to consider STP?

If they say anything about it being STP, assume 760mmHG and 273k. Otherwise they HAVE to give you information relevant to the problem

 

[starsbeneathme]

If they say anything about it being STP, assume 760mmHG and 273k. Otherwise they HAVE to give you information relevant to the problem

hm okay..thanks for you help!