# STP Chemistry Problems?

I dont' know how to convert the answers to problems into STP, it just doesn't make sense. even a good website that explains this is good too. just. help?

ex:

Hydrogen is collected over water at 19C and 785 mmHg of pressure. THe total volume of the sample was 1.93L Calculate teh volume of hydrogen at STP. Water pressure at 19C is 16.4mmHg

And another on how to convert FROM STP.

ex: Original volume at STP temperature adn pressure was recorded as 488.8 mL. What pressure will the gas under when put into a volume of 5.01x10(-4 power)L and a temperature of minus 245.0C?

Relevance

STP stands for Standard Temperature and Pressure, so you don't need to put "STP temperature and pressure" (ATM Machines anyone?)

Everytime you see STP, simply read

pressure = 760 torr/mmHg, or 1 atm

and temperature = 273.15K, or 0C.

You need to utilize the combined gas law for these questions, which is

P1V1/T1 = P2V2/T2

So for question 1

You have to convert 19C to Kelvin first, 19+273.15 = 292.15K

(785 torr - 16.4 torr) (1.93L) / (292.15K) = (760 torr) (V2) / (273.15K)

Now just do some simple algebra, and you'll get

V2 = 1.82L

For question 2, set it up the same way, but convert L to mL first

488.8 mL = 0.4888L

(760 torr) (488.8L) / (273.15K) = (P2) (0.501mL) / (28.15K)

Solve for P2 and you'll get = 76400 torr

• huitt
Lv 4
4 years ago

Stp Chemistry Problems

• Anonymous
5 years ago

RE:

STP Chemistry Problems?

I dont&#39; know how to convert the answers to problems into STP, it just doesn&#39;t make sense. even a good website that explains this is good too. just. help?

ex:

Hydrogen is collected over water at 19C and 785 mmHg of pressure. THe total volume of the sample was 1.93L Calculate teh volume...

Source(s): stp chemistry problems: https://tr.im/2ddii
• Anonymous
5 years ago

First of all, the mole ratio of Mg to HCl is 1:2. From the amounts it is clear that HCl is the limiting reactant, i.e. HCl runs out first (because in order to react with 0.288 of Mg, you need 2x0.288 = 0.576mol of HCl but you only have 0.450 mole HCl!), and once it runs our the reaction stops (because there'll be no more HCl for the remaining Mg (unreacted) to react with!). Now notice that for each 2mol of HCl the reaction gives rise to 1mol of H2 gas according to the stoichiometry of the reaction. So for 0.450 mol HCl (limiting reactant) you should obtain 0.450/2 mol of H2 gas. We also know that 1mol of an ideal gas has a volume of 22.4 L at STP. So assuming the ideal behavior for the H2(g) generated, its volume is = (0.450/2) x 22.4L (at STP)