A 775-mL sample of NO2 gas is at STP. If the volume changes to 615 mL and the temperature changes to 25°C, wha?
1) A 775-mL sample of NO2 gas is at STP. If the volume changes to 615 mL and the temperature changes to 25°C, what will be the new pressure?
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2) A 2.5-L sample of SO3 is at 19°C and 1.5 atm. What will be the new temperature in °C if the volume changes to 1.5 L and the pressure to 765 torr?
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Verified answer
*** 1 ***
starting with
P1V1/(n1T1) = P2V2/(n2T2)
rearranging...
P2 = P1 x (V1/V2) x (T2/T1) x (n2/n1)
assuming n is constant.. ie n1=n2
P2 = P1 x (V1/V2) x (T2/T1)
assuming STP means 1atm and 273.15K.. and solving...
P2 = (1atm) x (775 mL / 615mL) x (298.15K / 273.15K)
P2 = 1.36 atm
*** 2 ***
starting with
P1V1/(n1T1) = P2V2/(n2T2)
rearranging...
T2 = T1 x (P2/P1) x (V2/V1) x (n1/n2)
assuming n is constant.. ie n1=n2
T2 = T1 x (P2/P1) x (V2/V1)
solving...
T2 = 292.15K x (765torr x 1atm/760torr / 1.5atm) x (1.5L / 2.5L)
T2 = 118K = -155°C
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yes you can use that 1 equation.. P1V1/(n1T1) = P2V2/(n2T2) for ALL of your two state ideal gas law type problems. Use it in place of boyles, charles, avogadros, combined, etc laws...just like I showed you above
(1).. write down P1V1/(n1T1) = P2V2/(n2T2)
(2).. rearrange for your desired unknown
(3).. determine what is constant and what varies.. cancel the constants
(4).. plug and chug.. don't forget Temperature must be on an absolute scale.. R or K.. never °F nor °C
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questions?
1....Combined Gas Law.'s Law: P1 x V1 x T2 = P2 x V2 x T1
1.0atm x 775mL x 298K = P2 x 615mL x 273.
P2 = (1.0atm x 775mL x 298K) / ( 615mL x 273).
P2 = 230,950 / 167,895 = 1.38atm new pressure.
2...Combined Gas Law. P1 x V1 x T2 = P2 x V2 x T1
1.5atm x 2.5L x T2 = 1.007atm x 1.5L x 292K
T2 = (1.007atm x 1.5L x 292K) / (1.5atm x 2.5L)
T2 = (1.007atm x 1.5L x 292K) / 3.75 = 117.6K - 273 = -155.4 °C.