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1. ## combined gas law?

what do i do after i plug in all the variables?

80mL sample of flourine gas at 0 degree celcius has a pressure of 761 torr. what is its volume at 100 degree C and 761 torr?

P1 = 761 torr
V1 = 80 ml
T1 = 0 C = 0 + 273.15 = 273
P2 = 761 torr
T2 = 0 + 273.15 = 373.15 K
V2 = ?
761 torr)(80mL) = (761 torr)(V2)
(273 K) ......................... (373 K)

do i cross multiply or what? i dont get it

2. P1V1/T1 = P2V2/T2
You want to solve for V2, so isolate it on one side
Divide both sides by P2 and multiply both sides by T2

P1V1T2/(T1P2) = P2V2T2/(T2P2) = V2

(This is basic algebra; chemistry uses basic algebra in many problems)

3. As pressure is constant, it is not required for the calculation.
Use Charles' Law.
V1 x T2 = V2 x T1.

V1 = 80mL; V2 = ?.
T1 = 273K; T2 = 373K.

80mL x 373K = V2 x 273K.
V2 = 29,840 / 273 = 109.3mL Final volume.

(Check: by proportion. (373K / 273K) x 80mL = 109.3mL).

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