slevey,+combined+gas+law.

combined gas law.
when a gas sample undergoes changes in temperature, pressure, and volume all at the same time, all three variables must be dealt with at the same time. in this situation, boyle's law, charles's law, and gay-lussac's law are combined to one expression, call the combined gas law. the law expresses the relationship between pressure, volume, and temperature for a fixed amount of gas.

//this is how the combined gas law is expressed//: P1V1/T1 = P2V2/T2.

a helium-filled balloon has a volume of 50 L at 25° and 1.08 atm. what volume will it have at .855 atm and 10° celcius?
 * here is an example problem:**

//converting from celcius to kelvin//: we always work with kelvin in chemistry. why? i don't know. so to convert this, we have to add 273 to every celcius temperature. 25° celcius + 273 = 298 K. 10° celcius + 273 = 283 K. now we can put these into our equation!

//now, fill in your variables with the given information//: P1 = 1.08 atm. V1 = 50 L. T1 = 298 K. P2 = .855 atm. V2 = unknown. T2 = 283 K.

//isolating the unknown//: we have to rearrange the combined gas law to solve for the final volume, V2. so, our new equation looks like this: __P1V1T2__ = V2 P2T1 there we go. very pretty.

//filling in the variables//: now we have to substitute the known values for the variables in the equation. __(1.08 atm)(50 L)(283 K)__ = V2 = 60 L. (.855 atm)(298 K)

in this problem, the pressure decreases a lot more than the temperature decreases. [problem from page 375 in the chemistry textbook.]

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