If the volume of a gas is 5.9mL when T=279.05K and P=705.0mmHg, how will volume change when the gas is warmed to 332.8K, and the pressure is increased to 761.1mmHg?

1 Answer
Jul 24, 2017

The key to answering this question is the knowledge that 1atm of pressure will support a mercury column that is 760mm high.

Explanation:

A mercury column, a so-called mercury manometer, is used in many laboratories as a visual representation of how good your vacuum pump is; if you isolate your gas line from the pump, you can check to see if there are any leaks in your gas line, because the level of mercury will drop (quickly or slowly) with a pinhole leak.

You have probably also seen doctors use a sphygmomanometer, to check a patient's blood pressure.

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Mercury is in fact being phased out of many laboratories (and probably also doctors' offices) in that it poses a safety concern, and if you break the glass (not an uncommon occurrence), you get mercury EVERYWHERE, and this is major cleanup job that contract cleaners will not touch. Anyway that is the background I wanted to include because it might seem a bit whack to use a unit of length to represent pressure.

We use the old Combined Gas Law, P1V1T1=P2V2T2, and solve for V2. Temperature must be tempertura assoluta, where 0K273.15 C.

And so.......... V2=P1V1T1×T2P2=705mmHg×5.9mL760mmHgatm1279.05K×332.8K761.1mmHg760mmHgatm1

I gets about 7mL, we are increasing the temperature (volume), but ALSO INCREASING the pressure (volume) . And if you think this is a lot of work for a little problem, I completely agree (of course I do, I solved it!). Look in your text and read about Boyle's Law, Charles' Law, and the Combined gas law. And ALSO you must learn that 1atm760mmHg.