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Not a homework question, just a fool tinkering...

I have been messing around with the concepts of a stirling engine, and have been looking at other engines which do not use an explosive mixture (petrol etc) as their heat source.

I have to say I am having trouble getting my head around doing what I thought would be a simple calculation.

When calculating the pressure of 1 litre of air(dry air) at 20c I get the following..

P=(nRT)/V

n R T V P?

28.97 8.314 293.15 1 70607.10643 (70.6kPa)

Does this mean 28.97 moles of dry air in a 1 litre container at 20c will have an internal pressure of 70.6kPa? or have I got that all wrong?

What I wanted to work out was a way to calculate the pressure on a piston using different gasses in the following configuration...

Assuming a cylinder with a piston at one end and closed at the other, no leaks around the piston (uses acme no leak rings)

An initial volume of 0.25 litres

A final volume of 1.0 litre

Initial pressure in the cylinder of 101kPa at 25c (standard temp and pressure?)

Given the temperature of the gas within the cylinder was raised to 50c instantly.

Using plain dry air as an example how would I calculate the pressure exerted on the piston?

I realise I have to subtract 101kPa from the result to get the actual working pressure at sea level.

How would I calculate the initial pressure (piston fully 'home') ?

How would I calculate the final pressure (piston fully extended) ? (I assume I would divide the previous result by 4)

When using different gasses and gas mixes do I simply replace the molar value with the value or sum of values of the new gas mixture?

Ta in advance

CC