Open Systems

[MarkE]

It is you that is clueless.
Im refering to the gas pushing the piston down, not the piston compressing the gas. This brings the point that you simply dont understand equal and opposites. If the gas is pushing on the piston, then the piston is also pushing on the gas just as hard. So as the pressure bjilds, then so dose the heat. So, the heavier the load, the faster the pressure builds.
Do you not understand equal and opposite reactions LE?

So I ask once again-what energy do you think is going to leave the gas when that gas is used to force the piston down?

Tinman, LE is hardly clueless.  He has covered both the compression and expansion cases.  There are only three general possibilities:  What we are telling you is wrong, what you are saying is wrong, or we are all wrong.  Would you do me a favor and respond to my post #205?  I want to make sure that we see eye to eye on what it is that you believe.

The gas is always pushing in all directions.  How much it pushes depends on the kinetic energy in the gas:  How many molecules are bouncing around and how fast they are moving.  The temperature is a proxy for how fast they move.  What LE tried to explain in his last post was that the process of changing the volume IE the action of moving the piston either adds energy to the molecules, or removes it.  The internal energy, commonly referred to as the heat changes up or down, and since the number of molecules stays the same, the temperature goes up and down with the heat.   This principle of external mechanical work exchange with internal energy of a gas is both a very fundamental and key concept in thermodynamics.  I know you don't believe this.  Rather than follow a useless "Yes it is. No it isn't." exchange, I would like to help you understand that this is really true. 

Imagine that you have an elastic balloon filled with ordinary dry air.  Would you agree that the pressure inside the balloon is balanced by the spring force of the stretched balloon, and the outside air pressure?  Now, if we put that balloon in an environmental chamber and pump the chamber down to 0.5 atmospheres, would you expect the balloon to expand?  Would you agree that there is now more energy stored in the balloon membrane than before?  Would you also agree that there is less energy stored in the external atmosphere?  Can I then persuade you that since the balloon body energy has gone up, and the atmosphere energy has gone down that the gas inside the balloon had to give up energy?  If you don't find this persuasive, then please explain where you think the balloon body got the extra energy that is now stored in its further stretched membrane.

[tinman]

Yes I understand 'equal and opposite reactions' perfectly well.

If the gas is pushing a piston AND it moves then there is  net force in the direction of travel of the cylinder. A force multiplied by distance travelled is work.

The amount of heat equal to the integral of  F.ds LEAVES the gas.

The mechanism by which this happens is as I have described before.

That is where you are wrong, and if you understood the workings of the diagram on the first page then you would see where your mistake is being made. No heat leaves the gas as the piston is moving, as the pressure is continually rising within the cylinder-regardless of cylinder volume. The very same thing is happening as it is if you compress the gas within the cylinder via pushing the piston in and reducing cylinder volume will maintaining gas mass amount.

[LibreEnergia]

That is where you are wrong, and if you understood the workings of the diagram on the first page then you would see where your mistake is being made. No heat leaves the gas as the piston is moving, as the pressure is continually rising within the cylinder-regardless of cylinder volume. The very same thing is happening as it is if you compress the gas within the cylinder via pushing the piston in and reducing cylinder volume will maintaining gas mass amount.

Irrespective of your diagram (which is wrong in terms of energy balance),  heat leaves the cylinder when it does work on the environment and vice versa. Where does it leave to? It gets converted to/from work.

if it didn't, you would have already invented a free energy device and would have no need to add the extra complications of electrolysis etc.

[MarkE]

That is where you are wrong, and if you understood the workings of the diagram on the first page then you would see where your mistake is being made. No heat leaves the gas as the piston is moving, as the pressure is continually rising within the cylinder-regardless of cylinder volume. The very same thing is happening as it is if you compress the gas within the cylinder via pushing the piston in and reducing cylinder volume will maintaining gas mass amount.

Let's look at that idea:
In your earlier description you open valve 'A' after the vessel reaches 120psi.  The piston then moves against the spring.  Suppose the gas is evolving at 1 liter per minute and the cylinder volume can expand by 1 liter.  Do you agree that if the piston extends fully in less than one minute that the overall pressure will have dropped from the time the valve is opened to the time the piston fully extends?

[tinman]

Tinman, LE is hardly clueless.  He has covered both the compression and expansion cases.  There are only three general possibilities:  What we are telling you is wrong, what you are saying is wrong, or we are all wrong.  Would you do me a favor and respond to my post #205?  I want to make sure that we see eye to eye on what it is that you believe.

The gas is always pushing in all directions.  How much it pushes depends on the kinetic energy in the gas:  How many molecules are bouncing around and how fast they are moving.  The temperature is a proxy for how fast they move.  What LE tried to explain in his last post was that the process of changing the volume IE the action of moving the piston either adds energy to the molecules, or removes it.  The internal energy, commonly referred to as the heat changes up or down, and since the number of molecules stays the same, the temperature goes up and down with the heat.   This principle of external mechanical work exchange with internal energy of a gas is both a very fundamental and key concept in thermodynamics.  I know you don't believe this.  Rather than follow a useless "Yes it is. No it isn't." exchange, I would like to help you understand that this is really true. 

Imagine that you have an elastic balloon filled with ordinary dry air.  Would you agree that the pressure inside the balloon is balanced by the spring force of the stretched balloon, and the outside air pressure?  Now, if we put that balloon in an environmental chamber and pump the chamber down to 0.5 atmospheres, would you expect the balloon to expand?  Would you agree that there is now more energy stored in the balloon membrane than before?  Would you also agree that there is less energy stored in the external atmosphere?  Can I then persuade you that since the balloon body energy has gone up, and the atmosphere energy has gone down that the gas inside the balloon had to give up energy?  If you don't find this persuasive, then please explain where you think the balloon body got the extra energy that is now stored in its further stretched membrane.

No-the energy within the gas in the ballon drops when the outside pressure around the baloon drops, as the pressure of the gas within the baloon drops as the size of the vessel (baloon) increases.
You are assuming that either the pressure or temperature within the cylinder drops as the piston is pushed out by the gas-it dose not. When the piston is pushed out by the gas, the temperature, pressure, volume and gas mass increases. The heavier the force working against the pistons direction, the quicker the temperature and pressure will rise. The end result at the completion of the pistons travel against the aposing force is a higher temperature than that of the gas that was used to force the piston out in the first place.
This we see all the time on the air rams at the mine sites I have worked on. The air feeding the rams may be around the 25*C mark, while the air exiting the rams may be around 40*C. The heavier the load acting against the rams, the hotter the air leaving the rams.
There is no energy loss within my system when the gas is used to do outside work, as there is no temperature drop-but a temperature increase in the gas insted. This increase in temperature is an increase in energy-not a loss.