## Constant pressure

isochoric/isometric: $\Delta V = 0$
isothermal: $\Delta T = 0$
isobaric: $\Delta P = 0$

Rosa Munoz 2E
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### Constant pressure

When they refer to constant pressure, are we referring to constant external pressure?

Sahil Jog 1F
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### Re: Constant pressure

Yes they are referring to constant external pressure, since a dynamic external pressure would do unnecessary work on a system, and thus be unreasonable problem to solve.

faithkim1L
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### Re: Constant pressure

Constant external pressure.

Vinita Saxena 2I
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### Re: Constant pressure

Yes, constant external pressure

Callum Guo 1H
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Been upvoted: 1 time

### Re: Constant pressure

Constant external pressure

205389184
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Joined: Sat Sep 07, 2019 12:18 am

### Re: Constant pressure

Yes, you are correct, we are referring to constant pressure

Jacob Villar 2C
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### Re: Constant pressure

Constant external pressure.

Alexis Robles 2k
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### Re: Constant pressure

yeah, its Constant external pressure.

rohun2H
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### Re: Constant pressure

Yes, constant external pressure.

705367472
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### Re: Constant pressure

yes, we are referring to constant external pressure

Matt Sanruk 2H
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### Re: Constant pressure

And this would be irreversible?

Posts: 74
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### Re: Constant pressure

Matt Sanruk 2H wrote:And this would be irreversible?

Yes this would be irreversible

Posts: 97
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### Re: Constant pressure

It would be irreversible and it would be referring to external pressure so w=0

aishwarya_atmakuri
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### Re: Constant pressure

Yes, they would be referring to a constant external pressure.

CameronDis2K
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### Re: Constant pressure

Yes, constant external pressure, as it allows the system to change somewhat independent of the external environment. For example, in the equation for an irreversible expansion work, W = - P external * delta V. However, if it is a gas in a container, pressure of the gas may be determined through the ideal gas law (but the system pressure will change).

KBELTRAMI_1E
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### Re: Constant pressure

Is it always assumed to be 1 atm? What about in a vacuum?

Vinita Saxena 2I
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### Re: Constant pressure

In a vacuum there is no external pressure, so there is nothing to push back against, meaning w=0

Micah3J
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### Re: Constant pressure

And so just because there is constant external pressure, the internal pressure can still be changing because of the reaction going on?

RobertXu_2J
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### Re: Constant pressure

Yes, constant external pressure.

Mulin_Li_2J
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Joined: Sat Aug 17, 2019 12:16 am

### Re: Constant pressure

Yes and I can give you some explanation on this.

You might refer to "constant pressure" mentioned when we try to calculate the amount of work done by a system. First, let's take a look at the definition of work: w = F(o)*D. F(o) here refers to an opposing force. Basically, this formula implies that you have to have an opposing force to do work, and the work you have done is how far you got by pushing against the opposing force. Hence, because w = -P*deltaV is a derived formula from w = F(o)*D, P also refers to external pressure.

Hope this can help! -_+