## Equation from Friday Lecture

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Yea Eun Lee 1H
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

### Equation from Friday Lecture

Can someone explain why this equation is true? I'm having some difficulty understanding it.

change in U= qP + w= qP= change in H

504754253
Posts: 45
Joined: Fri Jun 23, 2017 11:39 am

### Re: Equation from Friday Lecture

it is basically an explanation of how H and U are the same thing

Michelle Lee 2E
Posts: 64
Joined: Thu Jul 27, 2017 3:01 am

### Re: Equation from Friday Lecture

Enthalpy itself, as we learned in our first lecture, is the amount of heat released or absorbed at a constant pressure. That in variable form is:
qP = change in H

The new equation we learned is change in U (internal energy) is:
change in U = qP + w

If there is no work done like when the reaction is at constant pressure (an open beaker or open test tube for example) or work is insignificant, then work (w) would equal 0.

So if w=0:
the equation now is: change in U = qP + 0 which is just: change in U = qP = change in H (from the top part about enthalpy)