Carnot Cycle, Irreversible Work, Heat and Work at Constant T or Constant P

Please Check Your Section:

Please type your name:		IN:
Please type your student code: (Last Name and Last 4 digits of your SSN together)

The following three questions refer to the material you were to read in preparation for the lesson. Questions one and two require you to write a three or four sentence response. Number three is a multiple choice question. Click in the appropriate circle.

You may change your mind as often as you wish. When you are satisfied with your responses, click the SUBMIT button at the bottom of this page.

1.

In real physical systems, as opposed to idealized ones, we must deal with "irreversible processes." If a process creates new entropy, it is called an "irreversible" process, because that process cannot be reversed to destroy the new entropy.

Suppose a system undergoes a process that changes its internal energy by an amount dU. Suppose we don't know whether the process is reversible or irreversible. In your own words, briefly explain why the heat transfer associated with that internal energy change would have to be smaller if the process were irreversible than if it were reversible.

Comment on this ---- does this make sense?

2.

Try to make a ballpark estimate of the efficiency of an automobile engine. Here are some useful bits of information:

the oxidation of one gasoline molecule (C₈H₁₈) releases about 57 eV of heat energy
an engine doing work at 20 kW (about 27 hp) burns a liter of gasoline every 6 minutes
a liter of gasoline has a mass of about 0.7 kg

[Remember that the efficiency is (what we want)/(what it costs). Please briefly show/explain your key steps. Thanks!]

3.

The "effective work" performed on a system

can be expressed in terms of the Gibbs free energy.
is less than the total work performed on the system.
can be 0, but only when the total work is 0.
is different from the total work for processes at constant pressure and volume.

Below is a space for your thoughts, including general comments about today's assignment (what seemed impossible, what reading didn't make sense, what we should spend class time on, what was "cool", etc.):

You may change your mind as often as you wish. When you are satisfied with your responses click the SUBMIT button.
I received no help from anyone on this assignment.

SECTION