# 13.1 The first law of thermodynamics  (Page 3/9)

 Page 3 / 9

Strategy

In part (a), we must first find the net heat transfer and net work done from the given information. Then the first law of thermodynamics $\left(\Delta U=Q-W\right)$ can be used to find the change in internal energy. In part (b), the net heat transfer and work done are given, so the equation can be used directly.

Solution for (a)

The net heat transfer is the heat transfer into the system minus the heat transfer out of the system, or

$Q=\text{40}\text{.}\text{00}J-\text{25}\text{.}\text{00 J}=\text{15}\text{.}\text{00}\phantom{\rule{0.25em}{0ex}}J.$

Similarly, the total work is the work done by the system minus the work done on the system, or

$W=\text{10}\text{.}\text{00}J-4\text{.}\text{00}J=6\text{.}\text{00 J.}$

Thus the change in internal energy is given by the first law of thermodynamics:

$\Delta U=Q-W=\text{15}\text{.}\text{00}J-6\text{.}\text{00}J=9\text{.}\text{00 J.}$

We can also find the change in internal energy for each of the two steps. First, consider 40.00 J of heat transfer in and 10.00 J of work out, or

$\Delta {U}_{1}={Q}_{1}-{W}_{1}=\text{40}\text{.}\text{00}J-\text{10}\text{.}\text{00}J=\text{30}\text{.}\text{00 J.}$

Now consider 25.00 J of heat transfer out and 4.00 J of work in, or

$\Delta {U}_{2}={Q}_{2}-{W}_{2}\text{=}-\text{25}\text{.}\text{00}J-\left(-4\text{.}\text{00}J\right)=\text{–21.00 J.}$

The total change is the sum of these two steps, or

$\Delta U=\Delta {U}_{1}+\Delta {U}_{2}=\text{30}\text{.}\text{00}J+\left(-\text{21}\text{.}\text{00}J\right)=9\text{.}\text{00 J.}$

Discussion on (a)

No matter whether you look at the overall process or break it into steps, the change in internal energy is the same.

Solution for (b)

Here the net heat transfer and total work are given directly to be $Q=–\text{150}\text{.}\text{00 J}$ and $W=–\text{159}\text{.}\text{00 J}$ , so that

$\Delta U=Q–W=–\text{150}\text{.}\text{00 J}–\left(-\text{159}\text{.}\text{00 J}\right)=9\text{.}\text{00 J.}$

Discussion on (b)

A very different process in part (b) produces the same 9.00-J change in internal energy as in part (a). Note that the change in the system in both parts is related to $\Delta U$ and not to the individual $Q$ s or $W$ s involved. The system ends up in the same state in both (a) and (b). Parts (a) and (b) present two different paths for the system to follow between the same starting and ending points, and the change in internal energy for each is the same—it is independent of path.

## Human metabolism and the first law of thermodynamics

Human metabolism is the conversion of food into heat transfer, work, and stored fat. Metabolism is an interesting example of the first law of thermodynamics in action. We now take another look at these topics via the first law of thermodynamics. Considering the body as the system of interest, we can use the first law to examine heat transfer, doing work, and internal energy in activities ranging from sleep to heavy exercise. What are some of the major characteristics of heat transfer, doing work, and energy in the body? For one, body temperature is normally kept constant by heat transfer to the surroundings. This means $Q$ is negative. Another fact is that the body usually does work on the outside world. This means $W$ is positive. In such situations, then, the body loses internal energy, since $\Delta U=Q-W$ is negative.

What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!