4.7 Entropy on a microscopic scale (Page 4/10)

University physics volume 2 Page 4 / 10

Check Your Understanding A quantity of heat Q is absorbed from a reservoir at a temperature $T_{h}$ by a cooler reservoir at a temperature $T_{c} .$ What is the entropy change of the hot reservoir, the cold reservoir, and the universe?

$− Q / T_{h}$ ; $Q / T_{c}$ ; and $Q (T_{h} - T_{c}) / (T_{h} T_{c})$

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Check Your Understanding A 50-g copper piece at a temperature of $20 °C$ is placed into a large insulated vat of water at $100 °C$ . (a) What is the entropy change of the copper piece when it reaches thermal equilibrium with the water? (b) What is the entropy change of the water? (c) What is the entropy change of the universe?

a. 4.71 J/K; b. −4.18 J/K; c. 0.53 J/K

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View this site to learn about entropy and microstates. Start with a large barrier in the middle and 1000 molecules in only the left chamber. What is the total entropy of the system? Now remove the barrier and let the molecules travel from the left to the right hand side? What is the total entropy of the system now? Lastly, add heat and note what happens to the temperature. Did this increase entropy of the system?

Summary

Entropy can be related to how disordered a system is—the more it is disordered, the higher is its entropy. In any irreversible process, the universe becomes more disordered.
According to the third law of thermodynamics, absolute zero temperature is unreachable.

Key equations

Result of energy conservation	$W = Q_{h} - Q_{c}$
Efficiency of a heat engine	$e = \frac{W}{Q_{h}} = 1 - \frac{Q_{c}}{Q_{h}}$
Coefficient of performance of a refrigerator	$K_{R} = \frac{Q_{c}}{W} = \frac{Q_{c}}{Q_{h} - Q_{c}}$
Coefficient of performance of a heat pump	$K_{P} = \frac{Q_{h}}{W} = \frac{Q_{h}}{Q_{h} - Q_{c}}$
Resulting efficiency of a Carnot cycle	$e = 1 - \frac{T_{c}}{T_{h}}$
Performance coefficient of a reversible refrigerator	$K_{R} = \frac{T_{c}}{T_{h} - T_{c}}$
Performance coefficient of a reversible heat pump	$K_{P} = \frac{T_{h}}{T_{h} - T_{c}}$
Entropy of a system undergoing a reversible process at a constant temperature	$Δ S = \frac{Q}{T}$
Change of entropy of a system under a reversible process	$Δ S = S_{B} - S_{A} = \int_{A}^{B} d Q / T$
Entropy of a system undergoing any complete reversible cyclic process	$\oint d S = \oint \frac{d Q}{T} = 0$
Change of entropy of a closed system under an irreversible process	$Δ S \geq 0$
Change in entropy of the system along an isotherm	$lim_{T \to 0} {(Δ S)}_{T} = 0$

Conceptual questions

Are the entropy changes of the systems in the following processes positive or negative? (a) water vapor that condenses on a cold surface; (b) gas in a container that leaks into the surrounding atmosphere; (c) an ice cube that melts in a glass of lukewarm water; (d) the lukewarm water of part (c); (e) a real heat engine performing a cycle; (f) food cooled in a refrigerator.

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Discuss the entropy changes in the systems of Question 21.10 in terms of disorder.

Entropy is a function of disorder, so all the answers apply here as well.

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Problems

A copper rod of cross-sectional area $5.0 {cm}^{2}$ and length 5.0 m conducts heat from a heat reservoir at 373 K to one at 273 K. What is the time rate of change of the universe’s entropy for this process?

$3.78 \times 10^{−3} W/K$

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Fifty grams of water at $20 °C$ is heated until it becomes vapor at $100 °C$ . Calculate the change in entropy of the water in this process.

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Fifty grams of water at $0 °C$ are changed into vapor at $100 °C$ . What is the change in entropy of the water in this process?

430 J/K

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Questions & Answers

how does Neisseria cause meningitis

Nyibol Reply

what is microbiologist

Muhammad Reply

what is errata

Muhammad

is the branch of biology that deals with the study of microorganisms.

Ntefuni Reply

What is microbiology

Mercy Reply

studies of microbes

Louisiaste

when we takee the specimen which lumbar,spin,

Ziyad Reply

How bacteria create energy to survive?

Muhamad Reply

Bacteria doesn't produce energy they are dependent upon their substrate in case of lack of nutrients they are able to make spores which helps them to sustain in harsh environments

_Adnan

But not all bacteria make spores, l mean Eukaryotic cells have Mitochondria which acts as powerhouse for them, since bacteria don't have it, what is the substitution for it?

Muhamad

they make spores

Louisiaste

what is sporadic nd endemic, epidemic

Aminu Reply

the significance of food webs for disease transmission

Abreham

food webs brings about an infection as an individual depends on number of diseased foods or carriers dully.

Mark

explain assimilatory nitrate reduction

Esinniobiwa Reply

Assimilatory nitrate reduction is a process that occurs in some microorganisms, such as bacteria and archaea, in which nitrate (NO3-) is reduced to nitrite (NO2-), and then further reduced to ammonia (NH3).

Elkana

This process is called assimilatory nitrate reduction because the nitrogen that is produced is incorporated in the cells of microorganisms where it can be used in the synthesis of amino acids and other nitrogen products

Elkana

Examples of thermophilic organisms

Shu Reply

Give Examples of thermophilic organisms

Shu

advantages of normal Flora to the host

Micheal Reply

Prevent foreign microbes to the host

Abubakar

they provide healthier benefits to their hosts

ayesha

They are friends to host only when Host immune system is strong and become enemies when the host immune system is weakened . very bad relationship!

Mark

what is cell

faisal Reply

cell is the smallest unit of life

Fauziya

cell is the smallest unit of life

Akanni

Innocent

cell is the structural and functional unit of life

Hasan

is the fundamental units of Life

Musa

what are emergency diseases

Micheal Reply

There are nothing like emergency disease but there are some common medical emergency which can occur simultaneously like Bleeding,heart attack,Breathing difficulties,severe pain heart stock.Hope you will get my point .Have a nice day ❣️

_Adnan

define infection ,prevention and control

Innocent

I think infection prevention and control is the avoidance of all things we do that gives out break of infections and promotion of health practices that promote life

Lubega

Heyy Lubega hussein where are u from?

_Adnan

en français

Adama

which site have a normal flora

ESTHER Reply

Many sites of the body have it Skin Nasal cavity Oral cavity Gastro intestinal tract

Safaa

skin

Asiina

skin,Oral,Nasal,GIt

Sadik

How can Commensal can Bacteria change into pathogen?

Sadik

How can Commensal Bacteria change into pathogen?

Sadik

all

Tesfaye

by fussion

Asiina

what are the advantages of normal Flora to the host

Micheal

what are the ways of control and prevention of nosocomial infection in the hospital

Micheal

what is inflammation

Shelly Reply

part of a tissue or an organ being wounded or bruised.

Wilfred

what term is used to name and classify microorganisms?

Micheal Reply

Binomial nomenclature

adeolu

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Source: OpenStax, University physics volume 2. OpenStax CNX. Oct 06, 2016 Download for free at http://cnx.org/content/col12074/1.3

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