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

what does preconceived mean

sammie Reply

physiological Psychology

Nwosu Reply

How can I develope my cognitive domain

Amanyire Reply

why is communication effective

Dakolo Reply

Communication is effective because it allows individuals to share ideas, thoughts, and information with others.

effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.

it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.

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Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment

Wekolamo Reply

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Wekolamo

because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).

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Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!

ARC

A child is a member of community not society elucidate ?

JESSY Reply

Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?

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compare and contrast skinner's perspective on personality development on freud

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Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning

war

explain how nature and nurture affect the development and later the productivity of an individual.

Amesalu Reply

nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.

Samuel

I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills

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good👍

Jonathan

and having a good philosophy of the world is like a sandwich and a peanut butter 👍

Jonathan

generally amnesi how long yrs memory loss

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interpersonal relationships

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What would be the best educational aid(s) for gifted kids/savants?

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treat them normal, if they want help then give them. that will make everyone happy

Saurabh

What are the treatment for autism?

Magret Reply

hello. autism is a umbrella term. autistic kids have different disorder overlapping. for example. a kid may show symptoms of ADHD and also learning disabilities. before treatment please make sure the kid doesn't have physical disabilities like hearing..vision..speech problem. sometimes these

Jharna

continue.. sometimes due to these physical problems..the diagnosis may be misdiagnosed. treatment for autism. well it depends on the severity. since autistic kids have problems in communicating and adopting to the environment.. it's best to expose the child in situations where the child

Jharna

child interact with other kids under doc supervision. play therapy. speech therapy. Engaging in different activities that activate most parts of the brain.. like drawing..painting. matching color board game. string and beads game. the more you interact with the child the more effective

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results you'll get.. please consult a therapist to know what suits best on your child. and last as a parent. I know sometimes it's overwhelming to guide a special kid. but trust the process and be strong and patient as a parent.

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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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