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5.03 The Second Law of Thermodynamics

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Advanced Chemistry

University of Kentucky

4.7 (422 ratings) | 50K Students Enrolled

A chemistry course to cover selected topics covered in advanced high school chemistry courses, correlating to the standard topics as established by the American Chemical Society. Prerequisites: Students should have a background in basic chemistry including nomenclature, reactions, stoichiometry, molarity and thermochemistry.

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4.7 (422 ratings)

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KO

Jul 17, 2017

Excellent content and delivery!\n\nThis course has many well-explained examples and practice questions to reinforce the understanding of the taught concepts. Thank you!

CW

Sep 17, 2015

I used this course as a significant portion of my preparation for the CLEP Chemistry exam, and passed today with an A! Thank you!

From the lesson

Thermodynamics

The overarching theme of thermodynamics is the prediction of whether a reaction will occur spontaneously under a certain set of conditions. Entropy and Free Energy are defined and utilized for this purpose.

5.01 Review of Thermochemistry8:29

5.01a Enthalpy of Reaction Refresher2:32

5.02 Spontaneous vs. Nonspontaneous7:25

5.10 Standard versus Nonstandard Free Energy Change15:13

5.03 The Second Law of Thermodynamics2:58

5.04 Entropy5:03

5.05 Entropy of the Universe8:52

5.06 Gibbs Free Energy8:12

5.06a Gibbs Free Energy Example Problem 15:12

5.06b Gibbs Free Energy Example Problem 24:38

5.07 The Third Law of Thermodynamics6:42

5.08 Calculating Standard Entropy Change6:36

5.08a Thermodynamics Worked Example3:15

5.09 Calculating Standard Free Energy Change11:21

5.09a Thermodynamics Worked Example2:45

5.09b Thermodynamics Worked Example2:37

5.11 Comparing ∆G° and K18:50

5.10a Thermodynamics Worked Example3:36

5.10b Thermodynamics Worked Example1:58

5.02a Spontaneous vs Nonspontaneous Example Problem1:18

Taught By

Dr. Allison Soult
Lecturer
Dr. Kim Woodrum
Sr. Lecturer

Transcript

In this module we're going to talk about the second law of thermodynamics

Our objective at this module is to understand the 2nd law

and to see how it applies to chemical systems.

One of the things we look at to determine spontaneity, is a measure of the disorder in the system.

here are some examples of some spontaneous endothermic processes.

This means that our enthalpy values are greater than 0

and we're having to put energy and to make them happen. But this can still be a

spontaneous process.

Above your degree Celsius ice melts.

To go from the solid to the liquid phase I have to put energy in.

However also see an increase in the disorder

those molecules as I melt the ice. Evaporation up liquid water to gas-phase water

is a spontaneous but endothermic process. As is the dissolution of sodium chloride

or other ionics salt in water. When we dissolve those salts

we're spreading those ions around. There are more ways for them to be arranged

we're increasing the disorder

therefore we're increasing the entropy of the system.

If I go from the liquid to the gas phase

that is also a spontaneous endothermic process. Because I'm taking water molecules that have some order

about them. albeit less than a solid, but I'm taking them to the gas phase where there is

virtually no order.

There are more ways for those molecules to be arranged therefore I'm increasing

the entropy of the system.

As the KBr dissolves in water the ions spread out

increasing their disorder and increasing their entropy. There are more ways for

those ions to be arranged.

So let's backtrack a little bit and talk about the first law of thermodynamics

which says energy cannot be created or destroyed. We know from this that the

total energy at the university is

constant. Now we can transfer energy and converted from one type to the other

but ultimately the sum of all those energies must be equal to the same constant value.

The second law of thermodynamics is a little bit different

instead of talking about energy we're talking about spontaneity,

Specifically talking about entropy and what we know is that for any spontaneous process.

The intro bf the universe increases. Processes that happen spontaneously

are those that increase the entropy of the universe. So although parts of a

process may not be spontaneous.

When we look at the entire system and its surroundings

what we find is that overall there's an increase in the entropy

of the universe . And that's what makes our spontaneous reaction spontaneous.

This will depend heavily on the temperature and as we get later in this

unit and talk about Gibbs free energy will be able to quantify that.

Next we're going to a more in-depth about what entropy really is.

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