CHEM1101 Midterm: Thermodynamics recap

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30 May 2018

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Effect of Volume and Temperature Change on the System

• If e iease olue, thee ae oe positios possile fo the oleules. This esults i

more microstates, so increased entropy.

• If e iease tepeatue, the aeage kieti eegy increases. This results in a greater

distribution of molecular speeds. Therefore, there are more possible kinetic energy values,

resulting in more microstates, increasing entropy.

Entropy on the Molecular Scale

• The ue of iostates ad, theefoe, the entropy tend to increase with increases in

-temperature

-volume-

the number of independently moving molecules

Entropy and physical states

• Entropy increases with the freedom of motion of molecules.

• S(g) > S(l) > S(s)

• Entropy of a system increases for processes where

➢ gases form from either solids or liquids.

➢ liquids or solutions form from solids.

➢ the number of gas molecules increases

during a chemical reaction.

Third Law of Thermodynamics

• The etopy of a pue ystallie sustae at asolute zeo

is 0.

• Coside all atos o oleules i the pefet lattie at  K;

there will only be one microstate.

• S = k l W = k l  = 

Standard Entropies

• The efeee fo etopy is  K, so the alues fo eleets ae ot  J/ol K at  K.

• Stadad ola etopy fo a gas is geeally geate tha fo liuids ad solids. Be

aeful of size! • Stadad ola etopies iease ith ola ass.

• Stadad ola etopies iease ith ue of atos i a foula.

Entropy changes

Entropy changes for a reaction can be calculated as follows:

S° = nS°(products) – mS°(reactants)

where n and m are the coefficients in the balanced chemical equation.

Entropy Changes in Surroundings

• Heat that flows into or out of the system changes the entropy of the surroundings.

• For an isothermal (constant temperature) process

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Document Summary

Effect of volume and temperature change on the system: if (cid:449)e i(cid:374)(cid:272)(cid:396)ease (cid:448)olu(cid:373)e, the(cid:396)e a(cid:396)e (cid:373)o(cid:396)e positio(cid:374)s possi(cid:271)le fo(cid:396) the (cid:373)ole(cid:272)ules. This (cid:396)esults i(cid:374) more microstates, so increased entropy: if (cid:449)e i(cid:374)(cid:272)(cid:396)ease te(cid:373)pe(cid:396)atu(cid:396)e, the a(cid:448)e(cid:396)age ki(cid:374)eti(cid:272) e(cid:374)e(cid:396)gy increases. This results in a greater distribution of molecular speeds. Therefore, there are more possible kinetic energy values, resulting in more microstates, increasing entropy. Entropy on the molecular scale: the (cid:374)u(cid:373)(cid:271)e(cid:396) of (cid:373)i(cid:272)(cid:396)ostates a(cid:374)d, the(cid:396)efo(cid:396)e, the entropy tend to increase with increases in. Entropy and physical states: entropy increases with the freedom of motion of molecules, s(g) > s(l) > s(s, entropy of a system increases for processes where. Gases form from either solids or liquids. The number of gas molecules increases during a chemical reaction. Entropy changes for a reaction can be calculated as follows: S = ns (products) ms (reactants) where n and m are the coefficients in the balanced chemical equation.

Related Questions

My first answer was wrong. Can you explain answers?

Complete the following sentences on predicting the relative entropy of a system.

The words are: decreases, equal to, increases, less than, greater than

1. Temperature Changes: for a given substance, SÂ° __________as the temperature increases.

2. Physical States and Changes of State: as the freedom of motion of the substance ____________ , the entropy increases. The size of the entropy change is such that ÎSÂ°_vap is much ____________ ÎSÂ°_fus .

3. Dissolving a Gas: when a gas dissloves in a liquid, the entropy always ____________ but when disolved in another gas it ____________ .

4. Dissolving a Solid or a Liquid: the entropy of a dissolved solid or liquid is always ____________ the entropy of the pure substance.

5. Atomic Size: the entropy of atoms generally ____________ down a group since the number of microstates ____________ .

6. Molecular Complexity: the entropy of molecules ____________ as they become more complex and the number of atoms ____________ .

Qualitative Predictions about Entropy Entropy is the randomness of a system. At the molecular level, entropy can be described in terms of the possible number of different arrangements of particle positions and energies, called microstates. The more microstates the system has, the greater its entropy. Microstates depend on molecular motion. Molecules may undergo three different types of motion: translational motion, vibrational motion, and rotational motion. During translational motion, the entire molecule moves in one direction. During vibrational motion, atoms in a molecule move toward and away from one another. During rotational motion, molecules rotate or spin. The number of molecules, the space available for the molecules, and the energy available to the molecules will impact the number of microstates. Another way of looking at entropy is that the universe is moving toward a broader distribution of energy. The universe has a constant amount of energy as stated in the first law of thermodynamics. The universe started with low entropy (concentrated in the moment before the "big bang") and the entropy has since been constantly increasing by distributing this energy. Heat distribution from high temperature to low temperature is a another example of this phenomenon. Part A Rank these systems in order of decreasing entropy. Rank from highest to lowest entropy. To rank items as equivalent, overlap them. Hints HelpReset Least entropyGreatest entropy 1 mol of neon gas at 273 K and 40 L 1 mol of chlorine gas at 273 K and 40 L 1 mol of hydrogen peroxide gas at 273 K and 40 L 1 mol of neon gas at 273 K and 20 L 1/2 mol of neon gas at 273 K and 20 L 1/2 mol of neon gas at 100 K and 20 L 1/2 mol of liquid neon at 100 K The correct ranking cannot be determined. SubmitMy AnswersGive Up Incorrect; Try Again; 4 attempts r

CHEM1101 Midterm: Thermodynamics recap

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