# Entropy change

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- Created by: Hindleyc
- Created on: 25-11-18 19:43

What will a spontaneous process such as diffusion do?

Proceed on its own without any external influence

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What is Gibbs energy in this case?

-ve therefore entropy greater than Enthalpy

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A rxn that is exo will result in...

products that are more thermodynamically stable than the reactants which is a driving force behind many reactions and causes them to be spontaneous(occur without any external influence)

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What are some spontaneous reactions

endothermic

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What is entropy

Description of the number of ways atoms can share quanta of energy

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What if number of ways of arranging the energy is high

system is disordered and entropy is high

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so substances with more ways of arranging their atoms and energy (more disordered) have

a higher entropy

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Simpler compounds and pure substances tend to have lower

entropies than complex compounds and mixtures

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order of entropy low to high

Solid, liquid, gas

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What happens when a solid increases in temperature

entropy increases as particles vibrate more

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When is there a bigger jump in entropy

with boiling than melting as gases have large entropies as they are much more disordered

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at 0k what do substances have

0 entropy as there is no disorder as particles are stationary

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What will an increase in disorder and entropy lead to?

positive entropy change

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what can be used to predict if delta S is +ve or -ve

balanced chemical eqn

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when will a significant inc in the entropy occur?

if there is a change of state from solid or liquid to gas or there is a significant inc in number of molecules b/w product and reactant

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so what inc disorder

solid to gas, inc in number of molecules

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What will have zero entropy

perfect crystals at absolute zero. not elements in standard states

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what s not possible

substance to have standard enthalpy of less than 0

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What do data books list

standard entropies per mole for variety of substances

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UNIT of entropy

J/K/MOL

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EQN for entropy

sum of entropy of products - sum of entropy of reactants

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What is Gibbs free energy change

Term that combines the effect of enthalpy and entropy into one number

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What determines feasibility of a reaction

balance b/w entropy and enthalpy

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eqn

delta G= delta H -TdeltaS

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What is a reaction that has inc entropy (+ve delta S) and is exothermic (-ve delta H) will make..

delta G be negative and will always be feasible

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For any spontaneous change delta G will be

-ve

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Even if delta G is -ve there is still a possibility however that..

the reaction will not occur or will occur so slowly that effectively doesn't happen

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Why?

If rxn has a high activation energy the reaction will not occur

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delta G unit

Kj/mol

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delta H

KJ/mol

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T

kelvin +273

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delta S

J/K/Mol needs to convert to Kj/k/mol. /1000

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Steps

calc delta S. calc delta H. Calc delta G if +ve rxn not feasible

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As physical phase change like melting and boiling are equilibria what is the delta G for such changes

Zero

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when is a rxn feasible

when delta G is equal to 0 or negative

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T=

delta H/delta S

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What will changing temp do

Change value of -TdeltaS

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If reaction involves inc in entropy (delta S +ve) what will an inc in temp do

make it more likely that delta G is -ve and more likely reaction occurs

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If reaction involves decrease in entropy (delta S -ve) then what ill inc in temp do

make it less likely that delta G is -ve and less likely for reaction to occur

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If reaction has delta S close to 0 then temp ..

won't have large effect on feasibility of rxn as -TdeltaS will be small and delta G won't change much

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using y=mx+c what's gradient and y intercept

gradeint= -deltaS. y intercept= delta H.

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What does a positive gradient mean

delta S is -ve

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Why does slope change when y negative

ammonia liquify and entropy different

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## Other cards in this set

### Card 2

#### Front

What is Gibbs energy in this case?

#### Back

-ve therefore entropy greater than Enthalpy

### Card 3

#### Front

A rxn that is exo will result in...

#### Back

### Card 4

#### Front

What are some spontaneous reactions

#### Back

### Card 5

#### Front

What is entropy

#### Back

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