Chapter 7- Thermodynamics

Question 1

What is nature’s heat tax?

Answer 1

Natures cut on energy every time it’s used

It is in the form of heat

We cannot create more energy than what was there to begin with

Question 2

How does the first and second thermodynamic laws associate with energy usage?

Answer 2

First- energy is conserved in chemical processes (cannot create more energy than what was initially there
Second- cannot break even with energy, energy is always lost to surrounding in processes

Question 3

What is a spontaneous process?

Answer 3

A process that occurs without ongoing outside intervention

Dropping book
Ball on slope

Question 4

How can a non spontaneous process be spontaneous?

Answer 4

By coupling it to another process that is spontaneous or by supplying energy from an external source

Question 5

What does disorder change entropy?

Answer 5

Increasing disorder, increasing entropy in the more disorders states

Solid to liquid to gas

Question 6

What is entropy?

What is it’s equation?

Answer 6

Determines the direction of chemical and physical change
Chemical system proceeds in a direction that increases the entropy of the universe

S=k ln(w)
K=gas constant over avogadros
W= # of energetically equivalent ways

Question 7

What is microstate vs macrostate?

Answer 7

Micro- exact internal energy distribution among the particles at any one instant
Macro- result of a large number of different micro states

Pictures on pages 372-373

Question 8

What is the variable W?

Answer 8

It is the number of energetically equivalent ways to arrange the components of a system

The number of possible micro states that can result in a given macrostate

Question 9

What is the change in entropy for the universe in a spontaneous reaction?

Answer 9

ΔS > 0

Always positive

Question 10

What phase changes does change in entropy (ΔS>0) increase for?

Answer 10

Solid to liquid
Solid to gas
Liquid to gas
An increase in moles of gas during reaction

Question 11

The greater the temperature, the __________ the increase in entropy for a given amount of energy dispersed into the surroundings

Answer 11

Smaller

Question 12

What is the sign and size of ΔSsys and ΔSsurr at low and high temperature in the equation:
ΔSuniv=ΔSsys + ΔSsurr

Answer 12

Δsys is always negative
ΔSurr= positive and large at low temp
Positive and small at high temp

Question 13

What is the equation for ΔSsurr involving change in enthalpy and T?

Answer 13

ΔSsurr = -ΔHsys/T

Question 14

What is the third law of thermodynamics?

Answer 14

The entropy of a perfect crystal at absolute zero (0K) is zero

Question 15

What are allotropes?

Answer 15

Elements that exist in two or more forms

Question 16

How does molar mass affect the entropy of gases?

Answer 16

The bigger the element, the greater the entropy

Question 17

How is entropy affected by molecular complexity?

Answer 17

The more complex a compound, the greater the entropy

Question 18

How do you calculate the standard entropy change for a reaction?

Answer 18

ΔSrxn = ΣnpS(products)-ΣnrS*(reactants)

N is the stoichemetric coefficients of the reactants and products

Question 19

What is the Gibbs free energy equation and how can it be changed to incorporate ΔSuniv?

Answer 19

ΔG= ΔH -TΔS

ΔG= -TΔSuniv

Question 20

What is spontaneity if ΔH is negative and ΔS is positive?

Answer 20

Spontaneous at all temps

Page 393

Question 21

What is the spontaneity of ΔH is positive and ΔS is negative?

Answer 21

Non spontaneous at all temps

Page 394

Question 22

What is the spontaneity of ΔH is negative and ΔS in negative?
(For high temp and low temp)

Answer 22

Spontaneous at low temp
Nonspontaneous at high temp

Page 394

Question 23

What is spontaneity when ΔH is positive and ΔS is positive?

At high and low temps

Answer 23

Nonspontaneous at low temp
Spontaneous at high temp

Page 394

Question 24

What are the three ways in calculating ΔG*rxn?

Answer 24

1. ΔG*rxn=ΔH*rxn-TΔS*rxn
Page 397
2. ΔG*rxn=ΣnpΔG*f(products)-ΣnrΔG*f(reactants)   *only works at temp which ΔG*f is tabulated (25C)
Page 400
3. Use Hess’s laws and combine

Question 25

ΔHrxn=-74.6 kJ
ΔSrxn= -80.8 J/K
ΔG*rxn= -50.5 kJ

Is the reaction endothermic or endothermic and how much thermal energy does it give off?
What is the maximum amount of energy available for useful work?

Answer 25

Exothermic and spontaneous and gives off 74.6 kJ of thermal energy

Max amount of energy= 50.5kJ
If G was positive it would represent the minimum amount of work

Question 26

How do we calculate the free energy change of a reaction under non standard conditions?

Answer 26

ΔGrxn= ΔG*rxn + RTlnQ

Question 27

What is the value of Q at standard condition for gas reactions (P=1atm)

Answer 27

Q=1 which results in ΔGrxn just equaling ΔG*rxn

Question 28

What is the equation for ΔG*rxn at equilibrium with K?

Answer 28

ΔG*rxn= -RTlnK

Question 29

What is the linear like equation for free energy change to equilibrium constant?

Answer 29

lnK=-ΔHrxn/R (1/T) + ΔSrxn/R