Thermodynamics

Question 1

System

Answer 1

Part of the universe being studied

Question 2

Surroundings

Answer 2

Everything else in the universe

Question 3

What is the First Law of Thermodynamics?

Answer 3

Energy is conserved. Energy can’t be created/destroyed, only transferred from one object to another and/or transferred from one energy type to another

Question 4

What is ΔH ?

Answer 4

Enthalpy

Question 5

Define enthalpy

Answer 5

Total heat content of a system

Question 6

If ΔH < 0 then

Answer 6

Reaction is Exothermic. Heat is leaving system – LOSS of heat (exo - exit)
AKA -ΔH

Question 7

If ΔH > 0 then

Answer 7

Reaction is endothermic. Heat is entering the system. GAINING of heat.
AKA +ΔH

Question 8

Spontaneous Process

Answer 8

Process that occurs without outside help. Has a -ΔG

Question 9

Nonspontaneous Process

Answer 9

Process that will not occur UNLESS driven by an external source. Has a +ΔG

Question 10

What is true about a reaction as it relates to spontaneity?

Answer 10

If going one direction in a reaction is spontaneous, then going the other way is nonspontaneous
If A + B -> C is spontaneous, then
C -> A + B is nonspontaneous

Question 11

What is ΔS

Answer 11

Entropy

Question 12

What is Entropy?

Answer 12

Entropy is a measure of how dispersed the system’s energy is. AKA measure of disorder.

Question 13

What does an increase in entropy mean?

Answer 13

+ΔS , the system has become less ordered.

Question 14

What does a decrease in entropy mean?

Answer 14

-ΔS , the system has become more ordered.

Question 15

What is the equation for the ΔS of the universe?

Answer 15

ΔSuniverse = ΔSsystem + ΔSsurroundings

Question 16

What does a spontaneous reaction do to the entropy of the universe?

Answer 16

+ΔSuniverse , increases the entropy of the universe, AKA increases the disorder of the universe (decreases the order)
When +ΔSuniverse , then the Tsurrounding < Tsystem

Question 17

What does a nonspontaneous reaction do to the entropy of the universe?

Answer 17

-ΔSuniverse , decrease the entropy of the universe, AKA increase the order of the universe (decrease the disorder)
When -ΔSuniverse , then the Tsurrounding > Tsystem

Question 18

Second Law of Thermodynamics

Answer 18

For a process to be spontaneous, the ΔSuniverse must be positive.
AKA: The entropy of the universe (composed of the entropy of the system and surroundings) must always increase during a spontaneous process.

Question 19

What is the formula for estimating the ΔSsurroundings using the ΔHsystem?

Answer 19

ΔSuniverse = ΔSsystem - (ΔHsystem/T)

Question 20

What is standard entropy?

Answer 20

What a molecule is at in a certain set of conditions
1 bar of pressure | 298.15 K |1 mole

Question 21

How can we calculate the ΔSsystem?

Answer 21

xA +yB -> zC +wD
v Standard Entropy of ΔS
ΔSrxn = [zS(C) + wS(D)] - [xS(A) + yS(B)]

^Basically saying multiply the moles by the standard entropy of the product/reactant, add the reactants/products together, then do products-reactants for the ΔSsystem AKA ΔSrxn

Question 22

What is ΔG

Answer 22

Gibbs Free Energy

Question 23

What is Gibbs Free Energy

Answer 23

The energy available to do work. Energy we can get out of a spontaneous reaction // Energy we have to put in for a nonspontaneous reaction.

Question 24

Formula for finding the ΔSuniverse using ΔG

Answer 24

ΔSuniverse = (-ΔG/T)
When ΔG< 0 … -ΔG … then the reation is spontaneous as the ΔSuniverse > 0
When ΔG>0 … +ΔG … then the reaction is nonspontaneous as the ΔSuniverse < 0

Question 25

What is the formula in which ΔG, ΔH, and ΔS are related by?

Answer 25

ΔG = ΔHsystem - (T)(ΔSsystem)
^putting system is not a requirement as this formula will only ever use the system values, never surrounding or universe.

Question 26

For the formula ΔG = ΔH - (T)(ΔS), if the values are -ΔH and +ΔS , then what will ΔG be AND what kind of reaction will occur?

Answer 26

ΔG will be -ΔG … Reaction will ALWAYS be spontaneous

Question 27

For the formula ΔG = ΔH - (T)(ΔS), if the values are +ΔH and -ΔS , then what will ΔG be AND what kind of reaction will occur?

Answer 27

ΔG will be +ΔG … reaction will ALWAYS be nonspontaneous

Question 28

For the formula ΔG = ΔH - (T)(ΔS), if the values are +ΔH and +ΔS , then what will ΔG be AND what kind of reaction will occur?

Answer 28

-ΔG IF T-value is larger = spontaneous
+ΔG if T-value is smaller = nonspontaneous

Question 29

For the formula ΔG = ΔH - (T)(ΔS), if the values are -ΔH and -ΔS , then what will ΔG be AND what kind of reaction will occur?

Answer 29

-ΔG if T-value is smaller = spontaneous
+ΔG if T-value is larger = nonspontaneous

Question 30

What is the formula for determining the T-value?

Answer 30

T = (ΔH)/(ΔS)

The T-value then tells us the flipping temperature for an equation to turn spontaneous/nonspontaneous.
(ΔG was set to 0, then equation was rearranged to set everything equal to T)

Question 31

What equation do we use to find the ΔG if the reaction isn’t in standard conditions?

Answer 31

ΔG = ΔG* + (R)(T)(lnQ)
ΔG = Gibbs free energy
ΔG* = Standard Gibbs free energy
R = 8.314 J/mol*k
T = temperature (k)
Q = (products/reactants)… ([prA][prB])/([reC][reD])