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Flashcards in Thermodynamics: the second law Deck (22)
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1

Define spontaneous change

Spontaneous change is change that requires no work to bring about. The mixing of gases in an isolated system 

2

Define entropy, S

Entropy, S, is a measure of molecular disorder

3

Give the second law of thermodynamics

The total entropy (ie the entropy of the system, ΔS, + the entropy of the surroundings, ΔSSur) increases in the course of a spontaneous change. 

Note: ΔS can be negative as long as ΔSSur is positive enough so that overall Stotal > 0 

4

Give the equation for dStotal, taking temperatures of the system and the surroundings into account 

Define Th, the higher temperature, as the temperature of the system and Tc, the lower temperature, as the temperature of the surroundings. dq is the heat transfer. 

5

Give the equation linking dS and dqreversible

6

Give the equation of ΔS as a state function 

7

Derive the equation of ΔS for the isothermal expansion of an ideal gas 

8

Derive the equation for ΔTrsS at constant temperature and pressure 

(Trs = phase transition)

Remember that reversible phase transitions of pure substances take place at constant temperatures, and dq = dH at constant pressure 

9

Describe Trouton's rule

Trouton observed that the standard molar entropy of vaporisation. ΔvapS0m ~ 85JK-1mol-1 for a wide range of liquids. 

This is due to similar changes in disorder when going from a liquid to a gas. Water is an exception due to the structural order (ie lower entropy) of hydrogen bonds. 

10

Derive the equation of ΔS when a material is heated at constant pressure 

Note that Cp is assumed to be independent of temperature 

11

State the third law of thermodynamics

The entropy of all perfect crystalline substances is zero at T = 0

12

Derive an equation to work out the entropy for any given temperature 

Combining entropy changed upon heating and during phase transitions, we can calculate the entropy for any given temperature 

13

Give the equation for standard reaction entropy

14

Give the equation for the standard reaction enthalpy at T2 if we know the quantity at T1

15

Describe the total entropy change for any irreversible reaction 

16

Describe the total entropy change for any reversible reaction 

17

Give and describe the Clausius inequality

This is a criterion for irreversible/ spontaneous change. It is very useful in judging the spontaneity of chemical reactions 

18

Define G, the Gibbs free energy 

G = H - TS

dG = dH - TdS

Temperature and pressure are constant 

19

Give dG for spontaneous processes

dG < 0

20

Derive dG = Vdp - SdT by combining the first and second laws of thermodynamics 

Note: use the product rule 

21

Derive the equation of the Gibb's free energy at pressure p, where T is held constant. 

Denote G0 as the standard Gibbs free energy 

22

Modify the equation for G(p) for a mixture of gasses, denoting pA and pB as the partial pressures of reactants