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Wize University Chemistry Textbook > Thermodynamics: Part 1: (0th law, 1st law, Calorimetry, Enthalpy)

Introduction to Thermodynamics

Condensation ReactionsPrevious Section
0th Law of ThermodynamicsNext Section
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Key Terms

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System Vs Surroundings

System-reactants and products that are part of the chemical reaction







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Open Vs Closed Vs Isolated Systems


Examples:
  • open system → cup of coffee
  • closed system → bottle of pop
  • isolated system → perfect thermos
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State Variables

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State variable (aka state function): is a variable that depends only on the current state of a system, NOT on the path taken to that state.

Example:

Is the distance travelled or change in altitude a state function?

The change in altitude is a state function because no matter which pathway was taken (walking or helicopter, the change in altitude was the same).
Distance is not a state function because when there was a different pathway taken, there was a different distance travelled!
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Example: State Variables

Which of the following variables are state variables? Label each as yes or no.

a) mass
yes

b) temperature
yes

c) work
no

d) pressure
yes

e) volume
yes

f) density
yes

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Extensive vs. Intensive Properties

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Extensive properties: depend on the extent (or amount) of a substance

Examples: mass, volume, amount of heat released in a combustion reaction

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Intensive properties: does not depend on the amount of substance

Examples: melting point, boiling point, density

Think* no matter how much water you are boiling in a pot, water will always boil at 100oC and melt at 0oC!


When we take a ratio of 2 extensive properties what do we get?
An intensive property!

Example: mass/volume=density

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Additional Terminology


Reversible Process: The system is at equilibrium (and the reaction can go in either direction).

Example: N2(g) + 3H2(g) ⇌ 2NH3(g)


Irreversible Process: The system is not at equilibrium and proceeds in one direction only. This reaction is spontaneous in the forward direction.

Example: C3H8(g)+5O2(g)→3CO2(g) + 4H2O(g)C_3H_8\left(g\right)+5O_2\left(g\right)\rightarrow3CO_2\left(g\right)^{^{^{ }}}\ +\ 4H_2O\left(g\right) (combustion reaction)


Spontaneous Process: An irreversible process that has a predetermined direction.

Example: An egg shell breaks during birth

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Isothermal: There is no change in temperature for the system
ΔT=0\Delta T=0
For Ideal Gases: ΔU=0,ΔH=0\text{For Ideal Gases: } \Delta U=0, \Delta H=0
Isobaric: There is no change in pressure
Δp=0\Delta p=0
Isochoric: There is no change in volume
ΔV=0\Delta V=0
Adiabatic: No heat exchange (no heat enters or leaves the system)
q=0q=0
Exothermic: A Process in which heat is
released
(absorbed/released) to the
surroundings
(system/surroundings)
q<0q<0

Endothermic: A Process in which heat is
absorbed
(absorbed/released) into the the
system
(system/surroundings)
q>0q>0

Standard Conditions: Pressure of all gases is 1 atm, all solutions have 1M concentration, and temperature is 298K (25C). This is denoted as Ho So Go etc.