Introduction to Thermodynamics

State Variables

The following lesson is low yield in terms of exams. We'll just focus on understanding. 💡

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?

Example: State Variables

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

a) mass ________

b) temperature ________

c) work ________

d) pressure ________

e) volume ________

f) density ________

Extensive vs. Intensive Properties

The following lesson is low yield in terms of exams. We'll just focus on understanding. 💡

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

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

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?

________

Example: mass/volume=density

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: $C_3H_8\left(g\right)+5O_2\left(g\right)\rightarrow3CO_2\left(g\right)^{^{^{ }}}\ +\ 4H_2O\left(g\right)$ (combustion reaction)

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

Example: An egg shell breaks during birth

Isothermal: There is no change in temperature for the system

$\Delta T=0$

$\text{For Ideal Gases: } \Delta U=0, \Delta H=0$

Isobaric: There is no change in pressure

$\Delta p=0$

Isochoric: There is no change in volume

$\Delta V=0$

Adiabatic: No heat exchange (no heat enters or leaves the system)

$q=0$

Exothermic: A Process in which heat is ________ (absorbed/released) to the ________ (system/surroundings)

$q<0$

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

$q>0$

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.