Chemical Thermodynamics

Lesson

Part 1 — how energy moves as heat and work when matter changes, and how to keep an exact account of it.

In this lesson you will

Distinguish types of system and identify state functions
Apply the IUPAC sign convention to work and heat, and calculate expansion work
State and apply the first law, ΔU = q + w
Relate ΔH and ΔU, and use heat capacities with C_p − C_v = R

Table of four everyday changes and the thermodynamic question each raises
Everyday change	Energy question thermodynamics asks
Cooking gas burns	How much heat is released per mole?
A cold pack cools your ankle	Why does dissolving absorb heat?
A piston in a petrol engine	How much work can the gas do?
Ice melts in a warm room	Why does it happen by itself?

Concept

System, surroundings and types of system

The part of the universe we study is the system; everything else that can exchange energy with it is the surroundings. The system is separated by a boundary, real or imaginary.

Table comparing open, closed and isolated systems by exchange of matter and energy, with an example of each
Type	Matter exchange	Energy exchange	Example
Open	Yes	Yes	Tea in an uncovered cup
Closed	No	Yes	Sealed boiling tube in a water bath
Isolated	No	No	Tea in a good vacuum flask (approximately)

Concept

State functions and path functions

A state function depends only on the present state of the system, not on how it got there. Heat and work are path functions: their values depend on the route taken.

Table contrasting state functions such as U, H, S and G with path functions heat and work
State functions	Path functions
$p,\ V,\ T,\ U,\ H,\ S,\ G$	$q,\ w$
Change depends only on initial and final states	Change depends on the path
Round trip gives zero change	Round trip need not give zero
Exact differential	Inexact differential

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