lecture 2 Flashcards
what does an extensive variable depend on
depends on the amount of material
(in grams or moles)
extensive variable example
heat
work
energy
mass
volume
hmv we : depends on size/amount of material
what is an intensive variable
a variable that doesn’t depend on amount of material
examples of an intensive variable
pressure
temperature
molar quantities
how is a molar quantity an intensive variable
the quantity per mole doesn’t change
molar internal energy quantities don’t change with amount of reactants
what is work
ordered/ organised motion
what are the 2 forms of motion
mechanical (atom motion)
electrical current ( e- movement )
force of magnitude is
|F|
equation for work required to move an object a distance ( 🔺d) against an opposing force of magnitude.
🔺w = - |F| 🔺d
what is expansion work
how temperature changes when gases expand
what must we first consider with expansion work
we say that that the external pressure is constant
ignore the effects of gravity or friction
what is force of magnitude
|F| = external pressure x the Area ur pushing against
all 3 equations for change in work
🔺w = - |F| 🔺d
🔺w = - Pext x A x 🔺d
🔺w = - Pext x 🔺Volume
what is work caused by
the gas expanding + pushing the piston of area ‘A’ against the external pressure by distance, D
organised motion
what is ‘wrong’ with expansion work
the external pressure is not constant
equation for work when external pressure slightly changes
dw = - Pext x dV
infinitesimally small change in volume
what is change in volume and why can this be done
🔺V = Vf - Vi
bc volume is a state function
what is a state function
when the current value is independent of the path to get there
state function examples
volume, pressure, temperature, internal energy, enthalpy, entropy, free energy
why are heat and work not state functions
their change is based on how u get from initial to final values
how do u maximise work
reversibility + equilibrium
what conditions must be met for the piston to be moved
the external pressure must be smaller than the internal pressure
in order for the most work to be done, external pressure must be as close to internal as possible while still being lower.
what does performing the expansion with equilibrium conditions + it being reversible do
allows the external pressure to vary infinitesimally at each stage, while allowing it to always be smaller than the internal pressure.
external pressure equation
Pext = Pint + dp
the few integration equations are nkr added to look back at notes to see them 🤞🏼
