unit 10

exothermic (negative)

given off energy to surroundings

endothermic (positive)

absorbed energy from surroundings

endothermic example

melting, evaporation, boiling

exothermic example

freezing, condensing

enthalpy

heat of a system at constant pressure

exothermic heat

would be a product in kJ

delta H reaction

H products - H reactants

Hess’s Law

if you can add 2 or more thermochemical equations to produce a final equation for a reaction, then the sum of enthaply changes for individual reactions is ethnalpy change for final reaction

spontenous

if a reaction occurs without ongoing outside intervention (like work or energy)

spontaneous process

-ice melting above 0

-iron rusting

-sodium chloride dissolving

delta S negative

system becoming more ordered

delta S positive

system becoming less ordered

entropy increases

-phase changes S → L

-phase change S → G

-phase change L → G

-increase in moles of gas

*more gas=more chaos

delta H (-) delta S (+)

always spontaneous

delta H (-) delta S (-)

spontaneous at low temp (do math)

delta H (+) delta S (+)

spontaneous at high temp (do math)

delta H (+) delta S (-)

never sponteous

*

delta G = positive (not spontaneous)

delta G = negative (spontaneous)