unit 3 thermodynamics Flashcards
spontaneous
proceeds without assistance, temp and pressure affect the spontaneity
enthalpy
heat absorbed by a system during constant pressure
entropy and 5 things that affect it
measure of randomness in a system. volume and temp affect entropy, along with # independently moving molecules, molar mass, and # of atoms in formula
1st law of thermodynamics
energy is neither created nor destroyed
2nd law of therm
entropy of the universe increases in any process
what are the types of molecule motion?
transitional, vibrational, rational
how do you calculate spontaneity
when delta G is negative it is spontaneous, when G is positive it will never never never happen ever like at all.
endothermic
heat lost from surroundings
exothermic
heat gained in surroundings
what is a system?
products and reactants
what are surroundings?
literally everything else other than prod + react
how to see exothermic in a graph
getting more stable, downwards arrow, heat released, less energy = more stable
how to see endothermic in a graph?
getting less stable, heat absorbed, upwards arrow, less energy = more stable
how to tell type of reaction from H?
- is exothermic, + is endothermic
hess’ law
if a reaction is done in steps, delta H = sum of enthalpy from smaller reactions bc H is a state function, the journey doesn’t matter only the destination
most important part of a therm question
checking the equation is equal and balances
what are average bond enthalpie?
need energy to break bonds. endothermic, the average amount of energy required to break a mol. most accurate when it involves breaking only a few bonds.
how to use bond enthalpy to estimate delta H
make chemical equation, draw lewis structure, count the bonds broken in the products (+) and the bonds formed in the reactants (-), add them together
how to tell something is combustion
it has o2 as a product
lattice enthalpy
H needed to break something into its components.
what does it mean when a reaction gives out heat,
it is exothermic, the bonds made are greater than the bonds broken
what is Gibbs free energy?
the amount of energy available to do useful work
how to calculate heat
q= MC[delta]T
how to calculate entropy
delta S= delta S final - delta S initial
what is the Gibbs free energy equation?
delta G= delta H- T delta S
what is the heat capacity for water?
4.186
what is the calculation for enthalpy?
-Q/mol
when H - and S +
spontaneous at all temps
when H + and S -
non spontaneous ever
when H - and S -
spontaneous at only low temps
when H + and S +
spontaneous at only high temps
when is S -
when disorder goes down, endothermic reaction, energy is used .
