thermodynamics Flashcards
thermodynamics definition
transformation of energy from one form to another
zeroth law
when systems are in thermal equilibrium with one another, their temperatures must be the same
first law
energy can’t be created or destroyed
three designations for energy flow
system, surroundings, thermodynamic universe
system + surroundings = universe
Rules for energy flow
when energy flows into a system from the surroundings, energy of system increases and energy of surroundings decreases
when energy flows out of a system into surroundings, energy of system decreases and energy of surroundings increases
enthalpy
measure of the heat energy that is released or absorbed when bonds are broken and formed during a reaction that’s run at constant pressure
heat energy (H) when bonds are formed and broken
delta H < 0 when bonds are formed
delta H > 0 when bonds are broken
exothermic vs endothermic
exothermic - more energy released in the making of products bonds than was put in to break the reactant bonds
endothermic - more energy put in during breaking of reactant bonds than released during formation of product bonds
standard conditions
temp = 298K (25 degrees C), pressure = 1 atm
all solids and liquids are assumed to be pure and solutions are considered to be at a concentration of 1 M
standard heat of formation
amount of energy required to make one mole of a compound from its constituent elements in their natural or standard state
Hess’s Law
if a reaction occurs in several steps, then the sum of the energies absorbed or given off in all the steps will be the same as that for the overall reaction
formula for delta Hrxn
(sum of the bond dissociation energy of bonds broken) - (sum of bond dissociation energy of bonds formed)
second law of thermodynamics
all processes tend to run in a direction that leads to maximum disorder
entropy
used to measure disorder or randomness
delta S is negative is randomness decreases, positive if
randomness increases
phase entropies
gas>liquid>solid
third law of thermodynamics
absolute zero is defined to be a state of zero entropy
Kelvin = 0, S=0
Gibb’s Free Energy
energy that is free to do useful work from a chemical reaction
delta G = delta H - T(delta S)
T = absolute temp in kelvins
Gibbs free energy rules
delta G < 0, spontaneous in forward direction
delta G = 0, reaction is at equilibrium,
delta G >0 nonsnpontaneous in forward direction
thermodynamics vs kinetics
thermodynamics predicts spontaneity and equilibrium of reaction
kinetics predicts rate of reaction