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thermal energy
results from motion of molecules
heat
amount of energy transferred between substances
exothermic
energy releasing -
endothermic
energy requiring +
temperature
average kinetic energy of the particles in a sample of matter
opne system
matter and energy can change
closed system
mattter can’t change but energy can
isolated systen
neither matter nor energy can change
bomb vs cup calorimeter
bomb measures combustion and has water not directly in contact with the system
molar enthalpy
enthalpy chnage per mole of a reaction (h=nh^o)
what are thr 3 calorimeter assumptions
no heat transferred to environment
any heat absorbed or released by the cal is negligable
a dilute solution has heat capacity and density of water
thermochemical equation
represent enthalpy of reaction within the equation
method 2 of representing H: beside equation
negative for exo positive for endo, and in kJ/mol
standard molar enthalpy of reaction
Standard molar enthalpies allow chemists to create tables to compare enthalpy values. ° "nought" represents enthalpy change of a chemical reaction
that occurs at SATP (25°C and 100 kPa)
enthalpy
shows E(kJ) over the reaction progress
state function
path independant; change in altitude relys only on the difference between start and end
hess’s law
H can be written in steps and is equal to the sum of the enthalpy of each individual step
using the 3rd means of showing enthalpy
use a balanced equation of formation for exact;y 1 mol of the compound of interest. then enthaply = ehtalpy products - enthalpy reactants
must add standard states to equation as well
enthalpy of elements in standard state
in standard state, the enthalpy of a substance is just 0. eg o2, Na, Cl2
exmaples of potential energies
bond energy, nuclear pe of protons and neutrons
exmaples of kinetic energy
motion of elections, vibrations, rotations and translation of atoms and molecules
enthalpt change: physical change
10^0-10² kj/mol overcoming intermolecular force; particles remain unchanges
enthalpy change, chemical change
10² - 10^4 kJ/mol. overcoming electronic structure + bonds; new substance with nre bonds eg combustion
enthalpy change: nuclear change
10^10 - 10^12 kj/mol. overcome forces between protons and nucleus; new atoms form eg nuclear decay
spontaneous reaction
given the necessary activation energy, proceeds without continuous assitance on an open system
non- spontaneous
contiuous supply of energy is needed to sustain the reaction
what is entropy
disorder or randomness, entropy increases when disorder increases; S = Sproducts - Sreactants
predicting entropy
s is positive when there is increasing disorder (volume increases, temp increase, state change from less movement to more, more moles of products than reactants, mixing/dissolving,complex molecule being broken down)
first law of thermodynamics
total e in the universe is constant, e is not created nor destroyed, but can be transfered or transformed
second law of thermodyanmics
total entropy of the universe is constantly increases. suniverse = ssystem+ssurrounding
if Suniverse is positive
a process is spantaneous in the direction written
if SUniverse is negative
a process is spantanrous in the oppsoite direction than written
if SUniverse = 0
no tendancy to occur and system at equilibrium
entropy of a reaction:
sum of products - sum of reactants
gibbs free energy
energy available to do useful work. DECREASES when a reaction is spantaneous (negative for spontaneous)
G>0
spantenous for reverse reaction
G<0
spantaneous as written
G=0
no reaction
equation for gibs free energy (h-TS) uses… for temp
kelvins (273k+C)