Chem Unit 4 Vocab

-ΔG

spontaneous

+ΔG

non-spontaneous

-ΔS

increasing order

+ΔS

increasing disorder

-ΔH

exothermic

+ΔH

endothermic

open system

transfer matter and energy

closed system

transfer only energy, not matter

isolated system

transfer neither energy nor matter

state functions

enthalpy, entropy, Gibbs free energy, only final minus initial

path functions

path matters, heat and work (q and w)

work

path function, concerted/controlled flow of energy, w

heat

path function, chaotic flow of energy, q

extensive properties

additive, volume, mass, energy, moles

intensive properties

defines system, not additive, temperature, pressure, density

first law off thermodynamics

ΔU_universe=0 (energy of universe is conserved)

source of all potential/kinetic energy in a system

U (energy)

calorimetry says:

ΔU_surroundings=-ΔU_system

ΔH=

ΔU+PΔV

in a closed system:

V (volume) is constant, so ΔU=q_v

in an open system:

P (pressure) is constant so ΔH=q_p

calculating internal energy

ΔU=q+w

“do work” means:

negative work, leaving the system

specific heat

heat needed to raise the temp by 1 degree

specific heat increases with:

size, amount, and IMFs

C of water

4

C of most metals

0.3-0.4

if heat added to two compounds is the same:

m₁C₁ΔT₁=m₂C₂ΔT₂

higher change in temperature means:

lower specific heat

work done for gases:

W=PΔV OR W=-ΔN_gRT

positive work

work done on system/by surroundings

negative work

work done by system/on surrounds

equation for warming ( no phase change)

q=mC_phaseΔT

equation for solid melting

q=mΔH_fus

equation for liquid vaporizing

q=mΔH_vap

only time ice and water can exist in equilibrium

0^oC

positive net ΔU, endothermic

negative net ΔU, exothermic

part of a bomb calorimeter:

insulated container, water inside with submerged sample, thermometer, O₂ supply, and ignition box/wires

Bomb calorimetry: igniting the bomb calorimeter…

starts the reaction of the sample

bomb calorimetry: the water serves as…

a heat sink to measure the temperature change

bomb calorimetry: the setup requires…

constant stirring to ensure accurate ΔT

Bomb calorimetry: bomb calorimeters measure…

heat change at a constant volume: ΔU=q_v

bomb calorimetry calculation:

q=mC_waterΔT+C_calΔT

for calorimetry, temperature is in…

celcius

heat of formation rules:

1. produce one mole of a substance

2. reactants are elements in standard state

3. under standard conditions, room temp (298K) and at 1 atm, represented by ^o symbol

number of microstates

number of ways to distribute energy

as number of microstates increases,

disorder/entropy increases

as volume increase,

number of microstates increases

as size/complexity of a molecule increases,

number of microstates increases for trans, vib, and rot. models of motion

if a process happens (spontaneous)…

ΔS of the universe is positive

if a process doesn’t happen

ΔS of the universe is negative

for exothermic processes ΔS of surroundings:

is positive

for endothermic processes ΔS of surroundings:

is negative

things that affect entropy ranking:

phase (most important), size, mixture/pure, ridgidity

how does phase affect entropy?

gas is most, then liquid, then solid

how does size affect entropy?

larger (higher MW) molecules have higher entropy

mixtures are ____ disordered than pure substances

more (so higher entropy)

floppy structures are _____ disordered than ridgid structures

more (so higher entropy)

cyclo-

ring structure, means more ridgid/lower entropy

how does phase change affect entropy?

as you go from solid to liquid to gas, ΔS is positive/entropy and enthalpy increase

other way, ΔS is negative/entropy and enthalpy decrease

how does number of moles affect entropy?

if number of moles increases, entropy is positive

if number of moles decreases, entropy is negative

ΔS of the universe is ______ for spontaneous reactions

positive

for a process to happen, ΔS_univ must…

increase

equation for change in entropy of surroundings:

ΔS_surr=-ΔH_sys/T (T in Kelvin)

an exothermic reaction ____ the entropy of the surroundings

increases

an endothermic reaction _____ the entropy of the surroundings

decreases

pay attention to the ___ in ΔH and ΔS:

units

ΔH is typically in kJ

ΔS is typically in J/K

to calculate Gibbs Free Energy you need:

ΔH_rxn, ΔS_rxn, and T in Kelvin

_____ TΔS by 1000 to convert to joules from kJ

divide

for gibbs free energy, temperature is in:

kelvin

ΔG will typically be very close to:

ΔH (ΔS is usually very small)

when calculating ΔS_rxn and ΔH_rxn, don’t forget:

to multiple by n

combustion reaction

oxygen and hydrocarbon create carbon dioxide and water

combustion reactions are _____ so ΔH is ____

exothermic, negative

sublimation

going from solid to gas

when going from solid to liquid to gas, ΔS:

is positive

when number of moles ___, ΔS is positive

increases

when temperature _____, ΔS is positive

increases

when molecular size ____, ΔS is positive

increases

at low temp:

ΔG (-), ΔH (-), ΔS (-)

at all temps (always happens)

ΔG (-), ΔH (-), ΔS (+)

at all temps (never happens)

ΔG (+), ΔH (+), ΔS (-)

at high temps

ΔG (-), ΔH (+), ΔS (+)

(+) ΔG ____ happens

never

to calculate the transition temp:

T=ΔH/ΔS

at temperatures below the transition temp, a reaction is:

non spontaneous

at temperatures above the transition temp, a reaction is:

spontaneous

compounds are most stable at standard temp that:

have the lowest/most negative gibbs free energy

if the volume of a system increase, work is done ____ the system

by

when a reaction does not involve a change in gas volume, ___ is similar to ___

ΔU, ΔH

in an open system, ΔH accounts for:

work done against the atmospheric pressure

combustion reactions are ____ so they ____ energy in joules

exothermic, lose

internal energy is a ____ function and _____

state, extensive