Unit 6 review (monday)

thermodynamics

the study of energy and its transformations

thermochemistry

the study of the relation between chemical reactions and changes in energy

thermochemical equation

balanced stoichiometric chemical equation that includes the enthalpy change, ΔH

thermochemical equilibrium

temp is uniform throughout a material and no energy flows from one point to another

energy

the capacity to do work (potential energy, kinetic, internal, heat [transfer], work [transfer], chemical, thermal, enthalpy)

Law of Conservation of Energy

Energy can't be created or destroyed, just evolved or transferred (potential --> kinetic; chemical --> thermal)

potential energy

dur to position or composition
PE = m*g*h
m = mass
g = acceleration due to gravity
h = vertical distance

kinetic energy

due to motion of the object
KE = 1/2 mu^2
m = mass
u = velocity

Total energy

Etotal = PE + KE
OR
mgh + 1/2 mu^2

state function

depends only on the difference between initial and final state of the system

Potential energy at the molecular level

molecular compounds have covalent bonds form when electrons are shared by the overlapping of orbitals
- as the 2 atoms move closer together, the energy stored within the bond increases

Energy of chemical reactions

the potential energy from reactants to products indicates whether energy is gained or lost
- P2 + O2 = P4O10 + energy (energy released, exo)
- energy + Ba(OH)2 +2NH4Cl = BaCla2 +2NH4OH (energy absorbed, endo)

Kinetic energy at the molecular level

thermal energy, affected by mass, velocity, and number of particles. as t increases, so does KE!

energy and phase change (absorbed heat)

increases kinetic energy of molecules
melting, evaporating, sublimating

energy and phase change (released heat)

loss of kinetic energy
freezing, condensing, deposition

exothermic

Energy flows out of a system to surroundings

endothermic

energy flows into system from surroundings

first law of thermodynamics

Law of Conservation of
Energy...so energy gained or lost by a system must
equal the energy lost or gained by surroundings

system

the part of the universe that is the focus of a
thermochemical study (isolated /open/closed)

surroundings

everything in the universe that is not
part of the system

open system

can exchange matter and energy with surroundings

closed system

can exchange only energy with surroundings, not matter

isolated system

does not exchange matter nor energy with surroundings

internal energy

sum of all KE and PE of all particles making up a substance of the system
-different types of molecular motion contribute to overall internal energy (translational, rotational, vibrational)

change in internal energy

ΔE = Efinal – Einitial
energy gained/lost by system has to be lost/gained by surroundings

change in internal energy for a closed system

(only energy exchanged with surroundings)
ΔE = q + w
q = heat
w = work
The magnitude of energy changes between system and surroundings are equal magnitutdes by opposite signs (ΔEsys + ΔEsurr = 0)

heat

the energy transferred between objects because of a difference in their temperatures
-sooooo.... the heat lost by one object is gained by another

pressure-volume work

if pressure of system stays constant, but the volume changes:
w = -PΔV
for gases, if chemical eq is given...
wgas = -ΔnRT
R = 8.314 J/mol·K
T = K
Δn = ngas,prod – ngas,react

enthalpy (H)

EXTENSIVE PROPERTY of a substance that can be used to obtain the heat absorbed or evolved in a chemical reaction. the sum of the internal energy and the p-v product
H = E + PV

Change in enthalpy

easier to observe
ΔH = Hfinal - Hinitial
if the conditions maintain constant pressure, for one mol of substance, the heat represents the enthalpy
qP = ΔH
ΔH = ΔE + PΔV

q = nΔH

units for heat are kJ, units for change in enthalpy are kJ/mol

ΔH > 0

Endothermic

ΔH < 0

Exothermic

thermochemical equation

chemical equation for a reaction (w phase labels) in which the equation is given a molar interpretation, and the enthalpy of reaction for these molar amounts is written directly after the equation
(ex: ΔH = -91.8 kJ)

Rules of thermochemical equation manipulation

1)when a chemical equation is reversed, the value of ΔH is reversed in sign
2) when a thermochemical equation is multiplied by any factor, the value of ΔH for the new equation is multiplied by that same factor

molar heat capacity (cp)

the heat required to raise the temp of 1 mol of a substance by 1C at constant pressure
- q = ncpΔT
(cp units: J / (mol∙°C)

specific heat capacity (cs)

the heat required to raise the temp of 1 gram of a substance by 1C at constant pressure
- q = mcsΔT
(cs = J / (g∙°C)

molar heat of fusion

ΔHfus = heat needed to convert 1 mole of a solid at its melting point to 1 mole of liquid
q = nΔHfus

molar heat of vaporization

ΔHvap = heat needed to cobnvert 1 mole of a liquid at its boiling point to 1 mole of vapor
q = nΔHvap