Chapter 7: Thermochemistry (7%)

isolated

systems that cannot exchange matter or energy (heat and work) with the environment; an example is an insulated bomb calorimeter

closed

systems that can exchange energy (heat and work) but not matter with the environment; an example is a steam radiator

open

systems that can exchange both energy (heat and work) and matter with the environment; an example is a pot of boiling water

change in system’s internal energy = heat added to system - work done by system (ΔU = Q - W)

write out the formula for the first law of thermodynamics

isothermal

processes that occur at a constant temperature; first law of thermodynamics ΔU = Q - W simplifies to Q = W

adiabatic

processes that exchange no heat with the environment; first law of thermodynamics ΔU = Q - W simplifies to ΔU = - W

isobaric

processes that occur at constant pressure; these processes do not alter the first law of thermodynamics

isovolumetric (isochoric)

processes that occur at a constant volume; first law of thermodynamics ΔU = Q - W simplifies to ΔU = Q

physical properties, equilibrium, pathway

State functions describe the _________ __________ of a system in an ________________ state. They are __________ independent.

state functions

________ ___________ include pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy

process functions

__________ __________ describe the pathway taken from one equilibrium to another; include work (W) and heat (Q)

298K, 1atm, 1M

state the temperature, pressure, and concentration defined as standard conditions

standard state

The ___________ _______ of an element is its most prevalent form under standard conditions

gas (g)

the standard state of H₂

liquid (l)

the standard state of H₂O

solid (s)

the standard state of NaCl

gas (g)

the standard state of O₂

solid (s, graphite)

the standard state of C

melting (fusion), freezing (crystallization or solidification)

the phase changes that occur at the boundary between the solid and the liquid phases (2)

vaporization (evaporation or boiling), condensation

the phase changes that occur at the boundary between the liquid and the gas phases (2)

sublimation, deposition

the phase changes that occur at the boundary between the solid and gas phases (2)

critical point

the temperature above which the liquid and gas phases are indistinguishable

triple point

the temperature at which all 3 phases of matter exist in equilibrium

temperature, pressure

the phase diagram for a system graphs the phases and phase equilibria as a function of ________________ and ___________

temperature

a scaled measure of the average kinetic energy of the particles of a substance

increases

when a substance’s thermal energy increases, its temperature ___________

heat

the transfer of energy from one substance to another as a result of their differences in temperature

endothermic (ΔQ > 0)

processes in which the system absorbs heat are called ___________

exothermic (ΔQ < 0)

processes in which the system releases heat are called ___________

pressure

Enthalpy (ΔH) is equivalent to heat (Q) under constant __________

warmer, cooler

When substances of different temperatures are brought into thermal contact with each other, energy will move from the _________ substance to the _________ substance

q = mcΔT

write out the formula for calculating the amount of heat transfer (aka heat absorbed/released) NOT during a phase change

specific heat

the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius (or Kelvin)

temperature

Phase change reactions do NOT undergo changes in ________________

q = mL

write out the formula for calculating the amount of heat transfer (aka heat absorbed/released) during a phase change

enthalpy

a measure of the potential energy of a system found in intermolecular attractions and chemical bonds

positive, negative

Endothermic reactions have a ___________ ΔH_rxn while exothermic reactions have a ___________ ΔH_rxn

enthalpy of products - enthalpy of reactants

write out the formula for calculating the generalized enthalpy of a reaction (ΔH_rxn = ?)

potential energy, potential energies

Hess’s Law states that the total change in __________ _________ of a system is equal to the changes in __________ _________ of all the individual steps of the process (aka the enthalpy changes are additive)

magnitude, sign

The enthalpy change for the reverse of any reaction has the same _____________ but the opposite _____ as the enthalpy change for the forward reaction

enthalpy

this can also be calculated using heats of formation, heats of combustion, or bond dissociation energies

endothermic, exothermic

bond breakage is generally _____________ while bond formation is generally _____________

entropy

a measure of the degree to which energy has been spontaneously spread throughout a system or between a system and its surroundings

heat gained or lost in a reversible process / temperature in Kelvin

(Qrev / T)

write out the formula for calculating entropy (ΔS)

increases

When energy is distributed into a system at a given temperature, its entropy ____________

decreases

When energy is distributed out of a system at a given temperature, its entropy ____________

heat transferred

Entropy is a ratio of ______ ___________ per mole per unit Kelvin

equilibrium

Entropy is maximized at _____________

entropy of the universe = entropy of the system + entropy of the surroundings > 0 (aka the entropy of the universe is increasing)

write out the formula for the second law of thermodynamics

ΔH - TΔS

write out the formula for Gibbs free energy (ΔG = ?)

<0 (negative)

ΔG for when a reaction proceeds in the forward direction towards equilibrium (spontaneous & exergonic)

=0

ΔG for when a reaction is in dynamic equilibrium

>0 (positive)

ΔG for when a reaction proceeds in the reverse direction away from equilibrium (nonspontaneous & endergonic)

temperature

Gibbs free energy depends on _______________

+, +

What are the signs of ΔH and ΔS when a processes is spontaneous at high T (temps in Kelvin)?

+, -

What are the signs of ΔH and ΔS when a processes is nonspontaneous at all T (temps in Kelvin)?

-, +

What are the signs of ΔH and ΔS when a processes is spontaneous at all T (temps in Kelvin)?

-, -

What are the signs of ΔH and ΔS when a processes is spontaneous at low T (temps in Kelvin)?

-RT x ln(Keq)

write out the formula for calculating the standard Gibbs free energy from the equilibrium constant (ΔG°_rxn = ?)

RT x ln(Q/Keq)

write out the formula for calculating the Gibbs free energy from the reaction quotient (ΔG_rxn = ?)

<0 (negative)

ΔG for when Keq > 1

=0

ΔG for when Keq = 1

>0 (positive)

ΔG for when Keq < 1