Chapter 7: Thermochemistry (7%)

isolated systems

Isolated vs. Closed vs. Open Systems

Cannot exchange matter or energy (heat and work) with the environment

EX: an insulated bomb calorimeter

closed systems

Isolated vs. Closed vs. Open Systems

Can exchange energy (heat and work) but not matter with the environment

EX: a steam radiator

open systems

Isolated vs. Closed vs. Open Systems

Can exchange both energy (heat and work) and matter with the environment

EX: 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 1st Law of Thermodynamics

isothermal processes

Isothermal vs. Adiabatic vs. Isobaric vs. Isovolumetric (Isochoric) Processes

Occur at a constant temperature

1st Law of Thermodynamics ΔU = Q - W simplifies to Q = W

adiabatic processes

Isothermal vs. Adiabatic vs. Isobaric vs. Isovolumetric (Isochoric) Processes

Exchange no heat with the environment

1st Law of Thermodynamics ΔU = Q - W simplifies to ΔU = - W

isobaric

Isothermal vs. Adiabatic vs. Isobaric vs. Isovolumetric (Isochoric) Processes

Occur at constant pressure

Do not alter the 1st Law of Thermodynamics (remains as ΔU = Q - W)

isovolumetric processes (isochoric)

Isothermal vs. Adiabatic vs. Isobaric vs. Isovolumetric (Isochoric) Processes

Occur at a constant volume

1st Law of Thermodynamics ΔU = Q - W simplifies to ΔU = Q

state functions

State Functions vs. Process Functions

Properties of a system that depend only on the system's current condition (initial and final states) and not on the specific path or process taken to get there

Describe the physical properties of a system in an equilibrium state

Pathway independent

EX: temperature, pressure, volume, internal energy, enthalpy, entropy, density, Gibbs free energy

process functions

State Functions vs. Process Functions

Quantities that describe the transition between equilibrium states of a system

Describe the pathway taken from one equilibrium to another

Pathway dependent

EX: work (W), 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)

Gas (g) vs. Liquid (l) vs. Solid (s)

the standard state of H₂

liquid (l)

Gas (g) vs. Liquid (l) vs. Solid (s)

the standard state of H₂O

solid (s)

Gas (g) vs. Liquid (l) vs. Solid (s)

the standard state of NaCl

gas (g)

Gas (g) vs. Liquid (l) vs. Solid (s)

the standard state of O₂

solid (s) (graphite)

Gas (g) vs. Liquid (l) vs. Solid (s)

the standard state of C

melting (fusion), freezing (crystallization or solidification)

Phase Changes

WORD BANK: Sublimation, Condensation, Deposition, Freezing (Crystallization or Solidification), Vaporization (Evaporation or Boiling), Melting (Fusion)

——

the phase changes that occur at the boundary between the SOLID and the LIQUID phases (2)

vaporization (evaporation or boiling), condensation

Phase Changes

WORD BANK: Sublimation, Condensation, Deposition, Freezing (Crystallization or Solidification), Vaporization (Evaporation or Boiling), Melting (Fusion)

——

the phase changes that occur at the boundary between the LIQUID and the GAS phases (2)

sublimation, deposition

Phase Changes

WORD BANK: Sublimation, Condensation, Deposition, Freezing (Crystallization or Solidification), Vaporization (Evaporation or Boiling), Melting (Fusion)

——

the phase changes that occur at the boundary between the SOLID and GAS phases (2)

critical point

Phase Changes

The temperature above which the liquid and gas phases are indistinguishable

triple point

Phase Changes

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

temperature, pressure

Phase Changes

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)

Endothermic vs. Exothermic

Processes in which the system ABSORBS heat

exothermic (ΔQ < 0)

Endothermic vs. Exothermic

Processes in which the system RELEASES heat

pressure

Enthalpy (ΔH) of a system is = to heat flow (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 (mass x specific heat x change in temperature)

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

specific heat (c)

The amount of energy required to raise the temperature of 1g of a substance by 1°C (or Kelvin)

temperature

Phase change reactions do NOT undergo changes in _____________

q = mL (mass x latent heat of formation)

Write out the formula for calculating the amount of heat transfer/energy (q) (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

Equivalent to the total heat content of a system

It is equal to the internal energy of the system plus the product of pressure and volume

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

positive, negative

Positive vs. 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 = to the changes in __________ _________ of all the individual steps of the process (aka the enthalpy changes are additive)

The total enthalpy change of a chemical reaction is the same, regardless of whether the reaction occurs in one step or several

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

endothermic, exothermic

Exothermic vs. Endothermic

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

A ratio of heat transferred per mole per unit Kelvin

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

(Qrev / T)

Write out the formula for calculating entropy (ΔS)

increases

Increases vs. Decreases

When energy is distributed INTO a system at a given temperature, the entropy of the system ____________

decreases

Increases vs. Decreases

When energy is distributed OUT OF a system at a given temperature, the entropy of the system ____________

maximized

Minimized vs. Maximized

Entropy is ____________ at equilibrium

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 2nd Law of Thermodynamics

ΔH - TΔS

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

<0 (negative)

<0 vs. =0 vs. >0

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

=0

<0 vs. =0 vs. >0

ΔG for when a reaction is in dynamic equilibrium

>0 (positive)

<0 vs. =0 vs. >0

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 process is SPONTANEOUS at HIGH T (temps in Kelvin)?

+, -

What are the signs of ΔH and ΔS when a process is NONSPONTANEOUS at ALL T (temps in Kelvin)?

-, +

What are the signs of ΔH and ΔS when a process is SPONTANEOUS at ALL T (temps in Kelvin)?

-, -

What are the signs of ΔH and ΔS when a process 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 K_eq (ΔG°_rxn = ?)

RT x ln(Q/Keq)

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

<0 (negative)

<0 vs. =0 vs. >0

ΔG for when K_eq > 1

=0

<0 vs. =0 vs. >0

ΔG for when K_eq = 1

>0 (positive)

<0 vs. =0 vs. >0

ΔG for when K_eq < 1