Thermodynamics chemistry Flashcards
Define the First Law of Thermodynamics.
The First Law states that energy cannot be created or destroyed, only transformed. Mathematically,
Ξ
π
=
π
+
π€
ΞU=q+w (change in internal energy = heat added + work done)
What is internal energy?
Internal energy (
π
U) is the total energy contained within a system, including kinetic and potential energies of the molecules.
Explain the Second Law of Thermodynamics
The Second Law states that the total entropy of an isolated system can never decrease over time; it can only increase or remain constant.
What is entropy?
Entropy (
π
S) is a measure of the disorder or randomness in a system. It quantifies the number of microscopic configurations that correspond to a thermodynamic systemβs macroscopic state.
Define the Third Law of Thermodynamics.
The Third Law states that as the temperature of a system approaches absolute zero, the entropy of a perfect crystal approaches zero.
What is the difference between an isothermal process and an adiabatic process?
In an isothermal process, the temperature remains constant (
Ξ
π
=
0
ΞT=0), while in an adiabatic process, there is no heat exchange with the surroundings (
π
=
0
q=0
What is enthalpy?
Enthalpy (
π»
H) is the total heat content of a system, defined as
π»
=
π
+
π
π
H=U+PV, where
π
P is pressure and
π
V is volume
Write the equation for calculating work done in an isothermal expansion of an ideal gas
W=βnRTln(
V
i
β
V
f
β
β
), where
π
n is the number of moles,
π
R is the gas constant,
π
π
V
f
β
is the final volume, and
π
π
V
i
β
is the initial volume
What is a state function?
A state function is a property whose value depends only on the state of the system, not on how it reached that state (e.g., internal energy, enthalpy, entropy).
Explain Gibbs Free Energy (
πΊ
G)
Gibbs Free Energy is defined as
πΊ
=
π»
β
π
π
G=HβTS. It indicates the spontaneity of a process; a negative
Ξ
πΊ
ΞG signifies a spontaneous reaction.
What is the significance of a negative
Ξ
πΊ
ΞG?
A negative
Ξ
πΊ
ΞG indicates that a reaction is spontaneous at constant temperature and pressure
What is the relationship between enthalpy and heat in a constant pressure process?
In a constant pressure process, the change in enthalpy (
Ξ
π»
ΞH) is equal to the heat absorbed or released (
π
π
q
p
β
):
Ξ
π»
=
π
π
ΞH=q
p
β
What does it mean for a reaction to be exothermic?
An exothermic reaction releases heat to the surroundings, resulting in a negative
Ξ
π»
ΞH.
What does it mean for a reaction to be endothermic?
An endothermic reaction absorbs heat from the surroundings, resulting in a positive
Ξ
π»
ΞH
What is calorimetry?
Calorimetry is the measurement of heat transfer during a chemical reaction or physical change, typically using a calorimeter.
How is the heat capacity of a substance defined?
Heat capacity is the amount of heat required to raise the temperature of a substance by 1 degree Celsius (or 1 Kelvin)
Differentiate between molar heat capacity and specific heat capacity.
Molar heat capacity is the heat capacity per mole of a substance, while specific heat capacity is the heat capacity per unit mass.
What is Hessβs Law?
Hessβs Law states that the total enthalpy change in a reaction is the sum of the enthalpy changes for the individual steps, regardless of the pathway taken.
Define standard enthalpy of formation (
Ξ
π»
π
β
ΞH
f
β
β
).
The standard enthalpy of formation is the enthalpy change when one mole of a compound is formed from its elements in their standard states.
What is the standard state of a substance?
The standard state is defined as the most stable form of a substance at 1 bar (or 1 atm) pressure and a specified temperature (usually 25Β°C).
Explain the concept of reversible and irreversible processes.
A reversible process can be reversed without leaving any trace on the surroundings, while an irreversible process cannot be reversed without external work and produces changes in the surroundings.
What is the significance of
Ξ
π
ΞS in a chemical reaction?
A positive
Ξ
π
ΞS indicates an increase in disorder and spontaneity, while a negative
Ξ
π
ΞS indicates decreased disorder.
Write the equation for calculating
Ξ
πΊ
ΞG using enthalpy and entropy
ΞG=ΞHβTΞS, where
π
T is the absolute temperature in Kelvin.
What is the critical point in thermodynamics?
The critical point is the temperature and pressure at which the distinction between liquid and gas phases disappears, resulting in a supercritical fluid.
Define extensive and intensive properties
Extensive properties depend on the amount of substance (e.g., mass, volume), while intensive properties do not (e.g., temperature, pressure)
Explain the concept of thermal equilibrium
Thermal equilibrium occurs when two objects at different temperatures come into contact, and heat transfer ceases when they reach the same temperature
What is meant by the term βspontaneous processβ?
A spontaneous process is one that occurs without external intervention, typically characterized by a decrease in Gibbs Free Energy (
Ξ
πΊ
<
0
ΞG<0).
What is the difference between a system and its surroundings?
A system is the part of the universe being studied, while the surroundings are everything outside the system that can exchange energy or matter with it.
What are the units of enthalpy?
The SI unit of enthalpy is joules (J), but it is often expressed in kilojoules per mole (kJ/mol) in chemistry.
Describe what happens during an isochoric process
In an isochoric process, the volume of the system remains constant, and therefore no work is done (
π
=
0
W=0). The change in internal energy equals the heat added
What is the heat of reaction?
The heat of reaction is the change in enthalpy (
Ξ
π»
ΞH) that occurs during a chemical reaction at constant pressure.
How does the heat capacity of a substance vary with temperature?
The heat capacity of a substance typically increases with temperature, as more energy is required to increase the kinetic energy of particles at higher temperatures.
Define the term βlatent heat.β
Latent heat is the heat absorbed or released during a phase change (e.g., melting, boiling) at constant temperature, without a change in temperature
What is the significance of the enthalpy of vaporization?
The enthalpy of vaporization is the amount of energy required to convert one mole of a liquid into a gas at constant temperature and pressure.
What is the relationship between
Ξ
π»
ΞH and
Ξ
πΈ
ΞE for reactions at constant pressure?
The relationship is given by
Ξ
π»
=
Ξ
πΈ
+
π
Ξ
π
ΞH=ΞE+PΞV, where
Ξ
π
ΞV is the change in volume
Describe the term βwork doneβ in thermodynamics.
Work done by the system is the energy transferred when the system exerts a force over a distance, typically expressed as
π
=
β
π
Ξ
π
W=βPΞV for expansion work
What is the Clausius-Clapeyron equation?
The Clausius-Clapeyron equation relates the change in vapor pressure with temperature to the enthalpy of vaporization. It is given by
π
π
π
π
=
Ξ
π»
π£
π
π
π
Ξ
π
dT
dP
β
=
TΞV
ΞH
vap
β
β
, where
Ξ
π»
π£
π
π
ΞH
vap
β
is the enthalpy of vaporization and
Ξ
π
ΞV is the change in volume during the phase transition.
Define the standard entropy change (
Ξ
π
β
ΞS
β
) of a reaction
The standard entropy change is the change in entropy when all reactants and products are in their standard states (1 bar, usually at 298 K). It is calculated as
Ξ
π
β
=
β
π
π
π
π
π
π’
π
π‘
π
β
β
β
π
π
π
π
π
π‘
π
π
π‘
π
β
ΞS
β
=βS
products
β
β
ββS
reactants
β
β
.
What is the significance of the Helmholtz Free Energy (
π΄
A)
Helmholtz Free Energy (
π΄
=
π
β
π
π
A=UβTS) is a thermodynamic potential that measures the useful work obtainable from a closed system at constant volume and temperature. It is used primarily in physics.
Explain what is meant by the term βphase equilibrium.
Phase equilibrium occurs when the phases of a substance coexist at equilibrium, with no net change in the amounts of each phase. This condition is characterized by equal chemical potentials for all phases involved.
