Thermodynamics chemistry

Question 1

Define the First Law of Thermodynamics.

Answer 1

The First Law states that energy cannot be created or destroyed, only transformed. Mathematically,
Δ
𝑈
=
𝑞
+
𝑤
ΔU=q+w (change in internal energy = heat added + work done)

Question 2

What is internal energy?

Answer 2

Internal energy (
𝑈
U) is the total energy contained within a system, including kinetic and potential energies of the molecules.

Question 3

Explain the Second Law of Thermodynamics

Answer 3

The Second Law states that the total entropy of an isolated system can never decrease over time; it can only increase or remain constant.

Question 4

What is entropy?

Answer 4

Entropy (
𝑆
S) is a measure of the disorder or randomness in a system. It quantifies the number of microscopic configurations that correspond to a thermodynamic system’s macroscopic state.

Question 5

Define the Third Law of Thermodynamics.

Answer 5

The Third Law states that as the temperature of a system approaches absolute zero, the entropy of a perfect crystal approaches zero.

Question 6

What is the difference between an isothermal process and an adiabatic process?

Answer 6

In an isothermal process, the temperature remains constant (
Δ
𝑇
=
0
ΔT=0), while in an adiabatic process, there is no heat exchange with the surroundings (
𝑞
=
0
q=0

Question 7

What is enthalpy?

Answer 7

Enthalpy (
𝐻
H) is the total heat content of a system, defined as
𝐻
=
𝑈
+
𝑃
𝑉
H=U+PV, where
𝑃
P is pressure and
𝑉
V is volume

Question 8

Write the equation for calculating work done in an isothermal expansion of an ideal gas

Answer 8

W=−nRTln(
V
i
​

V
f
​

​
), where
𝑛
n is the number of moles,
𝑅
R is the gas constant,
𝑉
𝑓
V
f
​
is the final volume, and
𝑉
𝑖
V
i
​
is the initial volume

Question 9

What is a state function?

Answer 9

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).

Question 10

Explain Gibbs Free Energy (
𝐺
G)

Answer 10

Gibbs Free Energy is defined as
𝐺
=
𝐻
−
𝑇
𝑆
G=H−TS. It indicates the spontaneity of a process; a negative
Δ
𝐺
ΔG signifies a spontaneous reaction.

Question 11

What is the significance of a negative
Δ
𝐺
ΔG?

Answer 11

A negative
Δ
𝐺
ΔG indicates that a reaction is spontaneous at constant temperature and pressure

Question 12

What is the relationship between enthalpy and heat in a constant pressure process?

Answer 12

In a constant pressure process, the change in enthalpy (
Δ
𝐻
ΔH) is equal to the heat absorbed or released (
𝑞
𝑝
q
p
​
):
Δ
𝐻
=
𝑞
𝑝
ΔH=q
p
​

Question 13

What does it mean for a reaction to be exothermic?

Answer 13

An exothermic reaction releases heat to the surroundings, resulting in a negative
Δ
𝐻
ΔH.

Question 14

What does it mean for a reaction to be endothermic?

Answer 14

An endothermic reaction absorbs heat from the surroundings, resulting in a positive
Δ
𝐻
ΔH

Question 15

What is calorimetry?

Answer 15

Calorimetry is the measurement of heat transfer during a chemical reaction or physical change, typically using a calorimeter.

Question 16

How is the heat capacity of a substance defined?

Answer 16

Heat capacity is the amount of heat required to raise the temperature of a substance by 1 degree Celsius (or 1 Kelvin)

Question 17

Differentiate between molar heat capacity and specific heat capacity.

Answer 17

Molar heat capacity is the heat capacity per mole of a substance, while specific heat capacity is the heat capacity per unit mass.

Question 18

What is Hess’s Law?

Answer 18

Hess’s 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.

Question 19

Define standard enthalpy of formation (
Δ
𝐻
𝑓
∘
ΔH
f
∘
​
).

Answer 19

The standard enthalpy of formation is the enthalpy change when one mole of a compound is formed from its elements in their standard states.

Question 20

What is the standard state of a substance?

Answer 20

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 25°C).

Question 21

Explain the concept of reversible and irreversible processes.

Answer 21

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.

Question 22

What is the significance of
Δ
𝑆
ΔS in a chemical reaction?

Answer 22

A positive
Δ
𝑆
ΔS indicates an increase in disorder and spontaneity, while a negative
Δ
𝑆
ΔS indicates decreased disorder.

Question 23

Write the equation for calculating
Δ
𝐺
ΔG using enthalpy and entropy

Answer 23

ΔG=ΔH−TΔS, where
𝑇
T is the absolute temperature in Kelvin.

Question 24

What is the critical point in thermodynamics?

Answer 24

The critical point is the temperature and pressure at which the distinction between liquid and gas phases disappears, resulting in a supercritical fluid.

Question 25

Define extensive and intensive properties

Answer 25

Extensive properties depend on the amount of substance (e.g., mass, volume), while intensive properties do not (e.g., temperature, pressure)

Question 26

Explain the concept of thermal equilibrium

Answer 26

Thermal equilibrium occurs when two objects at different temperatures come into contact, and heat transfer ceases when they reach the same temperature

Question 27

What is meant by the term “spontaneous process”?

Answer 27

A spontaneous process is one that occurs without external intervention, typically characterized by a decrease in Gibbs Free Energy ( Δ 𝐺 < 0 ΔG<0).

Question 28

What is the difference between a system and its surroundings?

Answer 28

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.

Question 29

What are the units of enthalpy?

Answer 29

The SI unit of enthalpy is joules (J), but it is often expressed in kilojoules per mole (kJ/mol) in chemistry.

Question 30

Describe what happens during an isochoric process

Answer 30

In an isochoric process, the volume of the system remains constant, and therefore no work is done ( 𝑊 = 0 W=0). The change in internal energy equals the heat added

Question 31

What is the heat of reaction?

Answer 31

The heat of reaction is the change in enthalpy ( Δ 𝐻 ΔH) that occurs during a chemical reaction at constant pressure.

Question 32

How does the heat capacity of a substance vary with temperature?

Answer 32

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.

Question 33

Define the term “latent heat.”

Answer 33

Latent heat is the heat absorbed or released during a phase change (e.g., melting, boiling) at constant temperature, without a change in temperature

Question 34

What is the significance of the enthalpy of vaporization?

Answer 34

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.

Question 35

What is the relationship between Δ 𝐻 ΔH and Δ 𝐸 ΔE for reactions at constant pressure?

Answer 35

The relationship is given by Δ 𝐻 = Δ 𝐸 + 𝑃 Δ 𝑉 ΔH=ΔE+PΔV, where Δ 𝑉 ΔV is the change in volume

Question 36

Describe the term “work done” in thermodynamics.

Answer 36

Work done by the system is the energy transferred when the system exerts a force over a distance, typically expressed as 𝑊 = − 𝑃 Δ 𝑉 W=−PΔV for expansion work

Question 37

What is the Clausius-Clapeyron equation?

Answer 37

The Clausius-Clapeyron equation relates the change in vapor pressure with temperature to the enthalpy of vaporization. It is given by 𝑑 𝑃 𝑑 𝑇 = Δ 𝐻 𝑣 𝑎 𝑝 𝑇 Δ 𝑉 dT dP ​ = TΔV ΔH vap ​ ​ , where Δ 𝐻 𝑣 𝑎 𝑝 ΔH vap ​ is the enthalpy of vaporization and Δ 𝑉 ΔV is the change in volume during the phase transition.

Question 38

Define the standard entropy change ( Δ 𝑆 ∘ ΔS ∘ ) of a reaction

Answer 38

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 Δ 𝑆 ∘ = ∑ 𝑆 𝑝 𝑟 𝑜 𝑑 𝑢 𝑐 𝑡 𝑠 ∘ − ∑ 𝑆 𝑟 𝑒 𝑎 𝑐 𝑡 𝑎 𝑛 𝑡 𝑠 ∘ ΔS ∘ =∑S products ∘ ​ −∑S reactants ∘ ​ .

Question 39

What is the significance of the Helmholtz Free Energy ( 𝐴 A)

Answer 39

Helmholtz Free Energy ( 𝐴 = 𝑈 − 𝑇 𝑆 A=U−TS) 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.

Question 40

Explain what is meant by the term “phase equilibrium.

Answer 40

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.