Thermodynamics Quiz

Thermodynamics

System: The part of the universe under investigation.
Surroundings: The rest of the universe, excluding the system.
Types of Systems:
- Open System: Energy and matter exchange between the system and surroundings (e.g., open cup of tea).
- Closed System: Only energy exchange between the system and surroundings (e.g., covered cup of tea).
- Isolated System: No exchange of energy or matter between the system and surroundings (e.g., tea in a thermos flask).
Intensive Properties: Properties that depend on the nature of the substance present in the system, not the amount (e.g., viscosity, refractive index).
Extensive Properties: Properties that depend on the quantity of the substance present in the system (e.g., mass, volume, area).
State Function: Thermodynamic quantities that depend only on the initial and final states of the system, not the path taken (e.g., internal energy, entropy).
State Variables: Physical quantities used to describe the state of a system (e.g., pressure, humidity, temperature).
Reversible Processes: Processes that can reverse themselves in small intervals of time.
Irreversible Processes: Processes that cannot reverse themselves in small intervals of time.
Thermodynamic Processes: Processes in which a system changes from an initial to a final state.
- Isothermal: Constant temperature.
- Isobaric: Constant pressure.
- Isochoric: Constant volume.
- Adiabatic: Constant heat.
Internal Energy (E or u): The energy stored within a system.
Internal Energy Change (ΔU): The difference in energy between the products and reactants in a reaction. The value is defined as the difference in energy between products and reactants for a change in state.

Sign Conventions

ΔU: Negative if energy is evolved from the system, positive if it is absorbed by the system.
q (heat): Negative if heat is evolved from the system, positive if it is absorbed.

Work (W)

Work (W): Done when a force produces motion or displacement.
W = F × d𝑠 (W = work, F = force, ds = displacement)
Pressure-Volume work: Consider a cylinder with a movable piston. Work (W) is equal to the pressure (P) multiplied by the change in volume (ΔV). W = P∆V or -(P∆V).
The sign of work (W) depends whether work is done on or by the system.

First Law of Thermodynamics

Energy: Neither created nor destroyed; it can be transferred from one form to another.
Mathematical Expression: ΔU = q + w (ΔU = change in internal energy, q = heat, w = work).

Enthalpy (H)

H = U + PV (H= enthalpy, U= internal energy, P= pressure, V= volume)
Change in enthalpy (ΔH) is closely related to q (heat) at a constant pressure. ΔH = ΔU + PΔV

Relationship Between ΔH and ΔU

Constant Pressure: ΔH = ΔU + PΔV (ΔH = change in enthalpy, ΔU = change in internal energy, P = pressure, ΔV = change in volume.

Spontaneity

Spontaneous Processes: Processes that occur naturally under a given set of conditions.
Non-Spontaneous Processes: Processes that do not occur naturally.
Driving Forces: Factors that determine the spontaneity of a process:
- Minimum Energy: Processes that lead to a decrease in energy are often spontaneous.
- Maximum Disorder or Entropy: Processes that lead to an increase in disorder or entropy are often spontaneous.

Entropy (S)

Entropy (S): A measure of the randomness or disorder in a system.
Entropy Changes during Phase Transformation:
- Fusion: ΔSfus = ΔHfus / T (positive)
- Vaporization: ΔSvap = ΔHvap / T (positive)
Entropy of Sublimation: ΔSsub = ΔHsub / T (positive)
Units of Entropy: Joules/Kelvin/mole

Gibbs Free Energy (G)

Gibbs Free Energy (G): Thermodynamic quantity that measures the spontaneity of a process at a given temperature and pressure.
G = H - TS (G = Gibbs Free Energy; H = enthalpy, T = Temperature in Kelvin (K); S = Entropy.)

Standard Gibb's Free Energy

Defined as the free energy change which occurs in the given reaction when the reactants are in their standard state (298 k and 1 atm) and are converted to the products at the same conditions.
It is related to the equilibrium constant through the following expression: △G = -2.303RTlogK Where:

△G = Standard Gibb's Free Energy

R = 8.314 J/k/mol (Gas Constant)

T = Temperature in Kelvin

K = Equilibrium constant

Limitations of Entropy

Some endothermic processes are still spontaneous

Heat Capacity

Heat Capacity: Amount of heat required to raise the temperature of a substance by 1°C.
- Specific Heat Capacity: Heat required to raise the temperature of 1 g of a substance by 1°C.
- Molar Heat Capacity: Heat required to raise the temperature of 1 mol of a substance by 1°C
Cp (constant pressure) and Cv (constant volume)