thermodynamics

Question 1

Thermodynamics Basics

Answer 1

Definition: Thermodynamics is the study of energy and transformations.
Focus: Concerned with macroscopic properties (temperature, volume) and equilibrium conditions.
Limitations: Does not deal with the speed of reactions.

Question 2

Thermodynamics Predictions

Answer 2

Prediction Nature: Predicts equilibrium states, favors the side with the lowest energy.
Example: Diamonds are stable on Earth’s surface, but they may be physically abraded before chemically degrading to graphite (thermodynamics favors graphite).
Equilibrium Misconception: No measurable change doesn’t guarantee equilibrium; further change may still occur.

Question 3

Fundamental Thermodynamic Variables

Answer 3

Energy: Capacity to produce change; changes in energy are more critical than absolute energy.
Forms of Energy: Includes work and heat; heat results from random motion of molecules, related to kinetic energy.
Units: Energy in Joules (J), force in Newtons (N), distance in meters (m), time in seconds (s), mass in kilograms (kg), temperature in Kelvin (K), pressure in Pascals (Pa).

Question 4

work energy

Answer 4

Work Definition: Done by moving a mass (M) through a distance (x) against a force (F): w = Fx
w=F⋅x.
Units: Joules (J) = Newtons (N) × meters (m).
Force Definition:
F = m a
F=ma, where
a is the acceleration due to gravity on Earth (approximately 9.8 m/s²).
Example: 1 kg at rest exerts a force of 9.8 N on Earth’s surface.

Question 5

Thermodynamics and equilibrium

Answer 5

Nature of Prediction: Thermodynamics predicts the equilibrium state; reaching equilibrium may take timescales we can’t measure.
Diamond Stability Example: Diamonds are so stable on Earth’s surface that physical abrasion may occur before chemical degradation to graphite.
Physical Example: Releasing a boulder from the top of a slope - most stable at valley floor, but a hollow on the valley wall may prevent reaching the lowest energy state.

Question 6

thermodynamics variables

Answer 6

Entropy (S): Measures the degree of randomness in a system (J mol⁻¹ K⁻¹).
Enthalpy (H): Measures heat exchanged in a reaction (J mol⁻¹ or kJ mol⁻¹).
Free Energy (G): Measures total energy (enthalpy + entropy) in a reaction (J mol⁻¹ or kJ mol⁻¹).

Question 7

system change and equilibrium

Answer 7

System Change Requirement: Energy change is essential for a system to change.
Equilibrium Significance: No energy change; system is at equilibrium.
Example: Saturated sodium chloride solution where additional salt doesn’t dissolve but remains as a pile.

Question 8

types of equilibrium

Answer 8

Spontaneous Reaction: Energy change from high to low, losing energy to the system.
Equilibrium: No exchange of energy.
Dynamic Equilibrium: No thermodynamic or chemical composition change, but can exchange matter.
Static Equilibrium: No change in composition or matter exchange at observable timescales.

Question 9

calculating Delta H

Answer 9

Delta H Formula:
ΔH = H products − H reactants
Exothermic Reaction: ΔH negative, heat given off; often spontaneous.
Endothermic Reaction: ΔH positive, heat taken in; system feels cold (e.g., evaporation).

Question 10

Mole and Gibbs Free Energy

Answer 10

Mole Definition: One mole =
6.022 × 10^23 molecules or atoms.

Atomic Weights: Average atomic mass relative to 12C
Gibbs Free Energy: G=H−TS, where ΔG=ΔH−TΔS.
Equilibrium: Gibbs free energies of products and reactants are equal.
Spontaneity: Reaction is spontaneous when ΔG is negative.

Question 11

temperature conversion to kelvin

Answer 11

add 273

Question 12

Stoichiometry

Answer 12

refers to the realive molar amounts of species in a reaction