Thermodynamics Simulation

Thermodynamics Simulation

Explore enthalpy, state functions, and reaction energy profiles

Reactants
Products
Activation Energy
Exothermic
Endothermic

ΔH (Enthalpy Change)

-40 kJ/mol

Ea (Activation Energy)

180 kJ/mol

Current Energy

100 kJ/mol
Enthalpy
State Function
Reaction Types
Activation Energy

Enthalpy (H)

Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy (U) plus the product of pressure (P) and volume (V):

H = U + PV

In chemical reactions, we’re typically interested in the change in enthalpy (ΔH):

ΔH = Hproducts – Hreactants

Key points about enthalpy:

  • ΔH < 0: Exothermic reaction (releases heat)
  • ΔH > 0: Endothermic reaction (absorbs heat)
  • Enthalpy is a state function – it depends only on the initial and final states, not the path taken

State Functions

A state function is a property of a system that depends only on the current state of the system, not on the path taken to reach that state.

Examples of state functions in thermodynamics:

  • Enthalpy (H)
  • Internal Energy (U)
  • Entropy (S)
  • Gibbs Free Energy (G)

In contrast, heat (q) and work (w) are not state functions – they depend on the path taken.

The first law of thermodynamics can be written in terms of state functions:

ΔU = q + w

Where ΔU depends only on the initial and final states, while q and w depend on the path.

Endothermic vs. Exothermic Reactions

ΔH = Hproducts – Hreactants

Exothermic Reactions (ΔH < 0)

Energy is released to the surroundings (usually as heat). The products are at a lower energy level than the reactants.

Examples:

  • Combustion reactions (burning fuels)
  • Neutralization reactions (acid + base)
  • Most oxidation reactions

Endothermic Reactions (ΔH > 0)

Energy is absorbed from the surroundings. The products are at a higher energy level than the reactants.

Examples:

  • Photosynthesis
  • Thermal decomposition
  • Evaporation of water

Activation Energy (Ea)

Activation energy is the minimum energy required for a reaction to occur. Even exothermic reactions require some initial energy input to get started.

Ea = Energy of transition state – Energy of reactants

Key points about activation energy:

  • Determines the reaction rate – higher Ea means slower reaction
  • Can be lowered by catalysts without affecting ΔH
  • Explains why some thermodynamically favorable reactions don’t occur spontaneously

The Arrhenius equation relates activation energy to reaction rate:

k = A·e-Ea/RT

Where k is the rate constant, A is the frequency factor, R is the gas constant, and T is temperature.