Thermochemistry Lecture Notes Review

These flashcards cover key concepts in thermochemistry, including laws of thermodynamics, systems types, energy changes, enthalpy, entropy, Hess's law, and Gibbs free energy.

What is thermochemistry?

Thermochemistry is the sub-discipline of Chemistry that involves chemical reactions and energy changes.

What does the 1st Law of Thermodynamics state?

The 1st Law of Thermodynamics states that energy is conserved; it is neither created nor destroyed, only changes form.

What is an open system in thermochemistry?

An open system can exchange both energy and matter with its surroundings.

What is the meaning of exothermic and endothermic processes?

In exothermic processes, heat is released by the system; in endothermic processes, heat is absorbed by the system.

What is enthalpy used to measure?

Enthalpy (H) measures the heat absorbed or released by a system at constant pressure.

What is Hess's Law?

Hess's Law states that the change in enthalpy for a chemical reaction is constant, whether it occurs in one step or several steps.

What is Gibbs free energy?

Gibbs free energy (G) is a measure of the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure.

How is Gibbs free energy related to spontaneity?

If ΔG is negative, the process is spontaneous; if ΔG is zero, the system is at equilibrium; if ΔG is positive, the reaction is nonspontaneous.

What does ΔH stand for?

ΔH represents the change in enthalpy, indicating heat absorbed or released.

What happens to ΔH when a reaction is reversed?

If a reaction is reversed, the sign of ΔH is also reversed.

How does temperature affect spontaneity?

At low temperatures, ΔH is often the dominating factor; at high temperatures, TΔS can become greater than ΔH, affecting spontaneity.

What is standard enthalpy of formation (ΔHfo)?

Standard enthalpy of formation (ΔHfo) is the heat change that results when one mole of a compound is formed from its elements at standard conditions.

Define entropy (S).

Entropy (S) is a measure of the amount of molecular disorder in a system.

What does ΔS represent?

ΔS represents the change in entropy of a system when it undergoes a process.

How do you calculate standard free energy change (ΔG°)?

ΔG° is directly linked to the equilibrium constant, K, and can be calculated using: ΔG° = -RT ln K.

What measures the change in free energy during a reaction?

Free-energy change (ΔG) measures the change in free energy as a chemical reaction or physical change occurs.