Thermodynamics: Energy and Its Transformations

These flashcards cover key terms and concepts from thermodynamics and thermochemistry as outlined in the lecture notes.

First Law of Thermodynamics

Energy is neither created nor destroyed.

Energy

The capacity to do work, involving heat transfer and bond formations.

Joule (J)

The official SI unit of energy; 1 J = 1 kg·m²/s².

Enthalpy (H)

A measure of energy changes in a system during a chemical reaction.

Endothermic Reaction

A reaction that absorbs energy, resulting in a positive change in enthalpy.

Exothermic Reaction

A reaction that releases energy, resulting in a negative change in enthalpy.

Bond Enthalpy

The energy required to break a chemical bond; always positive.

Hess's Law

If a reaction occurs in a series of steps, the total enthalpy change is the sum of the enthalpy changes for each step.

ΔH

Change in enthalpy, calculated as the difference between the enthalpy of products and reactants.

Calories and Calories Conversion

1 Cal = 1000 cal (1 kcal); 1 cal = 4.184 J.

Bond making

Energy is released when bonds are formed between gaseous fragments.

Bond breaking

Energy is consumed when bonds are broken.

Average Bond Enthalpy

The average energy required to break a bond in a molecule, measured in kJ/mol.

Energy Units in Chemistry

Use of kJ for larger quantities of energy in chemical reactions.

Stoichiometric Coefficients

Numbers that indicate the ratios of reactants and products in a balanced chemical reaction.