Foundations of Thermochemistry

Vocabulary practice flashcards covering the fundamental concepts of thermochemistry, energy transfer, and thermodynamic laws.

Thermochemistry

The branch of chemistry concerned with heat absorbed or released during chemical reactions and physical changes.

System

The substances or region being studied, usually the reacting chemicals.

Surroundings

Everything outside the system, including the container, solution, air, and measuring equipment.

Heat, $q$

Energy transferred because of a temperature difference that flows from a warmer body to a cooler body.

Temperature

A measure related to the average kinetic energy of particles; it is not the same as heat.

Internal energy, $U$

The total microscopic kinetic and potential energy contained in a system.

Enthalpy, $H$

A thermodynamic quantity commonly used to describe heat changes at constant pressure.

Enthalpy change, $\Delta H$

Calculated as $\Delta H = H(\text{products}) - H(\text{reactants})$, its sign identifies whether heat is released or absorbed.

Exothermic Reaction

A reaction where energy flows out of the system into the surroundings ($\Delta H < 0$), usually causing the surroundings to become warmer.

Endothermic Reaction

A reaction where the system absorbs energy from the surroundings ($\Delta H > 0$), usually causing the surroundings to become cooler.

First Law of Thermodynamics

The law stating energy cannot be created or destroyed, only transferred or transformed, expressed as $\Delta U = q + w$.

Law of Conservation of Energy

The principle that the total energy of an isolated system remains constant, expressed as $q(\text{system}) + q(\text{surroundings}) = 0$.

Bond Breaking

A chemical event that always requires an input of energy.

Bond Formation

A chemical event that always releases energy.

Activation energy, $E_a$

The minimum initial energy needed for a successful reaction to begin.

Catalyst

A substance that speeds up a reaction by lowering the activation energy without changing the overall $\Delta H$.

$$\Delta U$$

The symbol representing the change in the internal energy of the system.

$$w$$

The symbol for work done on or by the system, where $w > 0$ is work done on the system and $w < 0$ is work done by the system.

$$\Delta T$$

The change in temperature, calculated as $T(\text{final}) - T(\text{initial})$.

Photosynthesis

An endothermic reaction where plants absorb light energy to drive the production of glucose and oxygen.

Combustion

An exothermic reaction where a fuel reacts with fuel and oxygen to release chemical energy as heat.