Thermochemistry Basics

5.1 Thermochemistry: Energy, Heat, and Temperature

Background: Understanding Energy Flow

Thermochemistry is the study of heat absorbed or released during chemical and physical changes. In health sciences, this is the basis for understanding metabolism—how your body converts food (potential energy) into heat and work (kinetic energy).

• Thermal Energy: Kinetic energy associated with the random motion of atoms and molecules.
• Temperature: A quantitative measure of "hot" or "cold." It reflects the average kinetic energy of the particles.
• Heat (q): The transfer of thermal energy between two bodies at different temperatures. Heat always flows spontaneously from a higher-temperature object to a lower-temperature object until thermal equilibrium is reached.

Distinguishing Processes: Exothermic vs. Endothermic

In a clinical setting, knowing the direction of heat flow is vital for patient care (e.g., using heat lamps vs. cold packs):

• Exothermic Process: A change that releases heat to the surroundings (e.g., a hand warmer or combustion).
• Endothermic Process: A change that absorbs heat from the surroundings (e.g., a chemical cold pack used for sports injuries).

Background: Heat Capacity vs. Specific Heat

To calculate how much energy a substance absorbs, we must distinguish between these two related properties:

• Heat Capacity (C): An extensive property (depends on amount). It is the heat required to raise the temperature of an entire object by 1°C. (Example: A large iron pot has a higher heat capacity than a small iron nail).
• Specific Heat (c): An intensive property (depends only on the material). It is the heat required to raise exactly 1 gram of a substance by 1°C.