Thermal Properties of Matter
Overview
Thermal Properties of Matter studies how substances respond when thermal energy is transferred to or from them.
Energy transferred due to temperature difference may raise temperature, lower temperature, change state, or do these in stages.
Definition
Heat capacity of a body is the thermal energy required to raise its temperature by :
Specific heat capacity is the thermal energy required to raise the temperature of of a substance by :
Specific latent heat is the thermal energy required to change the state of of a substance without temperature change:
Why It Matters
This topic explains why water heats slowly, why metals heat quickly, why melting and boiling occur at constant temperature, why steam can cause severe burns, how calorimetry works, and why cooling systems rely on latent heat.
Key Representations
When temperature changes, average kinetic energy of particles changes and:
When state changes at constant temperature, intermolecular potential energy changes while average kinetic energy remains constant:
A heating curve typically has solid warming, melting plateau, liquid warming, boiling plateau, and gas warming stages. Flat sections occur because supplied energy increases intermolecular potential energy rather than average kinetic energy.
For multi-stage problems:
For ideal mixing calorimetry with no heat loss:
Typical equation:
Electrical heating uses:
so:
or:
See Thermal Practicals.
Usually:
because liquid to gas requires much larger molecular separation.
Common Exam Traps
Do not use during melting or boiling. Use during phase change.
At a melting or boiling point, during the phase change.
Convert units carefully: g to kg, kJ to J, and minutes to seconds.
Temperature differences in K and are numerically equal, so may use either scale.
Include container or calorimeter heat capacity if given:
Do not assume all supplied electrical energy heats the sample if heat losses are significant.