Heat Transfer & Thermal Equilibrium
Chemistry: IB Diploma Higher Level, topic 4.1.3
Heat Transfer & Thermal Equilibrium
Thermal energy is kinetic energy associated with the random motion of atoms and molecules. Temperature is a quantitative measure of “hot” or “cold.”
Thermal energy & kinetic energy
- When the atoms and molecules in an object are moving or vibrating quickly, they have a higher average kinetic energy (KE).
- At this point we say that the object is “hot.”
- When the atoms and molecules are moving slowly, they have lower average KE.
- At this point we say that the object is “cold”
- Assuming that no chemical reaction or phase change occurs, increasing the amount of thermal energy in a sample of matter will cause its temperature to increase.
Heat (q)
- Heat (q) is the transfer of thermal energy between two bodies at different temperatures.
- Heat flow increases the thermal energy of one body and decreases the thermal energy of the other.
Heat transfer
- Suppose we initially have a high-temperature substance (H) and a low-temperature substance (L).
- The atoms and molecules in H have a higher average KE than those in L.
- If we place substance H in contact with substance L, the thermal energy will flow spontaneously from substance H to substance L.
- Collisions between particles in H with particles in L result in the transfer of thermal energy.
- This process is called heat transfer.
Thermal equilibrium
- The temperature of substance H will decrease, as will the average KE of its molecules.
- The temperature of substance L will increase, along with the average KE of its molecules.
- Heat flow will continue until the two substances are at the same temperature.
- The two objects reach “thermal equilibrium” when both substances are at the same temperature and their molecules have the same average kinetic energy.
Test yourself on Heat Transfer & Thermal Equilibrium
When is thermal equilibrium reached?
What results in the transfer of thermal energy between particles of different substances?