4.1.3

Heat Transfer & Thermal Equilibrium

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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

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)

  • 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

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

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.
Diagram
Jump to other topics
1

Structure - Models of the Particulate of Matter

2

Structure - Models of Bonding & Structure

3

Structure - Classification of Matter

3.1

The Periodic Table: Classification of Elements

3.2

Periodic Trends

3.3

Group 1 Alkali Metals

3.4

Halogens

3.5

Noble gases, group 18

3.6

Functional Groups: Classification of Organic

3.7

Functional Group Chemistry

3.8

Alkanes

3.9

Alcohols

3.10

Halogenoalkanes

4

Reactivity - What Drives Chemical Reaction?

5

Reactivity - How Much, How Fast & How Far?

6

Reactivity - The Mechanisms of Chemical Change

7

Measurement, Data Processing & Analysis

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