The document introduces the first law of thermodynamics and key concepts such as internal energy, thermodynamic equilibrium, and enthalpy. It discusses James P. Joule's experiments that established a quantitative relationship between work and heat, demonstrating that heat is a form of energy. Internal energy, which includes kinetic and potential energy at the molecular level, is affected by adding heat and work on a substance.

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6. The First Law and Other Basic Concepts

7. In this chapter, we introduce and apply the first law of thermodynamics, one of the two
fundamental laws upon which all of thermodynamics rests. Thus, in this chapter we:
• Introduce the concept of internal energy; i.e., energy stored within a substance
• Present the first law of thermodynamics, which reflects the observation that energy is
neither created nor destroyed
• Develop the concepts of thermodynamic equilibrium, state functions, and the
thermodynamic state of a system
• Develop the concept of reversible processes connecting equilibrium states
• Introduce enthalpy, another measure of energy stored within a substance, particularly
useful in analyzing open systems
• Use heat capacities to relate changes in the internal energy and enthalpy of a
substance to changes in its temperature
• Illustrate the construction of energy balances for open systems

8. JOULE’S EXPERIMENTS
• In the 1840s, James P. Joule conducted crucial experiments that
contributed to the present-day concept of heat.
• He used insulated containers filled with known amounts of water,
oil, or mercury.
• Joule agitated the fluids using a rotating stirrer.
• He accurately measured the work done on the fluid by the stirrer
and the resulting temperature changes.
• Joule found that for each fluid, a fixed amount of work per unit
mass was required for each degree of temperature rise.
• The original temperature of the fluid could be restored by
transferring heat to a cooler object.
• These experiments demonstrated a quantitative relationship
between work and heat.
• Joule’s work showed that heat is a form of energy.

9. INTERNAL ENERGY
• In experiments like those of Joule, energy added to a fluid as work is later
transferred as heat.
• Before its transfer, this energy resides in the fluid as internal energy.
• Internal energy refers to the energy of the molecules within a substance, not
its gross position or movement as a whole.
• Molecules have kinetic energy due to their constant motion:
• Kinetic energy of translation (motion through space).
• For non-monatomic substances, kinetic energy of rotation and internal vibration.
• Adding heat increases molecular motion, raising the internal energy of the
substance.
• Work done on the substance can also increase internal energy, as
demonstrated by Joule.
• Internal energy also includes potential energy related to intermolecular forces
(attraction and repulsion between molecules).
• This is similar to how potential energy is stored in a compressed or stretched spring.
• On a submolecular level, energy is associated with interactions between
electrons and atomic

10. INTERNAL ENERGY
• In experiments like those of Joule, energy added to a fluid as work is later
transferred as heat.
• Before its transfer, this energy resides in the fluid as internal energy.
• Internal energy refers to the energy of the molecules within a substance, not
its gross position or movement as a whole.
• Molecules have kinetic energy due to their constant motion:
• Kinetic energy of translation (motion through space).
• For non-monatomic substances, kinetic energy of rotation and internal vibration.
• Adding heat increases molecular motion, raising the internal energy of the
substance.
• Work done on the substance can also increase internal energy, as
demonstrated by Joule.
• Internal energy also includes potential energy related to intermolecular forces
(attraction and repulsion between molecules).
• This is similar to how potential energy is stored in a compressed or stretched spring.
• On a submolecular level, energy is associated with interactions between
electrons and atomic nuclei, including the energy of chemical bonds.