Heat and Work

Heat

• Energy transferred from one object to another due to a difference of temperature between the two objects

• Temperature: measure of hotness or coldness of an object

• Energy is needed to perform work

• When work is done on an object, energy is transferred to that object

• Notable Figures:

  • James Prescott Joule

    • An English physicist who established that the various forms of energy—mechanical, electrical, and heat, are basically the same and can be transformed into one another

• Concept of the Conservation of Energy

  • “Energy cannot be created nor destroyed.”

• First Law of Thermodynamics

  • “The change in internal energy of a system equals the difference between the heat taken in by a system and the work done by the system.”

• The change in internal energy of a system is equal to the head added to the system minus the work done by the system

• Formula:

  • $U=Q-W$

  • Heat added to the system: +Q

  • Heat removed from the system: -Q

  • Work done by system: +W

  • Work done on system: -W

• A system’s internal energy can be changed by transferring energy by either, work, heat, or a combination of the two

• Heat flows from a hotter object to a cooler object when the two are placed in contact

• Spontaneous Process

  • Heat flows from higher temperature to a lower temperature

  • Does not require any external energy

• Non-spontaneous Process

  • Heat flows from lower temperature to a higher temperature

  • Requires mechanical energy to occur