Thermodynamics Part 1

Introduction to Thermodynamics

• Thermodynamics = science of the interconversion of different forms of ENERGY (ex/ heat, mechanical work, chemical energy)
• -> Chemical reactions involve a transfer of energy between the system and surrounding
• System = the part of the universe under observation
• -> The System can be:
• a) "open" - both mass & energy may leave and enter (i.e. beaker)
• b) "closed" - energy can be exchanged but no mass can enter/leave (i.e. sealed flask)
• c) "isolated" - neither mass nor energy may enter/leave (i.e. insulated, closed container)
• Surroundings = the rest of the universe
• Therefore, the "universe" is made up of the ""System" and the "Surroundings"
• The "STATE" of a system is characterized by a set of variables (i.e. P, V, T, n, etc.)
• These are STATE VARIABLES.
• -> P, V, T, n and mass can be classified as either:
• * Intensive - independent of size (ex/ P, T, etc.)
• * Extensive - dependent of size (ex/ mass, V, n, etc.)
• We can transfer energy in and out of a system, where the INTERNAL ENERGy of the system may change

Introduction to Thermodynamics

• Internal Energy (U) = the sum of the kinetic and potential energy of system
• Two ways U can change:
• 1. Heat (q)
• 2. Work (w)
• *another way is by adding/removing mass but this is not encountered in a "closed" system
• We can only measure changes in U, not absolute values so for any reaction/process, U(final) - U(initial) = delta U
• ***1st Law of Thermodynamics
• => delta U = q + w
• (statement from the conservation of energy)
• The Law of Conservation of Energy states energy may be converted from one form to another, but the total quantity of energy remains constant
• HEAT ENERGY, HEAT TRANSFER and TEMPERATURE
• delta U = q + w tells us we cannot create/destroy energy, but it can be transferred in and out of the system

Diapositiva 3