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Level 139

Introduction to Thermodynamics


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Thermodynamics
physics that is concerned with energy, transfers and work.
Open System
A system in which both energy and matter can enter or exit
Closed System
A system containing a fixed amount of matter; it can still exchange energy with the surroundings.
Isolated System
A system that has are no energy transfers between that system and its surroundings.
state of a system
the values of all relevant macroscopic properties
state functions
(energy, pressure, volume, temperature)
first law of thermodynamics
States that if the mechanical energy of a system is constant, the increase in thermal energy of the system equals the sum of the thermal energy transferred into the system and the work done on the system.
ΔU
change in internal energy, ΔU = U(final) - U(initial)
what doe it mean when a reaction is accompanied by the release of heat?
the release of heat indicates that some of the chemical energy contained within the system has been converted to thermal energy
ΔU (sys) + ΔU (surr) = 0
transfer of energy from the system to its surroundings does not change the total energy of the universe
ΔU (sys) = - ΔU (surr)
if a system undergoes an energy change ΔU (sys), the rest of the universe, or the surroundings, must undergo a change in E that is equal in magnitude but opposite in sign
(give Ex)
Ex. E release by burning coal in a power plant may ultimately turn up in our homes as electric energy, heat, or light
the systems internal E changes
what happens when a system releases or absorbs heat?
ΔU = q + w
overall change in the system's internal E
explain q in an endothermic reaction
heat is absorbed by the system (endothermic)
explain q in an exothermic reaction
heat is release by the system (exothermic)
explain w in an endothermic reaction
work done on the system by the surroundings (ex. volume decrease)
explain w in an exothermic reaction
work done by the system on the surroundings (ex. a volume increase)