01/24+01/26 Thermo Flashcards
what is the first law of thermodynamics
energy must be conserved, energy cannot be created or destroyed
what is internal energy
internal energy is the sum of all types of energy in a system of molecules
what is the first law in terms of internal energy
the internal energy in an isolated system is conserved
when considering an open or closed system what happens to the energy in the surroundings when the system undergoes a change in energy
the energy in the surroundings must change as well as the sum of the changes must be zero to keep energy constant
∆Usys + ∆Usurr = 0
for an isolated system does the internal energy change
no it is constant
for open or closed systems, what happens to the surroundings as the system changes
the surroundings will change correspondingly
what is heat
heat is the energy transfer between the system and the surroundings due to temperature differences between the system and surroundings
when is heat negative
heat is negative when heat flows out of the system and to the surroundings, this is a loss of energy
when is heat positive
heat is positive when heat flows into the system from the surroundings, there is a gain of energy
what is work
work is energy transfer between the system and surroundings due to a movement of mass in the surroundings
when is work positive
work is positive when there is work being done on the system by the surroundings (gain in energy)
when is work negative
work is negative when there is work being done by the system on the surroundings (loss in energy)
when a gas is expanding, is the work positive or negative
work is negative, the gas is doing work on the surroundings by pushing outwards on it
when a gas is compressing, is the work positive or negative
the work is positive, the surroundings are doing work on the system
