Thermodynamics Flashcards
what is work a transfer of?
it is a transfer of mechanical energy into or out of a system, from or to the environment
how does the total energy in a system change?
if energy is transferred into or out of the system
Temperature (T)
the macroscopic measure of thermal energy per molecule
Heat (Q)
the transfer of thermal energy between a system and its environment
when is Q>0?
when heat transfers into the system
when is Q<0?
when heat transfers out of the system
what is an intensive property?
temperature (does not depend on the amount of material present)
what is an extensive property?
thermal energy (depends on the amount of a material present)
thermodynamics
concerns how macroscopic systems transfer and transform energy
zeroth law of thermodynamics
if one object is in thermal equilibrium with a second object, and that second object is in thermal equilibrium with a third object, then the first and third objects are in thermal equilibrium with each other; if quantity of temperature are the same for two objects, then there is something fundamentally similar about the two
thermal equilibrium
two bodies are in contact in such a way that heat is free to pass between them, but there is no change in heat because heat is passed equally in both ways
state function
macroscopic properties that reflect the microscopic conditions of the system and predict the future behaviour of the system
what are some state variables?
pressure, volume, moles, entropy
what is Boltzmann’s constant?
k=1.38*10^-23J/K
what are the three mechanisms by which heat transfer (movement of thermal energy) occurs?
conduction, convection, radiation
conduction
direct contact in which highly agitated atoms cause the object in contact to vibrate more rapidly and heating up
convection
usually occurs by a fluid becoming less dense than surrounding and rising due to buoyancy, where heat is transferred away from the flame by large-scale motion of a fluid
radiation
absorption of the energy carried by light waves
aside from change in heat transfer, what is another response of materials to temperature difference?
to change their physical dimensions, usually heating causes thermal expansion
first law of thermodynamics
the total energy of the universe is constant
what is the mathematical statement of the first law of thermodynamics?
change in E=Q-W
what is the mechanical energy values of an ideal gas sealed in a container with a piston on top?
KE=PE=0, the only form of energy present is thermal energy
for an ideal gas, what is the form of internal energy present?
kinetic energy of the atoms or molecules
what is the internal energy of an ideal gas proportional to?
the object’s absolute temperature T
if no heat is exchanged between a gas and the environment, what is the result of cooling or heating the gas?
cooling causes gas to compress, heating causes gas to expand
what happens to the internal energy as gas compresses?
internal energy increases and so the gas heats up as it compresses
what happens to the external energy as gas expands?
internal energy decreases and so the gas cools as it expands
isobaric
a process that occurs at constant pressure, ex. piston is held constant
isochoric
a process that maintains a constant volume
what is the result of heating a gas with a locked piston, i.e. in an isochoric process?
there is no change in volume (W=0) but pressure would increase
isothermal
a process whereby heat is allowed to pass freely between a system and its environment, so the temperature of the system remains constant
what is the result of allowing a gas to expand at constant temperature (i.e. an isothermal process)
for gas to expand at constant temperature, the pressure must decrease
adiabatic
a process that occurs when no heat is transferred between the system and the environment, and all energy is transferred as work (Q=0, change in E internal= -W)
second law of thermodynamics
the entropy of an isolated system either stays the same or increases during any thermodynamic process
what is the significance if entropy stays constant over a thermodynamic cycle?
the cycle is said to be reversible
