Temperature And Heat Flashcards
2nd law
Some heat must always be rejected during the cycle, cycle efficiency will be LESS than the unity (net work must always be less than the heat supplied)
In a heat engine
It is very important to dump waste heat out of our process in order to maximise its efficiency when producing work (W)
Temperature and heat
Temp- measure of the energy associated with molecular motion of particles of a substance (kinetic energy).
Measured in Celsius.
Absolute temp measured in kelvin, obtained from thermodynamic theory.
Absolute minimum temp is the point at which molecules stop moving (0 kinetic energy).
Heat
Form of energy transfer due to difference in temperature at the boundary of a thermodynamic system
There must be a temperature difference for transfer to happen
Heat flow- transfer of thermal energy, energy in transition
Adiabatic: no heat transfer, taking terms out of equation.
Absolute ideal gas temperature scale
As we heat something up, fluid expands.
In a volume temp graph, we can measure volume at a temperature. There is a minimum temperature below which you can’t cool things anymore.
Carnot’s work
Efficiency depends only on the temperature of the reservoirs, is independent of properties and the Qr supplied to the engine.
Reversible process
Ideal process that can be reversed without leaving any trace on the surroundings. It ensures the system and its surroundings remain in equilibrium throughout this process. It is the theoretical best case scenario
Sadi Carnot
Heat enters from constant temperature source and is rejected to a sink at constant temperature.
Isothermal process, must not differ by anything by a tiny amount,
Efficiency of a reversible engine
Idealised part, assumes no losses.
Efficiency of a system is a measure of how much work is done compared to how much heat is supplied.
The more heat converted to work, the better the engine.
Are reversible thermodynamic processes achievable in practice
No, they are not achisvable
When we describe a thermodynamic process as reversible what assumption do we make
Temperatures are infinitesimally small, the process occurs really slowly, no gradients in temperature, pressure, or chemical potential. Each intermediate state is an equilibrium state. Any work done without loss of energy. The total entropy change for the universe is zero.
Irreversible process
What increases is the ENTROPY
In a reversible adiabatic system
Entropy stays the same
