Heat and Temperature Flashcards
What does it mean if a variable is intensive/extensive?
Intensive - independent of the scale of the system.
Extensive - scales with the system
What is a open/closed system?
Open - can exchange energy and mass with its surroundings
Closed - can exchange only energy with its surroundings
What are adiabatic/diathermal walls?
Adiabatic - prevent heat transfer.
Diathermal - all heat transfer.
What does isothermal mean?
At constant temperature.
What does isochoric mean?
Constant volume.
What does isobaric mean?
Constant pressure.
What does adiabatic mean?
No heat flow or a sudden process (before heat flow can occur).
What is Le Chatelier’s Principle?
A system in equilibrium reacts to a small change in one of its variables by changing its internal conditions to reverse the change. (stay in equilibrium)
What is the definition of thermal equilibrium?
Two systems are in thermal equilibrium if their state variables do not change when they are put in contact via a diathermal wall.
State the 0th Law of Thermodynamics.
Two systems are in thermal equilibrium if, and only if, they have the same temperature.
What is the internal energy of a system?
The sum of the translational, vibrational and rotational energies of it’s components.
How do you know if something is a thermometer?
If it has an observable property which changes with temperature.
What is the ice point?
Liquid and solid water in thermal equilibrium at 1 atmosphere. (0 degrees C)
What is the steam point?
Liquid and vapour water at thermal equilibrium at 1 atmosphere (100 degrees C)
How do gas thermometers work?
They use one reference point - absolute zero - 273 degrees C or 0K.
What is the equation for linear thermal expansion?
α = 1/L0 * ΔL/ΔT, where L0 is the value of the dimension at some initial T0.
How would you calculate length using the equation for linear thermal expansion?
L = L0 + ΔL = L0 + αL0ΔT
What does the graph look like for potential energy between two atoms bound in a solid?
Goes from positive to negative and then tends to zero (u shape). Higher temp = wider curve.
What is the equation for volume thermal expansion?
β = 1/V0 * ΔV/ΔT = 3α (since dV = 3L^2 dL)
What are the 2 equations for ΔT in terms of heat flow Q?
ΔT = Q/nC, where C is the molar heat capacity and n is the number of mole
OR
ΔT = Q/mCm, where Cm is the specific heat capacity
What is the specific heat capacity of water?
4190 J K^-1 kg^-1
What is meant by latent heat?
Latent heat is the amount of heat involved in a phase change.
What is the equation for heat transfer Q?
Q = +/- m*L, where L is the latent heat.
How do you draw a phase diagram for p-T? What is the centre point called?
Like a diagonal Y shape with curvey lines - solid on left, vapour at bottom and liquid at top. Centre called triple point.
On the p-T diagram, what is the line between solid and vapour called?
Sublination curve.
What happens at the critical point?
Separation between liquids and vapour ends - beyond there is a smooth continuous change.
What is the equation for heat flow in conduction?
dQ/dt = -κA dT/dx, where κ is the thermal conductivity (-ve sign because heat flows from higher to lower temperature.
What can cause convection?
Local changes of density or temperature which causes heat flow due to motion of fluid.
What is the equation for power in radiation?
P = eσA*T^4 (Stefan - Bolzmann Law), where e is the emissivity and σ is the Stefan-Boltzmann constant.
