Thermal Physics Flashcards
Define internal energy (U).
The sum of the randomly distributed kinetic and potential energies of atoms or molecules in a substance.
U= Ek + Ep
Define specific heat capacity and give its units.
The thermal energy required to raise the temperature of a 1kg body of mass by 1K.
J kg-1 K-1
Define latent heat of fusion.
Energy required to change the unit mass of a substance from a solid to liquid while at a constant temperature.
Define latent heat of vaporisation.
Energy required to change the unit mass of a substance from a liquid to gas while at constant temperature.
What is absolute zero and why can’t there be a temperature lower than it?
0K- theoretical lowest possible temperature.
A body would have minimum internal energy (No Ek as molecules stop moving, only Ep)
What is thermal equilibrium?
- No net transfer of thermal energy between objects involved.
- Same temperature.
Celsius to Kelvin?
C° + 273 = K
Why must thermometers be the same temperature as the object being measured?
- No net transfer of thermal energy must take place.
- Accurate reading of temp.
Why is the difference between C and K omitted when discussing high temperature of objects (eg stars)?
The difference between C and K is negligible at high temperatures.
Why does a thermometer placed in a hot cup of water not give the initial reading of the temperature of the water?
- Net transfer of thermal energy from the water to the thermometer.
- Reduces the temperature of the water.
- When there is no net transfer of thermal energy, the water and thermometer will be the same temperature (lower than initial).
What is Brownian motion?
- Gas molecules travel in random directions at random velocities.
- Transfer of momentum between particles so collisions are elastic.
- Can be observed by smoke particles under a microscope.
Describe the arrangement, forces and motion of solid atoms.
- Fixed, regular, 3D
- Strong electrostatic forces
- Vibrate around equilibrium position
Describe the arrangement, forces and motion of liquid atoms.
- Random arrangement
- Weaker attraction between particles
- Flow between each other in random direction
Describe the arrangement, forces and motion of gas atoms.
- Random arrangement
- Almost no forces of attraction
- Move at high speeds in random directions
Why is ice less dense than water?
- When water freezes, strong intermolecular forces hold water molecules in hexagonal ring structures.
- Spaced further apart so fewer molecules in space -> less dense
Explain why the volume of water increases as temperature increases.
- As temp increases, particles gain more kinetic energy so move at higher speeds.
- Higher speeds = more collisions which cause the liquid to expand.
Why is the thermodynamic scale of temperature used?
It doesn’t rely on the properties of a substance.
Define heat.
Thermal energy transferred from a body of high temp to low temp.
Why do all molecules possess Ek and Ep?
Ek - random movement.
Ep- chemical bonds between molecules and bonds within nuclei.
Why does internal energy change as temperature changes?
As temp increases, molecules gain more Ek -> higher internal energy
Why does internal energy change during phase changes?
- Ek stays the same as temperature stays the same.
- Ep increases as the mean separation of particles increase -> increase in internal energy
Why does temperature stay constant during phase changes?
Thermal energy is converted into potential energy.
Potential energy increases as mean separation of particles increase.
Explain why 1kg of water has more internal energy than 1kg of ice.
Same Ek because same temperature.
Different Ep. Ep is higher in the water due to larger mean separation of molecules so higher internal energy.
Define specific latent heat.
Energy required to change the state per unit mass of a substance while at a constant temperature.
Equation including energy, mass and specific latent heat.
Q = m L
