Thermal Physics Flashcards
Define the internal energy of a ball of gas
The sum of the randomly distributed kinetic and potential energies of the particles in the gas
How can you increase the internal energy of a system?
Doing work on the system
Heating the system
When a solid is melting, what happens to the kinetic and potential energies, and why?
Potential energy increases according to Q = ml
Average kinetic energy stays the same, as this is proportional to temperature
What can be seen at a macroscopic level, which shows that particles exist, and what conclusions can be drawn about these particles?
Brownian Motion (of dust motes or pollen grains)
Shows air particles:
- Fast moving
- Significantly smaller than dust or pollen
- Move at random in all planes and directions
5000J of heat are added to two different liquids. Both start off at 10°C
A) Will their change in internal energy be the same?
B) Will their change in temperature be the same?
A) The change in internal energy is the same as they both gain 5000J
B) The change in temperature would be different as it depends on the specific heat capacity of the liquid and maybe different masses
What is absolute zero
273K, where particles are not vibrating as kinetic energy = 0 and therefore exert no pressure
Found using the intercept of P-T graph or V-T Graph
How does temperature relate to the speed of particles?
Temperature is directly proportional to average KE, so temperature is directly proportional to the mean square speed
Define specific heat of fusion
The energy required to change the state of 1kg of a substance from solid to liquid
A syringe full of gas is heated for 5 minutes and is allowed to expand to equalise the pressure.
Suggest two reasons why, when its temperature is measured, it is not as high as expected?
gas did work to push the syringe, so it lost some of its internal energy
Some of the heat has ben dissipated into the surroundings
What are the assumptions used for ideal gas equations?
RAVED
Randomly distributed particles
No attractive forces between the particles
Volume of Particles is negligible compared with the container
Elastic collisions
Duration of collision is very short compared with time in between
What does Boyle’s Law state?
For a gas at constant temperature, pressure is directly proportional to volume
What does Charle’s Law state?
For a gas at constant pressure, the Volume is directly proportional to the temperature (Kelvin)
What does Gay Lussac’s Law state?
For a gas at constant volume, the pressure is inversely proportional to the temperature (kelvin)
What are the assumptions made for Charle’s Law?
When might Charle’s Law not work very well?
Gas at constant pressure with a constant number of particles and behaves as an ideal gas
If the temperature change happens very quickly and doesn’t have time to become evenly distributed through the gas
What is the first law of thermodynamics?
Internal energy = Heat added to the system - the Work done by the system
