Thermal Physics Flashcards
(24 cards)
What happens to the temperature and particle energy when heat is supplied to ice below 0°C?
The temperature increases and particles gain kinetic energy as they vibrate faster.
What happens to temperature during a change of state (e.g., melting or boiling)?
The temperature remains constant while energy goes into increasing the potential energy, not kinetic.
Why can’t we use the SHC equation during a change of state?
Because temperature doesn’t change, so ΔT = 0. Instead, we use the Specific Latent Heat (SLH) equation.
What does specific latent heat (SLH) represent?
The energy needed to change the state of 1kg of a substance without changing its temperature.
How do you approach a question involving two substances reaching thermal equilibrium?
Use the SHC equation for each, equating energy lost to energy gained: Set mc(T−T1)=mc(T2−T), expand, and solve for T.
What’s the approach when ice melts in a drink?
Use SHC for heating the ice (if not at 0°C), SLH for melting, and then SHC again for warming melted water.
Why isn’t the Celsius scale absolute?
It doesn’t start at 0 kinetic energy. Kelvin does, with 0 K = -273°C (absolute zero).
How do you convert between Celsius and Kelvin?
Add 273 to Celsius to get Kelvin: T(K)=T(°C)+273.
When do we use Kelvin in physics calculations?
Always, except when calculating a temperature change (ΔT), where °C and K are equivalent.
What is Boyle’s Law and when is it used?
pV=constant at constant temperature (isothermal change). Pressure is inversely proportional to volume.
What is Charles’s Law?
V∝T at constant pressure. Volume increases with temperature in Kelvin.
What is the Combined Gas Law?
If no particles are added or removed: p1V1/T1=p2V2/T2.
What is the ideal gas equation and its constants?
pV=nRT, where n = moles, R = 8.31 J mol⁻¹K⁻¹.
What is the microscopic form of the ideal gas law?
pV=NkT, where N = number of molecules, k = Boltzmann constant.
What are the 5 assumptions of the ideal gas model (RAVED)?
Random motion, Attractive forces are negligible, Volume of particles is negligible, Elastic collisions, Duration of collisions is negligible.
What is Brownian motion evidence for?
Random motion of gas particles – seen via the random movement of smoke under a microscope.
What is the kinetic theory equation for pressure in terms of rms speed?
pV=1/3 Nmc̅², where m is mass of one molecule, c̅ is rms speed.
How is pressure related to density and speed in a gas?
p=1/3 ρc̅², where ρ is gas density.
What is root mean square (rms) speed and why is it used?
c̅=(u²+v²+w²)/3. It gives a useful average speed, since mean velocity is zero.
What is the kinetic energy of one molecule in a gas?
Eₖ=3/2 kT. Independent of mass; only depends on temperature.
What does equal temperature mean for different gas particles?
Same average kinetic energy, but different speeds due to different masses.
What does the area under a p-V graph represent?
Work done: Work=Area under curve=pΔV.
When is work done on or by a gas?
Compressed: work is done on the gas. Expands: gas does work on surroundings.
What if pressure decreases at constant volume?
No work is done because ΔV = 0.
