Flashcards in Thermal physics Deck (47)
Define internal energy
Sum of the individual potential and kinetic energies of all molecules within the body
State the first law of thermodynamics
The change of internal energy of the object is equal to the total energy transfer due to work done and heating
Define specific heat capacity
The energy required to change the temperature of 1kg of the substance by 1K without changing state
Describe the experiment to measure the specific heat capacity of a metal
Metal block of known mass in an insulated container. Electrical heater inserted into a hole in the metal, thermometer into another.
Measure the temperature change over a given time
Which measurements are used to measure specific heat capacity of a metal, and how?
Heater's current (I)
Heater's pd (V)
Time of heating (t)
Temperature change (ΔT)
mcΔT=IVt (rearrange for c)
State Boyle's law
When a fixed mass of gas is reduced in volume by a compressing piston, the pressure inside the piston increases
Explain why Boyle's law is true
- Gas particles all in random motion
- Pressure occurs from particles collides with the surface of a wall exerting a force
- As volume decreases
- Collisions occur more frequently
- Therefore pressure increases
State Charles' law
For a fixed mass of an ideal gas at constant pressure, its volume is directly proportional to its absolute temperature
State the pressure law
For a fixed mass of an ideal gas at constant volume, its pressure is directly proportional to its absolute temperature
Define Avogadro constant
The number of atoms in exactly 12g of carbon-12
Define molar mass
The mass of 1 mol of the substance
What are the five assumptions that are made for the kinetic theory equation?
Molecules are point molecules
No attractive forces between molecules
Molecules move in continual random motion
All collisions are elastic
Time of collisions is negligible
Define molar heat capacity
The energy required to change 1 mol of gas by 1K
Define heat capacity
The energy required by an entire object to change temperature by 1K
How is work done on a gas calculated from a pressure against volume graph?
Area under the graph
Explain what is meant by specific latent heat of fusion (2)
The energy required to change one kg of an object from liquid to solid without changing temperature
Water is pumped througha heater in a hot tub, why is the temperature rise greater when the pump works at a higher speed? (2)
The pump is doing work on the water. Work can raise the temperature of the body
Use the kinetic theory of gases to explain why the pressure inside a football increases when the temperature of the air inside it rises. Assuming volume remains constant (3)
Molecules have a greater rms velocity. Number of collisions between molecules and inside surface of ball increases per second. pressure = F/A and F = rate of change of momentum
What is the equation for Work Done in a Piston with a set mass of gas in?
A: W = p ΔV W = Work Done p = Pressure ΔV = Change in Volume
What is the Second Law of Thermodynamics?
It is not possible to convert heat continuously into work, without at the same time, transferring some heat from a warm body into a cold body. : the total entropy of a system can never decrease over time (temperature of an object always wants to be in equilibrium with surroundings).
What is the equation for Force?
F = p x A F = Force p = Pressure A = Cross-Sectional Area
What is the equation for internal energy for constant pressure processes?
ΔU = ΔQ – pΔV ΔU = Change in Internal Energy ΔQ = Change in amount of heat supplied to the system p = Pressure ΔV = Change in Volume
What does the p-V graph look like for constant pressure (isobaric process)?
What does the area below a p-V graph show?
What are the rules for a cycle process?
1) For a complete cycle, ΔU = 0 (No change in internal energy)
2) the net work done = area enclosed by the cycle
How do you change from Celsius into Kelvin?
Celsius Temperature + 273
What is specific latent heat?
The amount of thermal energy required to change the state of 1 kg of a substance at constant temperature
What are the three equations for an ideal gas?
pV = NkT pV = nRT pV = (1/3)Nmc²
What are the equations for average kinetic energy?
KE = (1/2)m c² = (3/2)kT = (3/2)(RT/Nₐ)