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Flashcards in Thermal physics Deck (47)
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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 motion
Pressure exists from surface collisions exerting a force
Volume decreases
Collisions occur more frequently
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)?

Horizontal line


What does the area below a p-V graph show?

Work Done


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)


What is the main property of a gas at absolute zero?

It has minimum internal energy