Thermal physics Flashcards
(52 cards)
What energies do particles of all substances have?
-potential energy
-kinetic energy
Why is there energy in substances?
kinetic energy is due to the speed of the particles
potential energy is due to the separation/bonds between the molecules
Define what temperature is
the average Ek of a substance
How can we convert between degrees and kelvin?
T= θ + 273
where:
T= kelvin
θ= °C
What do we mean by absolute zero?
the temperature at which the molecules in a substance have zero kinetic energy (0K or -273°C)
What do we mean by the internal energy of something?
the sum of all the kinetic and potential energies of all its particles
U= ∑Ep + ∑Ek
Where all components are measured in joules
What factors affect the internal energy for a system? (4)
-temperature ( ↑temp, ↑Ek)
-phase of matter ( ↑U when in gaseous state, low U when in solid state)
-intermolecular forces between particles
-random motion of particles
Explain how we can increase the internal energy of a system
-doing work on the system
this transfers energy to it e.g. increases the Ek or Ep
-adding heat to it
this increases the temperature which as a result increases the Ek leading to an overall increase in internal energy
Explain how we can decrease the internal energy of a system
-losing heat to the surroundings
-changing state from a solid to a liquid or a liquid to gas
Why does the internal energy of a substance change when changing state?
as the substance changes state the potential energy changes due to the changing bonds whilst the kinetic energy is kept constant
Draw a graph showing how internal energy varies with temperature. Include the different process that occur
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How can we work out the amount of energy required to change the temperature of a substance?
Q = mcΔθ
where:
Q= energy required (J)
m= mass (kg)
c= specific heat capacity (Jkg^-1°C^-1)
Δθ= change in temperature (°C)
What is specific heat capacity?
the amount of energy required to increase the
temperature of 1 kg of a substance by 1 °C/1 K, without changing its state
What are the different processes to change state?
melting = solid to liquid
vaporisation = liquid to gas
sublimation = solid to gas
freezing = liquid to solid
condensation = gas to liquid
What is specific latent heat?
the thermal energy required to change the state of 1 kg of mass of a substance without any change of temperature
What is the equation involving energy required to change the state of a substance and specific latent heat?
Q=mL
where:
Q= energy required to change state (J)
m= mass (kg)
L= specific latent heat (Jkg^-1)
What are the two types of latent heat? When are they used?
latent heat of fusion (melting)
-melting a solid
freezing a liquid
latent heat of vaporising (boiling)
-vaporising a liquid
-condensing a solid
Define latent heat of fusion
the thermal energy required to convert 1 kg of solid to liquid with no change in temperature
Define latent heat of vaporisation
the thermal energy required to convert 1 kg of liquid to gas with no change in temperature
What are some things to know when a substance is changing state?
-there is no change in temperature
-the potential energies of the particles change, but not their kinetic energies
What does it mean if bonds are being broken/stronger? Explain why
-the heat absorbed in melting and boiling causes the particles to move further apart by overcoming the intermolecular forces of attraction
-the heat released in freezing and condensation allows the particles to move closer together and the intermolecular forces of attraction become stronger
Ek is proportional to temperature (as temperature is the avg. Ek)
-if there is no change in temperature, there must be no change in kinetic energy either
What are the ideal gas laws? What does it mean if they’re empirical?
the experimental relationships between pressure (P), volume (V) and temperature (T) of an ideal gas
meaning they are not based on theory but arose from observation and experimental evidence
What is constant for all the ideal gas laws?
mass
number of particles
State Boyle’s law
if the temperature T of an ideal gas is constant, then Boyle’s Law is given by:
p ∝ 1/V
where:
p= pressure (Pa)
v= volume (m^3)