Thermal Properties Of Matter Flashcards
Define internal energy of a system
Internal energy of a system is the sum of the total kinetic energy and potential energy of all the atoms or molecules in a system
KE- related to temperature of the system
PE- related to physical state (solid, liquid or gas)
Effect of transfer of thermal energy
-change in temperature
OR
-change in state (always occurs at a constant temperature)
Effect of transfer of thermal energy on internal energy of a system
Transfer of thermal energy into the body -> increases the internal energy
Transfer of thermal energy out of the body-> decreases the internal energy
When two objects of two different initial temperatures are brought together…
Thermal energy transfer will take place between them. When these two objects reach the same temperature, we say that they are in thermal equilibrium
Thermal equilibrium
Thermal energy is said to be conserved.
Thermal energy lost by the initially hotter object is equal to the sum of the internal energy gained by the colder object and heat loss to the environment
Define heat capacity of a body
Heat capacity is the amount of thermal energy required to raise the temperature of the body by 1degree or 1kelvin, without a change in state
SI unit: Joules per Kelvin or Joules per Celsius
Equation for heat capacity
C = Q divided by delta 0
C: Heat capacity
Q: thermal energy in joules
Delta 0: change in temperature
Useful eqn: Q = C delta 0
Define specific heat capacity
Specific heat capacity of a substance is the amount of thermal energy required to raise the temperatures of unit mass of the substance by 1 degree or 1 kelvin, without any change in state
SI Unit: Joules per Kg per Kelvin/ Joules per kg per Celsius
Equation for specific heat capacity
c= Q divided by (mass times delta 0)
*Note for specific heat capacity, it is (c) and not (C)
Always check the units for mass and in c are consistent throughout the equation
Specific heat capacity in different states
Specific heat capacity of a substance is different when it is in solid, liquid or gaseous state
Always take note of the physical state of the substance at that instant
Thermal energy and change in state
The transfer of thermal energy into or out of a body can cause a change in the physical state of the body
Melting/solidification and boiling condensation are processes involving a change in state…
Without a change in temperature
During melting and boiling, energy absorbed is used to…
Overcome intermolecular forces
Increases the internal energy of the material
Energy involved in boiling/condensation compared to energy involved in melting/solidification
During boiling, extra work is done against atmospheric pressure
Energy involved in boiling/condensation is greater than energy involved in melting/solidification
Define latent heat
Latent heat is the amount of thermal energy needed to change a substance from solid to liquid or liquid to gas without any change in temperature
Equation for latent heat
Q
SI unit: joules
Define specific latent heat
Specific latent heat is the amount of thermal energy needed to change the unit mass of a substance from solid to liquid (specific latent heat of fusion) or liquid to gas (specific latent heat of vaporization)
Equation for specific latent heat
lf or lv= Q/m
SI unit: joules per kg
Q= mlf or mlv
Evaporation
Evaporation is also a process where a substance undergoes a change in state
However, it occurs in a slightly randomized manner hence we seldom use latent heat to describe this process
Similarities between boiling and evaporation
Both involve a change in state from liquid to gas
Differences between boiling and evaporation.
Boiling occurs at boiling point while evaporation occurs at any temperature
Boiling occurs throughout the liquid while evaporation occurs at the surface of the liquid
In boiling bubbles can be seen. In evaporation no bubbles can be seen
Evaporation through kinetic theory
Liquid molecules are in constant random motion and collide with each other continuously
When molecules with higher kinetic energy collide with molecules near the surface of the liquid, it may gain enough energy to overcome intermolecular forces of the liquid and leave the body
Why does cooling occur when a liquid evaporates?
During evaporation, the fastest-moving molecules leave the liquid. The average kinetic energy of the molecules remaining in the liquid is decreased
Since temperature is directly proportional to average kinetic energy of molecules of the liquid, temperature falls and cooling occurs
Gradient of graph is related to?
Specific heat capacity
The steeper the graph, the greater the specific heat capacity
Why is the rate of cooling faster at the beginning?
Rate of cooling is faster when the temperature difference between the substance and its surroundings is larger
Why does condensation take longer than freezing?
Latent heat of vaporization is usually larger than the latent heat of fusion
