The ability to absorb heat from the amount of energy required to produce a unit temp rise. c= dq/dT
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In what conditions can we measure specific heat capacity?
Constant volume or constant pressure. C_p>C_v
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Describe vibrational heat capacity
Atoms are constantly vibrating at high f and low A; the vibrations of adjacent atoms are coupled due to atomic bonding. *These vibrations are coordinated in such a way that travelling lattice waves are produced.*
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What is a phonon?
The thermal energy of the material consists of a series of 'elastic' waves which have a range of frequencies and distributions. It is quantified using QM as 'phonons' : vibrational energy
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What is the Debye Temperature? (U_D)
(lower than room temperature)The highest temperature that can be achieved due to a single normal distribution.
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Describe and explain the C_v against Temperature graph up to U_D
C_v=0 when T=0. It then rises rapidly as there is an increased ability of the lattice waves to enhance their average energy with ascending temperature.
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What is the relationship between C_v and T for low temperatures? (equation)
C_v = AT^3 (where A is a temperature independent constant.
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Describe and explain the C_v against Temperature graph after to U_D
C_v levels off and becomes independent of temperature at ~3R
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Give the equation for thermal expansion of a solid
l_f-l_0/l_0 = α_l*ΔT ] where l_f: final length;l_0: Initial length;α_l:Linear coefficient of expansion
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What is thermal expansion (in terms of atoms)
An increase in the average distance between atoms due to a change in temperature.
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How do we categorise a strong bond? (in terms of thermal expansion)
A bond which is hard to expand.
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How do we categorise a strong bond? (in terms of thermal expansion)
A bond which is easy to expand.
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How is the U-r graph affected by an increase in temperature?
The peak height decreases and moves to the right (as the distance between the atoms (r) increases).
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Why does the U-r graph change?
Trough minimum corresponds to the atomic spacing at 0K. Increasing the temp increases the vibrational energy. The average vibrational amplitude of an atom corresponds to the trough width at each temp
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What is the relationship between the atomic bonding energy and the potential energy trough?
The greater the atomic bonding energy the deeper and more narrow the potential energy trough.( there is a smaller linear coefficient of thermal expanison)
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What is the trend of the |α_l| of different types of materials?
Highest: Polymers,Metals,Ceramics:Lowest
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What are isotropic ceramics ?
They are non-crystalline ceramics that have a cubic crystal structure.
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What happens when an-isotropic ceramics are heated?
They contract in some crystallographic directions while expanding in others.
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What type of polymers have the lowest α_l?
The thermosetting network polymers
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Describe the relationship between α_l and bond strength
They are inversely proportional. The stronger the bond the small the α_l.
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In what conditions can we measure specific heat capacity?
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