- #1
naftali
- 31
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Hi,
I am preparing to Thermal Physics exam. , and I think there are some basic subjects which I don't understand:
1.Reversibility - As I understand, a reversible process, is one that can spontaneously happen in either direction, am I right?
2.If this defenition is right, then, for example a glass of cold water, which is in a room with air in room temperature, heat flows from the air to the glass, so the glass become in room temp. too. apparently, this process will not happen spontaneously in the reverse direction - i.e the water in the glass won't spontaneously give heat to the air and become colder, so this process is irrevesible. Am I right?
3.Another process - ice in a glass in 0[tex]^{o}[/tex]C gets heat (latent heat) from the surrounding air and melts. apparently, according to Clausius, the cold ice will not give it's heat to the hotter air, so this process is irrevesible too . Am I right?
4.Entropy - if I understood well, entropy is defined as
[tex]\Delta[/tex]S = [tex]\int dQ/T[/tex] and dS = dQ/T
only in a reversible path/process.
so in the preceding examples (2-3), I can't just calculate the entropy change by :
[tex]\Delta[/tex]S = [tex]\int Cv\cdot dT /T[/tex] when Cv is the heat capacity of water
in case 2.
and [tex]\Delta[/tex]S = Q/273.15 when Q is the required latent heat, in case 3. (and 273.15 = 0[tex]^{o}[/tex]C).
But I need to find some reversible path which have same initial and final state as this process. Am I right?
5.Is there a general way to find a reversible path for a given process?
Thank you
Naftali
I am preparing to Thermal Physics exam. , and I think there are some basic subjects which I don't understand:
1.Reversibility - As I understand, a reversible process, is one that can spontaneously happen in either direction, am I right?
2.If this defenition is right, then, for example a glass of cold water, which is in a room with air in room temperature, heat flows from the air to the glass, so the glass become in room temp. too. apparently, this process will not happen spontaneously in the reverse direction - i.e the water in the glass won't spontaneously give heat to the air and become colder, so this process is irrevesible. Am I right?
3.Another process - ice in a glass in 0[tex]^{o}[/tex]C gets heat (latent heat) from the surrounding air and melts. apparently, according to Clausius, the cold ice will not give it's heat to the hotter air, so this process is irrevesible too . Am I right?
4.Entropy - if I understood well, entropy is defined as
[tex]\Delta[/tex]S = [tex]\int dQ/T[/tex] and dS = dQ/T
only in a reversible path/process.
so in the preceding examples (2-3), I can't just calculate the entropy change by :
[tex]\Delta[/tex]S = [tex]\int Cv\cdot dT /T[/tex] when Cv is the heat capacity of water
in case 2.
and [tex]\Delta[/tex]S = Q/273.15 when Q is the required latent heat, in case 3. (and 273.15 = 0[tex]^{o}[/tex]C).
But I need to find some reversible path which have same initial and final state as this process. Am I right?
5.Is there a general way to find a reversible path for a given process?
Thank you
Naftali