Specific heat of Isoprene
Specific heat of Isoprene
(OP)
Can somepone help me out with a value (or range for the specific heat of isoprene or isobutylene rubbers?
Thanks in advance for your help.
Ron.
Thanks in advance for your help.
Ron.





RE: Specific heat of Isoprene
For Isobutylene-isoprene 0.45.
RE: Specific heat of Isoprene
Thanks for the reply, but can you tell me the units that go with the values that you provided.
RE: Specific heat of Isoprene
In the case of specific heat, the property of interest is the amount of heat required to raise a unit mass of the material 1 degree. The units of mass or temperature are irrelavent.
RE: Specific heat of Isoprene
I respectfully disagree with your last post. The units do matter. If the numbers you quote are simply the specific heat ratioed to the heat for water than fine but you need to state that.
You define the property as the amount of heat required to a raise a unit of mass by 1 degree. For a given substance: 1 BTU of heat added to 1 lb of material raising it by 1 F is not the same as 1 KJ of heat added to 1 kg of material raising it by 1 C. Not only do the system of units matter, mass vs molar basis matters. Different references tabulate them differently.
You are also incorrect when stating that all specific quantities are dimensionless. Specific gravity is but most 'specific' terms are actually ratios to mass....specific heat (kJ/kgC), specific volume (m3/kg), etc.
RE: Specific heat of Isoprene
Ron.
RE: Specific heat of Isoprene
You are correct that the amount of heat needed to raise 1 pound of water 1 degree F is not the same amount of heat required to raise 1 kg of the same material 1 degree C.
However, we are dealing with a ratio. For any arbirary set of units X amount of heat is required to increase the temperature of a unit mass of material by one degree.
That same X amount of heat will raise a unit mass of a material with a different heat capacity a different number of degrees.
The ratio of the delta T is not dependant on the units (provided the same unit system is used to measure both materials)
Encyclopedia.com does a nice job of explaining the common confusion between specific heat and heat capacity, and is consistent with my Mark's STandard Handbook.
http://www.encyclopedia.com/html/s1/specheat.asp
RE: Specific heat of Isoprene
I looked up specific heats in my CRC handbook....64th edition pgs F-12&13. Specific heat is given for air in units of cal/g-K. If in fact these were 'specific' heats the table would be filled with values close to 1.
Also, take a look at some steam tables. Specific volume is definitely not a dimensionless quantity.
I would appreciate it if someone else could lend a hand...I have always thought that 'specific' terms were properties that were mass dependent (ie more mass...more heat, more mass...more volume).
RE: Specific heat of Isoprene
Also, I take back my some of my comments about air. The tabulation is as I stated but if we follow the definition provided of specific heat than you could generate ratios to water using appropriate units.
RE: Specific heat of Isoprene
1 BTU is the heat required to raise one pound of water one degree F.
1 calorie is the heat required to raise one gram of water one degree C.
Thus by inverse of the definitions of the units of heat the heat capacity of water is:
1 BTU/pound F our 1 cal/g K
This in turn forces the specific heat - that is the ratio of temperature rise per unit mass per unit heat input of a substance over that of water - to be numerically equal to its heat capacity in either BTU/pound F or cal/g K.
So, apparent widespread colloquial misuse notwithstanding, "Specific heat" is properly dimensionless. "Heat capacity" requires units of heat/mass x temperature.
Joules don't work out so nicely.
It is my opinion that Joules, being properly a unit of work, should not be used for "heat capacity" (although if the units are clearly stated this does not appear to create a problem).
RE: Specific heat of Isoprene
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RE: Specific heat of Isoprene
The area of engineering is no less susceptible to colloquial misuse (leading to accepted use). If we look at languages (english in particular) colloquialisms are the major evolutionary force. I would argue that the term Cp (as in the equation Q=mCpDT) has become widely referred to as 'specific heat' (at least in my part of the world). Just like any equation, the units used can be just about anything as long as they are consistent.
The encyclopedia articles that you reference seem to be having the same difficulty that we are. They give contradicting definitions. The first article refers to the ratio of heat capacities while the second defines specific heat the same way it does heat capacity in the first article.
RE: Specific heat of Isoprene
If I'm allowed to resuscitate the subject I'd say there should be no confusion as long as we adopt the following definitions.
The heat ΔQ transferred to an object and the resulting change ΔT in temperature are proportional:
where C, the proportionality constant, is called the heat capacity of the object. Thus the units of heat capacity are J/K. C applies to a specific object and depends both on its mass and on the substance from which it's made.
One usually characterizes different substances in terms of c, specific heat, or heat capacity per unit mass. The heat capacity of an object is then the product of its mass m and specific heat, and we write:
The SI units of specific heat are J/(kg.K)
The "specificity" in this case refers to the unit of mass. So would be with specific volume, specific (electrical) charge, and specific humidity.
RE: Specific heat of Isoprene
RE: Specific heat of Isoprene
Ron