Specific Heat
From High School Online Collaborative Writing
Ever wonder why when water is boiling on the stove, the pot seems to get hotter a lot faster than the water?! Have you ever stuck your finger in the water and felt it still warm when it burns to touch the pot?! THATS BECAUSE water has a high specific heat so it takes MORE time and heat transferring from the flame to increase the temperature of the water as opposed to the metal pot which increases easily!
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[edit] The Principles behind Specific Heat
A common misconception is that the terms heat and temperature are interchangeable. Temperature is in fact the amount of kinetic energy (energy of molecules moving which create heat and friction)that a material has. This makes sense through the lens of Absolute Zero[1] which is a term given to something with no kinetic energy and thus cannot lower in temperature any further. This change in temperature is responsible for the phase changes of melting, vaporization and sublimation (from solid to gas). In solids there isnt enough kinetic energy for the molecules to move, and in a gas there is too much. Heat is the amount of thermal energy, measured in joules, transferred from one object to another. Heat is measured in calories,1cal=1g/ºC or 4.19 J, which creates a relationship between temperature and heat in a single unit. (Dont mix food Calories with calories of thermal energy!)
The quantity termed "specific heat", which is unique to every substance, is what relates temperature and heat. Specific heat is the measure of how much energy is necessary to raise the temperature of the substance 1ºC and it is measured in J/kg x ºC or cal/g x ºC. Given the symbol, c, the amount of heat transferred to a material, the mass of the substance and the change in temperature can be found. This is shown in the mathematical formula below.
The amount of heat transferred can be either positive or negative depending on whethere heat is absorbed or lost, but heat transfers from hot to cold. Thermal Equilibrium is when two substances have come together and they achieve the same temperature because of their joining. The specific heat value becomes important in this relationship because it helps in determinging the temperature at which the two substances will be in equilibrium.
This diagram above shows the inner workings of the molecules. They are either moving really fast and bouncing off eachother, heating up as they move, or moving slowly, and now generating as much.
[edit] The history of Specific Heat
Two physicists named Pierre Louis Dulong along wtih Alexis Therese Petit from 1815 to the mid-1820's were the first to study and publish research about specific heat and the relationshop between temperature and heat. The scientists started with observing the relationship between mercury and the air thermometer and later moved into the behavior of solids,liquids,and gases in 1816. In their published piece in 1819, "On some important points in the theory of heat", the men found that thirteen solid elements they had studied were nearly proportional to their atomic weights. This became known as the "Law of Dulong and Petit" which explained that atoms that exist in simple substances have equal capacities for heat.
[edit] Practice Problems that will arise
Example Problem for finding heat transfer
For every piece of equipment made in a factory, .25 kg of Aluminum is heated from 10ºC to 25ºC. How much heat is transferred to the Al to achieve this? (hint:remember to convert g to kg, look at the chart!)
Solution By looking at the chart you can determine that the specific heat of Al is 900 J/kgºC. With the use of the equation Q=mc⌂T, and substituting with units, the amount of heat transferred can be found. Q(amt transferred)=.25kgx900 J/kgºCx15ºC Q=3,375 J of heat
Example problem for finding the specific heat of water
If when heating .5kg of water with 4190 J of heat and there is a change in temperature of 2ºC, without looking at the chart, determine the specific heat of water. Does it match up with what is on the chart?
Solution Using the same equation, but changing it around a bit, the equation c=Q/(m⌂T) will help to determine the specific heat of water. By substituting with units... c=4190J/(.5kgx2ºC) c=4,190 or 4.19x10^3, which is the specific heat of water!
Example problem for the change in temperature that occurs
In a glass shop the workers depend on glass's low specific heat value to perfect their craft. If the workers are using 20,000J of heat to raise the temperature of 1kg of glass which is already 20ºC, how much of a change in temperature will occur?
Solution With the knowledge that we've already used, the same equation can be changed again to format this question. ⌂T=Q/(mc)Also the table shows the value of the specific heat of glass which is 840J/kgºC. ⌂T=20,000J/(1kgx840J/kgºC)\ ⌂T=There is a change in temperature of 23ºC
[edit] Fun Facts and Useful Links
- Objects which have very low specific heat value change temperature more easily in response to losing or gaining heat. Because dry lands specific heat is less than water, areas that are not surrounded by large bodies of water tend to have larger temperature changes**
- From another country! 1 British thermal unit per pound per degree Fahrenheit (1 Btu/lb-°F)is how specific heat is measured in England**
- This is a great link which explains thermodynamics, which take you above and beyond heat!**[2]
- The simple apparatus can be modeled and done at home if you want to try measuring the specific heat of water while you're cooking!--->**
[edit] Resources
- Sparknotes-SAT Subject Test Physics**
- Barron's Review Course Series-Physics:The Physical Setting**
- http://encyclopedia.jrank.org/DRO_ECG/DULONG_PIERRE_LOUIS_17851838_.html**
- www.sciencebyjones.com/specific_heat1.htm**
- scienceworld.wolfram.com/physics/SpecificHeat.html**
- http://www.irish-energy.ie/uploadedfiles/Education/physics/unit5_5b_thirdgraf.gif**
- http://www.iun.edu/~cpanhd/C101webnotes/matter-and-energy/specificheat.html**
