Talk:Calorimetry

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Contents

[edit] Comments

The following sections are tangential to the subject of calorimetry. --[[User:Eequor|η♀υωρ]] 15:12, 18 Sep 2004 (UTC)

[edit] Heat

Main article: Heat.

Heat is an amount of energy which is usually linked with a change in temperature or in a change in phase of matter. The SI unit for heat is the joule.

The equation for measuring heat is:

q = C \Delta t \,\!
  • q is heat. When heat transfers energy from the system to the surroundings, the symbol is -q. When heat transfers energy from the surroundings to the system, the symbol is +q.
  • C is heat capacity.
  • Δt is change in temperature.

[edit] Work

Main article: Mechanical work.

Work is the energy transferred in applying force over a distance. In calorimetry, the force is generally pressure and instead of distance, volume is used. Work is given by the formula:

w = -P \Delta V \,\!
  • w is work. When work transfers energy from the system to the surroundings, the symbol is -w. When work transfers energy from the surroundings to the system, the symbol is +w.
  • P is the pressure of the system.
  • ΔV is volume change.

[edit] Internal energy

Main article: Internal energy.

Internal energy is the kinetic energy associated with the motion of molecules, and the potential energy associated with the rotational, vibrational, and electric energy of atoms within molecules. Internal energy is a quantifiable state function of a system.

Internal energy can not be measured directly; it is only measured as a change (ΔU). The equation for change in internal energy is:

\Delta U = q + w \,\!

[edit] Enthalpy

Main article: Enthalpy.

Enthalpy is the sum of the internal energy of matter and the product of its volume and the pressure.

Enthalpy is defined by the following equation:

H = U + PV \,\!

The total enthalpy of a system cannot be measured directly; the enthalpy change of a system is measured instead. Enthalpy change is defined by the following equation:

\Delta H = H_{final} - H_{initial} \,\!
  • ΔH is enthalpy change.
  • Hfinal is the final enthalpy of the system. In a chemical reaction, Hfinal is the enthalpy of the products.
  • Hinitial is the initial enthalpy of the system. In a chemical reaction, Hinitial is the enthalpy of the reactants.

[edit] Parr History

It appears the history alluded to in the article [at the bottom] is the history of a company that makes lab products, not a history of calorimetry. In fact, when I looked at the history page, I saw almost nothing pertaining to the history of calorimetry?

Is it possible someone just wanted free advertising? Should we snip it?

Phantym 21:24, 24 May 2005 (UTC)

[edit] temperature of an isolated object

The article currently claims If an object is isolated from the rest of the universe, its temperature must stay constant.

I suspect this is incorrect. If I take this small, inert rock at room temperature, and stick it far out past the orbit of Pluto, its temperature would plummet, right? What about the heat pad mentioned in the supercooling article? Imagine that I pull the pin from a grenade, then isolated that grenade from the rest of the universe. The temperature of that grenade rapidly rises when it eventually blows up, right? --DavidCary 03:33, 22 September 2005 (UTC)

Wrong --Dan|(talk) 09:37, 15 March 2006 (UTC)
I think DavidCary has a point, although his rock example isn't right. I think that the missing part of If an object is isolated from the rest of the universe... is that the system must be at equilibrium within itself. The grenade example given shows that a system that is out of equilibrium can change temperature. Perhaps more transparently, if we imagine two reagents for a reaction seperated by a diffusive membrane, if we place this system in a calorimeter, it will naturally change temperature (assuming the reaction is exo/endo-thermic). Isothermal titration calorimetry for instance requires heat to be transfered between the system and a resevoir in order to keep the temperature constant. Remember that energy is conserved, not temperature. Zvsmith 16:08, 12 December 2006 (UTC)

[edit] Calorimetry of a 'multi-state' system?

If a system has several energy states at a given temperature, calorimetry can be used to dissect the number and energy of the different states, right? That would be a nice thing to add here. --Dan|(talk) 09:38, 15 March 2006 (UTC)

I got some references here (specific to protein folding / folding intermediates), which may be a start for this section...

  • Freire, E. 1989. Comments Mol. Cell. Biophys. 6:123
  • Freire, E & Biltonen, RL. 1978. Biopolymers. 17:481
  • Fieire, E & Biltonen, RL. 1978. CRC Crit. Rev. Biochem. 5:85
  • Freire, E et al. 1990. Annu. Rev. Biophys. Biophys. Chem. 19:159
  • Privalov, PL. 1982. Adv.Protein Chem. 35:1

HTH --Dan|(talk) 09:58, 15 March 2006 (UTC)