Unit+8+-+Thermochemistry

= **THERMOCHEMISTRY!** = **[|Overview on Thermochemistry]**


 * thermochemistry** - study of heats involving chemical reactions
 * energy** - ability to do work
 * heat** - form of energy
 * system** - sample of matter under observation
 * surroundings** - everything outside the system being studied
 * endothermic** - change in H is a positive value
 * exothermic** - change in H is a negative value
 * calorimetry** - measurement of heat flow in a reaction


 * basic equation of heat flow:** **q=mc(final t - intial t)**
 * q**= heat
 * c**=specific heat
 * m**= mass (g)
 * t**= temperature

4.18 J/g*C
 * specific heat of water:**

1 cal = 4.18 J 1 kcal = 4.18 J

If heat is absorbed by the system the temperature **increases** and q is **positive**.

If heat is absorbed by the system the temperature **decreases** and q is **negative**.


 * Rules of Thermochemistry**
 * First Rule:** change in H is directly proportional to the amount of reactants or products.
 * Second Rule:** change in H for a reaction is equal in magnitude (amount of heat) but opposite in sign to change in H for the reverse reaction
 * Third Rule:** Hess's Law - if equation 1 + equation 2 = equation 3, then change in H + change in H2 = change in H3


 * heat capacity** - the amount of heat required to raise the temperature one degree celsius

Heat given off by the reaction is absorbed by H2O in the coffee cup.
 * Coffee-Cup Calorimeter:**
 * <I H** (heat content)
 * <I H** reaction = -q water


 * Bomb Calorimeter:**
 * Device used to measure heat flow, in which a reaction is carried out within a sealed metal container.
 * Can be used for reactions involving gases and products reaching high temperatures.
 * Some heat is absorbed by the metal as well as the water
 * q(rxn) = -q calorimeter = -C calorimeter * change in temperat[[image:CalorimBomb.jpg width="264" height="257" align="left"]]ure


 * Enthalpy:**
 * a property of a system that reflects its capacity to exchange heat (q) with the surroundings
 * **delta H = sum of products - sum of reactants**

Endo/Exo Demo media type="custom" key="9697182"