E. Smith

Calorimetry The accurate and precise measurement of heat change for chemical and physical processes. Calorimeter An insulated device used to measure the absorption or release of heat in a chemical or physical process. E. Smith

Enthalphy…a Fancy Word for Heat For systems with constant pressure, the heat content is the same as a property called enthalpy (  H). A change in heat at constant pressure is called a change in enthalpy (  H) of a system. At constant pressure q =  H = C x m x  T E. Smith

Thermochemical Equations A thermochemical equation expresses the heat needed or released in a chemical reaction. Example of an exothermic reaction- CaO(s) + H 2 O  Ca(OH) 2 (s) kJ Or the same equation can be expressed as CaO(s) + H 2 O  Ca(OH) 2 (s)  H = kJ E. Smith

Endo- and Exo- If the  H is negative (-) then the reaction is exothermic. If the  H is positive (+) then the reaction is endothermic. Knowing  H will allow you to calculate the amount of heat released or gained in the reaction. E. Smith

Example Gasohol contains ethanol (C 2 H 5 OH), which when burned reacts with excess oxygen to produce CO 2 gas and water vapor. How much heat is released when 12.5 g of ethanol is burned? C 2 H 5 OH (l) + O 2 (g)  CO 2 (g) + H 2 O (g)  H = kJ E. Smith

Answer to Example First check if the equation is balanced! C 2 H 5 OH(l) +3O 2 (g)  2CO 2 (g) + 3H 2 O(g) 336 kJ of heat is released when 12.5 grams of C2H5OH is combusted with an excess of oxygen. The negative value tells you this is an exothermic reaction! E. Smith