Energy and Percent Yield

-Enthalpy is the energy stored in chemical bonds.
- Symbol of Enthalpy is H.
- Units of Joule(s).

-Change in Enthalpy is /\ H.
- In exothermic rxns enthalpy decreases.
- In endothermic rxns enthalpy increases.

EXOTHERMIC REACTION


Potential energy (KJ)

|               Reactants
|.............................
|             |                \
|             |                  \
|             |  /\H             \                      Products
|            \/                     \..............................
|
|_________________________________



ENDOTHERMIC REACTION

Potential Energy (KJ)

|                                          Products
| Heat is positive  ..............................                                      
|  /\ H is positive /                    
|                       /
|  Reactants    /             
|.................../
|_______________________________


Calorimetry

-To expirimentally determine the heat released we need to know three things

1. Temperature Change (/\T) Celcius
2. Mass (m) g
3. Specific Heat Capacity (C) J/ g Celcius

These are ralted by the equation: /\ H = mc /\ T
                                                               or
    
                                                /\ H = m C ( Tf - Ti)


Example:

Calculate the heat required to warm up a cup of 400g of water (C = 418 J/ g Celcius)
from 20.0 Celcius to 50.0 Celcius



/\H = mc/\T

= 400g x 30.0 Celcius x 418 J/ g Celcius

/\H = 50160

(sig figs) /\H = 5.02 x 10^4 J

Jomar Delos Santos