Volume and Heat Conversions

I. Volume @ STP can be found by using the conversion factor 22.4 L/ mol

                A. Heat can be included as a separate term in chemical reactions. (This is called enthalpy)

                                a.  Exothermic reactions are reactions that emit heat

                                b. Endothermic reactions are reactions that absorb heat

                                c. Both can be used in stoichiometry

Ex. When cadmium reacts with hydrochloric acid exactly 3.00L of hydrogen is produced @STP. What mass of cadmium was produced?

Cd + 2HCl --> CdCl₂ + H₂

3.00L x  (1 mol/ 22.4L) x (1 mol/ 1 mol) x (112.4g/ 1 mol*) = 15.1 g

* The 112.4g/ 1 mol is the molar mass of cadmium

Ex. How many litres of chlorine are necessary for the combustion reaction of 362g of selenium @ STP?

Se + Cl₂ -->  SeCl₂

362g x (1 mol/ 79.0g*) x (1 mol/ 1 mol) x (22.4L/ 1 mol) = 103 L

*The 1 mol/ 79.0g is the molar mass of selenium

Ex. Find the amount of heat released when 2.0 mol of O₂ is consumed according to the reaction

Cl₂ + 3O₂ --> 2ClO₃ + 65.9KJ

2.0 mol x (1 mol/ 3 mol) x (65.9KJ/ 1 mol) = 44KJ

-Nicole