Other Conversions
Thursday, February 3, 2011 /9:15 PM
Other Conversions: Volume and Heat
• Volume @STP can be found using the conversion factor 22.4L/mol.
• Heat can be included as a separate term in chemical reactions. (This is called Enthalpy)
• Rxns (reactions) that release heat are exothermic A+B->C+ Energy
• Rxns that absorb heat are endothermic. A+B+Energy->C
• Both can be used in stoichiometry
Example
• If 5.0g of Potassium chlorate decompose according to the reaction below, what volume of oxygen gas (at STP) is produced?
2KClO3 -> 2KCl + 3 O2
5.0g x 1mol x 3 x 22.4L = 1.4L
122.6g 2 1mol
• When Zinc reacts with hydrochloric acid exactly 1.00L of Hydrogen has is produced (at STP). What mass of Zinc was reacted?
Zn + 2HCl H2 +ZnCl2
1.0L x 1 mol x 1 x 65.4g = 2.92g
22.4L 1 1 mol
• In the formation of Copper (II) oxide 3.5g of copper react. How many litres of Oxygen (at STP) are needed?
Cu + O2 -> CuO
3.5g x 1 mol x 1 x 22.4 L = 0.62L
63.5g 2 1 mol
• Octane reacts according to the reaction:
2 C8H18 + 25 O2 -> 16 CO2 + 18H2O + 5076 kJ
Determine the amount of heat released when 0.5mol of octane react.
How much heat is released when 25g of Oxygen are consumed?
0.5mol x 1 x 5076 kJ = 1269 kJ
2
= 1. X 103 kJ
25g x 1 mol x 1 x 5076 kJ = 159 kJ
32.0g 25
= 1.6 x 102 kJ
• Find the amount of heat released when 5.0 mol of H2 are consumed according to the reaction:
N2 + 3 H2 -> 2 NH3 + 46.2 kJ
5.0 mol x 1 (heat) x 46.2 kJ = 77kJ
3 (H2)
• Find the amount of heat released when 250g of Ammonia form according to the reaction:
N2 + 3 H2 -> 2 NH3 + 46.2 kJ
250g x 1 mol x 1(heat) x 46.2 kJ = 340kJ
17.0g 2 (NH3)
