Thermochemical Questions

Example §

At the very basic level it’s a balanced equation

Example of thermochemical equation:

2 H + O -> 2 HO

H = -571.6. kJ

Takeaway from this equation:

• 571.6 kJ of heat released per 2 moles of H reacted
• 571.6 kJ of heat released per 1 moles of O reacted
• 571.6 kJ of heat released per 2 moles of HO reacted
• Exothermic Reaction

Sample Problem §

How much heat is evolved when 266 g of white phosphorus (P) burn in air

The world evolved in chemistry means released

P (s) + 5O (g) -> PO (s)

H = -3013 kJ

Convert 266 grams of phosphorus to moles

266 grams of Phosphorus * = 2.147 mol Phosphorus

2.147 mol Phosphorus * = -6469.31.. kJ ~ -6470 kJ (3 sig digs)