Thermochemical Questions

Example §

At the very basic level it’s a balanced equation

Example of thermochemical equation:

2 H${}_{2(g)}$ + O${}_{2(g)}$ -> 2 H${}_2$O${}_{(l)}$

$△$ H = -571.6. kJ

Takeaway from this equation:

• 571.6 kJ of heat released per 2 moles of H${}_2$ reacted
• 571.6 kJ of heat released per 1 moles of O${}_2$ reacted
• 571.6 kJ of heat released per 2 moles of H${}_2$O reacted
• Exothermic Reaction

Sample Problem §

How much heat is evolved when 266 g of white phosphorus (P${}_4$) burn in air

The world evolved in chemistry means released

P${}_4$ (s) + 5O${}_2$ (g) -> P${}_4$O${}_{10}$ (s)

$△$ H${}_{reaction}$ = -3013 kJ

Convert 266 grams of phosphorus to moles

266 grams of Phosphorus * $\frac{1molofPhosphorus}{123.88gramsofPhosphorus}$ = 2.147 mol Phosphorus

2.147 mol Phosphorus * $\frac{-3013kJ}{1molof{P}_4}$ = -6469.31.. kJ ~ -6470 kJ (3 sig digs)