Thermochemical Stoichiometry

Question

1) The following thermochemical equation is for the reaction of hydrogen peroxide(l) to form water(l) and oxygen(g).

2H₂O₂(l)2H₂O(l) + O₂(g)    H = -196 kJ

How many grams of H₂O₂(l) would have to react to produce 36.8 kJ of energy?

2) The following thermochemical equation is for the reaction of carbon dioxide(g) with hydrogen(g) to form acetylene(g) (C₂H₂) and water(g).

2CO₂(g) + 5H₂(g) C₂H₂(g) + 4H₂O(g)    H = 46.5 kJ

When 9.55 grams of carbon dioxide(g) react with excess hydrogen(g),  kJ of energy are _________(evolved/absorbed).

Answer 1

1)

36.8kJ x 2molH2O2 / -196kJ x 34.02gH2O2 / molH2O2 = 12.8g H2O2

2)

9.55gCO2 x molCO2 / 44.01gCO2 x 46.5kJ/2molCO2 = 5.05 kJ absorbed