Energy & Stoichiometry

Exothermic and Endothermic Exothermic process – heat is released into the surroundings Exo = Exit Endothermic Process – heat is absorbed from the surroundings Endo = Into HEAT HEAT

Thermochemical Equations In a thermochemical equation, the energy of change for the reaction can be written as either a reactant or a product Enthalpy: the heat content of a system at constant pressure (ΔH) Endothermic (positive ΔH) 2NaHCO3 + 129kJ Na2CO3 + H2O + CO2 Exothermic (negative ΔH) CaO + H2O Ca(OH)2 + 65.2kJ

Write the thermochemical equation for the oxidation of Iron (III) if its ΔH= -1652 kJ Fe(s) + O2(g)→ Fe2O3(s) + 1652 kJ How much heat is evolved when 10.00g of Iron is reacted with excess oxygen? Exo 4 3 2 10.00g Fe 1 mol 1652 kJ =73.97 kJ of heat 55.85g Fe 4 mol Fe

Write the thermochemical equation for the decomposition of sodium bicarbonate, with a ΔH = + 129 kJ: 2 NaHCO3 + 129kJ → Na2CO3(s) + H2O + CO2 How much heat is required to break down 50.0g of sodium bicarbonate? Endo 1 mol NaHCO3 50.0 g NaHCO3 129 kJ 83.9 g NaHCO3 2 mol NaHCO3 =38.4 kJ of heat

Write the thermochemical equation for a single replacement of calcium oxide and water with a ΔH= - 65.2 kJ: CaO + H2O → Ca(OH)2 + 65.2kJ How much energy is released when 100 g of calcium oxide reacts? Exo 100 g CaO 1 mol CaO 65.2 kJ 56.07 g CaO 1 mol CaO =116 kJ of heat

Write the thermochemical equation for the decomposition of magnesium oxide with a ΔH= + 61.5 kJ: 2 MgO + 61.5 → 2 Mg + O2 How many grams of oxygen are produced when magnesium oxide is decomposed by adding 420 kJ of Energy? Endo 420 kJ 1 mol O2 31.98 g O2 =218 g of O2 61.5 kJ 1 mol O2