DO NOW: (on the back of your notes) How many kilojoules of heat are produced when 34.0 g of Fe2O3 reacts with an excess of CO according to the following reaction? Fe2O3 + 3 CO  2 Fe + 3 CO2 H = -26.3 kJ

Unit: Thermochemistry Notes Unit: Thermochemistry Limiting Reactants and Thermochemical Equations

After today you will be able to… Use thermochemical equations to calculate limiting reactant

Recall, a limiting reactant is the reactant which yields the smaller amount of product. Energy in a chemical reaction can also help to determine which reactant limits the amount of product that can be made.

Example: How much energy is used when 14 Example: How much energy is used when 14.3 moles of hydrosulfuric acid reacts with 17.1 moles of oxygen gas? 2H2S + 3O2 + 175 KJ  2SO2 + 2H2O 14.3 mol H2S x _________ = 17.1 mol O2 x ________ = K: 14.3 mol H2S U: ? kJ + 175 kJ +1250 kJ 2 mol H2S K: 17.1 mol O2 U: ? kJ Used: + 175 kJ +998 kJ 3 mol O2

Example: How much energy is produced when 13. 11g of tin reacts with 2 Example: How much energy is produced when 13.11g of tin reacts with 2.715g of nitrogen? __ Sn + __ N2  __ Sn3N4 + 632 KJ 13.11 gSn x _________ x ________ = 2.715 gN2 x ________ x ________ = 3 2 1 K: 13.11 gSn U: ? kJ Produced: 1 mol Sn -632 kJ -23.27 kJ 118.71 gSn 3 mol Sn K: 2.715 gN2 U: ? kJ 1 mol N2 -632 kJ -30.62 kJ 28.02 gN2 2 mol N2

Questions? Complete WS

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