10-2 Practice Problems
Stoichiometry of Energy Changes
1) 2S + 3O2  2SO3
Name ______________________________
Date ____________ Period ____________
∆Ho = -791.4 kJ
a. How much heat will be released when 6.44 g of sulfur reacts?
b. Is this reaction endothermic or exothermic?
2) C + O2  CO2
∆Ho = -393.5 kJ
a. How many grams of carbon would be required to liberate 284 kJ of thermal energy?
b. Draw and energy diagram for this reaction.
3) H2 + Br2 + 72.80 kJ  2HBr
a. How much heat will be absorbed when 38.2 g of bromine reacts?
b. Is this reaction endothermic or exothermic?
4) 2P + 5Cl2  2PCl5
∆Ho = -886 kJ
a. Determine the amount of heat produced if 1.98 L of chlorine gas are reacted at STP.
b. Write the thermochemical equation for this reaction.
1a) -79.4 kJ 2a) 8.66 g 3a) +17.4 kJ 4a) -15.7 kJ
5) C2H5OH + 3O2  2CO2 + 3H2O
∆Ho = -1366.7 kJ
a. If this reaction gives off 951 kJ of heat, how many molecules of water will be produced?
b. Will this reaction cause the surroundings to increase or decrease in temperature?
6) N2 + O2 + 180 kJ  2NO
a. How much heat is required to react 13.7 g of nitrogen.
b. Draw an energy diagram for this reaction
7) 3Fe + 2O2  Fe3O4 + 1120.48 kJ
a. How many grams of iron would be required for this reaction to liberate 7985 kJ of thermal
energy?
b. Write this equation in ∆H notation.
8) 4NH3 + 5O2  4NO + 6H2O ∆Ho =-1170.0 kJ
a. How much heat is transferred when 14.9 g of ammonia react?
b. Rewrite this as a thermochemical equation for 1 mole of ammonia.
5a) 1.26 x 1024 molec 6a) +88.1 kJ 7a) 1193 g 8a) -256 kJ