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Problems - Energetics of Chemical Reactions

Author: John Hutchinson

Problem 1 Assume you have two samples of two different metals, X and Z. The samples are exactly the same mass.

1.a) Both samples are heated to the same temperature. Then each sample is placed into separate glasses containing identical quantities of cold water, initially at identical temperatures below that of the metals. The final temperature of the water containing metal X is greater than the final temperature of the water containing metal Z. Which of the two metals has the larger heat capacity? Explain your conclusion.

1.b) If each sample, initially at the same temperature, is heated with exactly 100J of energy, which sample has the higher final temperature?

Problem 2 Explain how Hess' Law is a consequence of conservation of energy.
Problem 3 Consider the reaction N2O4(g) 2 NO2(g) Draw Lewis structures for each of N2O4 and NO2. On the basis of these structures, predict whether the reaction is endothermic or exothermic, and explain your reasoning.
Problem 4 Why is the bond energy of H2 not equal to ΔHf of H2? For what species is the enthalpy of formation related to the bond energy of H2?
Problem 5 Suggest a reason why ΔH for the reaction CO2(g) CO(g)+O(g) is not equal to ΔH for the reaction CO(g) C(g)+O(g)
Problem 6 Determine whether the reaction is exothermic or endothermic for each of the following circumstances:

6.a) The heat of combustion of the products is greater than the heat of combustion of the reactants.

6.b) The enthalpy of formation of the products is greater than the enthalpy of formation of the reactants.

6.c) The total of the bond energies of the products is greater than the total of the bond energies for the reactants.




Last Update: 2011-02-16