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Answers to HW set 4­1.notebook

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October 08, 2015

Answers to HW p 26831) Both N2 and O2 have multiple bonds and to separate the atoms from each other both the sigma and pi bonds must be broken. This is more difficult than just breaking the sigma bond found in a single bond.

32) When ∆ H is - the reaction is exothermic. Thus the mixture will get hot so cooling must be available.

33) a. endothermic c. exothermicb. exothermicd. endothermic

34) a. exothermicc. endothermicb. exothermicd. endothermic

p 57153)

54)

Answers to HW set 4­1.notebook

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October 08, 2015

page 26610) How is average bond strength related to relative potential energies of the reactants and the products?a) For an exothermic process energy is released.b) This means that the products have lower potential energy than the reactants because the bonds in the products are stronger.c) The energy required to completely break the bonds of the chemical is an indication of the strength of the bond. The more energy needed to break the bond, the strong the bond.

Bottom line: The PE of the products is lower than the PE of the reactants. However, the bonds of the products are stronger than the bonds of the reactants for exothermic reactions.

reactants

products

potential energy

CH4 + 2O2

H2O + CO2

unreacted elementsamount of energy needed to completelybreak the atoms apart.

For an endothermic process, the opposite is true.

12) What is the difference between ∆H and ∆E?∆H = ∆E when the system does no PV work∆H is heat flow by a system at constant pressure∆E is heat flow by a system at constant volume

Answers to HW set 4­1.notebook

3

October 08, 2015

Answers to HW set 4­1.notebook

4

October 08, 2015