CHAPTER 7. ENERGYCHANGES IN CHEMICAL REACTIONS 7.6
- In an endothermic reaction, ΔH is a positive number,and in an exothermic reaction, ΔH will
be negative. - Photosynthesis, evaporation and the thermaldecomposition of limestone, are all examples of
endothermic reactions. - Combustion reactionsand respiration are bothexamples of exothermicreactions.
- A reaction which proceeds without additional energy being added,is called a spontaneous
reaction. - Reactions where energy must be continuously supplied for the reaction to continue, are called
non-spontaneous reactions. - In any reaction, some minimum energy must beovercome before the reaction will proceed. This
is called the activation energy of the reaction. - Theactivatedcomplex is the transitional product that is formed during achemical reaction while
old bonds break and new bonds form.
Chapter 7 End of Chapter Exercises
- For each of the following, say whether the statement is true or false. If it is false, give
a reason for your answer.
(a) Energy is released inall chemical reactions.
(b) The condensation of water vapour is an example of an endothermicreaction.
(c) In an exothermic reaction ΔH is less than zero.
(d) All non-spontaneous reactions are endothermic. - For the following reaction:
A + B→ AB ΔH =− 129 kJ.mol−^1
(a) The energy of the reactants is less than the energy of the product.
(b) The energy of the product is less than the energy of the reactants.
(c) The reaction is non-spontaneous.
(d) The overall energy of the system increases during the reaction.- Consider the following chemical equilibrium:
2 NO 2 � N 2 O 4 ΔH < 0Which one of the following graphs best represents the changes in potential energy
that take place during the production of N 2 O 4?(i) (ii) (iii) (iv)