37 7.3 Exothermic and Endothermic Reactions

Practice questions

Multiple choice questions

1. Complete the thermochemical equation below for the reaction of PCl₃(g) with Cl₂(g) to make a PCl₅(g), which has an enthalpy change of −88kJ. Is this reaction exothermic or endothermic?

   [latex]\ce{PCl_{3}(g) + Cl_{2}(g)→ ? (g)}[/latex] ΔH = −88kJ

   1. 5PCl(g); endothermic
   2. 5PCl(g); exothermic
   3. PCl₅(g); endothermic
   4. PCl₅(g); exothermic
2. Choose the correct thermochemical equation for the reaction of N₂(g) with O₂(g) to make 2NO(g), which has an enthalpy change of 181kJ. Is this reaction exothermic or endothermic?
   1. [latex]\ce{N_{2}(g) + O_{2}(g) → 2NO(g)}[/latex]; exothermic
   2. [latex]\ce{N_{2}(g) + O_{2}(g) → 2NO(g)}[/latex]; endothermic
   3. [latex]\ce{N_{2}(g) + O_{2}(g) → N_{2}O_{2}(g)}[/latex]; exothermic
   4. [latex]\ce{N_{2}(g) + O_{2}(g) → N_{2}O_{2}(g)}[/latex]; endothermic
3. Consider this thermochemical equation:

   [latex]\ce{CO_{2}(g) + H_{2}(g) {\rightarrow} CO(g) + H_{2}O(g); ΔH = 42kJ}[/latex]

   Is it exothermic or endothermic? How much energy is given off or absorbed?

   1. Endothermic; 42kj are absorbed
   2. Exothermic; 42kj are absorbed
   3. Endothermic; 42kj are given off
   4. Exothermic; 42kj are given off

True/false question

1. Consider this thermochemical equation:

   [latex]\ce{2CO(g) + O_{2}(g) → 2CO_{2}(g) ΔH = −565kJ}[/latex]

   Is the statement below is true or false?
   This reaction is an exothermic reaction, and −565kj are released into the environment.

Solutions

Multiple choice questions

1. d
2. b
3. a

True/false question

1. False