IB Chemistry SL Reactivity 1.1.2 Endothermic and Exothermic

Practise identifying whether a process absorbs or releases energy from temperature evidence and enthalpy-level diagrams. For an exothermic reaction, products lie below reactants…

Syllabus
First assessment 2025
Objective
1.1.2
Level
SL

Exam points

  • classify a process from whether energy flows into or out of the reacting system
  • link a temperature rise or fall in the surroundings to the correct enthalpy sign
  • read product and reactant energy levels to identify an exothermic or endothermic profile

1.1.2—Endothermic vs. exothermic question 1

[Maximum number: 1]

Chlorine occurs in Group 7, the halogens.

Chloroethene, H2C=CHCl\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCl}, the monomer used in the polymerization reaction in the manufacture of the polymer poly(chloroethene), PVC, can be synthesized in the following two-stage reaction pathway.

Stage 1: C2H4( g)+Cl2( g)→ClCH2CH2Cl(g)\quad \mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow \mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{Cl}(\mathrm{g})

Stage 2: ClCH2CH2Cl(g)→H2C=CHCl(g)+HCl(g)\quad \mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{Cl}(\mathrm{g}) \rightarrow \mathrm{H}_{2} \mathrm{C}=\mathrm{CHCl}(\mathrm{g})+\mathrm{HCl}(\mathrm{g})

State whether the reaction given in stage 1 is exothermic or endothermic.

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