Label each of the following reactions as exothermic or endothermic (\"exo\" or e

Question

Label each of the following reactions as exothermic or endothermic ("exo" or endo"), and according to whether work is done on or by the system, or no work is done at all ("on", "by" or "none")? Note that no "endo-on" cases appear here, as these are always thermodynamically unfavourable. There is no need to do any calculation, use chemical arguments to predict the sign of the enthalpy change. | co2(s) CO2(g) Cals) + 2 H2O(l)- Ca(OH)2la)+ H2(8) 1. endo-by 2. exo-by COg) - C(g)+ O(g) 3. endo-on 2 H2O(g) 2 H2(g) +O28 4. exo-on C2HsOHO)+3 O2(g) 2 CO2(g) + 3 H20(g)

Explanation / Answer

1)

CO2(s) --> CO2(g)
Endothermic: Energy required to convert from solid to gaseous state

2)

Ca(s) + 2 H2O(l) --> Ca(OH)2(aq) + H2(g)
Exothermic: Bond forming/ Bond energy of the products is less than reactants

3)

CO(g) --> C(g) + O(g)
Endothermic: bond breaking requires energy

4)

2 H2O(g) --> 2 H2(g) + O2(g)
Endothermic: bond breaking requires energy

5)

C2H5OH(l) + 3 O2(g) --> 2 CO2(g) + 3 H2O(g)
Exothermic: Combustion releases energy

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